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INA103 differential stage

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Anonymous
August 16, 2005 6:26:00 PM

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

My idea is to use a INA103 but without the second differential stage as
a mic-pre. One possibility would be of course to replace the
differential stage it with another OP or a discrete setup but my
question goes in another direction:

Since I want the output to be symmetrical anyway wouldn't it be possible
to amplify each phase separately with a single OP and use that as a
symmetrical output? Sounds a little to simple, I know. Am I missing
something here?


Thanks,
Rob
August 16, 2005 6:26:01 PM

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

>
> Maybe I am not completely aware of how the input stage of an
> instrumentation amp works. Is it possible to benefit from the balanced
> first stage when I use only one of the differential outputs and the
> other is grounded?
>
> >

Yes you get the full benefit of hum rejection of balanced input
realtive to the mic cable regardless of how you connect the output of
the pre-amp.


If you connect the output of the pre-amp as single ended, then you get
no benefit of hum rejection at the output cable but that does not
detract fomr the hum rejection at the balanced input. Think of it as a
new signal source starting a new trip.


The INA103 has a single ended output.

Mark
Anonymous
August 17, 2005 2:47:45 AM

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

"Robert Angst"
>
> My idea is to use a INA103 but without the second differential stage as a
> mic-pre. One possibility would be of course to replace the differential
> stage it with another OP or a discrete setup but my question goes in
> another direction:
>
> Since I want the output to be symmetrical anyway wouldn't it be possible
> to amplify each phase separately with a single OP and use that as a
> symmetrical output? Sounds a little to simple, I know. Am I missing
> something here?


** No - all you need is two op-amps.

Eg. a NE5532 dual op-amp configured as two inverters with 4.7 kohm input
and feedback resistors.

Balanced low noise in - balanced line level out.




............ Phil
Anonymous
August 17, 2005 2:47:46 AM

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

>
> ** No - all you need is two op-amps.

Ok, another thougt:
if I connect the symetrical output of the two OPs into a single ended
input (e.g. RNC) with + hot, - and shield grounded, I will loose the
entire benefit of the differential construction between mic and output.
If I'd leave the shield unconnected it should work. Is this correct?

I sure want to be fully balanced but want to keep compatibility with
single ended gear as well. Do I in that case have to go the classic
route: first differential amp and then splitting it up again in two
differential pairs? In that case I could include an insert jack for my
RNC fairly easy..

As an OP I would use an LT1469/8. I plugged them in my SX202 (as
suggested in this NG) and realy like the results.
Anonymous
August 17, 2005 2:47:46 AM

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

Phil Allison wrote:

> "Robert Angst"
> >
> > My idea is to use a INA103 but without the second differential stage as a
> > mic-pre. One possibility would be of course to replace the differential
> > stage it with another OP or a discrete setup but my question goes in
> > another direction:
> >
> > Since I want the output to be symmetrical anyway wouldn't it be possible
> > to amplify each phase separately with a single OP and use that as a
> > symmetrical output? Sounds a little to simple, I know. Am I missing
> > something here?
>
> ** No - all you need is two op-amps.
>
> Eg. a NE5532 dual op-amp configured as two inverters with 4.7 kohm input
> and feedback resistors.
>
> Balanced low noise in - balanced line level out.

Phil ! Are you feeling unwell ? He said a mic pre ! That configuration will be
noisy as hell.

Using two op-amps like that destroys CMRR too - unless you use say 0.1%
tolerance resistors.

The long tailed pair input has far better inherent common mode rejection.

Graham
Anonymous
August 17, 2005 5:20:03 AM

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

"Robert Angst"
>>
>> ** No - all you need is two op-amps.


** You trimmed out my name and everything but for one line.

That is very bad manners.



............ Phil
Anonymous
August 17, 2005 5:20:04 AM

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

Phil Allison schrieb:

> "Robert Angst"
>
>>>** No - all you need is two op-amps.
>
>
>
> ** You trimmed out my name and everything but for one line.
>
> That is very bad manners.
>
>
>
> ........... Phil
>

Sorry, won't happen again.
Anonymous
August 17, 2005 5:43:27 AM

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

"Robert Angst"
> Phil Allison
>>
>>>>** No - all you need is two op-amps.
>>
>>
>> ** You trimmed out my name and everything but for one line.
>>
>> That is very bad manners.
>
>
> Sorry, won't happen again.


