GSSL HELP THREAD!!!

[gyraf]

still unclear what exactly you measure, sorry

you put in say 1.2V AC (what waveform, freq, measured how?), set the unit to compress say 4dB, adjust makeup gain to 1.2V again - now what channel difference do you see? This is a real-world condition, and all that matters.

If you're within 2% here, all is well

There may be several border conditions like clipping points for various parts of control or audio chain that could influence balance but that are not relevant for our use-case

/Jakob E.

 

[Gustav]

Here’s a pic, no mods. Trying to get it right first. All this is what happened the first time I plugged it in, and this is PCB Grinder’s last incarnation kit, there are no trim pots. Hence why I was so curious as to why I put a 1.2 VAC signal in and with the output knob all the way counter-clockwise get up to 7 VAC on the output signal. So I can’t test it with any material, as my converters are dying as it is. My testing and troubleshooting brought me to the VCA’s as when I first fired it up I noticed radically different outputs on the left and right channel. So I took them out and tested them one by one. Thanks for the help, would love any insight.

I find it really difficult to follow your methodology,taking out and putting in VCAs one at a time. For example, I am confused wether you are treating the SC identically to the signal path VCAs.

Just to get a really clear picture. Could you...

1. Place all 3 VCAs in the circuit, send a 1Khz sine at 0dBU/0.775VAC to the unit, make sure treshold is set to max, and measure output (from the unit, not the VCA) at max and minimum gain at left and right respectively.

Id like to establish a base reading with known variables, at a familiar range, and see if we have discrepancies.

2. Swap the two VCAs on the left and right channel with each other, then measure output at max and minimum gain under the same conditions as before.

Id like to see if any discrepancies uncovered in step 1 follow the VCA, to make sure if the VCA is indeed the culprit.

Gustav

 

[Harpo]

Here’s a pic, no mods. Trying to get it right first. All this is what happened the first time I plugged it in, and this is PCB Grinder’s last incarnation kit, there are no trim pots. Hence why I was so curious as to why I put a 1.2 VAC signal in and with the output knob all the way counter-clockwise get up to 7 VAC on the output signal. So I can’t test it with any material, as my converters are dying as it is. My testing and troubleshooting brought me to the VCA’s as when I first fired it up I noticed radically different outputs on the left and right channel. So I took them out and tested them one by one. Thanks for the help, would love any insight.

From your pic, the sidechain-VCA seems to be fitted with reversed orientation. The VCA most likely won't survive this, once powered on. A broken chip will give you unpredictable, if any readouts.

 

[Gustav]

From your pic, the sidechain-VCA seems to be fitted with reversed orientation. The VCA most likely won't survive this, once powered on. A broken chip will give you unpredictable, if any readouts.

good eye

Gustav

 

[joshk34]

I find it really difficult to follow your methodology,taking out and putting in VCAs one at a time. For example, I am confused wether you are treating the SC identically to the signal path VCAs.

Just to get a really clear picture. Could you...

1. Place all 3 VCAs in the circuit, send a 1Khz sine at 0dBU/0.775VAC to the unit, make sure treshold is set to max, and measure output (from the unit, not the VCA) at max and minimum gain at left and right respectively.

Id like to establish a base reading with known variables, at a familiar range, and see if we have discrepancies.

2. Swap the two VCAs on the left and right channel with each other, then measure output at max and minimum gain under the same conditions as before.

Id like to see if any discrepancies uncovered in step 1 follow the VCA, to make sure if the VCA is indeed the culprit.

Gustav

Can do

Step 1: Left: .84 VAC to 6.106 VAC
Right: 6.69 VAC to 9.01 VAC

Step 2: With the VCA's swapped left and right
Left: 6.70 VAC to 9.00 VAC
Right: .875. VAC to 6.13 VAC

Thanks for pointing out the VCA, Harpo. I did have it reversed, but never turned it on like that. Just hastily put it back in at the end of the night and fixed it before powering on.

