GSSL HELP THREAD!!!

[MeToo2]

Guys, I have a funny problem on a recent GSSL: Its a build equipped with a turbo board, a crc board and a custom HPF for the side chain. Turbo and HPF are switchable. The switches are backlit with LEDs and the meter is equipped with a LED aswell. I take the power for these LEDS from the +12V rail.

Here comes the funny part: When I'm in bypass mode and turn the make-up pot all the way up all lights go off. this happens even if only the normal power LED is connected as usual.
When I enter compression mode all is fine.

So what's the deal here? I don't think any of the voltage regulators is broken since all is fine as long as i don't turn the makeup-gain all the way up in bypass mode.

Don't take any additional power from the (clean) 12V audio supply rail. It's meant to be especially quiet. If you also need 12V for lamps/ leds / relays etc. at higher currents, build yourself a simple separate (dirty) 12V logic supply. Search the thread for "regulator latching" if you want additional info. It's been covered many times.

 

[dangerousben]

Thanx for your reply. The only extras hooked to the +12 V rail were the extra lights which I took off now. So standard config with only the one Status LED connected. But this still keeps happening.
Plus it only happens in Bypass which makes the hole thing even more odd.

Edit:
I just checked, what happened to the +12V rail. When I crank the makeup in Bypass it breaks down to 0V. Damn.

 

[MeToo2]

Thanx for your reply. The only extras hooked to the +12 V rail were the extra lights which I took off now. So standard config with only the one Status LED connected. But this still keeps happening.
Plus it only happens in Bypass which makes the hole thing even more odd.

No. You are not on "standard config." Unless you have also removed your additional Turbo board (needs clean 12V) and your HPF side chain board (which generally includes a relay if its the "Super Side Chain"). Hint: The SSC relay is active in "bypass", depending on how you've wired it up of course. I modified my SSC board by cutting tracks so that the relay was connected to a dirty 12V supply.

 

[dangerousben]

No. You are not on "standard config." Unless you have also removed your additional Turbo board (needs clean 12V) and your HPF side chain board (which generally includes a relay if its the "Super Side Chain"). Hint: The SSC relay is active in "bypass", depending on how you've wired it up of course. I modified my SSC board by cutting tracks so that the relay was connected to a dirty 12V supply.

I did disconnect everything to come to the standard config plus my sidechain board uses the +15V for the relay. So no turbo and and side chain board were connected when I took the measurement.

 

[MeToo2]

No. You are not on "standard config." Unless you have also removed your additional Turbo board (needs clean 12V) and your HPF side chain board (which generally includes a relay if its the "Super Side Chain"). Hint: The SSC relay is active in "bypass", depending on how you've wired it up of course. I modified my SSC board by cutting tracks so that the relay was connected to a dirty 12V supply.

I did disconnect everything to come to the standard config plus my sidechain board uses the +15V for the relay. So no turbo and and side chain board were connected when I took the measurement.

Ok. Sorry. It should be obvious that this is a PSU related problem.
Can you measure the current draw (voltage across the 10R resistor) at the moment that the fault occurs?
Have you got a short somewhere around the makeup gain pot? (one leg is of this pot is connected to +12V)
Or in the pot itself?
Or the bypass switch?
Could it be make before break and the switch is shorting to Earth momentarily?

 

[Harpo]

When I'm in bypass mode and turn the make-up pot all the way up all lights go off. this happens even if only the normal power LED is connected as usual.
When I enter compression mode all is fine.

Faulty switch connection at the bypass switch (the half next to makeup gain pot/"E"). Switch pole goes to "E" and 620K resistor, switch throw ON goes to pot wiper, switch throw OFF goes to 0V reference voltage. You have connections "E" and ON flipped, shorting out the +12V rail with makeup pot in full CW position.
Don't connect any additional circuits to the +/-12V rails, especially if you might have a greater that center tapped 30VAC or 2*15VAC transformer secondary in front.* Connecting the turbo board is already challenging your Vregs.

edit: *this doesn't apply for the latest revisions #11 and #12 where the 78L12/79L12 are connected after the 7815/7915.

 

[dangerousben]

Wow guys, lot's of problem related info. I'm amazed and will check on all this later today, as I have been gigging the last two nights. Thanks Harpo and MeToo2 for taking your time and making up your minds.

 

[dangerousben]

Done! Thanks for the hint with the bypass switch, that's where the trouble came from:

According to Keith' info in this thread http://www.groupdiy.com/index.php?topic=34219.0 I redid the wiring of the switch. And as always I've double checked it and found it to be all right. However, this time I was wrong, I still had the wires coming from A and A2 the wrong way round and with the additional wire from A1 to ground all got messed up. Now I'm fine.

Thanks gents, you made my day.

 

[atticmike]

does anybody have a mouser bom?

 

[Ngr]

Hello everybody,
I have an SSL clone. It has begun to act funny: it was not compressing anymore unless I gave a good shook to the treshold pot. Then this remedy became useless. I opened it up and it seemed that tapping on the main board was solving the problem. Not anymore.
If I disconnect the molex of the treshold pot, I can see heavy compression and all of the controls appears to be working as they should, meter is ok, make up gain ok, attack and release ok. Only the treshold control does not work properly and prevents the compressor work. I checked its resistance with a multimeter and it appears to be working ok. I swapped the TL072s with no results. I could not change the tl074 since I don't have one. + and - 12V seems setady on the ICs power rails. Any suggestion or test to perform?