** OK.

As for your additional questions:

1. Shorting one side of a balanced line to ground is bad practice.

2. The majority of the CMRR of the INA103 mic-preamp comes from the first
(differential) stage - a common mode signal gets only unity gain.

3. The vast majority of external hum field rejection obtained with balanced
*mic* lines is due to the two wires inside the cable being twisted.


Sorry if this sounds like heresy.

It isn't.


.......... Phil
Anonymous
August 17, 2005 5:43:28 AM

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

Phil Allison schrieb:

> As for your additional questions:
>
> 1. Shorting one side of a balanced line to ground is bad practice.

Sure, I am just trying to make the box more idiot proof for 'emergency'
situations when only a TS cable is at hand (or the person who built it
isn't).

> 2. The majority of the CMRR of the INA103 mic-preamp comes from the first
> (differential) stage - a common mode signal gets only unity gain.

Maybe I am not completely aware of how the input stage of an
instrumentation amp works. Is it possible to benefit from the balanced
first stage when I use only one of the differential outputs and the
other is grounded?

> 3. The vast majority of external hum field rejection obtained with balanced
> *mic* lines is due to the two wires inside the cable being twisted.

That sounds like even if differential input is compromised it's still
good enough for these 'emergency' cases.

> Sorry if this sounds like heresy.
>
> It isn't.
>
>
> ......... Phil

I guess I'll build it the way you suggested and use proper cables if I
want to compress while tracking. That should make a nice two-chip pre.

Thanks
Rob
Anonymous
August 17, 2005 5:43:29 AM

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

Robert Angst wrote:
>
> Maybe I am not completely aware of how the input stage of an
> instrumentation amp works. Is it possible to benefit from the balanced
> first stage when I use only one of the differential outputs and the
> other is grounded?
>

Don't actually connect the other output to ground, but the first stage
of a classic instrumentation amp has whatever differential gain is
defined by the gain-defining resistor, and a common mode gain of 1
always. So for all gains above 1 you'll get some common mode rejection,
equal to the differential gain.

I don't know why you wouldn't want to use the second stage of the
INA103, which is a differencing amp with unity gain and CMR as good as
resistor tolerances will allow. The main limitation of a whole mic
preamp constructed that way is that the output stage of the INA103 isn't
the best thing for driving arbitrary loads on the end of possibly long
cables. (but then the input stage isn't any better...)

--
Anahata
anahata@treewind.co.uk -+- http://www.treewind.co.uk
Home: 01638 720444 Mob: 07976 263827
Anonymous
August 17, 2005 8:30:11 AM

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

On Tue, 16 Aug 2005 17:04:38 +0200, Robert Angst
<robert.angst@tu-berlin.de> wrote:

>
>>
>> ** No - all you need is two op-amps.
>
>Ok, another thougt:
>if I connect the symetrical output of the two OPs into a single ended
>input (e.g. RNC) with + hot, - and shield grounded, I will loose the
>entire benefit of the differential construction between mic and output.
>If I'd leave the shield unconnected it should work. Is this correct?
>
>I sure want to be fully balanced but want to keep compatibility with
>single ended gear as well. Do I in that case have to go the classic
>route: first differential amp and then splitting it up again in two
>differential pairs?

I was thinking there was something 'bad' about your original idea
of keeping the positive and negative signals separate, and now you've
mentioned it.
Another reason(s) to combine them is to cancel out any common-mode
signal from the input. Passing on such a common-mode signal reduces
the maximum signal (if the signal path can handle 15V peaks and your
common-mode noise is 10V peak, your biggest signal is 5V before
clipping. It also relies on the next device having good CMRR to cancel
common-mode stuff, which if the next device has an unbalanced input,
it obviously won't have.

You absolutely need the differential-conversion stage (with
highly=precise, matched resistors to get good CMRR) for a mic preamp,
as the mic signal could be a few millivolts and the common-mode signal
can be several volts. To turn the situation around so that the mic
signal is much larger instead, you need to cancel the common signal
with a very high precision.
The instrumentation amplifier configuration helps by giving (up to
about) 1,000 times gain for differential signals, and only a gain of 1
for common-mode signals, but you still need the differential stage to
cancel out the common-mode signals.

>In that case I could include an insert jack for my
>RNC fairly easy..
>
>As an OP I would use an LT1469/8. I plugged them in my SX202 (as
>suggested in this NG) and realy like the results.

