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Modifying Carver Sonic Hologram Generator - Slew Rate Ques..

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Anonymous
December 2, 2004 10:45:22 PM

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

If memory serves me, the B board on the C-4000 Sonic Holography
Autocorrelation PreAmp uses Texas Instruments RC4136 quad op-amps. These are
rather slow slew rate op-amps, and I was considering replacing them with
OP275 op amps or equivalent.

My question is this:

Does the Hologram Generator work it's magic BECAUSE of the slew rate
limiting of these op-amps, or would I stand to improve the hologram image at
higher audio frequencies by upgrading them?

My TI chips have degraded somewhat, causing audible distortion when the
hologram is switched in, until a 5-minute warmup has passed, after which it
sounds fine. So the question is whether to replace with the same type, or
attempt an upgrade with the possibility of improving high frequency imaging,
or ruining the whole effect altogether.

Has anyone thought about doing this, or better yet, actually tried it?



--
Take care,

Mark & Mary Ann Weiss

VIDEO PRODUCTION . FILM SCANNING . DVD MASTERING . AUDIO RESTORATION
Hear my Kurzweil Creations at: http://www.dv-clips.com/theater.htm
Business sites at:
www.dv-clips.com
www.mwcomms.com
www.adventuresinanimemusic.com
-

More about : modifying carver sonic hologram generator slew rate ques

Anonymous
December 2, 2004 11:41:18 PM

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

>If memory serves me, the B board on the C-4000 Sonic Holography
>Autocorrelation PreAmp uses Texas Instruments RC4136 quad op-amps. These are
>rather slow slew rate op-amps, and I was considering replacing them with
>OP275 op amps or equivalent.

If you replace 'em with faster op amps of any sort, take care to check
and perhaps upgrade the op amp power-supply bypassing arrangment, and
do some form of stability check on the outputs. Modern high-speed op
amps can be prone to oscillate when used in some circuits designed for
older, lower-speed op amps, due either to inadequate power-supply
decoupling, stray capacitance in the feedback path, excessive
capacitive loading, etc.

This may be an issue of additional concern since you're going to need
some sort of klugeboard arrangment to replace a single quad op amp
with a pair of duals. If you build such a board, I'd encourage you to
include a PC-board pattern which will let you stick .1 uF
monolithic-ceramic bypass caps right at the op amp V+ and V- pins, to
as short a ground trace as can reasonably be managed.

>My question is this:
>
>Does the Hologram Generator work it's magic BECAUSE of the slew rate
>limiting of these op-amps, or would I stand to improve the hologram image at
>higher audio frequencies by upgrading them?

I don't recall the details for certain, but my recollection is that
the hologram circuit is some form of cross-channel inverse-phase
mixer. My guess (and it's only a guess) is that any necessary
frequency shaping and equalization is performed through discrete RC
circuitry rather than through the op amps' limitations.

Replacing the op amps with better ones might reduce distortion or
noise to some extent, or it might have no audible effect at all, or
(if the replacement is done poorly) it might leave you with an
unstable circuit which oscillates in the ultrasonic or low RF
frequencies.

>My TI chips have degraded somewhat, causing audible distortion when the
>hologram is switched in, until a 5-minute warmup has passed, after which it
>sounds fine. So the question is whether to replace with the same type, or
>attempt an upgrade with the possibility of improving high frequency imaging,
>or ruining the whole effect altogether.

I suggest what I think is a much more likely suspect for the
distortion you are hearing: dried-out electrolytic capacitors. The
caps in your preamp are a quarter of a century old, and it's very
likely that some of them have gotten "leaky", changed capacitance,
developed a high equivalent series resistance, or some combination of
these. It's a common fault in older electronic equipment of all
sorts. I have a Singer FM radio service monitor whose 1 kHz
Wien-bridge oscillator wouldn't start up, for this very reason, and
it's of basically the same age as your Carver.

Dirty/oxidized switch contacts are another option. My Phase Linear
1000 autocorrelator (same basic circuit as is used in part of the
Carver) needed switch cleaning every couple of years, or it'd start
sounding distorted.

The cure, fortunately, is an easy one - re-cap the circuit and clean
the switches. From the fact that you mention distortion, but not hum,
I'd guess that it's the inter-stage AC-coupling caps which have
deteriorated, but it'd probably make sense to replace 'em all. Buy
yourself an assortment of high-quality 'lytics (the Panasonic
105-degree-C long-life types are a good choice), unsolder the old and
solder in the new, use a squirt of a good contact/control cleaner on
each of the rotary and pushbutton switches for good measure, and I
think you'll find that the preamp's performance has been restored.

