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DELTA - Cap Analysis; Cap Biasing

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Anonymous
April 22, 2005 11:45:23 PM

Archived from groups: rec.audio.pro (More info?)

In preparation for replacing or in some cases removing the electrolytics
in my Soundcraft Delta, I've been cataloging those in the signal path.
I've made offset measurements on both sides of many caps and found some
with zero offset on either side. Good candidates for removal, I'd guess.
(I did throw a 0.5 uf cap across the scope probe to filter the AC noise
component, which was obscuring the small DC offsets.)

I'm curious about two things. First, in a few cases where offset is
present (a few mV) the voltage is opposite the labeled polarity on the
cap. Obviously the cap hasn't blown apart from the small reversal, but
does the distortion go up?

Second item is why certain cap values were chosen by the designer. Most of
the interstage couplers are 47 uf/25 V -- perhaps a large enough value so
that after going through a number of them the LF roll off is still below
20 Hz. (Though if stuck using these, perhaps I should bump them up to 100
uf for better LF?)

What I don't quite get, though, are the 2.2 uf/50V parts on the fader
returns and outputs of most other rotary level controls. Is the idea to
band-limit the LF so that the control action is clean(er) across a wide
range of dirt in the part and aging? Or am I missing something?

Next, the input to the L/R mix summing amps (and aux bus summers) is 1000
uf/6.3V. Why the huge value here? Why not 100 or 470? (Not saying they
should be that way, just curious as to why.)

CAP BIASING - where electrolytic caps must be used, this seems like an
interesting idea to try, but I wonder how best to do this. How much bias V
do we need? If I grab, say, the 17V positive rail through dropping
resistors to provide a couple of volts, won't there be increased crosstalk
by some signal getting back into the pos. rail and into other bias
injection points? (Not to mention the op amps themselves.)

Should I use a little regulator, say a 7803 (if there is such a beast, or
a 7805 if not) local to each cap "pair" I'd want to bias? By pair I mean
two electros replacing an original single cap, with the + sides tied
back-to-back and the bias injected there. Would the output stages of such
regulators impact the signal fidelity?

Thanks again for the help and experiences in this area. Thanks to those
who have responded to these Delta threads in the past, especially Mr.
Williams, Mr. Dorsey, and Mr. Sank (sorry if I missed anybody).

Frank Stearns
Mobile Audio
--
.
Anonymous
April 22, 2005 11:45:24 PM

Archived from groups: rec.audio.pro (More info?)

Frank Stearns <franks.pacifier.com@pacifier.net> wrote:
>
>I'm curious about two things. First, in a few cases where offset is
>present (a few mV) the voltage is opposite the labeled polarity on the
>cap. Obviously the cap hasn't blown apart from the small reversal, but
>does the distortion go up?

Yes.

>Second item is why certain cap values were chosen by the designer. Most of
>the interstage couplers are 47 uf/25 V -- perhaps a large enough value so
>that after going through a number of them the LF roll off is still below
>20 Hz. (Though if stuck using these, perhaps I should bump them up to 100
>uf for better LF?)

For the most part, it's a matter of the low frequency corner vs. price and
space.

>What I don't quite get, though, are the 2.2 uf/50V parts on the fader
>returns and outputs of most other rotary level controls. Is the idea to
>band-limit the LF so that the control action is clean(er) across a wide
>range of dirt in the part and aging? Or am I missing something?

No, they are probably going into a thing with a high input impedance.
Remember the low end corner is set by the input impedance and the
series capacitance.

>Next, the input to the L/R mix summing amps (and aux bus summers) is 1000
>uf/6.3V. Why the huge value here? Why not 100 or 470? (Not saying they
>should be that way, just curious as to why.)

Because the input impedance on that amp is VERY low to keep the noise
down.

>CAP BIASING - where electrolytic caps must be used, this seems like an
>interesting idea to try, but I wonder how best to do this. How much bias V
>do we need? If I grab, say, the 17V positive rail through dropping
>resistors to provide a couple of volts, won't there be increased crosstalk
>by some signal getting back into the pos. rail and into other bias
>injection points? (Not to mention the op amps themselves.)

Enough that it never goes through the zero-crossing region ever.

>Should I use a little regulator, say a 7803 (if there is such a beast, or
>a 7805 if not) local to each cap "pair" I'd want to bias? By pair I mean
>two electros replacing an original single cap, with the + sides tied
>back-to-back and the bias injected there. Would the output stages of such
>regulators impact the signal fidelity?

No, you can use resistors since you have a rail that is clean.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."
April 22, 2005 11:45:24 PM

Archived from groups: rec.audio.pro (More info?)

Hi,

you mentioned you are looking at the DC bias with a scope. Good.

I hope it is a dual trace scope. I have a suggestion. Set up the two
channels of the scope by attaching the two probes to the same signal
and adjust the gain and position of the scope channels so the two
traces overlap. Use AC coupling on both channels of the scope.

After you have done that, now connect the two probes to the cap in
question, one probe on each side of the cap. Feed a tone through your
circuit. You can now easily compare the signal in and out of the cap.

At low audio frequencies you will probably see some phase shift. You
can also see if the waveform is distorted by the cap.

If you have a distortion analyzer or spectrum analyzer (RTA) (and a
good generator) you can do it that way too.


If you want to make these design changes, I suggest you try to measure
the problem first so you can see how much improvement you made. After
making the measurement you may decide you don't need to make the
changes.

Let us know what you find.

Regarding your question about the cap values. The cap value needed is
also a function of the impedance of the circuit. At 60 Ohms you need
about 270 uF for -3 dB at 10 Hz. At 6,000 Ohms you only need 2.7 uF
for -3 dB at 10 Hz.

Mark
Related resources
Anonymous
April 23, 2005 2:22:48 AM

Archived from groups: rec.audio.pro (More info?)

On Fri, 22 Apr 2005 19:45:23 -0000, in rec.audio.pro Frank Stearns
<franks.pacifier.com@pacifier.net> wrote:

snip
>Second item is why certain cap values were chosen by the designer. Most of
>the interstage couplers are 47 uf/25 V -- perhaps a large enough value so
>that after going through a number of them the LF roll off is still below
>20 Hz. (Though if stuck using these, perhaps I should bump them up to 100
>uf for better LF?)
>
>What I don't quite get, though, are the 2.2 uf/50V parts on the fader
>returns and outputs of most other rotary level controls. Is the idea to
>band-limit the LF so that the control action is clean(er) across a wide
>range of dirt in the part and aging? Or am I missing something?
>
snip.
Its quite interesting to look at the LF phase response, when simulated
in LT spice, using voltage followers instead of all the gain stages.
Just make 6 or so opamps with the usual AC coupling between stages and
analyse the o/p

wierd , probably says a lot about the "sound" of a console

>Thanks again for the help and experiences in this area. Thanks to those
>who have responded to these Delta threads in the past, especially Mr.
>Williams, Mr. Dorsey, and Mr. Sank (sorry if I missed anybody).
>
>Frank Stearns
>Mobile Audio



martin

After the first death, there is no other.
(Dylan Thomas)
Anonymous
April 23, 2005 8:22:54 AM

Archived from groups: rec.audio.pro (More info?)

Frank Stearns wrote:

> In preparation for replacing or in some cases removing the
> electrolytics in my Soundcraft Delta, I've been cataloging those in
> the signal path. I've made offset measurements on both sides of many
> caps and found some with zero offset on either side. Good candidates
> for removal, I'd guess. (I did throw a 0.5 uf cap across the scope
> probe to filter the AC noise component, which was obscuring the
small
> DC offsets.)

Interesting. It seems like this information would be pretty easy to
confirm from the schematics.

> I'm curious about two things. First, in a few cases where offset is
> present (a few mV) the voltage is opposite the labeled polarity on
the
> cap. Obviously the cap hasn't blown apart from the small reversal,
but
> does the distortion go up?

In theory yes, but at this point actual performance is the most
important thing.

If you're so worried about distortion, why haven't you measured it? If
you've got a PC with an audio interface, clever use of a free software
package called the Audio Rightmark will give you a pretty complete
report on noise, distortion, and frequency response in about a minute.

> Second item is why certain cap values were chosen by the designer.
> Most of the interstage couplers are 47 uf/25 V -- perhaps a large
> enough value so that after going through a number of them the LF
roll
> off is still below 20 Hz. (Though if stuck using these, perhaps I
> should bump them up to 100 uf for better LF?)

The size of the cap is only half the story - how big are the resistors
that load the cap down? Tubed equipment usually has coupling caps on
the order of 0.1 uF to 0.5 uF, but the load impedances are typically
higher.

> What I don't quite get, though, are the 2.2 uf/50V parts on the
fader
> returns and outputs of most other rotary level controls. Is the idea
> to band-limit the LF so that the control action is clean(er) across
a
> wide range of dirt in the part and aging? Or am I missing something?

