Adl1000 unlinear gain reduction

I recently had to modify an adl1000.
The problem was that the gr wasn't linear over the frequency range.
Ie there was an unintentional lpf effect in the sidechain.

It took me two hours of signal tracing to find out there was a resistor simply missing on the board... The resistor is r30 on the la2a schem. It's in series with a cap to ground on the sidechain link, ofcourse affecting the circuit when it's not linked as well. Without the resistor (cap to ground) the lpf frequency is obviously decreased, resulting in unlinear gr behaviour.

The difference was night and day. The compressor sounded very agressive before the mod.

I mailed adl about this. The problem on the pcb is known to them but I think it's a pitty that they're not spreading this info for other users that have same pcb version in theirs.

Anyway, i hope this is useful info for someone...


EDIT: typo

Is this the same problem that tylerp describes at the bottom of the post:
http://www.gearslutz.com/board/high-end/365265-adl-1000-audio-upgrades-optimization-smokin.html
Although, he talks about an issue with board layout, but I suppose he could mean that the board layout is missing a component.
The issue is also talked about in the Whitestone add on Ebay.

Hmm, I can't tell for sure but it's somewhat similar to my measurements.

I saw a frequency cut of several dB starting at 1KHz in de sidechain amp. These scope pics show the frequency response under gain reduction, so it's very likely to be the same problem.

Ofcoarse i can't tell the amplitude div from his scope but what I had measured is definetly not a parasitic effect from board traces.

Thanks for the hint, Arno.