strange GSSL problem

hello!

i'm having some trouble with my latest GSSL...
it's passing audio fine, makeup gain works, but no compression.

i've checked all the usual things - power rails, board interconnects, ICs, bypass switch, soldering is fine, and all components values were triple checked when placed etc.

a weird thing though - i noticed that when turning the ratio knob the meter twitched - so i found that if i held the ratio knob between two of the positions so its shorted, the unit starts working/compressing! also i can do the same thing by shorting pins A and B on the control board connector, thus sort of 'bypassing' the ratio section.

so is the problem around the ratio??? checked all resistor values, diode orientation etc.

any help is massively appreciated, i've been through the whole GSSL help thread and run out of ideas!
thanks in advance

This one shoulp be posted here:

http://www.groupdiy.com/index.php?topic=47.4380;topicseen

sorry, i did post in there but got no reply, seems that thread doesnt get checked very much for new posts...

update anyway:
although i get no compression at 4:1 or 10:1, at 2:1 (if i run a 1khz sine wave in at around +9dbu) i get about 4db of gain reduction with the threshold fully anticlockwise...

tracing with the scope, pin 1 of the TL072 is correctly moving from 12v to -12v when i move the threshold knob fully anticlockwise, but the output pin 7 of the TL074 is barely changing, when i should be getting a good signal at 2V, its about 0.1V, plus its distorted/clipped (compared against a working unit).

unfortunately im not knowledgable enough to know what's causing this already replaced all op amps and checked component values etc.

any help really appreciated... even just suggestions of more things to try replacing/checking... thanks

Hi Daveee,

If you have a working unit just work through the schemo, compare both units, eventually you will come across some thing that does not match, then bingo..its probably a wrong resistor or a short on the bottom of the pcb i bet..

Best
Pete

got it! thanks pete

33ohm resistor instead of 33k feedback resistor across the op amp after the sidechain VCA.