You're missing 50% of the relevant information, which is the impedance
that sets the time constant of an RC circuit, along with the size of
the cap.

> Next, the input to the L/R mix summing amps (and aux bus summers) is
> 1000 uf/6.3V. Why the huge value here? Why not 100 or 470? (Not
> saying they should be that way, just curious as to why.)

I guess that this circuit loads the caps down with lower impedances
than the other circuits.

> CAP BIASING - where electrolytic caps must be used, this seems like
an
> interesting idea to try, but I wonder how best to do this. How much
> bias V do we need?

Ideally, the bias should be larger than the peak signal voltage.

>If I grab, say, the 17V positive rail through
> dropping resistors to provide a couple of volts, won't there be
> increased crosstalk by some signal getting back into the pos. rail
> and into other bias injection points? (Not to mention the op amps
> themselves.)

The bias source should be heavily bypassed to ground to ensure that
this doesn't happen. Using large biasing resistors would help.

> Should I use a little regulator, say a 7803 (if there is such a
> beast, or a 7805 if not) local to each cap "pair" I'd want to bias?
> By pair I mean two electros replacing an original single cap, with
> the + sides tied back-to-back and the bias injected there. Would the
> output stages of such regulators impact the signal fidelity?

If you understand the purpose of bias, you will probably want to set
the biasing voltage as high as practically possible. Obviously, you
don't want to bias the caps beyond their working voltage. You don't
want to bias the caps to the point where their leakage currents upset
the operating points of the various circuits.

> Thanks again for the help and experiences in this area. Thanks to
> those who have responded to these Delta threads in the past,
> especially Mr. Williams, Mr. Dorsey, and Mr. Sank (sorry if I missed
> anybody).

I generally don't respond to recap and reopamp posts because they are
basically founded on the idea that some poorly-educated, inexperienced
guy who doesn't even know how capacitors are sized is going to improve
on a design by a well-experienced engineer who most likely does. ;-(.

My ego is plenty inflated but not so inflated that I totally
disrespect the engineering talents of the staff of the better-known,
widely respected firms like Soundcraft.
Anonymous
April 23, 2005 7:23:01 PM

Archived from groups: rec.audio.pro (More info?)

"Frank Stearns"
>
> I'm curious about two things. First, in a few cases where offset is
> present (a few mV) the voltage is opposite the labeled polarity on the
> cap. Obviously the cap hasn't blown apart from the small reversal, but
> does the distortion go up?
>

** No - not from just a few mV.


> Second item is why certain cap values were chosen by the designer. Most of
> the interstage couplers are 47 uf/25 V -- perhaps a large enough value so
> that after going through a number of them the LF roll off is still below
> 20 Hz. (Though if stuck using these, perhaps I should bump them up to 100
> uf for better LF?)


** By using a large value, the AC signal voltage across the cap is kept
small even at 20 Hz and full levels.


> What I don't quite get, though, are the 2.2 uf/50V parts on the fader
> returns and outputs of most other rotary level controls. Is the idea to
> band-limit the LF so that the control action is clean(er) across a wide
> range of dirt in the part and aging? Or am I missing something?
>


** The smaller value cap has lower DC leakage current - leakage would
create noise when the fader is moved.

Plus, the impedance of the circuit is higher here.


> Next, the input to the L/R mix summing amps (and aux bus summers) is 1000
> uf/6.3V. Why the huge value here? Why not 100 or 470? (Not saying they
> should be that way, just curious as to why.)


** The summing inputs are "virtual earth" points - so no signal voltage
appears at that point. This means that ( ideally) no signal crosstalk can
find its way from one channel to another via the summing resistors. A small
value cap at that point would allow low frequency crosstalk - so a big one
is used instead.



> CAP BIASING - where electrolytic caps must be used, this seems like an
> interesting idea to try, but I wonder how best to do this.


** Forget it - to messy and troublesome.

se bi-polar electos as these are *designed* to work with no bias and not
distort.



............... Phil
Anonymous
April 23, 2005 9:07:47 PM

Archived from groups: rec.audio.pro (More info?)

Scott Dorsey wrote:
> Frank Stearns <franks.pacifier.com@pacifier.net> wrote:
>>
>> I'm curious about two things. First, in a few cases where offset is
>> present (a few mV) the voltage is opposite the labeled polarity on
>> the cap. Obviously the cap hasn't blown apart from the small
>> reversal, but does the distortion go up?
>
> Yes.

Not really. With only a few mv DC across the cap, distortion is not an
issue. What matters is the ac level across it. This depends on the
resistance loading the cap.

>
>> Second item is why certain cap values were chosen by the designer.
>> Most of the interstage couplers are 47 uf/25 V -- perhaps a large
>> enough value so that after going through a number of them the LF
>> roll off is still below 20 Hz. (Though if stuck using these, perhaps
>> I should bump them up to 100 uf for better LF?)
>
> For the most part, it's a matter of the low frequency corner vs.
> price and space.

And cost possibly.

>
>> What I don't quite get, though, are the 2.2 uf/50V parts on the fader
>> returns and outputs of most other rotary level controls. Is the idea
>> to band-limit the LF so that the control action is clean(er) across
>> a wide range of dirt in the part and aging? Or am I missing
>> something?
>
> No, they are probably going into a thing with a high input impedance.
> Remember the low end corner is set by the input impedance and the
> series capacitance.
>
>> Next, the input to the L/R mix summing amps (and aux bus summers) is
>> 1000 uf/6.3V. Why the huge value here? Why not 100 or 470? (Not
>> saying they should be that way, just curious as to why.)
>
> Because the input impedance on that amp is VERY low to keep the noise
> down.

Actually the summing amp is essentially zero input resistance. The cap
size is chosen based on the series resister value feeding the virtual Ov
point, otherwise it would be several farads!

>
>> CAP BIASING - where electrolytic caps must be used, this seems like
>> an interesting idea to try, but I wonder how best to do this. How
>> much bias V do we need? If I grab, say, the 17V positive rail
>> through dropping resistors to provide a couple of volts, won't there
>> be increased crosstalk by some signal getting back into the pos.

The main issue here is noise form the power supply feeding into the
input.

>> rail and into other bias injection points? (Not to mention the op
>> amps themselves.)
>
> Enough that it never goes through the zero-crossing region ever.

What are you trying to say here? It dosnt make sense.

>
>> Should I use a little regulator, say a 7803 (if there is such a
>> beast, or a 7805 if not) local to each cap "pair" I'd want to bias?

This is making a mountain out of a mole hill. If one really needs to
have an unbiased electrolyte coupling cap, use a bi-polar one, which is
two back to back ones.



Kevin Aylward
informationEXTRACT@anasoft.co.uk
http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.
Anonymous
April 23, 2005 9:07:48 PM

Archived from groups: rec.audio.pro (More info?)

Kevin Aylward <see_website@anasoft.co.uk> wrote:
>
>>> rail and into other bias injection points? (Not to mention the op
>>> amps themselves.)
>>
>> Enough that it never goes through the zero-crossing region ever.
>
>What are you trying to say here? It dosnt make sense.

The problems with electrolytic linearity issues all have to do with
cases when there is very little voltage across the cap. So the
recommended design practice is to make sure there is sufficient DC
bias across the cap so that at any reasonable signal level, the cap
always has some voltage across it for any part of the waveform.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."
Anonymous
April 23, 2005 9:08:27 PM

Archived from groups: rec.audio.pro (More info?)

martin griffith wrote:
> On Fri, 22 Apr 2005 19:45:23 -0000, in rec.audio.pro Frank Stearns
> <franks.pacifier.com@pacifier.net> wrote:
>
> snip
>> Second item is why certain cap values were chosen by the designer.
>> Most of the interstage couplers are 47 uf/25 V -- perhaps a large
>> enough value so that after going through a number of them the LF
>> roll off is still below 20 Hz. (Though if stuck using these, perhaps
>> I should bump them up to 100 uf for better LF?)
>>
>> What I don't quite get, though, are the 2.2 uf/50V parts on the fader
>> returns and outputs of most other rotary level controls. Is the idea
>> to band-limit the LF so that the control action is clean(er) across
>> a wide range of dirt in the part and aging? Or am I missing
>> something?
>>
> snip.
> Its quite interesting to look at the LF phase response, when simulated
> in LT spice, using voltage followers instead of all the gain stages.
> Just make 6 or so opamps with the usual AC coupling between stages and
> analyse the o/p
>
> wierd , probably says a lot about the "sound" of a console

Unlikely.

Kevin Aylward
informationEXTRACT@anasoft.co.uk
http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.
Anonymous
April 23, 2005 9:17:05 PM

Archived from groups: rec.audio.pro (More info?)