 

[Gustav]

Can do

Step 1: Left: .84 VAC to 6.106 VAC
Right: 6.69 VAC to 9.01 VAC

Step 2: With the VCA's swapped left and right
Left: 6.70 VAC to 9.00 VAC
Right: .875. VAC to 6.13 VAC

Thanks for pointing out the VCA, Harpo. I did have it reversed, but never turned it on like that. Just hastily put it back in at the end of the night and fixed it before powering on.

We expect roughly 20dB gain, which is not really spot on at all, but close enough on the VCA on the left at step 1, and on the right at step 2 (comes to about 17?)

There is something wrong with the other VCA - I dont think Ive seen a broken one act like that, or maybe I never measured it quite so in depth, because it was just obviously off without going to such lenghts. Is the unit compressing and everything on the bad channel, just gaining excessively?

I only see bad VCAs, when I have put them in reversed - happens for the best of us. If you suspect other issues could be at play, you could ask the tech help at THAT. They are usually quite responsive.

Gustav

 

[joshk34]

We expect roughly 20dB gain, which is not really spot on at all, but close enough on the VCA on the left at step 1, and on the right at step 2 (comes to about 17?)

There is something wrong with the other VCA - I dont think Ive seen a broken one act like that, or maybe I never measured it quite so in depth, because it was just obviously off without going to such lenghts. Is the unit compressing and everything on the bad channel, just gaining excessively?

I only see bad VCAs, when I have put them in reversed - happens for the best of us. If you suspect other issues could be at play, you could ask the tech help at THAT. They are usually quite responsive.

Gustav

Thanks for the advice. I ended up ordering some more VCA's, but they don't arrive until November. Meanwhile, I finally got some time to dig in again, and it's not just the VCA's. The device doesn't seem to be compressing. While it passes signal, with the aforementioned errors, I ran program material through the "good" VCA and no matter what the controls were set at, the device did not compress at all. In fact, if I volume match it, it nulled with the GSSL in and out of bypass. The output volume seems to be the only thing that's working and will be affected whether the bypass switch in engaged. Ah well, back to the drawing board.

 

[Ilarrayoz2]

Hello!

I would apreciate any hepl with this issue.
After the assembly of the unit, the sound is passing thorught but there is no compresion.
I guess that I am having issue with the VCAs, by the way I am using the THAT218B.

The rest of the circuit it seem to work properly, since the DC values are changin when I am turning the different knobs, they look within the proper values, 0-1 V at the vac control pin.

The voltage at the pin 5 is around -2.8V for the 3 VCAs, when it should -8.5 V as it was mention here:
https://groupdiy.com/threads/gssl-help-thread.47/post-996134
Thanks!

 

[bxershrts]

ok - I have given up I purchased 2 boards and chassis 8 years ago built em both - and they never worked. I am at the point now that they have been shelved for so many years and I have exhausted ideas to get em running that I would now rather pay someone to get these working. If anyone is interested in resolving 2 gssl builds I will pay you for your time.

I am in Canada - but will ship

Let me know!

Thanks

 

[Script]

Eight years ? Frustrating indeed.

Can't help soldering (them / it), but what's wrong -- apart from them being dusty ?

 

[grid_stopper]

ok - I have given up I purchased 2 boards and chassis 8 years ago built em both - and they never worked. I am at the point now that they have been shelved for so many years and I have exhausted ideas to get em running that I would now rather pay someone to get these working. If anyone is interested in resolving 2 gssl builds I will pay you for your time.

I am in Canada - but will ship

Let me know!

Thanks

I am in canada, and have built a couple of these units in the past/would be happy to help. feel free to DM me

 

[smadge]

Hello - I have an older version of pcb and want to make extra filtering for the power supply to get rid of the ripple noise issues on the circuit. I would use an Expat audio CRC board, but with the postal service in my side of the world so slow because of COVID disruptions, I am waiting months and months sometimes for deliveries and I just can't wait that long.