--
Dave Platt <dplatt@radagast.org> AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!
Anonymous
December 3, 2004 3:54:35 AM

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

"Dave Platt" <dplatt@radagast.org> wrote in message
news:10quvfek9d94a34@corp.supernews.com...
> >If memory serves me, the B board on the C-4000 Sonic Holography
> >Autocorrelation PreAmp uses Texas Instruments RC4136 quad op-amps. These
are
> >rather slow slew rate op-amps, and I was considering replacing them with
> >OP275 op amps or equivalent.
>
> If you replace 'em with faster op amps of any sort, take care to check
> and perhaps upgrade the op amp power-supply bypassing arrangment, and
> do some form of stability check on the outputs. Modern high-speed op
> amps can be prone to oscillate when used in some circuits designed for
> older, lower-speed op amps, due either to inadequate power-supply
> decoupling, stray capacitance in the feedback path, excessive
> capacitive loading, etc.

Good post. I'm going to print this out for reference, as I tackle the
restoration of the preamp.

There is a thread on the internet about upgrading the Urei LA4 compressor,
which uses the same op amps. They link to a site that sells the circuit
boards to convert the OP275 to the pin configuration needed by the 4136.
That might be an option.
I will probably improve the decoupling circuitry while I'm at it. It seems
there is a lot to be desired in terms of PCB layout (with respect to
decoupling and grounding) and perhaps something to be gained by adding
electrolytics in parallel with ceramic or poly caps to provide a low ESR
across the band.


> This may be an issue of additional concern since you're going to need
> some sort of klugeboard arrangment to replace a single quad op amp
> with a pair of duals. If you build such a board, I'd encourage you to
> include a PC-board pattern which will let you stick .1 uF
> monolithic-ceramic bypass caps right at the op amp V+ and V- pins, to
> as short a ground trace as can reasonably be managed.

Good point about integrating the bypass caps. I'll check out that offering I
found on the Urei upgrade page to see if they include bypass caps on the
converters.


> >My question is this:
> >
> >Does the Hologram Generator work it's magic BECAUSE of the slew rate
> >limiting of these op-amps, or would I stand to improve the hologram image
at
> >higher audio frequencies by upgrading them?
>
> I don't recall the details for certain, but my recollection is that
> the hologram circuit is some form of cross-channel inverse-phase
> mixer. My guess (and it's only a guess) is that any necessary
> frequency shaping and equalization is performed through discrete RC
> circuitry rather than through the op amps' limitations.

I may order a copy of the service manual on Ebay, so I can study this
further. Hopefully you are correct.


> Replacing the op amps with better ones might reduce distortion or
> noise to some extent, or it might have no audible effect at all, or
> (if the replacement is done poorly) it might leave you with an
> unstable circuit which oscillates in the ultrasonic or low RF
> frequencies.

Good points. I will not do this upgrade without improving the decoupling
drastically.



> >My TI chips have degraded somewhat, causing audible distortion when the
> >hologram is switched in, until a 5-minute warmup has passed, after which
it
> >sounds fine. So the question is whether to replace with the same type, or
> >attempt an upgrade with the possibility of improving high frequency
imaging,
> >or ruining the whole effect altogether.
>
> I suggest what I think is a much more likely suspect for the
> distortion you are hearing: dried-out electrolytic capacitors. The
> caps in your preamp are a quarter of a century old, and it's very
> likely that some of them have gotten "leaky", changed capacitance,
> developed a high equivalent series resistance, or some combination of
> these. It's a common fault in older electronic equipment of all
> sorts. I have a Singer FM radio service monitor whose 1 kHz
> Wien-bridge oscillator wouldn't start up, for this very reason, and
> it's of basically the same age as your Carver.

Well, originally, this preamp had the A board. I heard about the B revision
hologram, so I had it upgraded at a shop. It was about a year or two later
that the distortion problem happened to appear. The preamp was less than
three years old at that time, being 1984 when I had it done.

I had the preamp apart last night, as part of a process of modifying the
chassis so it can be rack-mounted properly. While I was in there, I went
through and cleaned contacts and switches and I noticed a problem that had
plagued many of a product I used to service in the late 1970s. The techs
where I used to work referred to it as "TI crud", the silver plating that
tarnishes to black, forming dendrites between pins on the IC, thus causing
intermittent and varying resistance and making the op amps unstable. All of
the chips on the hologram board were black with tarnish! Drawing from my
experience with servicing thousands of FDM boards as a service tech in the
70s, I tried cleaning the tarnish off the pins (it cured the problem in 50%
of cases I serviced so long ago), but in this case, the preamp didn't fall
into the 50% that were successfully-remedied by this cleaning process. Often
the chips themselves are damaged, or the corrosion is underneath the pins
and inaccessible to cleaning.