On Sat, 23 Apr 2005 17:07:47 GMT, "Kevin Aylward"
<see_website@anasoft.co.uk> wrote:

>> Enough that it never goes through the zero-crossing region ever.
>
>What are you trying to say here? It dosnt make sense.

If the absolute voltage across the capacitor is reversed,
or actually even too low, the capacitor is nonlinear.


>This is making a mountain out of a mole hill. If one really needs to
>have an unbiased electrolyte coupling cap, use a bi-polar one, which is
>two back to back ones.

Yes, two unbiased ones.

Chris Hornbeck
"This has been an account for those who don't keep them"
J-LG, _Tout Va Bien_ 1972
Anonymous
April 24, 2005 10:16:51 AM

Archived from groups: rec.audio.pro (More info?)

Phil Allison wrote:
> "Frank Stearns"
>>
>> I'm curious about two things. First, in a few cases where offset is
>> present (a few mV) the voltage is opposite the labeled polarity on
>> the cap. Obviously the cap hasn't blown apart from the small
>> reversal, but does the distortion go up?
>>
>
> ** No - not from just a few mV.
>
>
>> Second item is why certain cap values were chosen by the designer.
>> Most of the interstage couplers are 47 uf/25 V -- perhaps a large
>> enough value so that after going through a number of them the LF
>> roll off is still below 20 Hz. (Though if stuck using these, perhaps
>> I should bump them up to 100 uf for better LF?)
>
>
> ** By using a large value, the AC signal voltage across the cap is
> kept small even at 20 Hz and full levels.
>
>
>> What I don't quite get, though, are the 2.2 uf/50V parts on the fader
>> returns and outputs of most other rotary level controls. Is the idea
>> to band-limit the LF so that the control action is clean(er) across
>> a wide range of dirt in the part and aging? Or am I missing
>> something?
>
>
> ** The smaller value cap has lower DC leakage current - leakage
> would create noise when the fader is moved.

In principle sure, in practise, irrelevant. The capacitor value at these
points are not chosen for leakage considerations. Capacitors are usually
chosen to be the smallest consistent with the desired frequency
response, and possible current noise for the mic input.

>
> Plus, the impedance of the circuit is higher here.
>
>
>> Next, the input to the L/R mix summing amps (and aux bus summers) is
>> 1000 uf/6.3V. Why the huge value here? Why not 100 or 470? (Not
>> saying they should be that way, just curious as to why.)
>
>
> ** The summing inputs are "virtual earth" points - so no signal
> voltage appears at that point. This means that ( ideally) no signal
> crosstalk can find its way from one channel to another via the
> summing resistors. A small value cap at that point would allow low
> frequency crosstalk - so a big one is used instead.

This is not why a summer junction is used. Typically the op-amps drive
the summer with a very low output resistance such that one signal
feeding the other through its summing resisters will have its x-talk
attenuated by this ideally zero output resistance, i.e. say 1/10k.

The virtual earth summer is used to prevent *level* interaction between
channels. Consider two channels sourced through say, 10k resisters with
the load 10k. If one channel was now switched off by opening the
resister, the gain of the other channel would change significantly due
to the open channel not being in parallel with the load. The virtual
summer keeps the resistance that each channel sees indepandant of the
other channels state for gain reasons. This has nothing to do with
x-talk.


Kevin Aylward
informationEXTRACT@anasoft.co.uk
http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.
Anonymous
April 24, 2005 10:17:14 AM

Archived from groups: rec.audio.pro (More info?)

Scott Dorsey wrote:
> Kevin Aylward <see_website@anasoft.co.uk> wrote:
>>
>>>> rail and into other bias injection points? (Not to mention the op
>>>> amps themselves.)
>>>
>>> Enough that it never goes through the zero-crossing region ever.
>>
>> What are you trying to say here? It dosnt make sense.
>
> The problems with electrolytic linearity issues all have to do with
> cases when there is very little voltage across the cap. So the
> recommended design practice is to make sure there is sufficient DC
> bias across the cap so that at any reasonable signal level, the cap
> always has some voltage across it for any part of the waveform.
> --scott

Ok, I understand what you are actually saying now with the term "zero
crossing" in this context. This is a little unconventional way of
talking about it. However, when there is litle signal accross a
capacitor, it won't generate any significant distortion, so its simply
not an issue.

For example, its not uncommon to have a single electrolytic cap in the
feedback network of a power amp putting out +/-70V. I can assure you
that such a cap typically allows for the amp to have 0.001% thd.

Kevin Aylward
informationEXTRACT@anasoft.co.uk
http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.
Anonymous
April 24, 2005 2:08:46 PM

Archived from groups: rec.audio.pro (More info?)

Replace the 47 uf caps with Panasonic FM 220 uf/25 v. This removes low
end rolloffs and phase shift. If you're wiggy about reverse bias, use
slow bipolar caps and bypass with a Wima MKP-2 .01 film cap. The fader
amp sees a 100k impedance, that's why the 2.2 uf value. Replace with a
Wima MKS-2 3.3 uf with a .01 MKP-2 across it.

Use a Black Gate N or NG for the 1000 uf sum cap. Bypass with good
films like MIT or InfiniCaps.

Opamps with higher gain bandwidth like 5532/OPA2134 etc. require a
redesign of the line input stage for stability. LT1358's will allow
direct coupling due to low offsets.

Replace the solo sum amp input cap to a 470 uf with a film bypass.
Replace the 22k feedback resistor with a 10 k for unity gain. Replace
the feedback cap with a 150 pf silver mica for stability.

Reverse bias is common in these mixers, the EQ section will shift bias
from positive to negative by simply rotating the frequency pot. I found
it more important to have a quality bypass around these caps, it
negates the slow response and allows the details through that normally
would be converted to heat through the electrolytic capacitor.

BTW, this info is offered as a help to the community, not to start any
trouble with you folks... So don't blow a gasket, it's only audio !

Jim Williams
Audio Upgrades
April 24, 2005 5:07:10 PM

Archived from groups: rec.audio.pro (More info?)

Frank,

if you decide to make all these changes, please make some before and
after distortion and frequency response measurements and share the
results with us.

thanks

Mark
Anonymous
April 24, 2005 9:20:36 PM

Archived from groups: rec.audio.pro (More info?)

Some pig arrogant pommy nut case:
>
Phil Allison wrote:
>
>>
>> ** The smaller value cap has lower DC leakage current - leakage
>> would create noise when the fader is moved.
>
> In principle sure, in practise, irrelevant. The capacitor value at these
> points are not chosen for leakage considerations.


** Arrant bullshit.


>
>>> Next, the input to the L/R mix summing amps (and aux bus summers) is
>>> 1000 uf/6.3V. Why the huge value here? Why not 100 or 470? (Not
>>> saying they should be that way, just curious as to why.)
>>
>>
>> ** The summing inputs are "virtual earth" points - so no signal
>> voltage appears at that point. This means that ( ideally) no signal
>> crosstalk can find its way from one channel to another via the
>> summing resistors. A small value cap at that point would allow low
>> frequency crosstalk - so a big one is used instead.
>
> This is not why a summer junction is used.


** Blatant straw man.

The issue is the reason for the high cap value.


> Typically the op-amps drive the summer with a very low output resistance
> such that one signal feeding the other through its summing resisters will
> have its x-talk attenuated by this ideally zero output resistance, i.e.
> say 1/10k.


** Wrong. In a great many desks, Soundcraft and others, group and main
buss summing resistors are driven from the wipers of the "pan" controls.




.............. Phil
Anonymous
April 24, 2005 9:20:37 PM

Archived from groups: rec.audio.pro (More info?)

Phil Allison wrote:
> Some pig arrogant pommy nut case:
>>
> Phil Allison wrote:
>>
>>>
>>> ** The smaller value cap has lower DC leakage current - leakage
>>> would create noise when the fader is moved.
>>
>> In principle sure, in practise, irrelevant. The capacitor value at
>> these points are not chosen for leakage considerations.
>
>
> ** Arrant bullshit.

Here we go again...

The dc leakage at the typical mv of offset between stages is completely
insignificant.

The capacitor is just there to ensure that as close to zero is on the
input of each stage, so that dc offsets don't multiply up. In the ideal
case, the caps dont do anything.

>
>
>>
>>>> Next, the input to the L/R mix summing amps (and aux bus summers)
>>>> is 1000 uf/6.3V. Why the huge value here? Why not 100 or 470? (Not
>>>> saying they should be that way, just curious as to why.)
>>>
>>>
>>> ** The summing inputs are "virtual earth" points - so no signal
>>> voltage appears at that point. This means that ( ideally) no signal
>>> crosstalk can find its way from one channel to another via the
>>> summing resistors. A small value cap at that point would allow low
>>> frequency crosstalk - so a big one is used instead.
>>
>> This is not why a summer junction is used.
>
>
> ** Blatant straw man.

