GSSL HELP THREAD!!!

[Harpo]

Hey taylor, I recently had 5dB offset on a gssl, turned out the two 27k (or 15k as sometimes written on the pcb) between the power transformer and the vcas had different values. That could be a starting point as they influence directly the level going to the vca inputs.
Hope it helps!

jules

Correcting obviously wrong value parts causing a 5dB mismatch is probably not the OPs subject. From his post, his imbalance is 0.5dB that probably is an add up of parts tolerances. In this build nearly all resistors can get you there. Tolerances in VCAs -6.1mV/dB control voltage can be in range of +/-2.3% and bypass condition might vary +/-0.1% as well. May last reply to this post could be an easy fix, if you don't want to measure each resistor out of circuit.

 

[johnmellor]

yeah in the schematic it says 27k, and on chef's boards there is 15k. so should it be 15k or 27k??

[quote author=tgauge]
Hey everybody, I just finished my first GSSL (besides the front panel and cosmetics) and everything went very very smooth... Almost too smooth.  Plugged it in, tested the voltage points, dropped in the VCAs and passed a mix through it.  The compressor sounds amazing and is dead quiet.  I have only worked on SCA kits and a DIY Summer before this.  I was quite impressed.

Here's the issue: My right channel volume is about .5 decibel lower than the left.  Is there an easy solution to the problem?  I'm assuming that it's due to variance in the resistors or something of that nature.  I can always just adjust the track digitally once it's back in Pro Tools but I would much rather know what the issue is and how to solve it for my next build.

Any suggestions?  I searched all over for the answer and couldn't find what I was looking for...

Thank you to everyone for your help and the endless amount of data here.  I am so inspired to take on the next challenge.

Happy DIYing!

-Taylor

Hey taylor, I recently had 5dB offset on a gssl, turned out the two 27k (or 15k as sometimes written on the pcb) between the power transformer and the vcas had different values. That could be a starting point as they influence directly the level going to the vca inputs.
Hope it helps!

jules
[/quote]

 

[j.frad]

it's 27k to have unity gain through the machine

 

[johnmellor]

it's 27k to have unity gain through the machine

because basically my problem just now I've got 15k's at the input of both left and right sides of the dbx202 emulation circuits, and my output left is approx 3db louder than right, could this be the problem or do you reckon its somewhere else? cheers

 

[Pieter001]

Your right john. So i unhoocked the SSC board. But the problem is still there. I still read the same voltages.
Maybe i destroyed some components when i miswired the trafo?

Pieter

 

[tgauge]

Thank you guys for the replies to my issue... I was doing the testing prior to hooking up the Turbo board because I wanted to make sure everything functioned well and in case it did not I didn't want to hurt the Turbo also.  Once I went ahead and hooked that up it looks like it is only about .2 dB difference and it's only when compressing (bypassed it is matched perfectly).  I can live with that value so I will just leave it for now.  I believe it is just a build up of non-matching resistors (damn 1% tolerance).  I had initially stuffed the PCB several months ago but have never finished it until recently.  In that period of reading I realized some people were measuring each resistor to make sure they matched in different areas.  I think when I get to building my second I will definitely take the time to do that because I can now see what the outcome can be.  Thanks again for your help!

-Taylor

P.S. Thanks again to everyone who made this project possible.  This GSSL is a monster.  I used to work on an SSL 6000 daily and this thing definitely has a real SSL vibe.  I'm impressed.

 

[noisecontrol]

Hi, I have created a small circuit board to control the lights/LEDs of my illuminated switches. However it creates a loud click (mostly in the left channel) whenever I turn the power to the relay off. Here is a circuit diagram of what I created:

I took a 15V supply from near the VCAS (the left one incidentally) here:

The bypass switch is a dpdt and controls the voltage for the light on one pole and the voltage for the relay on the other. The relay is alsl a dpdt which switches the makeup gain and compression off.
Do I need a cap in there or a diode perhaps? I read reference to a snubber in another thread but I don't understand how to implement it with this circuit. I'm clearly a bit of a noob

Cheers
Reuben

*EDIT* I found the solution was a diode needed in parallel to the power supply to the relay. The whole unit works great now. I just used one of the spare diodes (1n4148) I had left over from the build. Works a treat, the relay is now super quiet with no spikes or clicks The diode cathode was on the positive power side like this:

 

[johnmellor]

Thank you guys for the replies to my issue... I was doing the testing prior to hooking up the Turbo board because I wanted to make sure everything functioned well and in case it did not I didn't want to hurt the Turbo also.  Once I went ahead and hooked that up it looks like it is only about .2 dB difference and it's only when compressing (bypassed it is matched perfectly).  I can live with that value so I will just leave it for now.  I believe it is just a build up of non-matching resistors (damn 1% tolerance).  I had initially stuffed the PCB several months ago but have never finished it until recently.  In that period of reading I realized some people were measuring each resistor to make sure they matched in different areas.  I think when I get to building my second I will definitely take the time to do that because I can now see what the outcome can be.  Thanks again for your help!

-Taylor

P.S. Thanks again to everyone who made this project possible.  This GSSL is a monster.  I used to work on an SSL 6000 daily and this thing definitely has a real SSL vibe.  I'm impressed.