-----
http://www.mindspring.com/~benbradley
Anonymous
August 17, 2005 12:08:52 PM

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

In article <ddt5tu$ise$1@mamenchi.zrz.TU-Berlin.DE> robert.angst@tu-berlin.de writes:

> > 1. Shorting one side of a balanced line to ground is bad practice.
>
> Sure, I am just trying to make the box more idiot proof for 'emergency'
> situations when only a TS cable is at hand (or the person who built it
> isn't).

This is why the single-ended so-called "impedance balanced" output
configuration is so popular. It doesn't matter if you short the
non-driven side to ground because there's no signal on it. Much
cheaper than a transformer, simpler than a cross-coupled see-saw
output stage, and good enough for even some of the finest microphones.



--
I'm really Mike Rivers - (mrivers@d-and-d.com)
However, until the spam goes away or Hell freezes over,
lots of IP addresses are blocked from this system. If
you e-mail me and it bounces, use your secret decoder ring
and reach me here: double-m-eleven-double-zero at yahoo
Anonymous
August 17, 2005 4:19:17 PM

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

"Pooh Bear"
> Phil Allison wrote:
>> "Robert Angst"
>> >
>> > My idea is to use a INA103 but without the second differential stage as
>> > a
>> > mic-pre. One possibility would be of course to replace the differential
>> > stage it with another OP or a discrete setup but my question goes in
>> > another direction:
>> >
>> > Since I want the output to be symmetrical anyway wouldn't it be
>> > possible
>> > to amplify each phase separately with a single OP and use that as a
>> > symmetrical output? Sounds a little to simple, I know. Am I missing
>> > something here?
>>
>> ** No - all you need is two op-amps.
>>
>> Eg. a NE5532 dual op-amp configured as two inverters with 4.7 kohm
>> input
>> and feedback resistors.
>>
>> Balanced low noise in - balanced line level out.
>
> Phil ! Are you feeling unwell ? He said a mic pre ! That configuration
> will be
> noisy as hell.


** Try reading the context - dickhead.

The INA103 allows access on pins 5 & 12 to the differential stage's outputs.

http://focus.ti.com/lit/ds/symlink/ina103.pdf

The NE5532 would merely buffer those outputs.




........... Phil
Anonymous
August 17, 2005 4:19:18 PM

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

Phil Allison wrote:

> "Pooh Bear"
> > Phil Allison wrote:
> >> "Robert Angst"
> >> >
> >> > My idea is to use a INA103 but without the second differential stage as
> >> > a
> >> > mic-pre. One possibility would be of course to replace the differential
> >> > stage it with another OP or a discrete setup but my question goes in
> >> > another direction:
> >> >
> >> > Since I want the output to be symmetrical anyway wouldn't it be
> >> > possible
> >> > to amplify each phase separately with a single OP and use that as a
> >> > symmetrical output? Sounds a little to simple, I know. Am I missing
> >> > something here?
> >>
> >> ** No - all you need is two op-amps.
> >>
> >> Eg. a NE5532 dual op-amp configured as two inverters with 4.7 kohm
> >> input
> >> and feedback resistors.
> >>
> >> Balanced low noise in - balanced line level out.
> >
> > Phil ! Are you feeling unwell ? He said a mic pre ! That configuration
> > will be
> > noisy as hell.
>
> ** Try reading the context - dickhead.
>
> The INA103 allows access on pins 5 & 12 to the differential stage's outputs.
>
> http://focus.ti.com/lit/ds/symlink/ina103.pdf
>
> The NE5532 would merely buffer those outputs.

Ok, I follow you now. From what he said ( about simply amplifying each leg of
the mic input separately ) I got a different picture of what you meant.

Why not buffer those points using a voltage follower configuration though ?
Slightly less noisy without those 4k7s.

Graham
Anonymous
August 17, 2005 5:21:26 PM

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

"Pooh Bear"
> Phil Allison wrote:
>>>
>> >> ** No - all you need is two op-amps.
>> >>
>> >> Eg. a NE5532 dual op-amp configured as two inverters with 4.7 kohm
>> >> input and feedback resistors.
>> >>
>> >> Balanced low noise in - balanced line level out.
>> >
>> > Phil ! Are you feeling unwell ? He said a mic pre ! That configuration
>> > will be
>> > noisy as hell.
>>
>> ** Try reading the context - dickhead.
>>
>> The INA103 allows access on pins 5 & 12 to the differential stage's
>> outputs.
>>
>> http://focus.ti.com/lit/ds/symlink/ina103.pdf
>>
>> The NE5532 would merely buffer those outputs.
>
> Ok, I follow you now. From what he said ( about simply amplifying each leg
> of
> the mic input separately ) I got a different picture of what you meant.
>
> Why not buffer those points using a voltage follower configuration though
> ?
> Slightly less noisy without those 4k7s.