I am correcting your erroneous assertion.

>
> The issue is the reason for the high cap value.

The fundamental reason for the high capacitor value is ensure that the
gain settings of each channel do not interact with other. It is not
there for x-talk reduction, although it might well do that as well.

>
>
>> Typically the op-amps drive the summer with a very low output
>> resistance such that one signal feeding the other through its
>> summing resisters will have its x-talk attenuated by this ideally
>> zero output resistance, i.e. say 1/10k.
>
>
> ** Wrong. In a great many desks, Soundcraft and others, group and
> main buss summing resistors are driven from the wipers of the "pan"
> controls.

Oh dear...those cheaper ones...well, I'll give you some points for that
one...

Nothing changes mate. The fundamental reason, for the virtual earth
summer, as I correctly stated, is to prevent selection of one signal
effecting the level of another signal. Try adding voltages any other
way, and you'll get the point, but then probably not.


Kevin Aylward
informationEXTRACT@anasoft.co.uk
http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.
Anonymous
April 24, 2005 11:07:33 PM

Archived from groups: rec.audio.pro (More info?)

Kevin Aylward wrote:

> For example, its not uncommon to have a single electrolytic
> cap in the feedback network of a power amp putting out +/-70V.
> I can assure you that such a cap typically allows for the amp
> to have 0.001% thd.

Kevin, have you tried replacing that cap with something relevantly
non-electrolytic and listened?

> Kevin Aylward


Kind regards

Peter Larsen

--
*******************************************
* My site is at: http://www.muyiovatki.dk *
*******************************************
Anonymous
April 24, 2005 11:07:34 PM

Archived from groups: rec.audio.pro (More info?)

Kevin Aylward wrote:
>
> For example, its not uncommon to have a single electrolytic
> cap in the feedback network of a power amp putting out +/-70V.
> I can assure you that such a cap typically allows for the amp
> to have 0.001% thd.

Sure, and if the amp is well-designed, it has DC offset on the cap.
Not a hard thing to do (since the output should have zero quiescent
current and the input stage is easy to design to run with a higher
voltage on the base or grid).
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."
Anonymous
April 25, 2005 5:20:54 AM

Archived from groups: rec.audio.pro (More info?)

"Mark" <makolber@yahoo.com> writes:

>if you decide to make all these changes, please make some before and
>after distortion and frequency response measurements and share the
>results with us.

I will indeed. Some excellent suggestions have been made on these various
Delta threads and especially this one; the least I can do is report the
results -- what worked; what didn't.

Step one has been bringing the thing back to a starting point. Simply
replacing all the worn/noisy switches, failing 1/4" normalling phone
jacks, and the mother and monitor ribbon cables has made an obvious
difference already. I have new power supplies awaiting mounting on a rack
panel.

I have at least two shorted caps; several others I suspect of losing
value, as right now the bottom on this console just isn't what it ought to
be. Unfortunately I don't have access to an AP, nor can I plunk down
US$10K to get one. A friend has a Neutrik Minilyzer, but am not sure that
it will have the resolution to do precise measurements but will
investigate that, as well as PC-based analyzer options. I can still do
some crude tests with the generator and scope.

I'd like to have Jim Williams do the whole console, but alas funds are a
bit tight and more importantly, I wouldn't learn nearly as much as I have
by wrapping myself in the schematics and looking around with the scope.

The basic design of each Delta module seems pretty good (and it *is* a
modular console), but as is nearly always case these systems are designed
to a price point -- at least with parts. Nothing wrong with that of
course; meeting a stated design target on budget (and producing a good
value for the market) is good engineering.

But if in the process of replacing parts that need it anyway I can move
that equivalent price point a little (or a lot), and not screw up the
design, I should have a very sweet sounding console, and without getting
into huge piles of cash. I hope.

Thanks again to all for your input. More later.

Frank Stearns
Mobile Audio
--
.
Anonymous
April 25, 2005 11:43:17 AM

Archived from groups: rec.audio.pro (More info?)

Sounds like someone has blown a gasket. If you react so negativly to
freely offered information, I suspect you may have a heart attack if
anyone dared charge you for anything. I don't think you own a Delta
console so I wonder why you are even here...

BTW, I don't need to advertise for work, I have enough already, feel
free to not ever ask me for anything.

Go take a walk in the garden, find a girlfriend, go kill a cat and
switch to de-caf! One of these should work for you.

Jim Williams
Audio Upgrades
Anonymous
April 25, 2005 12:25:02 PM

Archived from groups: rec.audio.pro (More info?)

Have you actually _listened_ to said preamp?
Anonymous
April 25, 2005 2:21:50 PM

Archived from groups: rec.audio.pro (More info?)

Frank Stearns <franks.pacifier.com@pacifier.net> wrote:
>
>I have at least two shorted caps; several others I suspect of losing
>value, as right now the bottom on this console just isn't what it ought to
>be. Unfortunately I don't have access to an AP, nor can I plunk down
>US$10K to get one. A friend has a Neutrik Minilyzer, but am not sure that
>it will have the resolution to do precise measurements but will
>investigate that, as well as PC-based analyzer options. I can still do
>some crude tests with the generator and scope.

You can do some incredibly powerful tests with the generator and scope.

The handiest one is just running a 1 KHz square wave through the thing
with the controls flat. If the top of the squarewave slopes down, you
have a low frequency response problem. If it slopes up, you have a
high frequency response problem. If the leading edge rings, you have
an impulse problem of some sort. It is a very quick and easy way to get
a good notion of the average health of the system. And if you have a
problem, you can use the scope and go from stage to stage until you find
the offender.

>But if in the process of replacing parts that need it anyway I can move
>that equivalent price point a little (or a lot), and not screw up the
>design, I should have a very sweet sounding console, and without getting
>into huge piles of cash. I hope.

Replace all the electrolytics first.... switches and pots might be fixable
by cleaning and a little Cailube, but until you get the leaky caps out you
don't know if there's a real problem or not.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."
Anonymous
April 25, 2005 5:21:39 PM

Archived from groups: rec.audio.pro (More info?)

Scott Dorsey wrote:
> Kevin Aylward wrote:
>>
>> For example, its not uncommon to have a single electrolytic
>> cap in the feedback network of a power amp putting out +/-70V.
>> I can assure you that such a cap typically allows for the amp
>> to have 0.001% thd.
>
> Sure, and if the amp is well-designed, it has DC offset on the cap.

Not at all. There is no practical reason to run a DC offset on the cap,
and the majority of well designed professional power amps, imo, don't do
this. Do you have any in mind that do?


In principle, I am happier using a bipolar, but at the end of the day,
its matters little.

> Not a hard thing to do (since the output should have zero quiescent
> current and the input stage is easy to design to run with a higher
> voltage on the base or grid).
> --scott

I know of no standard power amps that this.

Kevin Aylward
informationEXTRACT@anasoft.co.uk
http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.
Anonymous
April 25, 2005 5:21:40 PM

Archived from groups: rec.audio.pro (More info?)

Kevin Aylward <see_website@anasoft.co.uk> wrote:
>Scott Dorsey wrote:
>> Kevin Aylward wrote:
>>>
>>> For example, its not uncommon to have a single electrolytic
>>> cap in the feedback network of a power amp putting out +/-70V.
>>> I can assure you that such a cap typically allows for the amp
>>> to have 0.001% thd.
>>
>> Sure, and if the amp is well-designed, it has DC offset on the cap.
>
>Not at all. There is no practical reason to run a DC offset on the cap,
>and the majority of well designed professional power amps, imo, don't do
>this. Do you have any in mind that do?

All the ones I can think of that use an overall feedback path do,
which includes everything from the old Citation II to the modern Adcom
555.

If there _wasn't_ any DC offset on it, you wouldn't need a cap there at
all, and you could save a few pennies.

>In principle, I am happier using a bipolar, but at the end of the day,
>its matters little.
>
>> Not a hard thing to do (since the output should have zero quiescent
>> current and the input stage is easy to design to run with a higher
>> voltage on the base or grid).
>
>I know of no standard power amps that this.

Most of them do it naturally. The input stage is a differential pair
with the input bases held at a reasonable bias point for the input stage
to be in class A. So there's some voltage on the base to begin with.
If the input stage is running off of split rails you can even do some
tinkering with the collector resistors so that the base voltage is
anywhere you want it to be with respect to ground.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."
Anonymous
April 25, 2005 5:22:48 PM

Archived from groups: rec.audio.pro (More info?)

Peter Larsen wrote:
> Kevin Aylward wrote:
>
>> For example, its not uncommon to have a single electrolytic
>> cap in the feedback network of a power amp putting out +/-70V.
>> I can assure you that such a cap typically allows for the amp
>> to have 0.001% thd.
>
> Kevin, have you tried replacing that cap with something relevantly
> non-electrolytic and listened?

