Need advice on possible SSL comp. calibration issue

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Flundran

Well-known member
Joined
Jul 4, 2004
Messages
209
Location
Sweden
Hello,

I recently began to use my GSSL compressor I've built. All controls work fine and the compression sounds right. But left and right channel doesn't compress quite the same amount. Yesturday I ran a mix thru it and recorded it into Logic Audio. See a picture of the mix in Logic. I've used gentle settings on the SSL, and the left channel doesn't compress as much as right channel. One can hear it also.

My SSL is using 202XT vca's.

Is this a calibration problem? My friend has an oscilloscope, he can probably do measurements on it if we know what to measure.

SSL_problem.jpg
 
My advise would be to switch the vca's around to see if you have a faulty one. If the problem persists, then you should trace your board for shorts.
 
Ok, I'm planning to flip the VCA's tomorrow.

It seems that the difference between L and R channel appears only on gentle threshold settings. If I lower the threshold (CCW) and compress harder, the two outputs appear identical.

/F
 
I've now tested to switch place of the VCA's. The problem remains on the same channel. The left channel does not compress quite as hard as right channel. I also have a 50Hz humming on left channel. It amplifies when i use the make-up and dissapears when the unit is in bypass-mode.

Is it a short somewhere? Anyone got any ideas?

/F
 
Good news reg. the humproblem. I moved my transformer connections from the middle of PCB to the edge, and this completely removed the groundnoise on the left channel.

However the compressor is still not compressing equal on both channels. Would appreciate any tip here.

/F
 
Based on what was said previously, double check resistors values in the signal path. Maybe you stuck a wrong one in somwhere. A sidechain problem would show up on both channels. Also, check for shorts.

Also, someone else had a similar problem when mounting an external trafo to the middle points... but then again, Jakob does say to use the pads in the corner when using an external trafo.
 
I ran a test today where i fed sound thru the SSL with no compression at all. The volume on right channel is weaker than left.

I will go thru the resistor values, seems like a possible source for this error.

/F
 
I found the fault today! It was a resistance in the left signal path with wrong value.

It runs perfect now. Yippee!
/F
 
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