** Are you feeling well - Pooh ??

The reason for preferring unity gain inverting is that it produces less
HD - since there is no common mode voltage at the inputs.

The self noise from a unity gain inverter, using an NE 5532 and 4.7 kohms is
about 3 uV rms ( 1 uV from the resistor, 1 uV from the op-amp & noise
gain of 2 ).

Relative to a 1 volt output level, this is a s/n ratio of 110 dB -
exceeding the spec for the INA103.

The noise from the preceding op-amp is gonna be more in any case - even at
unity gain the INA103 is speced at 10 uV output noise ( 70 nV rt Hz) .



............ Phil
Anonymous
August 17, 2005 5:21:27 PM

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

Phil Allison wrote:

> "Pooh Bear"
> > Phil Allison wrote:
> >>>
> >> >> ** No - all you need is two op-amps.
> >> >>
> >> >> Eg. a NE5532 dual op-amp configured as two inverters with 4.7 kohm
> >> >> input and feedback resistors.
> >> >>
> >> >> Balanced low noise in - balanced line level out.
> >> >
> >> > Phil ! Are you feeling unwell ? He said a mic pre ! That configuration
> >> > will be
> >> > noisy as hell.
> >>
> >> ** Try reading the context - dickhead.
> >>
> >> The INA103 allows access on pins 5 & 12 to the differential stage's
> >> outputs.
> >>
> >> http://focus.ti.com/lit/ds/symlink/ina103.pdf
> >>
> >> The NE5532 would merely buffer those outputs.
> >
> > Ok, I follow you now. From what he said ( about simply amplifying each leg
> > of
> > the mic input separately ) I got a different picture of what you meant.
> >
> > Why not buffer those points using a voltage follower configuration though
> > ?
> > Slightly less noisy without those 4k7s.
>
> ** Are you feeling well - Pooh ??
>
> The reason for preferring unity gain inverting is that it produces less
> HD - since there is no common mode voltage at the inputs.

That's an interesting assertion. I recall that being said in the 70s. The
reason being supposed 'common mode failure' of the input pair.

For a while I followed the 'inverting is best' suggestion but eventually
abandoned it since it generally leads to increased noise. I see no sign of this
issue with modern op-amps.


> The self noise from a unity gain inverter, using an NE 5532 and 4.7 kohms is
> about 3 uV rms ( 1 uV from the resistor, 1 uV from the op-amp & noise
> gain of 2 ).
>
> Relative to a 1 volt output level, this is a s/n ratio of 110 dB -
> exceeding the spec for the INA103.
>
> The noise from the preceding op-amp is gonna be more in any case - even at
> unity gain the INA103 is speced at 10 uV output noise ( 70 nV rt Hz) .

I'm just getting very fussy over *all* noise contributions these days. As you
correctly point out, even 4k7 makes a significant difference to the overall
noise of a 5532.

Graham
Anonymous
August 17, 2005 5:21:28 PM

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

"Pooh Bear" <rabbitsfriendsandrelations@hotmail.com> wrote in message
news:4302B5E7.BE5703E0@hotmail.com...

> For a while I followed the 'inverting is best' suggestion but eventually
> abandoned it since it generally leads to increased noise. I see no sign of
this
> issue with modern op-amps.

It's there, although more with FET-input op-amps than bipolars like the
5532. Try high-frequency IM tests on an OPA-604 or 2604 (same design, dual
package) in non-inverting mode, first with a low-impedance source, then with
something like 25k source impedance. More distortion.

Peace,
Paul
Anonymous
August 17, 2005 5:21:28 PM

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

Phil Allison wrote:

> Graham Stevenon - Studiomaster's biggest Enemy
> >
> > Phil Allison wrote:

< snip Phil's insults >


> >> All you are doing is mindless TROLLING and NETSTALKING me.
> >
> > If you think I'm trolling or stalking you - lol - then you clearly have a
> > serious mental problem.
> >
> > I'm contributing to a thread in a *public* newsgroup. Get over it.
>
> ** You will STOP posting your mindless garbage under every post I put up.