If the distortion is 0.001%, I see no reason to comparison listen to
them at all, and I don't.

Kevin Aylward
informationEXTRACT@anasoft.co.uk
http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.
Anonymous
April 25, 2005 5:22:49 PM

Archived from groups: rec.audio.pro (More info?)

Kevin Aylward <see_website@anasoft.co.uk> wrote:
>Peter Larsen wrote:
>> Kevin Aylward wrote:
>>
>>> For example, its not uncommon to have a single electrolytic
>>> cap in the feedback network of a power amp putting out +/-70V.
>>> I can assure you that such a cap typically allows for the amp
>>> to have 0.001% thd.
>>
>> Kevin, have you tried replacing that cap with something relevantly
>> non-electrolytic and listened?
>
>If the distortion is 0.001%, I see no reason to comparison listen to
>them at all, and I don't.

I can give you two amps with similarly low high-level distortion figures,
which sound audibly different in a very obvious way, and which have
very different looking outputs on a scope given a 1 KC square wave input.

This is why THD is no longer as useful as it used to be. It's still a
handy tool for comparing circuits of similar topology in similar
situations, but it's not very general-purpose.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."
Anonymous
April 25, 2005 7:30:19 PM

Archived from groups: rec.audio.pro (More info?)

Scott Dorsey wrote:
> Kevin Aylward <see_website@anasoft.co.uk> wrote:
>> Peter Larsen wrote:
>>> Kevin Aylward wrote:
>>>
>>>> For example, its not uncommon to have a single electrolytic
>>>> cap in the feedback network of a power amp putting out +/-70V.
>>>> I can assure you that such a cap typically allows for the amp
>>>> to have 0.001% thd.
>>>
>>> Kevin, have you tried replacing that cap with something relevantly
>>> non-electrolytic and listened?
>>
>> If the distortion is 0.001%, I see no reason to comparison listen
to
>> them at all, and I don't.
>
> I can give you two amps with similarly low high-level distortion
> figures, which sound audibly different in a very obvious way, and
> which have
> very different looking outputs on a scope given a 1 KC square wave
> input.

Well yes, but at last one of them is a bad amp. Most modern amps have
good nonlinear distortion performance at both low and high levels.
Anonymous
April 25, 2005 7:50:40 PM

Archived from groups: rec.audio.pro (More info?)

Arny Krueger <arnyk@hotpop.com> wrote:
>>
>> I can give you two amps with similarly low high-level distortion
>> figures, which sound audibly different in a very obvious way, and
>> which have
>> very different looking outputs on a scope given a 1 KC square wave
>> input.
>
>Well yes, but at last one of them is a bad amp. Most modern amps have
>good nonlinear distortion performance at both low and high levels.

Just one word: Stewart.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."
Anonymous
April 25, 2005 8:14:23 PM

Archived from groups: rec.audio.pro (More info?)

jwilliams3@audioupgrades.com wrote:
> Sounds like someone has blown a gasket. If you react so negativly to
> freely offered information, I suspect you may have a heart attack if
> anyone dared charge you for anything.

I have an aversion to people ripping of the general layman public with
snakeoilsmanship. I suppose you also sell those $200 mains cables that
add dynamic transparency to the overall sonic enjoyment.

>I don't think you own a Delta
> console so I wonder why you are even here...

Why on earth would I want to own one?

Kevin Aylward
informationEXTRACT@anasoft.co.uk
http://www.anasoft.co.uk/EE/index.html
http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.
Anonymous
April 25, 2005 8:14:54 PM

Archived from groups: rec.audio.pro (More info?)

TheBenevolentUniversePremise@gmail.com wrote:
> Have you actually _listened_ to said preamp?

Why? It will sound identical to any other preamp with 1/10 the spec, and
1/100 the price.

Kevin Aylward
informationEXTRACT@anasoft.co.uk
http://www.anasoft.co.uk/EE/index.html
http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.
Anonymous
April 25, 2005 8:15:32 PM

Archived from groups: rec.audio.pro (More info?)

Scott Dorsey wrote:
> Kevin Aylward <see_website@anasoft.co.uk> wrote:
>> Peter Larsen wrote:
>>> Kevin Aylward wrote:
>>>
>>>> For example, its not uncommon to have a single electrolytic
>>>> cap in the feedback network of a power amp putting out +/-70V.
>>>> I can assure you that such a cap typically allows for the amp
>>>> to have 0.001% thd.
>>>
>>> Kevin, have you tried replacing that cap with something relevantly
>>> non-electrolytic and listened?
>>
>> If the distortion is 0.001%, I see no reason to comparison listen to
>> them at all, and I don't.
>
> I can give you two amps with similarly low high-level distortion
> figures, which sound audibly different in a very obvious way, and
> which have very different looking outputs on a scope given a 1 KC
> square wave input.

Complete and utter nonsense. Well, not unless one has a BW of 1Khz and
the other 20Khz. Assuming the amps are competently designed, i.e. have
similar stability phase margins etc.

Nothing but mumbo jumbo I see here.

>
> This is why THD is no longer as useful as it used to be.

Oh dear...here we go again...

Nonsense.

>It's still a
> handy tool for comparing circuits of similar topology in similar
> situations, but it's not very general-purpose.
> --scott

If the thd/imd is below say, 0.01%, and say power BW of 50Khz, and the
amp is competently designed, i.e. no spurious dynamic biasing issues,
stable etc, then they all sound the same. Period.

Kevin Aylward
informationEXTRACT@anasoft.co.uk
http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.
Anonymous
April 25, 2005 8:16:47 PM

Archived from groups: rec.audio.pro (More info?)

Scott Dorsey wrote:
> Kevin Aylward <see_website@anasoft.co.uk> wrote:
>> Scott Dorsey wrote:
>>> Kevin Aylward wrote:
>>>>
>>>> For example, its not uncommon to have a single electrolytic
>>>> cap in the feedback network of a power amp putting out +/-70V.
>>>> I can assure you that such a cap typically allows for the amp
>>>> to have 0.001% thd.
>>>
>>> Sure, and if the amp is well-designed, it has DC offset on the cap.
>>
>> Not at all. There is no practical reason to run a DC offset on the
>> cap, and the majority of well designed professional power amps, imo,
>> don't do this. Do you have any in mind that do?
>
> All the ones I can think of that use an overall feedback path do,
> which includes everything from the old Citation II to the modern Adcom
> 555.

Weeeel, this is indeed news to me. I don't belive you untill I see a
circuit.

I can probably dig out 1000's that don't do what you claim.

>
> If there _wasn't_ any DC offset on it, you wouldn't need a cap there
> at all, and you could save a few pennies.
>
>> In principle, I am happier using a bipolar, but at the end of the
>> day, its matters little.
>>
>>> Not a hard thing to do (since the output should have zero quiescent
>>> current and the input stage is easy to design to run with a higher
>>> voltage on the base or grid).
>>
>> I know of no standard power amps that this.
>
> Most of them do it naturally.

Not at all.


> The input stage is a differential pair

Well, you got that bit right.

>
> with the input bases held at a reasonable bias point for the input
> stage to be in class A. So there's some voltage on the base to begin
> with.

No. Essentially, all split rail power amps that I have ever seen, have
the inputs connected to ground, and I have seen and designed quite a few
indeed.

>If the input stage is running off of split rails you can even
> do some tinkering with the collector resistors so that the base
> voltage is anywhere you want it to be with respect to ground.
> --scott

Oh dear...you want to mess with the collector resisters to have an
offset on the input? Ahmmm... and just how many amplifiers do you say
you have actually designed?

hint: http://www.anasoft.co.uk/EE/index.html

Kevin Aylward
informationEXTRACT@anasoft.co.uk
http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.
Anonymous
April 25, 2005 8:16:48 PM

Archived from groups: rec.audio.pro (More info?)

Kevin Aylward <see_website@anasoft.co.uk> wrote:
>
>Oh dear...you want to mess with the collector resisters to have an
>offset on the input? Ahmmm... and just how many amplifiers do you say
>you have actually designed?

Sure, you can have all the offset on the input that you want! After
all, there's a DC blocking cap! (Note that by input I was referring to
the negative-going input on the differential pair that is used for feedback,
but of course if you offset one side of the differential pair, you offset
both of them).

>hint: http://www.anasoft.co.uk/EE/index.html

Sorry, I tried to look at the "very low distortion amp" circuits, but the
resolution was very poor and they were pretty much unreadable, so I can't
judge anything either way.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."
Anonymous
April 25, 2005 8:26:16 PM

Archived from groups: rec.audio.pro (More info?)

