Aion FX L5 Preamp - compressor/limiter action drops output to zero

[phy7ajw]

Hi folks,

I'm testing out my build of Aion FX's L5 Preamp (really enjoyed the assembly, great PCB).  The Ch1 and Ch2 sound is great, knobs all appear to do what they should.  Calibrated successfully with correct values.  My only problem is the Compressor/Limiter. 

From scanning the interweb including many great threads on this forum, I'm aware that it's not a regular compressor.  The knob does appear to set the level at which the compressor acts but the problem is that immediately after the initial note attack the output drops to zero, regardless of knob or trim pot setting.  It sounds like any activation of the compressor just kills the output before it gently rises back up to some suitable level.  Demo video here:

https://youtu.be/ubmNxbUOzR8

I've reheated all joints in that corner of the board and paid close attention to IC11 and IC10. I've temporarily disconnected the Comp LED to see if that extra bit of current draw when the compressor acts was knocking out the Traco DC converter but no change.

Schematic is here.

Parts are almost all from the Mouser BOM, only substitutions were a few resistors and small caps and same values from other manufacturers were used. Power supply is capable of 1A.

Wondering if anyone can give me any clues given the symptoms, or point me at reference voltage values for test of this version (this is the 9VDC input version, I did see a link to test values for the older AC input version but the ICs don't match this one).

Obligatory PCB photos are here... appreciate any clues anyone can offer.

Cheers,

Andy

[aion]

I would focus on IC10, IC11, Q3 and Q4 which are the main active components in the compressor section. Q3 was previously called Q1, Q4 was previously called Q2, and IC11 was previously called IC12, but the voltages should all be largely the same.

IC11 has been merged with IC10, so it would be the left side of the LM13700 that you are investigating. Translating the pins of the CA3080 to the LM13700, the voltages should be:

1: -14.62V to -14.9V
2: ignore
3: 0V
4: 0V
5: 0.23V
6: -15V
7: ignore
8: ignore
11: +15V

Hopefully that gets you somewhere!

[phy7ajw]

Thanks for the pointers.    Are those voltages with the 30mV rms 1kHz test signal applied?  Or when the circuit is idle?