I do *not* post every single time you do. Just take a look and see. It does
happen often though since we both have similar expertise in the audio area -
and in turn you often reply to one of my posts. Entirely normal behaviour in a
newsgroup !


> That is criminal behaviour.
>

I suggest you go look up the meaning of criminal. You just make yourself look
stupid by posting such daft claims.

> That is netstalking.
>

If I wanted to netstalk you, trust me you'd know about it. I don't have that
mindset nor the interest, inclination, time, money whatever anyway !


> The one with metal issues is YOU - Graham Stevenon of Studiomaster UK.

Lol @ metal. Thankfully I'm able to shrug off such nonsence. I only wish you'd
grow up and get over your persecution complex.

Come on Phil, I'm sure you're capable of better than this ?


Graham
Anonymous
August 17, 2005 5:21:29 PM

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

Paul Stamler wrote:

> "Pooh Bear" <rabbitsfriendsandrelations@hotmail.com> wrote in message
> news:4302B5E7.BE5703E0@hotmail.com...
>
> > For a while I followed the 'inverting is best' suggestion but eventually
> > abandoned it since it generally leads to increased noise. I see no sign of
> this
> > issue with modern op-amps.
>
> It's there, although more with FET-input op-amps than bipolars like the
> 5532. Try high-frequency IM tests on an OPA-604 or 2604 (same design, dual
> package) in non-inverting mode, first with a low-impedance source, then with
> something like 25k source impedance. More distortion.

More THD with the high Z source ?

Ah well, I keep signal impedances low too ! ;-)

Graham
Anonymous
August 17, 2005 5:21:30 PM

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

"Pooh Bear" <rabbitsfriendsandrelations@hotmail.com> wrote in message
news:43030A15.E99D08CC@hotmail.com...
>
> Paul Stamler wrote:
>
>> "Pooh Bear" <rabbitsfriendsandrelations@hotmail.com> wrote in message
>> news:4302B5E7.BE5703E0@hotmail.com...
>>
>> > For a while I followed the 'inverting is best' suggestion but
>> > eventually
>> > abandoned it since it generally leads to increased noise. I see no sign
>> > of
>> this
>> > issue with modern op-amps.
>>
>> It's there, although more with FET-input op-amps than bipolars like the
>> 5532. Try high-frequency IM tests on an OPA-604 or 2604 (same design,
>> dual
>> package) in non-inverting mode, first with a low-impedance source, then
>> with
>> something like 25k source impedance. More distortion.

> More THD with the high Z source ?

IME that's how it usually works.

> Ah well, I keep signal impedances low too ! ;-)

...but not too low. ;-)
Anonymous
August 17, 2005 6:39:24 PM

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

"Ben Bradley"

> You absolutely need the differential-conversion stage (with
> highly=precise, matched resistors to get good CMRR) for a mic preamp,


** Bullshit - the input stage rejects common mode by the same factor as
it has gain.


> as the mic signal could be a few millivolts and the common-mode signal
> can be several volts.


** What planet are you living on ??????????

Don't just make things up - dickhead.



> To turn the situation around so that the mic
> signal is much larger instead, you need to cancel the common signal
> with a very high precision.

** There is virtually ZERO common mode signal with a microphone &cable in
normal circumstaces.


>The instrumentation amplifier configuration helps by giving (up to
> about) 1,000 times gain for differential signals, and only a gain of 1
> for common-mode signals, but you still need the differential stage to
> cancel out the common-mode signals.


** Like a record stuck in a groove - isn't he ??






............... Phil
Anonymous
August 17, 2005 6:53:55 PM

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

Mike Rivers schrieb:

> This is why the single-ended so-called "impedance balanced" output
> configuration is so popular. It doesn't matter if you short the
> non-driven side to ground because there's no signal on it. Much
> cheaper than a transformer, simpler than a cross-coupled see-saw
> output stage, and good enough for even some of the finest microphones.

That would get me going with just one op for the differencial stage and
two matched series resistors. But the way I understand it, this setup
will result in half the output amplitude if fed into a symmetrical
input. Is that correct?