On Mon, 25 Apr 2005 01:20:54 -0000, Frank Stearns
<franks.pacifier.com@pacifier.net> wrote:

>"Mark" <makolber@yahoo.com> writes:
>
>>if you decide to make all these changes, please make some before and
>>after distortion and frequency response measurements and share the
>>results with us.
>
>I will indeed. Some excellent suggestions have been made on these various

>...

>be. Unfortunately I don't have access to an AP, nor can I plunk down
>US$10K to get one. A friend has a Neutrik Minilyzer, but am not sure that
>it will have the resolution to do precise measurements but will
>investigate that, as well as PC-based analyzer options. I can still do
>some crude tests with the generator and scope.

Try this:
http://rightmark.org/

>Frank Stearns
>Mobile Audio

-----
http://mindspring.com/~benbradley
Anonymous
April 25, 2005 9:46:41 PM

Archived from groups: rec.audio.pro (More info?)

Kevin Aylward wrote:
> TheBenevolentUniversePremise@gmail.com wrote:
>
>>Have you actually _listened_ to said preamp?
>
>
> Why? It will sound identical to any other preamp with 1/10 the spec, and
> 1/100 the price.

I like this man. :-)


Bob
--

"Things should be described as simply as possible, but no
simpler."

A. Einstein
Anonymous
April 25, 2005 9:46:45 PM

Archived from groups: rec.audio.pro (More info?)

"Kevin Aylward" <see_website@anasoft.co.uk> writes:

>If the thd/imd is below say, 0.01%, and say power BW of 50Khz, and the
>amp is competently designed, i.e. no spurious dynamic biasing issues,
>stable etc, then they all sound the same. Period.

Kevin -

Thank you for your observations, but please -- could you describe your
room where you're making these peceptual observations -- LEDE? RFZ?
Hybrid? Other? Any acoustical treatment at all?

Indeed things often *do* sound much the same in a typical room, even with
high-end monitors. But as I found out moving into a properly-treated room
suddenly many new details were revealed, and the ease of hearing
differences (regardless of the item or project) went up dramatically.

Such rooms also help solidly eliminate imagined differences.

Frank Stearns
Mobile Audio

--
.
Anonymous
April 25, 2005 9:46:46 PM

Archived from groups: rec.audio.pro (More info?)

Frank Stearns wrote:
> "Kevin Aylward" <see_website@anasoft.co.uk> writes:
>
>> If the thd/imd is below say, 0.01%, and say power BW of 50Khz, and
>> the amp is competently designed, i.e. no spurious dynamic biasing
>> issues, stable etc, then they all sound the same. Period.
>
> Kevin -
>
> Thank you for your observations, but please -- could you describe
your
> room where you're making these peceptual observations -- LEDE? RFZ?
> Hybrid? Other? Any acoustical treatment at all?

Let's make it easy and do our listening tests with some really-pretty
good headphones - say HD 580s.
Anonymous
April 25, 2005 9:58:07 PM

Archived from groups: rec.audio.pro (More info?)

<jwilliams3@audioupgrades.com> wrote in message
news:1114440197.577541.75960@l41g2000cwc.googlegroups.com...
> Sounds like someone has blown a gasket. If you react so negativly to
> freely offered information, I suspect you may have a heart attack if
> anyone dared charge you for anything. I don't think you own a Delta
> console so I wonder why you are even here...


To spoil the party for a potentially large number of people around the world
who silently follow this thread with keen interest in the subject - which
happens to be related to rather popular Soundcraft Delta consoles and not to
some frustrations of personal nature - the people who stand a chance of
actually benefitting from your generous sharing of what could be considered
proprietary information.

That's how it looks from where I stand.

Predrag
Anonymous
April 25, 2005 9:58:08 PM

Archived from groups: rec.audio.pro (More info?)

"Predrag Trpkov" <predrag.trpkovNeSpamu@ri.htnet.hr> writes:
><jwilliams3@audioupgrades.com> wrote in message
>news:1114440197.577541.75960@l41g2000cwc.googlegroups.com...
>> Sounds like someone has blown a gasket. If you react so negativly to
>> freely offered information, I suspect you may have a heart attack if
>> anyone dared charge you for anything. I don't think you own a Delta
>> console so I wonder why you are even here...

>To spoil the party for a potentially large number of people around the world
>who silently follow this thread with keen interest in the subject - which
>happens to be related to rather popular Soundcraft Delta consoles and not to
>some frustrations of personal nature - the people who stand a chance of
>actually benefitting from your generous sharing of what could be considered
>proprietary information.

>That's how it looks from where I stand.

Indeed, Mr. Williams has been very generous with his time and help.

Years ago I was in the "if the numbers don't show it, it's not real"
camp. Then I got into a very good room with decent monitoring and a whole
new world opened up. Differences brought on by changing parts that spec'd
the "same" were no longer subtle or ambiguous, they were consistently (and
sometime painfully) obvious.

Numbers can tell the story -- problem is that after all these years we
*still* don't commonly use enough descriptive numbers to tell the whole
story. Moreover, marketing departments would have a hard time trying to
put a good spin on these numbers and not confuse the average user.

In the late 1940s engineers fought over whether AM radio would
benefit by extending the bandwidth from 5 KHz to 15 KHz. The advocates
were considered silly and ill-informed -- why, anyone knew that a 15KHz
bandwidth sounded terrible so why waste all that money upgrading the
systems?

If I remember the story correctly, Avery Fisher set up a *live* orchestra
behind an acoustically transparent (but visually opaque) curtain that in
turn had tunable acoustic elements behind it. The live audience would hear
either a 5KHz or 15KHz acoustical bandwidth. A nice ABX test. Of course,
the full-bandwidth sound won easily.

Follow-on research revealed that the original electrical systems had
terrible distortion in the high bands, something that in the day many
opposing engineers had not considered. It was outside their current
orthodoxy, so they ignored or belittled the notion of 15KHz bandwidth.

(We saw similar attitudes among some engineers early on with CDs. CDs
measured "perfect" therefore were perfect, until someone described the
notion of jitter -- with numbers -- and how it could affect the perceived
sound.)

And so it is with the modifications that Mr. Williams and others do --
there's nothing voodoo about them. (And many design engineers probably
know exactly the same tricks but are limited by management to a specific
design/build budget.)

One of my contentions is that some of these mods really show their true
worth at the very *end* of a signal chain -- the consumer's playback
system. The cleaner you start back at the very beginning, the more "room"
you have to accumulate various inevitable distortions before bumping into
the corresponding thresholds of human perception. And this accumulation
seems to be of a logrithmic nature, which reinforces the notion of keeping
that signal as pure as you can for as long as you can before those
accumulative step-ups start getting large.

Happy recording.

Frank Stearns
Mobile Audio
--
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Anonymous
April 25, 2005 10:50:29 PM

Archived from groups: rec.audio.pro (More info?)

Frank Stearns wrote:
> "Predrag Trpkov" <predrag.trpkovNeSpamu@ri.htnet.hr> writes:
>> <jwilliams3@audioupgrades.com> wrote in message
>> news:1114440197.577541.75960@l41g2000cwc.googlegroups.com...
>>> Sounds like someone has blown a gasket. If you react so negativly to
>>> freely offered information, I suspect you may have a heart attack if
>>> anyone dared charge you for anything. I don't think you own a Delta
>>> console so I wonder why you are even here...
>
>> To spoil the party for a potentially large number of people around
>> the world who silently follow this thread with keen interest in the
>> subject - which happens to be related to rather popular Soundcraft
>> Delta consoles and not to some frustrations of personal nature - the
>> people who stand a chance of actually benefitting from your generous
>> sharing of what could be considered proprietary information.
>
>> That's how it looks from where I stand.
>
> Indeed, Mr. Williams has been very generous with his time and help.

Yes, but like anyone who posts, its always for a purpose. He expects a
return. No one does anything that they know will be net detriment to
themselves. Its basic evolution.

http://www.anasoft.co.uk/replicators/index.html

I am not the bad guy here. The idea of trying to sell people gear at
outrageous prices on the basis of specs that are proven to be values is
criminal in my books.

>
> Years ago I was in the "if the numbers don't show it, it's not real"
> camp. Then I got into a very good room with decent monitoring and a
> whole new world opened up. Differences brought on by changing parts
> that spec'd the "same" were no longer subtle or ambiguous, they were
> consistently (and sometime painfully) obvious.

One needs to know what one means by specs the same. Sure, one might be
able to detect 1% second harmonic distortion from 1% 3rd harmonic
distortion, but try that at the 0.01% level with speakers at 1%, no
chance.

The problem with specs is that often the spec are wrong or misleading.
The specs tell the story if they are correct and fully understood.