Given this I decided I might just try to make a Vero strip board with the extra power supply filtering. I've tried to search but can't seem to see - does anyone have a schematic or Vero strip layout for extra off board filtering like the CRC board? I realise its just bridge, then cap, 10 ohm resistor, then cap etc but I'm a bit unclear how to do it.

Thanks!!

 

[gyraf]

there are no psu ripple noise issues in the old boards, absolutely no reason to add that. If anyone had issues, they came from elsewhere.

the reason for inclusion on latest edition is because of excess space when removing on board trafo combined with me caving in for then-popular demand

/Jakob E.

 

[smadge]

there are no psu ripple noise issues in the old boards, absolutely no reason to add that. If anyone had issues, they came from elsewhere.

the reason for inclusion on latest edition is because of excess space when removing on board trafo combined with me caving in for then-popular demand

/Jakob E.

Ah I see thanks for clarifying Jakob

 

[mypantsrblue]

Hi everyone,

Full disclosure, and maybe this explains to you guys my issue, but I powered up my build with the THAT2180Bs installed backwards. I don't know if that fried them, but if anyone can tell me a good way to test them, that would be awesome. Beyond that:

Maybe you all can help me track down where exactly the issue is on my build. Everything appears to be working including front panel controls and metering etc. The only issue i I have (so far) is that I have no output.... I have checked the obvious like wiring/cables etc, but I am also getting no voltage off the output connector of the board that goes to my xlrs, so I think the problem is on board.

I Have narrowed the issue down (i think) to losing voltage at both of the 470R resistors in the output section. I have around .4 DC on the side closest to the ICs, and then nothing on the other side of the resistor. I also have no voltage at some of the other resistors in the area. This is true for both sides of the output section, so I am really thinking my problem must be in that output section.

I tried searching through this but i can't figure out an easy way to tell what voltage I am supposed to have where. Is this listed anywhere? Thank you in advance, I am ready with a DMM!!!!!

 

[Script]

Fried all three VCAs by installing backwards ? If not, could pull SC VCA and try it in audio path. Yields proper sound on output?

Other than that, and maybe before swapping VCAs, you could pull all VCAs and bridge only audio VCA socket from input directly to output, using a bent paper clip or a cable. You get proper output sound ? If so, your input and output stages are good.

 

[mypantsrblue]

Fried all three VCAs by installing backwards ? If not, could pull SC VCA and try it in audio path. Yields proper sound on output?

Other than that, and maybe before swapping VCAs, you could pull all VCAs and bridge only audio VCA socket from input directly to output, using a bent paper clip or a cable. You get proper output sound ? If so, your input and output stages are good.

hey thanks for the reply. thats what i thought, because there was definitely a little smoke when I powered up that first time. I swapped the VCA (which is the THAT2180, if I understand right) from the sidechain section to one side of the VCA section and have the same result. It works as intended, but no output.

I'd love to try the jumping input to output but can you help me understand exactly what to jump?

thank you!

 

[Script]

2180 datasheet is here for identifying IN and OUT of IC

http://thatcorp.com/2180-series_Pre-Trimmed_Blackmer_IC_Voltage-Controlled_Amplifiers.shtml
And a pic of a partially populated board with said wire bridge.

 

[Gustav]

Hi everyone,

Full disclosure, and maybe this explains to you guys my issue, but I powered up my build with the THAT2180Bs installed backwards. I don't know if that fried them, but if anyone can tell me a good way to test them, that would be awesome.

Ive never seen one survive this, so I would assume they are dead.

Gustav

 

[mypantsrblue]

Ive never seen one survive this, so I would assume they are dead.

Gustav

I am going to do a test today with the jumpers, but if the VCAs were bad(or at least the one in the sidechain), which it sounds like they should be, shouldn't the unit not be compressing and the ratio / attack / release all not be working? Maybe I misunderstand the circuit?