Another thing I was hoping to achieve with this upgrade was the reduction of
hiss. Since the B board seems to move the hologram to a spot downstream of
the volume/balance controls, there is an audible hiss with the volume turned
down. Granted, it wouldn't be noticed on home hi-fi speakers, but this
particular C4000 is connected to a monster sound system with speakers that
have a 106dB @1W A@ 4' sensitivity, driven by a multi-amped setup of many
large power amps. If I can achieve any reduction in hiss in this circuit, it
would help greatly.


> Dirty/oxidized switch contacts are another option. My Phase Linear
> 1000 autocorrelator (same basic circuit as is used in part of the
> Carver) needed switch cleaning every couple of years, or it'd start
> sounding distorted.

Yes, the Carver has simply awful switches. The AC power switch became so
intermittent that I had to jumper it out. Other switches are intermittent. I
had to do a lot of cleaning and injecting of lubricants to get them working
well again.

As an aside, I have a Phase Linear 1100 Parametric EQ that developed a very
annoying problem with the output relay. It would lose the right channel
intermittently. Other times, the right channel would be there, but would
sound 'dark' and would also be about 10dB down from the left channel. I
finally opened that relay up and ran a thin strip of rough paper between the
contacts, then a strip of paper impregnated with Calilube R5 power booser
lubricant. It seems fine since then.

As for the dried out cap story, I have a Phase Linear D500 power amp in my
rack that saw some early failures in the control circuits. The low voltage
(approx 150VDC) power supply smoothing cap decided to open one day, causing
relay chatter. I have another cap failing somewhere, because since July of
2000, the D500 started powering itself on, even when the power switch is
off!

While I'm busy making the rack modification (involves countersinking the
holes for the handles and replacing the 1/4-20 pan head screws with 1/4-20
countersinking heads, so I can get this thing to mount flush against the
rack rails, I'm going to investigate another annoyance: the hum in the left
channel. Since the power transformer is on the left side of the amp (all
78lbs or so of it), I figure the low level audio circuits are getting
hammered with mucho magnetic fields. So I'm going to experiment with
different shielding methods to try and clean that up. (I'm in the midst of a
major overhaul of the two amplifier racks, to solve the hum problems caused
by the D500 magnetizing the rack and injecting hum into all other rack
devices. I'm planning to move all the low level stuff into a separate rack
and put the power stuff in the other rack.) The right channel is silent, but
the left channel has what sounds like a capacitively-coupled AC hum
(harmonics only). Big project, doing it a little bit at a time.


> The cure, fortunately, is an easy one - re-cap the circuit and clean
> the switches. From the fact that you mention distortion, but not hum,
> I'd guess that it's the inter-stage AC-coupling caps which have
> deteriorated, but it'd probably make sense to replace 'em all. Buy
> yourself an assortment of high-quality 'lytics (the Panasonic
> 105-degree-C long-life types are a good choice), unsolder the old and
> solder in the new, use a squirt of a good contact/control cleaner on
> each of the rotary and pushbutton switches for good measure, and I
> think you'll find that the preamp's performance has been restored.

Yes, I think I'm eventually going to re-cap most of this gear. The Phase
Linear stuff has been notorious for dried out caps, mostly in control
circuits, rather than audio paths, but I think it's time to recap all of it.

I'm thinking it might be possible to improve the accuracy of the hologram
generator by improving the slew rate of the chips, such that the hologram
would be effective above 5khz. A difficult thing to measure, and largely a
subjective listening issue.


--
Take care,

Mark & Mary Ann Weiss

VIDEO PRODUCTION • FILM SCANNING • DVD MASTERING • AUDIO RESTORATION
Hear my Kurzweil Creations at: http://www.dv-clips.com/theater.htm
Business sites at:
www.dv-clips.com
www.mwcomms.com
www.adventuresinanimemusic.com
-
Anonymous
December 3, 2004 4:17:13 AM

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

In article <fPOrd.1668$714.854@newsread2.news.atl.earthlink.net>,
Mark & Mary Ann Weiss <mweissX294@earthlink.net> wrote:

>Good post. I'm going to print this out for reference, as I tackle the
>restoration of the preamp.
>
>There is a thread on the internet about upgrading the Urei LA4 compressor,
>which uses the same op amps. They link to a site that sells the circuit
>boards to convert the OP275 to the pin configuration needed by the 4136.
>That might be an option.

Sounds like a good approach... probably a lot easier than handwiring
up little converters yourself.

