[BUILD]CAPI 2-ACA-Bo~Official Support Thread

[jsteiger]

You are gonna have to trace signal thru the entire chain and see where the level drops off. Start my measuring the AC level at the output of your interface then after the 1st stage, then after the 2nd stage etc etc.

 

[31cc7]

After reading your post I started mentally preparing myself to take everything apart, but I thought before I do this I'll just check the outputs first in case it is a cable.
I setup Ableton session to play sine waves at -18dBfs on each channel. I connected oscilloscope to first output and... everything looks normal. All left channels are being summed okay (but just a little hotter than coming in - perhaps because the the resistor divider I chose). I checked the cables then, and cables are okay. What the...
So I connected everything again and it works
The summed signal comes about 4dB louder than summed ITB but I can live with that for now (I will be able to drive the converters ;-)).

When I was at it, I also plugged power meter and I read that this summing mixer takes around 31W. No wonder the old PSU was crying. Current PSU gets warm, but no strange noises etc.

What slightly worries me is that I can hear slight hum and other noises at around -70dB. I would probably need to think about getting the wiring to look more sensible, plan the grounding etc. I'll see if I can live with what it is now first.

I am extremely happy this is working 8) Thank you for making products enabling me to do it.

 

[madbeavis]

Hello all,

I am having an issue that I cant seem to pin down with the talkback/mute circuit on the BO side.  On power up I can pass audio for about 30 seconds after which the mute becomes engaged. I can short the G and S pins of the J111 and it will start passing audio for another 30 seconds before repeating the same behavior.

I initially thought it was some charge from the FB or coupling capacitors but I was not able to measure any with a meter. I do have the mute pins grounded to the PSU ground mult, not sure if that makes a difference here.

I am using the J111-D26Z as described in the build docs:
https://www.mouser.com/ProductDetail/ON-Semiconductor-Fairchild/J111-D26Z?qs=sGAEpiMZZMv4z0HnGdrLjlAuB7fe22XlO1Ow%2Fw%252BxqNuNTjpCCHmXxw%3D%3D

Any ideas on what the cause could be?

Thanks,

Chris

 

[jsteiger]

Hello all,

I am having an issue that I cant seem to pin down with the talkback/mute circuit on the BO side.  On power up I can pass audio for about 30 seconds after which the mute becomes engaged. I can short the G and S pins of the J111 and it will start passing audio for another 30 seconds before repeating the same behavior.

I initially thought it was some charge from the FB or coupling capacitors but I was not able to measure any with a meter. I do have the mute pins grounded to the PSU ground mult, not sure if that makes a difference here.

I am using the J111-D26Z as described in the build docs:
https://www.mouser.com/ProductDetail/ON-Semiconductor-Fairchild/J111-D26Z?qs=sGAEpiMZZMv4z0HnGdrLjlAuB7fe22XlO1Ow%2Fw%252BxqNuNTjpCCHmXxw%3D%3D

Any ideas on what the cause could be?

Thanks,

Chris

The audio signal flows between Drain and Source. The only pin you would ground would be the Gate.

 

[madbeavis]

Thanks for the response Jeff,

The Pins I referred to as grounded are the 2 Mute KK header pins. The J111 is soldered in place on the PCB, matching the orientation on the layout mask.  If I momentarily short the Source and Gate pins using a probe then signal will pass again.

Thanks,

Chris

 

[jsteiger]

Thanks for the response Jeff,

The Pins I referred to as grounded are the 2 Mute KK header pins. The J111 is soldered in place on the PCB, matching the orientation on the layout mask.  If I momentarily short the Source and Gate pins using a probe then signal will pass again.

Thanks,

Chris

Gate goes to the header. Signal flows thru source to drain (or drain to source).

 

[madbeavis]

Any idea why its muting after 30 seconds with the Gate grounded?

 

[jsteiger]

Any idea why its muting after 30 seconds with the Gate grounded?

The only way I can think of is there's enough DC on the gate to open it. Something is wrong with your circuit somewhere. Measure DCV at the gate of the FET and see what the conditions are when it closes and then when it opens.

 

[madbeavis]

Its totally possible I screwed something up here. This gives me a good starting point however, ill verify DCV at the mute header pins and maybe try a chassis ground instead of using the PSU mult.

Thanks for your help!

Chris

 

[jsteiger]

Its totally possible I screwed something up here. This gives me a good starting point however, ill verify DCV at the mute header pins and maybe try a chassis ground instead of using the PSU mult.

Thanks for your help!

Chris

The PSU 0V reference should be fine. I think there's maybe something else going on.

 

[madbeavis]

I dont have R4, R6, and C8 populated (C4 is still on the board, I removed C8 while troubleshooting) and the talkback header pins are not there.  Thats the only difference from the schematic, but I dont see how any of that could affect the N-Channel. Im willing to bet your right about DC on the ground, im going to start with that. If I needed to bypass the N-Channel all together I should be able to remove the J111 and jumper the S and D pads together right?

Thanks,

Chris

 

[31cc7]

What are you trying to achieve? I decided to not use mute or talkback, so I only soldered in the required parts and that works.