>
> Numbers can tell the story
>-- problem is that after all these years we
> *still* don't commonly use enough descriptive numbers to tell the
> whole story. Moreover, marketing departments would have a hard time
> trying to put a good spin on these numbers and not confuse the
> average user.
>
> In the late 1940s engineers fought over whether AM radio would
> benefit by extending the bandwidth from 5 KHz to 15 KHz. The advocates
> were considered silly and ill-informed -- why, anyone knew that a
> 15KHz bandwidth sounded terrible so why waste all that money
> upgrading the systems?

This is a poor argument as we know a lot more now then we do then.
Extensive tests have now been done that quantifies much that was guessed
at at that time.

>
> If I remember the story correctly, Avery Fisher set up a *live*
> orchestra behind an acoustically transparent (but visually opaque)
> curtain that in turn had tunable acoustic elements behind it. The
> live audience would hear either a 5KHz or 15KHz acoustical bandwidth.
> A nice ABX test. Of course, the full-bandwidth sound won easily.
>
> Follow-on research revealed that the original electrical systems had
> terrible distortion in the high bands, something that in the day many
> opposing engineers had not considered. It was outside their current
> orthodoxy, so they ignored or belittled the notion of 15KHz bandwidth.

I doubt this. The considered it, and ignored it.


>
> (We saw similar attitudes among some engineers early on with CDs. CDs
> measured "perfect" therefore were perfect, until someone described the
> notion of jitter -- with numbers -- and how it could affect the
> perceived sound.)

They were never measured perfect. The limitations were always known. We
had a lot of hype from companies trying to sell product despite the
shortcomings of that equipment.

>
> And so it is with the modifications that Mr. Williams and others do --
> there's nothing voodoo about them. (And many design engineers probably
> know exactly the same tricks but are limited by management to a
> specific design/build budget.)

Selling a two channel mic amp for $1500 is snake oil. There is zero
chance that its value for money.

>
> One of my contentions is that some of these mods really show their
> true worth at the very *end* of a signal chain -- the consumer's
> playback system. The cleaner you start back at the very beginning,
> the more "room" you have to accumulate various inevitable distortions
> before bumping into the corresponding thresholds of human perception.
> And this accumulation seems to be of a logrithmic nature, which
> reinforces the notion of keeping that signal as pure as you can for
> as long as you can before those accumulative step-ups start getting
> large.
>

There is a sensible limit. Anything better is worthless. You cant get
any better then the weakest link in the chain. This is the speakers. To
get distortion lower then 1% costs you an arm and a leg. To get speakers
flat to 1db, costs the other arm and leg.

Kevin Aylward
informationEXTRACT@anasoft.co.uk
http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.
Anonymous
April 25, 2005 10:51:59 PM

Archived from groups: rec.audio.pro (More info?)

Frank Stearns wrote:
> "Kevin Aylward" <see_website@anasoft.co.uk> writes:
>
>> If the thd/imd is below say, 0.01%, and say power BW of 50Khz, and
>> the amp is competently designed, i.e. no spurious dynamic biasing
>> issues, stable etc, then they all sound the same. Period.
>
> Kevin -
>
> Thank you for your observations,

Not just mine, but reputable and repeatable experiments by many
researches.

> but please -- could you describe your
> room where you're making these peceptual observations -- LEDE? RFZ?
> Hybrid? Other? Any acoustical treatment at all?

Name any room you like. It matters squat. Its a dead issue.

>
> Indeed things often *do* sound much the same in a typical room, even
> with high-end monitors. But as I found out moving into a
> properly-treated room suddenly many new details were revealed, and
> the ease of hearing differences (regardless of the item or project)
> went up dramatically.
>
> Such rooms also help solidly eliminate imagined differences.
>

This has all been thrashed 30 odd years ago. Loads of AB tests etc. It
was all the rage. Those golden ear ears boys all claiming differences
that proved as worthless as astrology. Why this sort of nonsense is
still persisting today is pretty much incredible.

Just considering a 1% distortion of a speaker for 1% verses 1.01% should
tell one something about how dubious to be able to detect 0.01%
differances.

High end audio is a scam to make money. Its that simple.

Kevin Aylward
informationEXTRACT@anasoft.co.uk
http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.
Anonymous
April 25, 2005 10:52:00 PM

Archived from groups: rec.audio.pro (More info?)

Kevin Aylward <see_website@anasoft.co.uk> wrote:
>Just considering a 1% distortion of a speaker for 1% verses 1.01% should
>tell one something about how dubious to be able to detect 0.01%
>differances.

If the 1% is all second harmonic distortion and the 0.1% is high order
non-harmonic trash, it's not dubious at all.

>High end audio is a scam to make money. Its that simple.

Much of it is, but what does that have to do with anything?
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."
Anonymous
April 25, 2005 11:03:31 PM

Archived from groups: rec.audio.pro (More info?)

Kevin Aylward wrote:
> TheBenevolentUniversePremise@gmail.com wrote:
> > Have you actually _listened_ to said preamp?
>
> Why? It will sound identical to any other preamp with 1/10 the spec,
and
> 1/100 the price.

So Jim's preamp sounds the same as a two channel preamp that costs $15?
Anonymous
April 25, 2005 11:15:25 PM

Archived from groups: rec.audio.pro (More info?)

Scott Dorsey wrote:
> Kevin Aylward <see_website@anasoft.co.uk> wrote:
>>
>> Oh dear...you want to mess with the collector resisters to have an
>> offset on the input? Ahmmm... and just how many amplifiers do you say
>> you have actually designed?
>
> Sure, you can have all the offset on the input that you want! After
> all, there's a DC blocking cap!

But one doesn't do that by tinkering with the collector resistors of the
input transistors. That's, dare I say, just plain daft, and don't work.

Its like nails scratching nails down a blackboard to us analogue
designers. There are so many reasons not to try this. Indeed, in my
current designs, there arnt any, its all current sources.

>(Note that by input I was referring
> to the negative-going input on the differential pair that is used for
> feedback, but of course if you offset one side of the differential
> pair, you offset both of them)

You also offset the output, which don't do very nice things to the
speaker.

To further clarify, if you offset the + input, the negative input will
follow. If you offset the - input, you have to force the + input to
follow. By itself, it will stay just where you set it.

To do what you suggest requires having the + input as usual, that is
connected to Ov in order to ensure that the output is also zero. The
bypass capacitor is then offset with a voltage and fed via a resister.
The junction of the resister and cap would then be bypassed solidly to
the 0v reference point to minimise distortion and hum loops. Since we
now have two caps, it would be simpler to just wire them in series back
to back without the bias circuit at all.

Again, I have never seen a power amp using an offset bias in this
manner. I cant believe its done until I see some evidence for it. I
certainly don't see it gaining anything from a technical point of view.

>
>> hint: http://www.anasoft.co.uk/EE/index.html
>
> Sorry, I tried to look at the "very low distortion amp" circuits, but
> the resolution was very poor and they were pretty much unreadable,

Strange, it aint that good, but its certainly readable on my system.

> so
> I can't judge anything either way.

Well, if you download SuperSpice, I can send you the proper schematic so
that you can simulate it.

Kevin Aylward
informationEXTRACT@anasoft.co.uk
http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.
Anonymous
April 25, 2005 11:15:26 PM

Archived from groups: rec.audio.pro (More info?)

Kevin Aylward <see_website@anasoft.co.uk> wrote:
>Scott Dorsey wrote:
>input transistors. That's, dare I say, just plain daft, and don't work.
>
>Its like nails scratching nails down a blackboard to us analogue
>designers. There are so many reasons not to try this. Indeed, in my
>current designs, there arnt any, its all current sources.
>
>>(Note that by input I was referring
>> to the negative-going input on the differential pair that is used for
>> feedback, but of course if you offset one side of the differential
>> pair, you offset both of them)
>
>You also offset the output, which don't do very nice things to the
>speaker.

No. There is a capacitor in the way. That's the point. You want that
offset on the capacitor.

>
>To further clarify, if you offset the + input, the negative input will
>follow. If you offset the - input, you have to force the + input to
>follow. By itself, it will stay just where you set it.
>
>To do what you suggest requires having the + input as usual, that is
>connected to Ov in order to ensure that the output is also zero.

No, the + input is also floating above ground. There is a DC blocking
cap between the input jack and the + input. If you raise the voltage
of one input, you raise the voltage of the other.

>The
>bypass capacitor is then offset with a voltage and fed via a resister.
>The junction of the resister and cap would then be bypassed solidly to
>the 0v reference point to minimise distortion and hum loops. Since we
>now have two caps, it would be simpler to just wire them in series back
>to back without the bias circuit at all.

There is _already_ a bias circuit. We aren't _adding_ anything here.

>>> hint: http://www.anasoft.co.uk/EE/index.html
>>
>> Sorry, I tried to look at the "very low distortion amp" circuits, but
>> the resolution was very poor and they were pretty much unreadable,
>
>Strange, it aint that good, but its certainly readable on my system.

