diylan

Problem With GSSL Turbo Board, Please help!
« on: May 10, 2011, 08:39:50 PM »
So I'm having some crazy issues with a turbo board I'm trying to install into an already working GSSL build. I tried reviving an old thread with similar issues but didn't get any response. Please help! :'(

So the problem: When the turbo board is connected, and ICs socketed, the meter pegs when taken out of bypass. If I set the ratio @ 2:1, attack @ 30ms, and release @ .1s I can get the meter to show somewhere around 12db of reduction. A little more "gain reduction" as I slow the release, but any other attack or ratio setting maxes out the meter. Threshold and output pots don't affect the meter.

I've taken voltage readings on the TL074 socket and they don't seem normal:
1: 3.18
2: 3.41
3: 0
4: ~12
5: 0
6: 0
7: 2.8x (drops slowly in .01 increments when taking reading)
8: -.04
9: -.04
10: -.01
11: ~-12
12: 0
13: 3.41
14: 3.71

Also, my point "C" reads 0vdc when engaged, .05 when in bypass. And I've measured that resistance is switching across R6, but values seem a bit low.

Sorry for the info dump, but I tried this thing connected every appropriate way I could imagine. Switched turbo and hardwired turbo, I've lifted and tested all the resistors and diodes, and still it persists. Without the turbo connected the GSSL works as normal.

Any thoughts? ???


SSLtech

Re: Problem With GSSL Turbo Board, Please help!
« Reply #1 on: May 12, 2011, 08:26:39 AM »
The schematic for the Turbo is based around the TL074 and the VCA like in the original.

So... start with the VCA and TL074 pins 5, 6 and 7. Look at pin 7. It should have audio voltage on it. Everything else comes afterwards, just like in the GSSL.

You have two-point-something volts of DC on it. -Either your VCA is bad, or something is wrongly hooked up and the DC reference is off.

The only exception to the SSL schematic is pins 8, 9 & 10, which should unity-gain-buffer the threshold voltage. You should see pin 8 follow the threshold control setting with a DC voltage.

If you have about 3 volts of DC at pin 7, you will have about 3 volts at pins 1 and 14, so fix that and the rest should follow.

If you socketed the VCA, you can test it by removing it and jumpering pin 1 to pin 8. If the DC disappears, replace the VCA and see if that gets it. -If the DC remains, find out why the DC reference into the op-amp is wrong.

Keith
"A waist is a terrible thing to mind"
Quote from: PRR
Ah, but that was 1999; we don't party like that any more.

diylan

Re: Problem With GSSL Turbo Board, Please help!
« Reply #2 on: May 13, 2011, 12:17:51 PM »
Keith, thanks so much! That was just what I needed to figure this thing out.

All the connections in/out of the board were fine, it was the trace from the 22u electrolytic that was not making its connection to the 100p cap. So the voltage wasn't making its way through the 100p cap and the 33k resistor to pin 8 on the VCA... and on down the line.

I ended up having to jumper the + terminal of the 22u cap to the corresponding terminal of the 100p, but that did the trick. Works like a charm now! I don't know if I just got a bad board or what but it might be worth checking in others from your most recent batch.

SSLtech

Re: Problem With GSSL Turbo Board, Please help!
« Reply #3 on: May 13, 2011, 12:25:50 PM »
Excellent!

I'll bear it in mind; There haven't been TOO many problems, and usually they've been with the  installation rather than the boards, but this is good to know.

Also, it was good exercise for me to go back and think through the troubleshooting methodically. Having the DC at the first stage made things nice and easy.

Keith
"A waist is a terrible thing to mind"
Quote from: PRR
Ah, but that was 1999; we don't party like that any more.


 

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