 

[madbeavis]

Thanks for the info! I will also not populate these then.

This side for my build is summing reverb tanks, I actually run the ACABO in reverse: BO > Reverb > ACA. Everything else I have working but for some reason this is stubborn. I ordered some new boards and im going to start from scratch. Got a Hakko desouldering gun to get the 2623-4s off, hopefully that wont be too challenging.

 

[31cc7]

I had a little bit more time to test my summing mixer. Unfortunately after an hour or so channels started disappearing and when I disconnected the PSU it's got a squeaky sound for a second or so. The PSU inside was extremely hot. Maybe what the power meter is showing (the 30W) is max that the PSU can give, but the mixer itself needs more?

The LM333T/LM350T are still somewhere in customs so probably I won't be able to do much with it now.

I tried to look on eBay for something I could use and only thing that seems reasonable to me would be to buy one of those racked power supplies for mixing consoles (e.g. for Soundcraft or Behringer)? Problem is that these give +/-17V - +/-18V or more. Would 2S-LA and 2-ACA-Bo work fine with e.g. +/- 18V? I read that the gar2520 I am using should be okay.

edit: I skimmed through the thread and it looks to me that slightly higher voltage should be okay.

 

[Potato Cakes]

I had a little bit more time to test my summing mixer. Unfortunately after an hour or so channels started disappearing and when I disconnected the PSU it's got a squeaky sound for a second or so. The PSU inside was extremely hot. Maybe what the power meter is showing (the 30W) is max that the PSU can give, but the mixer itself needs more?

The LM333T/LM350T are still somewhere in customs so probably I won't be able to do much with it now.

I tried to look on eBay for something I could use and only thing that seems reasonable to me would be to buy one of those racked power supplies for mixing consoles (e.g. for Soundcraft or Behringer)? Problem is that these give +/-17V - +/-18V or more. Would 2S-LA and 2-ACA-Bo work fine with e.g. +/- 18V? I read that the gar2520 I am using should be okay.

edit: I skimmed through the thread and it looks to me that slightly higher voltage should be okay.

Are you using heat sinks on your regulators? Once those start getting hot the VDC will start to drop, affecting op amps. Those regulators are generally rated for 1A, but with thermal management. Put heat sinks on your regulators and retest.

I have an ACA-Bo in my TAC Scorpion that runs -/+17V and I have no issues with it.

Thanks!

Paul

 

[31cc7]

Yes, I have heatsinks although not too big. After I made sure the power supply is discharged I touched it in few places and everything was hot, transformer, capacitors etc. Now I read that LM317 would give out 15W at that voltage max, so that would make sense the mixer is maxing it out. Apart from 2-ACA-Bo, there are 8 2S-LA boards.
The case I used for PSU, however, is a bit small and not ventilated properly so this could also add to the struggle.

I scored a PSU for Soundcraft console on eBay, so I'll try my luck with this and also got on Ebay an old rack PSU for Soundtracs console - if that one will not work, I could re-use the case and hopefully by that time the higher rated voltage regulators will arrive.

I wish I had spent more time on PSU, it is so sad that I got this thing working but I cannot power it

 

[31cc7]

Today I got the Soundtracks PSU. From the outside it looked terrible so I didn't have much hope, but after cleaning inside it actually looks quite okay. I checked the voltages it gives +/- 16.6V which is great. But what worries me is 2.58V instead of 5V on one of the pins (but I would not use that one). Maybe the caps or the 5V regulator would need changing but visually they look good. Unfortunately I don't have 6-Pin XLR cable, so I am torn between waiting for one or replacing the XLR socket with 3-Pin one. This would be little messy as the socket is mounted with rivets.
The PSU is 3U and with my little summing mixer also being 3U, this turns out to become a 6U monster...

 

[jsteiger]

A 3-pin XLR for power is scary.

 

[31cc7]

A 3-pin XLR for power is scary.

Somehow I didn't realise I could do power supply input on the mixer via e.g. 4-6 pin XLR and that I had a couple of 5 DIN chassis sockets I used that  :  So that would be double scary haha
I found a 5 pin XLR plug though so I cobbled together a temporary cable without removing original socket and so far everything works brilliant!
Under full load the mixer takes 38W, so that's why the other PSU was struggling too.
The Soundtracs PSU doesn't seem to be bothered by that load.

 

[31cc7]

Ok something is happening that I don't understand. It is actually similar thing when the weak PSU couldn't cope.

I left it playing for over an hour. When I came back mostly left channel was playing (that is channel 1, 3, 5, 7 and also 8). Each pair is on one 2S-LA board.  1-2 is bottom left, 7-8 is top right.  Both the mixer and PSU feel warm to touch, but nothing worrying.
The power consuption increased to 39.5W.

So what happened next is that on channels 1/2 I increased the volume from -18 to 0, so see what will happen on channel 2. That resulted in very heavy distortion and then suddenly all other channels (2, 4 ,6) gone back to "normal".  When I pulled the volume down to -18 on 1/2 it started to sound okay again  ???

Not sure how to explain this. Could this still be a PSU issue? (Given it's probably 30 years old) I am not sure why would it gone back to normal shortly after maxing out channel 1 and 2.