Audioarts Model 1200 Compressor

Help Support GroupDIY:

jaymz168

Member
Joined
Aug 5, 2010
Messages
13
Hi all, first post here after a decade of lurking around  :p

A friend was cleaning out and gave me a pair of non-functional Audioarts Model 1200 compressors.  I haven't tried powering them yet because all of the electrolytics inside are leaky and one of them had some sort of destructive failure.  One of them has a completely toasted TL072 and socket and the area around the regulators on that unit looks pretty unhappy as well.  I'd like to have a schematic to work off of but it seems that even though these were fairly popular and at least one company, Revive Audio, modified them but I can't seem to find a schematic anywhere.  The board is pretty easy to follow so I've started to do a schematic in KiCad but I'm stumped on two parts:

https://i.imgur.com/WJq4Shn.jpg

https://i.imgur.com/JWZAC18.jpg


That's first mystery PDIP-14 chip.  This picture comes from the "very dead" unit and this package had a full coverage heatsink on it but it fell right off of this one.  The heatsink seems to still be well attached on the other unit.  This one is driven on pins 3 and 7 from the second and third opamps (pin6 from NE5534s).  It looks like it drives the fourth opamp from pins 5 and 8.  It has pins 1, 2, 9, 11, 13, and 14 tied to ground.  Pins 4 and 6 are paralleled and head off to the sidechain section. 

https://i.imgur.com/5QmUzUx.jpg

And here's the second mystery PDIP-14 chip.  I'm fairly certain this is the log-amp/VCA as it's over in the sidechain area with a handful of TL072S and a single NE5534.  I haven't gotten far enough in tracing signal through the board to take a guess on the pinout.  Searching around seems to imply "CA" means circuit assembly but no exact matches.

Hopefully these are both still functional but I'd still like to know what they are to produce a schematic so any help is welcome!

And here are some pics of the carnage in the "very dead" unit, I've got parts coming today to redo the PSUs, all electrolytics and film caps, and the toasted socket and some spare opamps.  Once the bad parts are out I'll check for shorts, etc. but given that it's the very first opamp that signal hits that died and the guy who had these does a lot of live sound so I wouldn't be surprised if it just took a big hit from something.  It's actually in what likes the driver for the peak detection circuit.

Anyway, on to the autopsy:

https://i.imgur.com/ux3PUoj.jpg

https://i.imgur.com/MImlGRA.jpg

https://i.imgur.com/shJGjY1.jpg

https://i.imgur.com/bshAH5m.jpg

https://i.imgur.com/YeUP398.jpg

https://i.imgur.com/NShOeCU.jpg

Full gallery here: https://imgur.com/a/Z2Hg18E

James








 

JohnRoberts

Well-known member
Staff member
Moderator
Joined
Nov 30, 2006
Messages
20,971
Location
Hickory, MS
jaymz168 said:
Hi all, first post here after a decade of lurking around  :p

A friend was cleaning out and gave me a pair of non-functional Audioarts Model 1200 compressors.  I haven't tried powering them yet because all of the electrolytics inside are leaky and one of them had some sort of destructive failure.  One of them has a completely toasted TL072 and socket and the area around the regulators on that unit looks pretty unhappy as well.  I'd like to have a schematic to work off of but it seems that even though these were fairly popular and at least one company, Revive Audio, modified them but I can't seem to find a schematic anywhere.  The board is pretty easy to follow so I've started to do a schematic in KiCad but I'm stumped on two parts:

https://i.imgur.com/WJq4Shn.jpg

That's first mystery PDIP-14 chip.  This picture comes from the "very dead" unit and this package had a full coverage heatsink on it but it fell right off of this one.  The heatsink seems to still be well attached on the other unit.  This one is driven on pins 3 and 7 from the second and third opamps (pin6 from NE5534s).  It looks like it drives the fourth opamp from pins 5 and 8.  It has pins 1, 2, 9, 11, 13, and 14 tied to ground.  Pins 4 and 6 are paralleled and head off to the sidechain section. 

https://i.imgur.com/5QmUzUx.jpg

And here's the second mystery PDIP-14 chip.  I'm fairly certain this is the log-amp/VCA as it's over in the sidechain area with a handful of TL072S and a single NE5534.  I haven't gotten far enough in tracing signal through the board to take a guess on the pinout.  Searching around seems to imply "CA" means circuit assembly but no exact matches.

Hopefully these are both still functional but I'd still like to know what they are to produce a schematic so any help is welcome!

And here are some pics of the carnage in the "very dead" unit, I've got parts coming today to redo the PSUs, all electrolytics and film caps, and the toasted socket and some spare opamps.  Once the bad parts are out I'll check for shorts, etc. but given that it's the very first opamp that signal hits that died and the guy who had these does a lot of live sound so I wouldn't be surprised if it just took a big hit from something.