BTW I tried to swap again tl072 with new ones and for a few minutes iy worked again (I could measure varying voltages on pin 1 and 7) but after a while it stopped working again: now I have about fixed 2V on pin 1 and -0.1 on pin 7 with ratio at 2;1 and treshold at -20. with ratio at 10:1 it compress a little but obviously not as it should.

 

[jcpanizza]

Hi guys,

I am currently building my 5th GSSL and have been a DIY enthusiast for a few years. I built GSSL's for me and for friends.
All the GSSL i built worked the first time, but i am having issues with the one i am building right now, it's from a kit i bought from pcb grinder. so i am using the latest revision of this pcb.

The audio passes through the unit but i have no compression at all. the makeup pot works normally but the other controls are ineffective.
I read this thread almost entirely and tried everything i could:
- double-checked the entire PCB's for shorts or cold solder
- double checked for components polarity and resistor values
- checked voltages - they're fine
- replaced TL074 and TL072
- checked the wiring , bypass switch wiring, etc.

I still have no compression and after a lot of hours spent on this unit, i can't seem to find the solution.

Any suggestion would be appreciated!

I noticed that signal on TL074 pins 1, 7, 8 is distorted.
I also noticed that the unit can actually compress cause it started compressing when i touched some solders with my multimeter to check for shorts. so i guess the problem is located in the sidechain?

thx very much for your help!

 

[MeToo2]

BTW I tried to swap again tl072 with new ones and for a few minutes iy worked again (I could measure varying voltages on pin 1 and 7) but after a while it stopped working again: now I have about fixed 2V on pin 1 and -0.1 on pin 7 with ratio at 2;1 and treshold at -20. with ratio at 10:1 it compress a little but obviously not as it should.

If you vary the makeup gain pot, does the voltage on pin 7 change and pin 1 stay constant?

If you vary the threshold pot, does the voltage on pin 7 stay constant and pin 1 change?

 

[gyraf]

... from pcb grinder. so i am using the latest revision of this pcb.

There is room for a (newly added) 3-pin connector close to the TL074 - this is for adding a sidechain filter. If no sidechain filter is used, this NEEDS to be shorted out - otherwize you'll get symptoms like yours.

Sorry about not yet updating instructions - too much commercial soldering lately (which is also good).

Jakob E.

 

[Ngr]

If you vary the makeup gain pot, does the voltage on pin 7 change and pin 1 stay constant?

If you vary the threshold pot, does the voltage on pin 7 stay constant and pin 1 change?

Yes to both of your questions

 

[jcpanizza]

Hi Jakob,

thanks for your help,
I noticed the newly added 3pin connector and i shorted it ; I looked for it on the schematic and figured out it has to be shorted.
so this is not the cause...

any other ideas?

thx!

 

[Harpo]

..unless I gave a good shook to the treshold pot...
..seemed that tapping on the main board was solving the problem...
..If I disconnect the molex of the treshold pot...

Problem seems mechanical/intermittend related.
Double check your molex connectors for making solid connection to its crimp pins and/or use a magnifying glass to spot a broken trace in this area.

 

[MeToo2]

If you vary the makeup gain pot, does the voltage on pin 7 change and pin 1 stay constant?

If you vary the threshold pot, does the voltage on pin 7 stay constant and pin 1 change?

Yes to both of your questions

Then the problem would appear to be earlier in the side chain then.

As Harpo suggests, your fault could be/ is likely to be purely mechanical, so make sure you check the connector from the main board to the control board.

You can also check through the side chain by generating a constant sine wave in your DAW and connecting it to the input of your GSSL.

Switch on and off the DAW signal generator and check for changes in AC volts measurements at:
Pin6 NE5534. Should be same on both channels and a debalanced version of the DAW signal.
Pin 7 TL074. Should be an attenuated or amplified version of the DAW signal. It's amplitude should vary when you rotate the threshold pot.
Pin1 & 14 of the TL074 should be a compressed version of the DAW signal. It should change when you change the ratio switch when you have a low threshold and a high signal. It may well look very distorted (normal) as this stage is very non-linear.
Check the pole of the bypass switch. This should be always be a negative AC voltage that varies as you alter the DAW level and the threshold level.
Also check that the bypass switch isn't shorting to Earth.
Pin 10 of the TL074 (point 'o') should be a rectified and smoothed negative DC control voltage that decays slowly over time as the DAW single is turned off (assuming you are using the longest release time).
Pin 8 of the TL074 likewise

Note: if you have a scope that these waveforms in the side chain will not be sine waves.....

 

[Ngr]

It seems that I have kind of traced the problem. Kind of...
Touching the threshold pot with the multimeter probe makes the pot work again, even if on unstable basis. It seems that shorting lugs to ground with the probe kind of restores the pot to its normal use. but after a while it stops working again.
Could it be a defective pot? I checked it with a multimeter and it appears to be ok but maybe when voltage is applied to it, it becomes unstable.

 

[MeToo2]

It seems that I have kind of traced the problem. Kind of...
Touching the threshold pot with the multimeter probe makes the pot work again, even if on unstable basis. It seems that shorting lugs to ground with the probe kind of restores the pot to its normal use. but after a while it stops working again.
Could it be a defective pot? I checked it with a multimeter and it appears to be ok but maybe when voltage is applied to it, it becomes unstable.

Very possible. Pots get dirty, wear and go wrong. It could also just be a "dry joint." Or a crack in the resistive track in the pot that is intermittent.

You can try swapping the threshold pot with the makeup gain pot and see if the problem moves with the pot.

 

[Ngr]

changing treshold pot seems to make the compressor work ok, let's see how long it will last.
Thanks for your help!