Rob
Anonymous
August 17, 2005 7:37:39 PM

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

"Pooh Bear" <rabbitsfriendsandrelations@hotmail.com> wrote in message
news:43030A15.E99D08CC@hotmail.com...
>
> Paul Stamler wrote:
>
> > "Pooh Bear" <rabbitsfriendsandrelations@hotmail.com> wrote in message
> > news:4302B5E7.BE5703E0@hotmail.com...
> >
> > > For a while I followed the 'inverting is best' suggestion but
eventually
> > > abandoned it since it generally leads to increased noise. I see no
sign of
> > this
> > > issue with modern op-amps.
> >
> > It's there, although more with FET-input op-amps than bipolars like the
> > 5532. Try high-frequency IM tests on an OPA-604 or 2604 (same design,
dual
> > package) in non-inverting mode, first with a low-impedance source, then
with
> > something like 25k source impedance. More distortion.
>
> More THD with the high Z source ?

More THD, especially at high frequencies and low gain, so the input sees a
high-level signal, and more high-frequency IMD.

> Ah well, I keep signal impedances low too ! ;-)

But sometimes you can't, at which point some interesting juggling becomes
necessary.

Peace,
Paul
Anonymous
August 17, 2005 11:35:15 PM

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

Robert Angst <robert.angst@tu-berlin.de> wrote:
>
>My idea is to use a INA103 but without the second differential stage as
>a mic-pre. One possibility would be of course to replace the
>differential stage it with another OP or a discrete setup but my
>question goes in another direction:

This works very well, and it reduces the total distortion considerably.
Most of the actual distortion of the INA103 comes from the output stage.

But if you're going to do this, you might as well just skip the INA103
altogether and just go with a discrete transistor array for the front
end.

>Since I want the output to be symmetrical anyway wouldn't it be possible
>to amplify each phase separately with a single OP and use that as a
>symmetrical output? Sounds a little to simple, I know. Am I missing
>something here?

Yes, but you don't have an instrumentation amp any more. Do you care
about CMRR? If you don't really care about CMRR, using a single op-amp
is just fine.

If you do care about CMRR, the guys at THAT have just produced a
chip that is a pin-compatible replacement for the SSM2017. Samples are
just now coming out. I can't tell you if it performs as well as the
data sheet yet, but once I get back from Colorado and get another dozen
higher priority (ie. better-paying) projects out of the way I hope to
give the things a try.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."
Anonymous
August 18, 2005 1:04:10 AM

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

Graham Stevenon - Net Stalker


** You will STOP posting your mindless garbage under every post I put up.

That is criminal behaviour.



> I suggest you go look up the meaning of criminal.

** I suggest you go straight into hell.



> If I wanted to netstalk you, trust me you'd know about it.


** You are net stalking me and I do know about it.

Stop or will contact your employers.

I promise that will not be the slightest bit funny.





............ Phil
Anonymous
August 18, 2005 2:37:51 AM

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

In article <ddvc12$i5$1@mamenchi.zrz.TU-Berlin.DE> robert.angst@tu-berlin.de writes:

> > This is why the single-ended so-called "impedance balanced" output

> That would get me going with just one op for the differencial stage and
> two matched series resistors. But the way I understand it, this setup
> will result in half the output amplitude if fed into a symmetrical
> input. Is that correct?

It's a matter of interpretation. With a symmetrical balanced output
stage, one side goes to -5V with reference to 0V when the other side
goes to +5V. To a differential input, that's a voltage difference of
10V.

With an impedance balanced, single ended output, one side of the
differential input always sees 0V since there's no
"opposite-but-equal" leg of the output. So when the hot side goes to
+5V, the differential input sees 5V.

So, yes, you can get twice the output from a symmetrical output stage
into a differential input because you're essentially connecting the
two outputs in series. You can't do that if you have only one ouptut,
of course, but all of that output voltage does indeed get to the
differential input.


--
I'm really Mike Rivers - (mrivers@d-and-d.com)
However, until the spam goes away or Hell freezes over,
lots of IP addresses are blocked from this system. If
you e-mail me and it bounces, use your secret decoder ring
and reach me here: double-m-eleven-double-zero at yahoo
Anonymous
August 18, 2005 7:09:17 AM

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

On Tue, 16 Aug 2005 14:26:00 +0200, Robert Angst
<robert.angst@tu-berlin.de> wrote:

>My idea is to use a INA103 but without the second differential stage as
>a mic-pre. One possibility would be of course to replace the
>differential stage it with another OP or a discrete setup but my
>question goes in another direction:
>
>Since I want the output to be symmetrical anyway wouldn't it be possible
>to amplify each phase separately with a single OP and use that as a
>symmetrical output? Sounds a little to simple, I know. Am I missing
>something here?