So in your personal opinion, obviously since you've worked with ssl boards, is it necessary to get the turbo board to get closer to the original sound. I love the sound of it but its quite easy to get over the top compression sounds, and so getting a turbo board doesn't really make sense to me? I've only ever used Amek and MTA boards before so your advice would be appreciated.

 

[tgauge]

If I'm understanding you correctly, you are afraid that adding a turbo board will make it compress more/act more aggresively.  If that's the question then no, the name "turbo" might make you think that but it's not the point of that add-on.  If you are unhappy with your threshold because the compressor "bites on too easy," just search for the threshold hold "mod."  Basically you can change out a resistor (if I remember, only one) and the threshold is less sensitive which was perfect for me because I'm usually only compressing about 2dB on the 2 buss.

As far as the question of sounding like a real SSL buss compressor, without the turbo board it definitely "sounds" like an SSL, but with the turbo board it "behaves" more like the real deal.

Funny story about that SSL 6000 I worked on, the buss compressor's bypass push button actually had "Fairydust" engraved into it.  I'm not sure if all of the 6K's were like that or not?

Hope that helps a little.

-Taylor

 

[mac]

Hey All,

I was hoping to be able to post this as a solved problem, but after a few days of trouble shooting I am a bit stumped.

I have an intermittent +12 rail. Once out of every 10 or so power ups it drops to -.8V. Through diagnostics I believe it has something to do with the TL072. I disconnected the control board, have no other op amps on the board except the TL072.

With the TL072 removed +12 and -12 are nice and stable. Pop the TL072 in and I get this intermittent behaviour.

I have tripple checked all solder joints, replaced the TL072, replaced the 78L12, removed and replaced some of the 100n caps and the values of the resistors immediately adjacent to the +12 rail.

What could drag the voltage down that much? I assumed it would have to be a faulty cap...??

Mac

 

[stereokillah]

should be from your tl072, check the specification, perhaps your voltage is to high or low for your tl072

 

[mac]

After the bridge there is +22 and -22 feeding the 79L12 AND 78L12 which reg down to +12v and -12v perfectly on most power ups. Then occasionally the +12 is being dragged down to -.8 intermittently on pin 8.

Texas instruments TL072CP datasheet says Vcc max 18v, so I dont see a problem.

I have now replaced every cap within the vicintiy, and it hasnt changed the behaviour.

I have some TL082CP which are a drop in replacement - maybe I shall try these next.

Mac

 

[mac]

Nope....Different TL072 and TL082's all provide the same result.

1 out of every 10 power ups drops the 12v rail to -.8v.

???

Mac

 

[stereokillah]

sorry it was a mistake, i talked about 78l12 not about tl072

 

[Biasrocks]

Mac

I would first try disconnecting the Pwr On LED connected off the ratio board. It's powered from the +12v line and could be causing a problem.

As I said before, the internal power supply can teeter very close to overload in this design.

Try changing the 10R resistors ahead of the 12volt regs to a slightly higher value (try 100ohms). This will end up burning more volts ahead of the regs and they will run cooler. Just make sure that you have a minimum of 15 volts ahead of the 12 volt regs, I would think that 16-17volts would be a better range for those guys as opposed to the 22 volts they are seeing now. Those little guys are dropping a ton of voltage, it may be causing a problem. You could also change out the regulator itself, perhaps it's experienced some stress and needs to be replaced.

Mark

 

[mac]

Hey Mark,
thanks for your pointers....

Yes, the first thing I did was disconnect the control board including the Led, so that I am working on as small a section of the circuit as possible. Yes I also changed out the 78L12 as one of the first things to try also - no good.

I didnt change the neg regulator, it seems fine.

I will try your 10k resistor change next...
Mac

P.S. I just stumbled onto the magic search term for my problem - "latch up". Appears to be a common problem with this board and these regulators.

Anyone come up with a solution that worked?? Or do I abandon this part of the board and build a separate 317 337 power supply and feed the board with 12v that way?

 

[Harpo]

...Yes I also changed out the 78L12...

...with a different brand of 78L12 ?
You might fix this start up latching by placing a diode (1N4148 should do) between gnd and output of the regulator (anode side to gnd, kathode to output).

 

[artosaudio]

Hello there you all,

I've waited as long as possible, because I actually like to troubleshoot... however this gssl I've built seems to have one or more faults I really cannot trace. I've built the one with the supersidechain add-onn.

This is what I get with the supersidechain connected. The left channel is giving a huge output en is completely distorted. The right channel is as clean as possible but however refuses to compress! threshold, make-up and all the other controls give me absolutely nothing. without the vca's installed and pin 1/pin8 directed linked in en output are perfectly clean, left and right.

Without the supersidechain connected the left channel still has the huge distorted output, right still clean. The only noticeble difference is that on the right channel the make-up works! however no compression or whatsoever.

I've checked the 15/-15 and the 12/-12 rails and they are ok. also I get relative voltages on the tl072 depending on me turning the threshold knob, so the controlboard seems well connected.

Can somebody help me please. My last Gssl worked (and works) flawless from day one...!

 

[Biasrocks]

I will try your 10k resistor change next...
Mac

Mac,

try 100R, not 10K.

Mark

 

[artosaudio]

ha i found something.

It appears that I've a capacitor with the wrong orientation. It's the one next to the tl074. It's value is 22uf. Can I replace that one for the moment with a 20uf of a 33uf? I've got no 22uf left and the stores are allready closed, could this do any harm?

thanx!