Anyway, on to the autopsy:

https://i.imgur.com/ux3PUoj.jpg

https://i.imgur.com/MImlGRA.jpg

https://i.imgur.com/shJGjY1.jpg

https://i.imgur.com/bshAH5m.jpg

https://i.imgur.com/YeUP398.jpg

https://i.imgur.com/NShOeCU.jpg

Full gallery here: https://imgur.com/a/Z2Hg18E

James
Just a wild guess the first part "could" be a transistor array, look for something like a ca3086?

The second part is likely a potted array of transistors... you may be able to identify base-emitter and base collector junctions.

JR
 

jensenmann

Well-known member
Joined
Oct 10, 2004
Messages
2,634
Location
Karlsruhe, Germany
The shape reminds me of the Allison ECG101 transistor array. These were blue, though. Maybe it´s an OEM.

Repairing that thing might not be rocket science. You say the caps are leaky, so replace them.

Some other faults are obvious, too. The PCB is browned around a diode, voltage regulator, etc. Replace all those suspect parts.

There´s a molten IC socket. That usually happens when the according chip died and shorted a rail for some time. Replace socket and chip. If you don´t know which chip then the fun begins. If it´s stereo then find that particular part of the circuit on the other channel and have a look what has been used there. If not then try to find out if the chip sits in the audio path. In a compressor the real audiopath is pretty short and consists of very few ICs usually. Follow the traces from the input sockets all the way to the output sockets. If your defective chip is in between then it´s most likely linear/an opamp. If it´s a single channel opamp can be determined if pin 4 and 7 supply the voltages. If it´s pin 4 and 8 then it´s a dual opamp.
 

jaymz168

Member
Joined
Aug 5, 2010
Messages
13
JohnRoberts said:
Just a wild guess the first part "could" be a transistor array, look for something like a ca3086?

The second part is likely a potted array of transistors... you may be able to identify base-emitter and base collector junctions.

JR

On closer look the 'R' looks like it's followed by a 'C' and some fiddling around on Google images sort of leads me to believe it's an RCA part but still no real part number unfortunately.  I added a picture of the bottom side of it up in the first post but googling that mark doesn't lead to anything.  And if I'm following the traces properly it doesn't seem like it would be a CA series part. 

I think I'll just put a CA3018 or something in the schematic as a placeholder while I finish tracing the rest of it, I have a feeling it will become more obvious once the rest of the circuit is figured out.
 

jaymz168

Member
Joined
Aug 5, 2010
Messages
13
jensenmann said:
The shape reminds me of the Allison ECG101 transistor array. These were blue, though. Maybe it´s an OEM.

Repairing that thing might not be rocket science. You say the caps are leaky, so replace them.

Some other faults are obvious, too. The PCB is browned around a diode, voltage regulator, etc. Replace all those suspect parts.

There´s a molten IC socket. That usually happens when the according chip died and shorted a rail for some time. Replace socket and chip. If you don´t know which chip then the fun begins. If it´s stereo then find that particular part of the circuit on the other channel and have a look what has been used there. If not then try to find out if the chip sits in the audio path. In a compressor the real audiopath is pretty short and consists of very few ICs usually. Follow the traces from the input sockets all the way to the output sockets. If your defective chip is in between then it´s most likely linear/an opamp. If it´s a single channel opamp can be determined if pin 4 and 7 supply the voltages. If it´s pin 4 and 8 then it´s a dual opamp.

Yeah the shape is similar, isn't it?  That's a good lead, I wonder if they re-engineered that module or something. 

As far as the rest, agreed, I'm going to replace and clean up all of the obvious stuff and see how it goes.  I don't think the two mystery chips are bad, I'm just curious really.  The one that blew up is a TL072 that looks like it drives the peak detector LED oddly enough.  I'd like to build up a schematic and then maybe look at seeing if modifying them might be beneficial.  But having one unit that looks fine will be helpful to use as a reference for the other I think.
 

JohnRoberts

Well-known member
Staff member
Moderator
Joined
Nov 30, 2006
Messages
20,971
Location
Hickory, MS
jaymz168 said:
On closer look the 'R' looks like it's followed by a 'C' and some fiddling around on Google images sort of leads me to believe it's an RCA part but still no real part number unfortunately.  I added a picture of the bottom side of it up in the first post but googling that mark doesn't lead to anything.  And if I'm following the traces properly it doesn't seem like it would be a CA series part. 
the CA 3086 transistor array is/was an RCA part.
I think I'll just put a CA3018 or something in the schematic as a placeholder while I finish tracing the rest of it, I have a feeling it will become more obvious once the rest of the circuit is figured out.
look at old national semi app notes for how to make log conversions. These were easier for dB math in compressor side chains. The transistor arrays I used had 5 NPNs on a common substrate.

