DIYSTUDIOTOYS CSG4000 issue

[innercityman]

Hi everyone,

I've finished building a CSG4000 from DIYSTUDIOTOYS. It's a kind of all options SSL4000 bus compressor clone. I've chosen quad THAT 2181 VCA option. I've started calibration and once it has been done I've tested the unit and get an issue... I get distortion / saturation on signal as soon as I start to compress. Signal clear when threshold pot at +15 so fully CW. Compression works and signal reduced but sound is saturated.
You can see it on my scope... Any suggestions where I should start troubleshooting ?


View attachment IMG_4404.mov

 

[abbey road d enfer]

Could be the side-chain is not correct; like the release time is extremely short. Can you check the wave form of the ontrol voltage?

 

[innercityman]

Could be the side-chain is not correct; like the release time is extremely short. Can you check the wave form of the ontrol voltage?

I'll check if I can.
Just to le t you know... I did side chain offset calibration as explain in the calibration process document of the unit and it was on off position when video was taken.

 

[gyraf]

does distortion change with release time? If not, that's what's missing

Also remember that compression IS distortion. Well-behaved, but still. You can only measure distortion in any meaningful way without compression.

On GSSL and variants, VCA's are always active (makeup gain). If you must, just measure without compression.

/Jakob E.

 

[abbey road d enfer]

I'll check if I can.
Just to le t you know... I did side chain offset calibration as explain in the calibration process document of the unit and it was on off position when video was taken.

I don't know anything about the "side chain offset calibration", nor teh particular schematic of this unit, but what does mean "it was on off position when video was taken"?

 

[innercityman]

I don't know anything about the "side chain offset calibration", nor teh particular schematic of this unit, but what does mean "it was on off position when video was taken"?

There's an OFF position on the side chain, I guess this calibration step is relative to that. Many trimmers on this unit... a pair for unity gain cal, distortion cal, mix, side chain offset, side chain level, ratio, and meter.

 

[innercityman]

does distortion change with release time? If not, that's what's missing

Don't think so. I'll check again...

 

[innercityman]

Just to let you know that after many tests and measurements, it ended up that it was a faulty switch, the release one. I've replaced it and problem gone. Thanks to Abbey Road d enfer and Jakob for putting me in the right direction.

 

[flyingeyepro]

good to know

 

[roofRob]

Hey @innercityman

I guess you're a pro builder(?)...
I'm about to start building this project and was hoping to get this done even without any kind of documentation- or did you find any?
But now that I see that you had issues with calibration- and I'm NOT a pro builder- is it safe to assume I can dig around any GSSL docs/threads to find what I might need in terms of directions?

Cheers and have a good ride into 2024,

Robert