My problem is that I couldn't read the numbers on the parts, either on
the screen or printing it out. So I can't say things like "what is the
base on Q1" set to, because I can't tell if that is Q1 or Q7.

>> so
>> I can't judge anything either way.
>
>Well, if you download SuperSpice, I can send you the proper schematic so
>that you can simulate it.

I'll pass, although we have Spice on the HP-UX boxes here.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."
Anonymous
April 25, 2005 11:19:13 PM

Archived from groups: rec.audio.pro (More info?)

"Kevin Aylward" <see_website@anasoft.co.uk> wrote in message
news:VZabe.5125$8d4.2309@fe1.news.blueyonder.co.uk...

> The problem with specs is that often the spec are wrong or misleading.
> The specs tell the story if they are correct and fully understood.

Trouble is, they never are. Never. Proper specs would include full harmonic
spectra at high *and* low levels, into various loads, and various two- and
three-tone intermodulation spectra. For example, I've measured some
sound-cards that tested wonderfully on every harmonic-distortion test I
tried, no problem. Then I tried three-tone high-frequency IM tests and,
whoa, some tested really well and some didn't. Manufacturers don't publish
those specs.

> Selling a two channel mic amp for $1500 is snake oil. There is zero
> chance that its value for money.

Excuse me, but that's tommyrot. I suggest you spend some time with a Great
River preamp and a cheaper preamp with as close a frequency response as you
can find. Do some listening tests, making sure you match levels carefully.
You will almost certainly hear the difference. Then use both for ten years,
and see which one is broken. More expensive preamps usually do sound better,
and they're also better built, which is part of what professional gear is
about.

But then, if it tests so well that you know you won't hear a difference, you
probably won't hear a difference. You will, however, notice the scratchy
pots and busted switches ten years down the road.

> There is a sensible limit. Anything better is worthless. You cant get
> any better then the weakest link in the chain. This is the speakers. To
> get distortion lower then 1% costs you an arm and a leg. To get speakers
> flat to 1db, costs the other arm and leg.

The latter points are quite correct. The former is not. The facts of
information theory are that the total chain is always *worse* than its
weakest link. If there is degradation of the signal in the early stages of
the chain, generating harmonic and intermodulation distortion products,
these products will generate further distortions downstream in addition to
the distortions generated by the original program material. Cleanliness is a
virtue even with imperfect devices at the end of the chain. And cleanliness
means keeping the distortions that are most annoying to the ear out of the
chain. Which is why that amp with .001% THD may still be a stinker, if the
distortion harmonic is 9th or 11th, and it produces IM at low levels.

Specs are useful things, but until we've found specs that correlate
perfectly with human hearing, and use them, they're at best an imperfect map
of the behavior of electronic devices.

Peace,
Paul
Anonymous
April 25, 2005 11:24:35 PM

Archived from groups: rec.audio.pro (More info?)

Scott Dorsey wrote:
> Kevin Aylward <see_website@anasoft.co.uk> wrote:
>> Just considering a 1% distortion of a speaker for 1% verses 1.01%
>> should tell one something about how dubious to be able to detect
>> 0.01% differances.
>
> If the 1% is all second harmonic distortion and the 0.1% is high order
> non-harmonic trash, it's not dubious at all.

I addressed this in another post. Its why I use the figure of 0.01%. I
don't claim that this figure is necessary, but I do claim that it is
sufficient.

Again, we have to compare this with the Doppler distortion of the
speakers themselves, in addition to harmonic distortions and
intermodulaton. That is the distortion cused by HF sounds being
generated by a source that is moving at some LF, say 100Hz.

>
>> High end audio is a scam to make money. Its that simple.
>
> Much of it is, but what does that have to do with anything?
> --scott

Because someone made an assertion of:

> I can give you two amps with similarly low high-level distortion
> figures, which sound audibly different in a very obvious way

I disagreed with that assertion.

Kevin Aylward
informationEXTRACT@anasoft.co.uk
http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.
Anonymous
April 25, 2005 11:35:31 PM

Archived from groups: rec.audio.pro (More info?)

"Kevin Aylward" <see_website@anasoft.co.uk> writes:

>> but please -- could you describe your
>> room where you're making these peceptual observations -- LEDE? RFZ?
>> Hybrid? Other? Any acoustical treatment at all?

>Name any room you like. It matters squat. Its a dead issue.

Oh my. Kevin, you're expressing perhaps unintentional gross ignorance
here. I'm speaking of rooms that properly control early reflections,
balance decay times, and mitigate LF problems as a way to help make
otherwise subtle elements and changes audible and unambiguous. Such rooms
are tools, just like a stone chisel -- or a laser milling machine.

You might try mixing or mastering a project in your untreated spare
bedroom v. Capital Records, Abbey Road, the old A&M Mastering studios or
Masterfonics, The Mastering Lab, or any other 1000s of studios
world-wide that have recognized the importance of this and built their
rooms accordingly.

Sure be nice if we didn't have to bother with this stuff (it can get
expensive and exasperating at times), but you can't change the laws of
physics.

And yes, transducers do distort more than any other component but that
does *not* mean that lesser problems are always obscured by this. As one
exmple, to some degree humans can readily hear a signal that is enveloped
in noise. (It's evolution, as you say -- the cave guy, with the waterfall
nearby, still manages to hear something and looks up and gets out of the
way of a charging sabertooth.)

- snip -

>> Such rooms also help solidly eliminate imagined differences.
>>

>High end audio is a scam to make money. Its that simple.

High-end consumer audio mostly is, agreed. But higher end pro audio, when
implemented properly, can make large differences in how our clients and
their listeners can more fully enjoy the art that has been captured and
reproduced. The general public doesn't give a damn whether there was a 741
in the signal path or a 2134, but one will most likely sound a leetle more
pleasant than the other.

Frank Stearns
Mobile Audio
--
.
Anonymous
April 25, 2005 11:54:57 PM

Archived from groups: rec.audio.pro (More info?)

"Arny Krueger" <arnyk@hotpop.com> writes:

>> Thank you for your observations, but please -- could you describe
>your
>> room where you're making these peceptual observations -- LEDE? RFZ?
>> Hybrid? Other? Any acoustical treatment at all?

>Let's make it easy and do our listening tests with some really-pretty
>good headphones - say HD 580s.

I was waiting for someone to mention headphones. And while in theory this
would be great, in practice (for me, anyway) using headphones just never
seems to cut it other than for a few limited applications. Mixing with
phones, for example, can result in mixes that are a little odd and don't
translate well. With phones monitoring some things are overemphasized,
others are lost.

It would seem that many mixing and mastering engineers feel the same,
otherwise why bother with buiding the really good rooms one finds at
reputable and well-known studios around the world? Be cheaper by orders of
magnitude to just hand everybody a pair of phones. But we don't do that --
I wonder why. (There's probably a doctoral thesis in there somewhere.)

Phones for these evals *might* work, but I'd prefer to use a good room, if
available.

Frank Stearns
Mobile Audio
--
.
Anonymous
April 26, 2005 2:07:43 AM

Archived from groups: rec.audio.pro (More info?)

Frank Stearns wrote:
> "Arny Krueger" <arnyk@hotpop.com> writes:
>
>>> Thank you for your observations, but please -- could you describe
>> your
>>> room where you're making these peceptual observations -- LEDE?
RFZ?
>>> Hybrid? Other? Any acoustical treatment at all?
>
>> Let's make it easy and do our listening tests with some
really-pretty
>> good headphones - say HD 580s.

> I was waiting for someone to mention headphones. And while in theory
> this would be great, in practice (for me, anyway) using headphones
> just never seems to cut it other than for a few limited
applications.

Silly me. I use them for all sorts of things.

> Mixing with phones, for example, can result in mixes that are a
> little odd and don't translate well.

So can mixing with the wrong speakers or the wrong person mixing.

>With phones monitoring some
> things are overemphasized, others are lost.

You never mix on the playback system that everybody uses. Therefore,
mixing is lots about translation. Learning to make mixes on one set of
monitors, and have them translate well on a goodly selection of other
listening systems is a matter of learning.

> It would seem that many mixing and mastering engineers feel the
same,
> otherwise why bother with buiding the really good rooms one finds at
> reputable and well-known studios around the world?

It's kind of hard to fit two people in one set of headphones.

>Be cheaper by
> orders of magnitude to just hand everybody a pair of phones. But we
> don't do that -- I wonder why. (There's probably a doctoral thesis
in
> there somewhere.)
>
> Phones for these evals *might* work, but I'd prefer to use a good
> room, if available.

One nice things about being able to track, monitor and mix on
headphones is that they are easier to carry around than a good
sounding room.
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