I don't know if Greg Snow was using Paul Buff's VCAs but I did back then...  8)

JR

 

jaymz168

Member
Joined
Aug 5, 2010
Messages
13
Well Wheatstone actually just got back to me and emailed me the manual that contains a schematic.  I can upload this to the Technical Documents section if you'd like.  The two mystery chips are still just empty blocks on the schematic of course, but I think having a look at it should help.  I'm going to use this to finish the KiCad schematic and and start pondering.
 

jaymz168

Member
Joined
Aug 5, 2010
Messages
13
OK, it's midnight here and I've managed to produce a KiCad schematic, I've attached it here in PDF format.  U5 is the IC with the heatsink and U10 is the module and the pots may not be the right way around, I'll double check them tomorrow.  It's getting late and I'm no expert so I'll check back in the morning  ;D

EDIT:  After some tracing it appears the Audioarts 1200 is actually slightly different from the Wheatstone 1201/1202 or at least mine is.  The output path is a bit different with the output gain actually being the in the feedback loop of the last opamp and not just a simple attenuator.  I'll be upload that Kicad file here as well as soon as I'm certain I've caught all of the differences.  So properly speaking, the file attached to this message currently is actually a Wheatstone 1201/1202.
 

Attachments

  • Audioarts 1200 KiCad schematic.pdf
    205.5 KB · Views: 31

JohnRoberts

Well-known member
Staff member
Moderator
Joined
Nov 30, 2006
Messages
20,971
Location
Hickory, MS
jaymz168 said:
OK, it's midnight here and I've managed to produce a KiCad schematic, I've attached it here in PDF format.  U5 is the IC with the heatsink and U10 is the module and the pots may not be the right way around, I'll double check them tomorrow.  It's getting late and I'm no expert so I'll check back in the morning  ;D
U5 looks like it may be a class A current ratio-ing VCA, but i don't see the control voltage (current) connection coming from the side chain.

U10 is probably a log conversion circuit... some incorrect looking connections, so perhaps recheck with fresh eyes.

JR
 

jaymz168

Member
Joined
Aug 5, 2010
Messages
13
JohnRoberts said:
U5 looks like it may be a class A current ratio-ing VCA, but i don't see the control voltage (current) connection coming from the side chain.

U10 is probably a log conversion circuit... some incorrect looking connections, so perhaps recheck with fresh eyes.

JR

So after double checking it against the printed version it all looks correct.  And yeah I'm pretty new at this stuff, especially gain reduction circuits, this is the first time I'm trying to understand one and it's confusing to me, too!  You can see that the only evident connection between the audio path and sidechain is the feedback from the output to feed the sidechain.  But given the CV is DC I wonder if one of two things could be involved:

  • I see +15V coming into the inverting inputs of the second and third opamps (U4, U6) which then feed U5
  • I see +15V coming into what looks like the outputs of U10 which reminds me of how tubes work with plate voltage coming in and signal coming out of the same pin.

So those make me wonder if the CV is riding on the audio input to U5 or maybe on the rails which seem to come in on the outputs of U5.

I'll attach the manual with schematic that was provided to me. Argh the file is too big by like 30 bytes or something  and I can't attach a ZIP file.

It is missing values for all of the pots except one which it lists as 25k but which measures (in circuit anyway) as 10k.  I also haven't verified all of the resistor values but every one I've checked has been correct as well as the film caps. 

Also I've started removing the electrolytics and regs from the one that doesn't look like it blew up so hopefully I'll have at least one working unit soon. 
 

jaymz168

Member
Joined
Aug 5, 2010
Messages
13
After tracing the board I can confirm an error in the provided schematic: Block 'K' outputs Vc which is the control voltage and connects to the U5 Vc input.  Still not idea what the U5 and U10 are, though.  I've now got one working unit and most of the parts to fix the other one but stupidly forgot to double my BOM for one value of electrolytic filter cap so I'll be waiting for those. 

Anyway, I'm onto trying to find an appropriate replacement for the output transformers on my units.  Mine have unbalanced outputs so I'd like to swap in something maybe a bit nicer.  Fitment will be an issue as there are filter caps around that area.  It's being driven by a 5534 into a 10R resistor, any 1:1 line output transformer should be fine here, right?  I don't think I'll be driving anything under 600ohms and if I'm doing current draw and dissipation calc correctly for 5534 in PDIP8 that should be ok?

Which leads to another thing, I've made up a schematic for an LM317/LM337 based +/-17V supply that would be a riser with jumpers to the existing LM78/79xxx pins.  It's tight with the reservoir caps on one side and the post reg filters on the other side, though the new caps are significantly smaller at the same value and rating than the OEMs.  I already have TO-220 heatsinks so I'm tempted to do a through hole version but I'm definitely worried about height.  I know I could fold them back, same with radial caps.

Any thoughts, part considerations? PCB routing pitfalls?  Should I just make some monstrous P2P chimera?  Is this just stupid?  "My" design is just a straight copy out of Self for the 17V supply with soldered terminals for the I/O...
 
Top