>I will probably improve the decoupling circuitry while I'm at it. It seems
>there is a lot to be desired in terms of PCB layout (with respect to
>decoupling and grounding) and perhaps something to be gained by adding
>electrolytics in parallel with ceramic or poly caps to provide a low ESR
>across the band.

Well, you don't want to go _too_ low in ESR. That can cause other
sorts of stability problems. If you bypass only with very-low-ESR
caps, you can end up with an unexpected resonance effect - the C in
the caps interacts with the L in the PC board traces, creating a
parallel-resonant tank circuit. At the resonance frequency, the tank
exhibits a high impedance, and your bypassing goes all to heck.

The approach I've seen suggested to deal with this, is a combination
of low-ESR caps right at the PC board pins, and a few tens of uF of
good aluminum electrolytic (or a few uF of tantalum) every few inches
on the board. The high-capacitance, moderate-ESR 'lytics "swamp" the
LC tank circuit, lowering its Q to the point where it isn't a problem.

Omitting either the low-ESR caps at the pins, or the "bulk" capacitors
on the rails, can lead to all sorts of nasty intermittent misbehavior.
I had an Ethernet card once (a Boca) which was acutely sensitive to
the data pattern in the incoming packets, and would reliably drop
certain packets with a CRC mismatch error, while passing most other
packets just fine. Turns out that Boca had omitted a bunch of the
caps that AMD (the chipmaker) had warned were absolutely critical.

>I may order a copy of the service manual on Ebay, so I can study this
>further. Hopefully you are correct.

'Twould be a good investment!

>Well, originally, this preamp had the A board. I heard about the B revision
>hologram, so I had it upgraded at a shop. It was about a year or two later
>that the distortion problem happened to appear. The preamp was less than
>three years old at that time, being 1984 when I had it done.
>
>I had the preamp apart last night, as part of a process of modifying the
>chassis so it can be rack-mounted properly. While I was in there, I went
>through and cleaned contacts and switches and I noticed a problem that had
>plagued many of a product I used to service in the late 1970s. The techs
>where I used to work referred to it as "TI crud", the silver plating that
>tarnishes to black, forming dendrites between pins on the IC, thus causing
>intermittent and varying resistance and making the op amps unstable. All of
>the chips on the hologram board were black with tarnish! Drawing from my
>experience with servicing thousands of FDM boards as a service tech in the
>70s, I tried cleaning the tarnish off the pins (it cured the problem in 50%
>of cases I serviced so long ago), but in this case, the preamp didn't fall
>into the 50% that were successfully-remedied by this cleaning process. Often
>the chips themselves are damaged, or the corrosion is underneath the pins
>and inaccessible to cleaning.

Ugh. That's a failure mode I wasn't aware of. I'll keep my eyes open
for it in the future.

>Another thing I was hoping to achieve with this upgrade was the reduction of
>hiss. Since the B board seems to move the hologram to a spot downstream of
>the volume/balance controls, there is an audible hiss with the volume turned
>down. Granted, it wouldn't be noticed on home hi-fi speakers, but this
>particular C4000 is connected to a monster sound system with speakers that
>have a 106dB @1W A@ 4' sensitivity, driven by a multi-amped setup of many
>large power amps. If I can achieve any reduction in hiss in this circuit, it
>would help greatly.

That's one area in which better op amps might help. The 4136 is (if I
recall correctly) basically a bevy of 741s in a single package, and
the 741 was never known as a particularly quiet amplifier.

>While I'm busy making the rack modification (involves countersinking the
>holes for the handles and replacing the 1/4-20 pan head screws with 1/4-20
>countersinking heads, so I can get this thing to mount flush against the
>rack rails, I'm going to investigate another annoyance: the hum in the left
>channel. Since the power transformer is on the left side of the amp (all
>78lbs or so of it), I figure the low level audio circuits are getting
>hammered with mucho magnetic fields. So I'm going to experiment with
>different shielding methods to try and clean that up.

You might want to consider swapping in a toroidal transformer, in
place of the EI-core type which is probably there. Quite a lot less
flux leakage. Replacement of the transformer might be easier than
trying to shield it.

>Yes, I think I'm eventually going to re-cap most of this gear. The Phase
>Linear stuff has been notorious for dried out caps, mostly in control
>circuits, rather than audio paths, but I think it's time to recap all of it.
>
>I'm thinking it might be possible to improve the accuracy of the hologram
>generator by improving the slew rate of the chips, such that the hologram
>would be effective above 5khz. A difficult thing to measure, and largely a
>subjective listening issue.

