GSSL turbo board issue

Hi,

I'm experiencing a strange behavior with my GSSL with turbo board wired permanently. The GSLL is inserted on the main mix buss of my analog console, and everything seemed to be fine until I mute right side signal on the mixer. What I got is an uncompressed sound on my left monitor and the vu meter needle of the GSSL stays desperately at 0, confirming that the sound isn't compressed. But when muting left side, I have a compressed signal on my right side monitor, and of course (witch is weird for me), I have both sides compressed when sending a stereo signal into the GSSL. So it seems that the left side signal (the one that goes into the turbo board) doesn't go into the turbo side chain. My first test was to bypass the turbo board and come back to the original GSSL design to see if the problem was coming from the GSSL or the turbo board itself, and I didn't have this strange behavior anymore, so the problem comes from the turbo. I checked the voltages on the TL074 of the turbo board and also the continuity between the TL074 on the GSSL board and the one on turbo board as advised on the turbo build guide and everything is ok.

So I would be glad if someone could help me with this.

Cheers

Pierrick

Hi,

you ever sorted out this problem?
I have the same problem with a unit on the testbench.  Wired as permanent Oxford/Turbo.

What is/was the issue?


I think I found the answer (by Harpo) in the GSSL add-on thread.: The 47R to pin 4 of the VCA for 2150 VCA is correctly installed on the Turbo board, but 2180 type VCA is socketed there . So the 47R needs removal. Or bend pin 4.

Harpo said:

(...) with THAT2180 sidechain-VCAs, double check, you only fitted one 47R resistor per sidechain-VCA (keep the one connecting to pin3. Leave out the 47R that connects to pin 4, ment for a 2150 type VCA.)

Click to expand...

No. That wasn't it. Problem still there... hmm

Same control (milli)voltage at sidechain-VCA pin3 (6.1mV/dB) with signal present when compressing ?
Same value of current setting resistor (3K9) in between -12VDC and sidechain-VCA pin5 ?
You didn't fit the 10K in between sidechain-VCA pin 3 / 5 (ment for a different type of VCA as a try to decrease control port modulation) ?

Harpo said:

Same control (milli)voltage at sidechain-VCA pin3 (6.1mV/dB) with signal present when compressing ?
Same value of current setting resistor (3K9) in between -12VDC and sidechain-VCA pin5 ?
You didn't fit the 10K in between sidechain-VCA pin 3 / 5 (ment for a different type of VCA as a try to decrease control port modulation) ?

Click to expand...

Both SC VCAs are 2181B.
Probably not the best choice cos not pre-trimmed like the 2180. But still...

- Yes. Same control(milli)voltage at pins3 when compressing.
- Yes. Same 3K9 current setting resistors between -12V and sidechain -VCA pin5
- The 10Ks between pins 3 and 5 are fitted on both channels. Added: Will take them out.

Did some quick measurements and CV out from the Turbo seems way off.

Modified:
Problem further dealt with in the 'GSSL add-on help thread' and solved here:
https://groupdiy.com/index.php?topic=65232.msg936232#msg936232