WNStudios said:
Sorry if this have been asked, actually i know it has once but he did not get an answer.
However i just bought a fully populated GSSL Rev 7 and picking up where he left off does create some confusion on my part. So i'm hoping someone can point me in the right direction.
The unit is compressing, and it does sound lovely. But even though the VU meter indicates different release times, different attack times and different ratios, i dont hear any difference. It's not behaving like it's supposed to and like it's showing. The VU meter can be slammed, but the sound i get is still a very transparent 2:1-type compression.
Then there's the bypass switch/makeup gain. At first when i put it in bypass i got this terrible noise and extreme volume, but lifting leg 4 on the 2180's seemed to do the trick so that is gone. But the Makeup gain only works when it's in bypass, isnt it supposed to do the opposite?
Also the release caps he put in there are Electrolytic, not Tantalums, would that make a huge difference?
Picking up a broken build requires experience of electronic debugging. If you don't have these skills you are going to need a lot of luck.
There are a few ways to debug this. First point is to use a standard test tone on the input for initial debugging: not music.
Doesn't really matter what it is but 1KHz 0dB will work. You'll also need a good high impedance voltmeter, or a scope.
Earlier in the thread I posted some test point measurements from my working build. You can search for that.
It gives test tones at various points through the schematic [to check e.g. that your de-balancer and balancer is working].
In your case since you are passing tones end to end, it's probably best to start by testing the threshold & make up gain controls with a static mono test tone on the input.
Moving the threshold pot from fully cw to ccw should cause DC voltage at point 'f' on the schematic to move from around -12v to ~+0.3V DC.
The TL072 should scale this linearly and add it to any existing control voltage to give a _change_ at pin 1 of approx 56/220 *12V = ~+3V DC as you move the pot from one extreme to the other.
Once you've got that control voltage working, you can make sure that it is having an effect on the side chain VCA.
AC Signal at Pin 7 of the TL074 in the sidechain should vary a lot as you change the threshold pot.
Now for the make up gain. Moving the make up gain pot from fully cw to ccw should cause a change at point 'e' on the schematic of around +12v to ~+0.0V DC.
The TL072 should scale this linearly and add it to any existing control voltage to give a _change_ at pin 7 of approx -100/620 *12V = ~-2V
Check that the bypass switch is wired the correct way around. i.e. in non-bypass mode, DC voltage at point 'e' should change, and you should see AC tone at the pole of the 'ATTACK' switch. In 'bypass' mode, DC voltage at point 'e' should not change as you move the pot, and you should see 0V AC at the pole of the ATTACK switch.
Once you've got that make up gain control voltage working, you can make sure that is having an effect on the main chain VCA.
Signal at Pin 1 of the 5532 should vary a lot as you change the make up gain.
That's the basics: you'll then know that your VCA's are working and 2 controls are working. You'll still have to check timing and ratios.
To quote wikipedia: The tantalum capacitor distinguishes itself from other capacitors in having high capacitance per volume and weight. Tantalum capacitors have lower equivalent series resistance (ESR), lower leakage, and higher operating temperature than other electrolytic capacitors, although other types of capacitors are even better in these regards.
Electrolytics will probably not sound the same in this application. I have to wonder what other shortcuts were taken in the build.