On the other hand, you may find that the Carver folks carefully
avoided the problems with slew-rate limiting in the 4136 by
deliberately limiting the bandwidth of the signal going into the
hologram-generator (cross-feed phase mangler) circuit. If so, faster
op amps by themselves might not make any difference, unless you defeat
the low-pass filter at the generator's input.

The service manual and schematic might yield some clues to this.

--
Dave Platt <dplatt@radagast.org> AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!
Anonymous
December 5, 2004 9:47:29 AM

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

> >There is a thread on the internet about upgrading the Urei LA4
compressor,
> >which uses the same op amps. They link to a site that sells the circuit
> >boards to convert the OP275 to the pin configuration needed by the 4136.
> >That might be an option.
>
> Sounds like a good approach... probably a lot easier than handwiring
> up little converters yourself.

I'm up against a significant amount of desoldering; even with the the
benefit of the adapters, this will be a substantial project. I'm not sure at
this point if it's worth the effort. I may simply replace the chips with new
ones, hopefully nailing the baddie in the bunch (cold turn-on
distortion/oscillation). My re-racking project is turning into a major
project involving machining, drilling, and hum troubleshooting.


> >I will probably improve the decoupling circuitry while I'm at it. It
seems
> >there is a lot to be desired in terms of PCB layout (with respect to
> >decoupling and grounding) and perhaps something to be gained by adding
> >electrolytics in parallel with ceramic or poly caps to provide a low ESR
> >across the band.
>
> Well, you don't want to go _too_ low in ESR. That can cause other
> sorts of stability problems. If you bypass only with very-low-ESR
> caps, you can end up with an unexpected resonance effect - the C in
> the caps interacts with the L in the PC board traces, creating a
> parallel-resonant tank circuit. At the resonance frequency, the tank
> exhibits a high impedance, and your bypassing goes all to heck.

Very good point! I hadn't even thought of that. Although the L in the PCB
would be distributed over many 'networks' of L, I think it would look and
behave more like a C in parallel with many L's of different inductances,
thus lowering the Q again.
I decided to do this trick with the Phase Linear D-500, putting 2.2uF 250V
poly caps across each of the 'upgraded' 40,000uF electrolytic caps I put in
a few years ago. That should stiffen the high end a bit, as the B+/B- leads
go pretty much straight to the output transistors now.



> The approach I've seen suggested to deal with this, is a combination
> of low-ESR caps right at the PC board pins, and a few tens of uF of
> good aluminum electrolytic (or a few uF of tantalum) every few inches
> on the board. The high-capacitance, moderate-ESR 'lytics "swamp" the
> LC tank circuit, lowering its Q to the point where it isn't a problem.

Yup, distribute the resonance over a broad range and damp it. When I design
circuits from scratch, that's my usual approach.


> Omitting either the low-ESR caps at the pins, or the "bulk" capacitors
> on the rails, can lead to all sorts of nasty intermittent misbehavior.
> I had an Ethernet card once (a Boca) which was acutely sensitive to
> the data pattern in the incoming packets, and would reliably drop
> certain packets with a CRC mismatch error, while passing most other
> packets just fine. Turns out that Boca had omitted a bunch of the
> caps that AMD (the chipmaker) had warned were absolutely critical.

Particular data pattern hits a resonance and presto--all havoc breaks loose.
Interesting. Must have been a bear to discover that one.


> >I may order a copy of the service manual on Ebay, so I can study this
> >further. Hopefully you are correct.
>
> 'Twould be a good investment!

Yup. Gonna do it. Methinks it's about time I ordered service manuals for
each of my pieces of gear.



<deleted>
> >where I used to work referred to it as "TI crud", the silver plating that
> >tarnishes to black, forming dendrites between pins on the IC, thus
causing
> >intermittent and varying resistance and making the op amps unstable. All
of
> >the chips on the hologram board were black with tarnish! Drawing from my
> >experience with servicing thousands of FDM boards as a service tech in
the
> >70s, I tried cleaning the tarnish off the pins (it cured the problem in
50%
> >of cases I serviced so long ago), but in this case, the preamp didn't
fall
> >into the 50% that were successfully-remedied by this cleaning process.
Often
> >the chips themselves are damaged, or the corrosion is underneath the pins
> >and inaccessible to cleaning.
>
> Ugh. That's a failure mode I wasn't aware of. I'll keep my eyes open
> for it in the future.

Yes, quite common with the TI chips made in the late '70s. I think TI
addressed the issue by '83, so subsequent parts came with solder-tinned legs
instead of silver-plated. Modems shipped in from humid souther climates had
the worst of these problems. It definately reacts in humid environments.