You really, really want to get your common-mode rejection
up-front and believable, preferably before any electronics
(but that costs money), and trusting to your electronics
to linearly handle the potentially large common mode
signal is foolish, not to put too fine a point on it.

In too many real-world situations *huge* common-mode
signals can bite one's butt. Don't trust your reputation
to wishful thinking and Internet wanking. Wanna be
professional? Think tough; think military; think medical.

And don't put too much confidence in certain... well....

Good fortune,

Chris Hornbeck
Anonymous
August 18, 2005 3:00:15 PM

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

Scott Dorsey schrieb:

<snip>

> But if you're going to do this, you might as well just skip the INA103
> altogether and just go with a discrete transistor array for the front
> end.

I read your postings about this approach but I guess I don't have
experience and time to design something like this from scratch. Now that
my SX202 is done I get into mic-tinkering again as well (neg. supply for
fig.8)

<snip>

> If you do care about CMRR, the guys at THAT have just produced a
> chip that is a pin-compatible replacement for the SSM2017. Samples are
> just now coming out. I can't tell you if it performs as well as the
> data sheet yet, but once I get back from Colorado and get another dozen
> higher priority (ie. better-paying) projects out of the way I hope to
> give the things a try.
> --scott
>

Actually the 103 was intendet to be my workaround for that. I am trying
to replace an SSM2017 and I was quite pleased with what I read in the
datasheet of the new THAT1512. Even lower noise than the THAT1510.
Trouble is I would have to buy 20 pieces or pay 20 EUR shipping if I buy
just two. I haven't found a single comment on its performance yet, but I
would realy like to try it. I'll look around a little more..
Rob
Anonymous
August 18, 2005 3:00:16 PM

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

In article <de1in2$avk$1@mamenchi.zrz.TU-Berlin.DE> robert.angst@tu-berlin.de writes:

> I was quite pleased with what I read in the
> datasheet of the new THAT1512. Even lower noise than the THAT1510.
> Trouble is I would have to buy 20 pieces or pay 20 EUR shipping if I buy
> just two. I haven't found a single comment on its performance yet, but I
> would realy like to try it. I'll look around a little more..

It's brand new, so you probably won't see any in products for a while
yet. Why not contact THAT and ask for a couple of samples? They're
still a small company and you can actually reach real people there.


--
I'm really Mike Rivers - (mrivers@d-and-d.com)
However, until the spam goes away or Hell freezes over,
lots of IP addresses are blocked from this system. If
you e-mail me and it bounces, use your secret decoder ring
and reach me here: double-m-eleven-double-zero at yahoo
Anonymous
August 18, 2005 4:36:12 PM

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

Robert Angst wrote:

> Scott Dorsey schrieb:
>
> <snip>
>
> > But if you're going to do this, you might as well just skip the INA103
> > altogether and just go with a discrete transistor array for the front
> > end.
>
> I read your postings about this approach but I guess I don't have
> experience and time to design something like this from scratch. Now that
> my SX202 is done I get into mic-tinkering again as well (neg. supply for
> fig.8)
>
> <snip>
>
> > If you do care about CMRR, the guys at THAT have just produced a
> > chip that is a pin-compatible replacement for the SSM2017. Samples are
> > just now coming out. I can't tell you if it performs as well as the
> > data sheet yet, but once I get back from Colorado and get another dozen
> > higher priority (ie. better-paying) projects out of the way I hope to
> > give the things a try.
> > --scott
>
> Actually the 103 was intendet to be my workaround for that. I am trying
> to replace an SSM2017 and I was quite pleased with what I read in the
> datasheet of the new THAT1512. Even lower noise than the THAT1510.
> Trouble is I would have to buy 20 pieces or pay 20 EUR shipping if I buy
> just two. I haven't found a single comment on its performance yet, but I
> would realy like to try it. I'll look around a little more..

You're really not being very sensible. You're virtually using only the input
differential pair on the INA103 - kind of a waste ot time.

A pair of 10 cent 2SA1084s is probably quieter.

Graham
Anonymous
August 19, 2005 9:31:21 AM

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

Phil Allison wrote:

> Graham Stevenon - Net Stalker

< snip >


> > If I wanted to netstalk you, trust me you'd know about it.
>
> ** You are net stalking me and I do know about it.
>
> Stop or will contact your employers.

Oh please do. They're not strictly my employers btw. They're a client.