> >Another thing I was hoping to achieve with this upgrade was the reduction
of
> >hiss. Since the B board seems to move the hologram to a spot downstream
of
> >the volume/balance controls, there is an audible hiss with the volume
turned
> >down. Granted, it wouldn't be noticed on home hi-fi speakers, but this
> >particular C4000 is connected to a monster sound system with speakers
that
> >have a 106dB @1W A@ 4' sensitivity, driven by a multi-amped setup of many
> >large power amps. If I can achieve any reduction in hiss in this circuit,
it
> >would help greatly.
>
> That's one area in which better op amps might help. The 4136 is (if I
> recall correctly) basically a bevy of 741s in a single package, and
> the 741 was never known as a particularly quiet amplifier.

Yup. I was rather irked to find these op amps throughout the whole pre-amp.
It's a paradox how it sounds so darned good despite this.



<deleted>
> >channel. Since the power transformer is on the left side of the amp (all
> >78lbs or so of it), I figure the low level audio circuits are getting
> >hammered with mucho magnetic fields. So I'm going to experiment with
> >different shielding methods to try and clean that up.
>
> You might want to consider swapping in a toroidal transformer, in
> place of the EI-core type which is probably there. Quite a lot less
> flux leakage. Replacement of the transformer might be easier than
> trying to shield it.

I don't think that's cost-effective. The transformer that's in there is
about the size of those SOLA constant voltage transformers we used to use to
power an entire rack of automate laser inspection equipment back in the 70s.
I think it's about 10KVA.

What I did find was terrible mechanical layout of the input wiring. They had
Belden foil shielded wire going from the rear apron RCA jack to the front
panel, all the while, bundled into a main harness which contained AC power
wires, DC power wires and audio. It brushes against the transformer just
before it loops over to the left channel audio pot. The audio PCB driver
board has a 5" run of parallel audio lines along the edge closest to the
transformer. My remedy was multifaceted: Shorten the path of the Belden
cables, undoing the harness, and rerouting them a shorter distance from the
panel to the pots. While I was at it, I shortened the DC power leads to the
output stage, cutting them out of the harness. I separated all AC and DC
wiring into separate bundles and tied them separately. Now all types of
signal/power are segregated.
The final thing I had to do was glue a short strip of G10 epoxy PCB material
to the back of the amplifier driver PCB, over the input lines, and run a
wire from it to ground, forming a shield. That did the trick. The hum in the
left channel is gone.
What remains is locating sensitive gear in another rack. This amp throws hum
into everything within 3' of it!




> >I'm thinking it might be possible to improve the accuracy of the hologram
> >generator by improving the slew rate of the chips, such that the hologram
> >would be effective above 5khz. A difficult thing to measure, and largely
a
> >subjective listening issue.
>
> On the other hand, you may find that the Carver folks carefully
> avoided the problems with slew-rate limiting in the 4136 by
> deliberately limiting the bandwidth of the signal going into the
> hologram-generator (cross-feed phase mangler) circuit. If so, faster
> op amps by themselves might not make any difference, unless you defeat
> the low-pass filter at the generator's input.
>
> The service manual and schematic might yield some clues to this.

Yes, I think you're right. There's probably little to be gained by modding
this circuit as discussed. But the manuals are my next item of shopping.

Thanks for the discussion!


--
Take care,

Mark & Mary Ann Weiss

VIDEO PRODUCTION • FILM SCANNING • DVD MASTERING • AUDIO RESTORATION
Hear my Kurzweil Creations at: http://www.dv-clips.com/theater.htm
Business sites at:
www.dv-clips.com
www.mwcomms.com
www.adventuresinanimemusic.com
-
Anonymous
December 5, 2004 11:07:04 AM

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

It sounds more like you have some capacitors that have become high in ESR
with age. I would have the caps ESR checked to verify this.

As for modification, take care. This can end up being more complex than a
simple parts change.

--

Jerry G.
=====

"Mark & Mary Ann Weiss" <mweissX294@earthlink.net> wrote in message
news:mhKrd.1642$Va5.613@newsread3.news.atl.earthlink.net...
If memory serves me, the B board on the C-4000 Sonic Holography
Autocorrelation PreAmp uses Texas Instruments RC4136 quad op-amps. These are
rather slow slew rate op-amps, and I was considering replacing them with
OP275 op amps or equivalent.

My question is this:

Does the Hologram Generator work it's magic BECAUSE of the slew rate
limiting of these op-amps, or would I stand to improve the hologram image at
higher audio frequencies by upgrading them?

My TI chips have degraded somewhat, causing audible distortion when the
hologram is switched in, until a 5-minute warmup has passed, after which it
sounds fine. So the question is whether to replace with the same type, or
attempt an upgrade with the possibility of improving high frequency imaging,
or ruining the whole effect altogether.