> I promise that will not be the slightest bit funny.

I expect that the Studiomaster guys will find it very funny indeed actually.
They could do with a laugh. I've already apprised them of your 'bohemian'
behaviour way back btw.

Now stop making hollow threats.

Graham
Anonymous
August 19, 2005 1:40:51 PM

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

Robert Angst <robert.angst@tu-berlin.de> wrote:
>Scott Dorsey schrieb:
>
>> But if you're going to do this, you might as well just skip the INA103
>> altogether and just go with a discrete transistor array for the front
>> end.
>
>I read your postings about this approach but I guess I don't have
>experience and time to design something like this from scratch. Now that
>my SX202 is done I get into mic-tinkering again as well (neg. supply for
> fig.8)

If you want a little bit of gain, and you want differential input and
differential output, you probably want just a simple differential amplifier
stage with two transistors.

Get the service manual for the Mackie 1202VLZ Pro and look at the front
end of the mike section. Steal the design. It's a really good one.

The RCA Radiotron Handbook has the best description of how the circuit
works, too. It's old and it uses tubes in the example, but the same
long-tailed-pair differential amp stage is still one of the most popular
circuit designs today.

>datasheet of the new THAT1512. Even lower noise than the THAT1510.
>Trouble is I would have to buy 20 pieces or pay 20 EUR shipping if I buy
>just two. I haven't found a single comment on its performance yet, but I
>would realy like to try it. I'll look around a little more..

I don't think more than a handful of people have actually tried them
yet. Don't know about European distribution but shoot them a letter. They
have talked about getting small quantity distribution through Mouser.
You might want to ask them if they can sign Buerklin up as well.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."
Anonymous
August 19, 2005 1:47:20 PM

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

In article <znr1124363024k@trad>, Mike Rivers <mrivers@d-and-d.com> wrote:
>In article <de1in2$avk$1@mamenchi.zrz.TU-Berlin.DE> robert.angst@tu-berlin.de writes:
>
>> I was quite pleased with what I read in the
>> datasheet of the new THAT1512. Even lower noise than the THAT1510.
>> Trouble is I would have to buy 20 pieces or pay 20 EUR shipping if I buy
>> just two. I haven't found a single comment on its performance yet, but I
>> would realy like to try it. I'll look around a little more..
>
>It's brand new, so you probably won't see any in products for a while
>yet. Why not contact THAT and ask for a couple of samples? They're
>still a small company and you can actually reach real people there.

They are right now being completely overwhelemed with sample requests.
This thing has been in the works for six years now and we keep hearing
about it, and it's finally out. So everyone and his brother is trying
to get samples out of THAT right now after years of hearing about it.

Preliminary tests look pretty damn good.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."
Anonymous
August 19, 2005 6:35:33 PM

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

Graham Stevenon - Net Stalker


> Oh please do. They're not strictly my employers btw. They're a client.


** As I suspected - you an posturing, unemployed fake.



>> I promise that will not be the slightest bit funny.
>
> I expect that the Studiomaster guys will find it very funny indeed
> actually.


** Then you have no idea what I intend.


> Now stop making hollow threats.


** Fair warning is no threat.

Go find out the law - you pig ignorant ass.




.............. Phil
Anonymous
August 19, 2005 6:35:34 PM

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

Phil Allison wrote:

> Graham Stevenon - Net Stalker
>
> > Oh please do. They're not strictly my employers btw. They're a client.
>
> ** As I suspected - you an posturing, unemployed fake.
>
> >> I promise that will not be the slightest bit funny.
> >
> > I expect that the Studiomaster guys will find it very funny indeed
> > actually.
>
> ** Then you have no idea what I intend.
>
> > Now stop making hollow threats.
>
> ** Fair warning is no threat.
>
> Go find out the law - you pig ignorant ass.

The law would say you're threatening me. It's such a lame threat I don't
concern myself about it.

You really are piece of astonishingly mentally defective detritus.

Graham
Anonymous
August 25, 2005 10:21:23 PM

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

Mike Rivers schrieb:

> It's brand new, so you probably won't see any in products for a while
> yet. Why not contact THAT and ask for a couple of samples? They're
> still a small company and you can actually reach real people there.

Looks like that was a good hint. One of the distributors in Germany
promised to send some.. *when* they get some.

Obviously you guys in the states are asking more samples than THAT can
produce ;-)

I'll report my findings when I have them plugged in and compared.

Rob
!