Has anyone thought about doing this, or better yet, actually tried it?



--
Take care,

Mark & Mary Ann Weiss

VIDEO PRODUCTION . FILM SCANNING . DVD MASTERING . AUDIO RESTORATION
Hear my Kurzweil Creations at: http://www.dv-clips.com/theater.htm
Business sites at:
www.dv-clips.com
www.mwcomms.com
www.adventuresinanimemusic.com
-
Anonymous
December 6, 2004 4:32:05 AM

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

>If memory serves me, the B board on the C-4000 Sonic Holography
>Autocorrelation PreAmp uses Texas Instruments RC4136 quad op-amps. These are
>rather slow slew rate op-amps, and I was considering replacing them with
>OP275 op amps or equivalent.
>
>My question is this:
>
>Does the Hologram Generator work it's magic BECAUSE of the slew rate
>limiting of these op-amps, or would I stand to improve the hologram image at
>higher audio frequencies by upgrading them?
>
>My TI chips have degraded somewhat, causing audible distortion when the
>hologram is switched in, until a 5-minute warmup has passed, after which it
>sounds fine. So the question is whether to replace with the same type, or
>attempt an upgrade with the possibility of improving high frequency imaging,
>or ruining the whole effect altogether.
>
>Has anyone thought about doing this, or better yet, actually tried it?
>
>Take care,
>
>Mark & Mary Ann Weiss

I originally bought my Carver Sonic Holography Unit in 1988. Some time within
the past 2 years I wanted to have it checked out. My local audio dealer sent
it to them. Only cost me $89 to have the work done. It was well worth it to
have the makers do their thing rather than trust just any ole person without
experience with it.


Best,

Mark Allen Zimmerman * Chicago
Anonymous
December 6, 2004 6:50:48 AM

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

This problem appeared when the C4000 was just two years old, and it came on
over a period of a few weeks. This was about a year after the B board was
installed. I find it difficult to buy the dried out caps theory on a 1-year
old board installed in a 2 year old preamp. I've been living with the
condition since late 1984.
However, the corroded pins with dendrites growing between them have caused
ultrasonic oscillation on TI op amps in modem FDM cards I used to service in
the 1970s. It is a classic symptom, and usually temperature-sensitive. When
my C4000 warms up for 5 minutes, the problem ceases.
Unfortunately, Bob didn't build this preamp to be easily-serviced--I can't
just put the card on an extender and probe away to find out which chip is
oscillating. I am sure it's ultrasonic oscillation because I can hear little
'hetrodynes' in the hiss, with no program present, until warmed up. With
program present, and the volume turned all the way down, there is only a
distorted version of the program (there should be nothing leaking through
with the volume turned down) at a background listening level, prior to warm
up.
At any rate, the whole thing will be recapped when I chose to embark on
re-chipping the hologram board.
In the meantime, I think I am going to replace the Linkwitz-Riley crossover
that I built in 1984 with a Behringer Ultradrive Pro DCX2496 Loudspeaker
Management System, as it addresses the timing issues that have plagued my
fourteen woofers since day one. The current crossover receives hum from the
Phase Linear D-500, when that amplifier is powered on. I have been isolating
components, to narrow down the cause of hum throughout the system. It is
challenging to get a 10kW sound system to be silent while idling. Even a hum
at -100dB produces a nearly 40dB ambient hum at 4', and due to the size of
the array of speakers, that hum carries for a great distance. Perhaps going
all-digital on the crossover and earlier stages will eliminate one major
source of the hum, while allowing me to time align all the woofer arrays so
they hit the listener at the same time. It looks like the Behringer unit
will allow me to accomplish all of this and more.

Take care,

Mark & Mary Ann Weiss

VIDEO PRODUCTION • FILM SCANNING • DVD MASTERING • AUDIO RESTORATION
Hear my Kurzweil Creations at: http://www.dv-clips.com/theater.htm
Business sites at:
www.dv-clips.com
www.mwcomms.com
www.adventuresinanimemusic.com
-




> It sounds more like you have some capacitors that have become high in ESR
> with age. I would have the caps ESR checked to verify this.
>
> As for modification, take care. This can end up being more complex than a
> simple parts change.
>
> --
>
> Jerry G.
> =====
>
> "Mark & Mary Ann Weiss" <mweissX294@earthlink.net> wrote in message
> news:mhKrd.1642$Va5.613@newsread3.news.atl.earthlink.net...
> If memory serves me, the B board on the C-4000 Sonic Holography
> Autocorrelation PreAmp uses Texas Instruments RC4136 quad op-amps. These
are
> rather slow slew rate op-amps, and I was considering replacing them with
> OP275 op amps or equivalent.
>
> My question is this:
>
> Does the Hologram Generator work it's magic BECAUSE of the slew rate
> limiting of these op-amps, or would I stand to improve the hologram image
at
> higher audio frequencies by upgrading them?
>
> My TI chips have degraded somewhat, causing audible distortion when the
> hologram is switched in, until a 5-minute warmup has passed, after which
it
> sounds fine. So the question is whether to replace with the same type, or
> attempt an upgrade with the possibility of improving high frequency
imaging,
> or ruining the whole effect altogether.
>
> Has anyone thought about doing this, or better yet, actually tried it?
>
>
>
> --
> Take care,
>
> Mark & Mary Ann Weiss
>
> VIDEO PRODUCTION . FILM SCANNING . DVD MASTERING . AUDIO RESTORATION
> Hear my Kurzweil Creations at: http://www.dv-clips.com/theater.htm
> Business sites at:
> www.dv-clips.com
> www.mwcomms.com
> www.adventuresinanimemusic.com
> -
>
>
>
>
>
>
Anonymous
December 6, 2004 6:58:40 AM

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

>
> I originally bought my Carver Sonic Holography Unit in 1988. Some time
within
> the past 2 years I wanted to have it checked out. My local audio dealer
sent
> it to them. Only cost me $89 to have the work done. It was well worth it
to
> have the makers do their thing rather than trust just any ole person
without
> experience with it.
>
>
> Best,
>
> Mark Allen Zimmerman * Chicago


I thought Carver was out of business a long time ago.

I did bring this in for service under warranty in the first year for a
grounding problem (the trace had burned out due to a ground loop) on the 2nd
pair of outputs. Well, it came back with the same problem. I ended up fixing
it myself with some #26 Kynar wire and a soldering iron. A lot of these
shops just aren't that competent. Many of them are staffed with high school
kids, or just out of high school, at least here in CT. I've learned long ago
that if you want something done right, you must do it yourself. (of course,
you must have skills and expertise in said area).
1988 was a cheaper era too. I'll bet it would cost $89 just to ship my unit
to Woodinville, WA today, much less the repair cost!
As a comparison, back in 1980, Electro-Voice used to charge $64.13 for a
recone job on the IP line of loudspeaker drivers. Around 1997 or so, the
most recent time I can recall having something reconed, the cost was more
than the original purchase price of the driver! Assuming there were an
authorized repair center for legacy Carver components, I'd reckon it'd be
quite pricey.


--
Take care,

Mark & Mary Ann Weiss

VIDEO PRODUCTION • FILM SCANNING • DVD MASTERING • AUDIO RESTORATION
Hear my Kurzweil Creations at: http://www.dv-clips.com/theater.htm
Business sites at:
www.dv-clips.com
www.mwcomms.com
www.adventuresinanimemusic.com
-
Anonymous
December 13, 2004 3:42:02 AM

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

>I thought Carver was out of business a long time ago.

From what I understand he and his wife got divorced and each got a part of the
business but put it under different names. If you need it I have a phone
number to call for service.
Best,

Mark Allen Zimmerman * Chicago
Anonymous
December 14, 2004 5:00:34 AM

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

"MarkZimmerman" <markzimmerman@aol.com> wrote in message
news:20041212194202.11419.00001903@mb-m29.aol.com...
> >I thought Carver was out of business a long time ago.
>
> From what I understand he and his wife got divorced and each got a part of
the
> business but put it under different names. If you need it I have a phone
> number to call for service.
> Best,
>
> Mark Allen Zimmerman * Chicago

A couple of years ago, I saw some papers on Carver's website that were
indicating the financial stats of the company. The stock value was under a
penny a share and there was a telephone number at the bottom of the site. I
called that number, with an interest in finding out if I could buy some
shares in the company and provide some seed money to get things going again,
but had never received a call back. It was an answering machine at that
number.

So this information you provided sheds some new perspective on the
situation.

So there are two companies now? One is Carver and the other is Sunfire?
A search on the web shows Carver Professional, a division of Phoenix Gold.
So they got absorbed by another company. Is this the service outlet for whom
you have contact info? If not, perhaps it would be good to have, if only for
reference purposes and parts orders.


--
Take care,

Mark & Mary Ann Weiss

VIDEO PRODUCTION • FILM SCANNING • DVD MASTERING • AUDIO RESTORATION
Hear my Kurzweil Creations at: http://www.dv-clips.com/theater.htm
Business sites at:
www.dv-clips.com
www.mwcomms.com
www.adventuresinanimemusic.com
-
!