GSSL add-on help thread

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Script

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I have a little doubt about the THAT2181C I put on turbo pcb which have no indicator for the pin 1 so maybe it's inversed ...
The Expat Audio board?
 

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babaorum

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Yes but it's not the board the problem it's the THAT which have not the little hole at the top 1 pin on it. The serigraphy seems to be always in the same side fortunately so I think it's ok maybe if it was inversed I think that I should have no sound in output. But I don't understand why I have less gain of compression in a side with the turbo board in activity.
 

Script

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As Potato Cake above already said.

And could swap THAT IC with corresponding one for RMS on main board to verify your Turbo board IC as well as the Turbo board (as a whole) works and is wired correctly.
 

Harpo

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Same resistor values on both gssl and turbo? Ie correct bias current setting 3K9, connecting to Vca pin5 on turbo board vs wrong value 5K1 at sidechain-Vca on gssl?
A reversed fitted vca most likely will not survive, once powered on.
 

babaorum

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Brilliant Harpo ! , does it mean that last version of main GSSL board is not matching with the turbo board ? I have effectively 5k1 on GSSL and 3.9k on turbo ... is only the R of the sidechain VCA concerned or also the other 2 VCA of the channels on GSSL board ? (5.1k for both all VCA on the GSSL ... )
 
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Harpo

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Brilliant Harpo ! , does it mean that last version of main GSSL board is not matching with the turbo board ? I have effectively 5k1 on GSSL and 3.9k on turbo ... is only the R of the sidechain VCA concerned or also the other 2 VCA of the channels on GSSL board ? (5.1k for both all VCA on the GSSL ... )
5K1 bias current setting resistors for the +/-15VDC powered audio-VCAs are correct. 3K9 for the +/-12VDC powered sidechain-VCA(s) needed.
 

babaorum

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Thanks Harpo, I just ordered 3.9k R , I'll let you know, I should receive it around 10th of June.
 

fritz

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Search GSSL help thread(!) for "needle" "drop", maybe also "47u" and "6u8" capacitor orientation, as well as "latch" or "latching".

I have a feeling you might want to use Google website translator to read the threads in German.
thanks for the information and search terms. i think i'm on the right way now. only use the google translator if I don't understand individual terms or contexts, otherwise it works without it. Before I try to measure the voltage, however, I have one more general question: It is about the connection "Point C" from the turbo board to the gssl main board. Does it matter whether the connection "point C" is connected to the gssl main board or to the control board (front panel)? the power connector section of the turbo board shouldn't really matter whether it's connected to the main or control board, right? Or should the connections mentioned only be connected to the main circuit board, as described in the instructions for the turboboard?The main board and the control board are connected via a molex connectors.
 

Script

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Or should the connections mentioned only be connected to the main circuit board
To eliminate the chance of introducing wrong connections, I'd simply wire and solder everything exactly as described in the well-written Turbo "Assembly and Installation Instructions". It creates stable connections that keep wires as short as possible and corresponding circuit parts as close to one another as possible.

Crimp connectors can make for flakey connections. Check for stable connectivity while wiggling the housing and also wiggling the individual cables.

Also make sure that all added cables do not connect to adjacent solder pads -- either via a tiny solder joint or a single wire strand sticking out. This can cause all sorts of unpredictable behaviour.
 

MaxSquare

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Hey, guys and girls. Is there any way how to use Serpent Audio quad VCA (got mine pair as a gift) in regular GSSL build? What needs to be cut or changed? SOS
 

babaorum

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Unfortunately on my main board it was already a 3.9k R for the THAT of the sidechain ... I have to have a more recent version of the board than that's in the shema of the pdf file construction ...

That could have been a good explanation ...

So I still have a level issue between standard and turbo mode.
 
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Script

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Wait a second, now you say 'mode'.

You mean mismatch in compression in turbo configuration when panning audio feed btw L and R ? When panning you get 'from compression to none' or 'from compression to some' compression ?

Or do you mean mismatch when switching between turbo mode and stock mode ?

Or both ?

///
Also not sure it's a good idea to power your switch LED from a 12V rail.
 

babaorum

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When I 'm in standard/stock, the GSSL works fine and when I test pan left or right the comp gain is less of -3dB like expected because in the center it's more than in the sides like expected.
In Turbo compressor seems to work fine but when I test to pan left and right : in left the level is less of -3dB like in stock/standard ("from compression to some' compression ") and when I pan in Right the comp level is the same than the center.

I saw a video which showed that in turbo mode the pan left and right has to be +3dB than the center, is it right ?

My conclusion is that there is a little issue on the turbo board or wiring.

Do you have some idea ?
 

Script

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Check 100R on main board. For Turbo installation, the 100R does not lift one leg off the board (unlike the 47K).

Pull THAT on Turbo board. Could measure with multimeter set to 'Diode'. Between pins one and two (Input and Ec+) you should get a reading. Between pins 7 and 8 (V+ and Output) you should get none.

THAT IC could be fried. Can check by inserting on main board.

Other than that check wiring again, as well as traces on T board for connectivity and bad solder joints.
 

fritz

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Hi guys. Regarding the needle problem, I found the following interesting post from Metoo2 with the help of the terms suggested by script: GSSL HELP THREAD!!!

So maybe check that your ±12V power supplies are holding up. Check pins 4 & 11 of the TL074 on the Turbo board for Vcc & Vss.
Both boards, i.e. main and turbo, show a value of plus / minus 12 V, so everything is ok.

If it still goes hard right that looks like mis-wiring or a short somewhere.
It could of course be a short. if there is a short, it should be on the turbo board because the compressor works perfectly without mods, right? Or is my reasoning wrong?

Check that the side chain input is connected up OK (audio in on one channel with 0 DC offset) arriving at pin 1 of the 2181. Your main board should only have the other channel feeding in for permanent turbo. Check the input levels are similar on pin 1 of the equivalent 2181 on the main board.
Both boards have a value of 0.001 V, so everything is correct, but I use 2180 B VCA's, which shouldn't play a role in this case.

Check pin 7 of the TL074 has little or no DC offset and that it passes audio OK (could be attenuated depending on the control voltage) Compare it to pin 7 of the TL074 on the main board
- Main: 0,340 V
- Turbo: 0,347 V............depending on the threshold, but always a bit higher than on the main board, but think that should be ok.

Check the control voltage on pin 3 of the 2181. It should be very near 0V and only go slightly negative (very few mV) when compressing. Compare it to pin 3 of the 2181 on the main board.
That's exactly what I can see on both boards. if it is not compressed it is 0.07 V and a little higher with compression. However, I only get negative values when I hold the red measuring tip to the ground and the black to the pin. Normally the black measuring tip should be used for measurements on the ground, right? I'm a bit confused now, because it could also be the mistake, right?

Check the wiring of your ratio switch..... remember this has to be electrically isolated from the original ratio switching (using a different pole on the same 4x3 switch is OK)
This was soldered exactly as described in the instructions for the turbo board. Do not think that this is the fault.

Furthermore, depending on the ratio, I also compared the voltages at pin 14 of the TL074 on both boards. Here I measured both with (sine tone generator) compression and without.

Mainboard (TL074 Pin 14):
- at 2:1 = 0,385 V (0,174 without)
- at 4:1 = 0,082 V (0,344 without)
- at 10:1 = 0,183 V (0,378 without)

Turbo (TL074 Pin 14):
- at 2:1 = 0,250 V (0,228 without)
- at 4:1 = 0,012 V (0,352 without)
- at 10:1 = 0,246 V (0,388 without)

Since the difference are in the mV range, I don't know now whether that is still ok or not. However, differences are clearly visible. I also checked the orientation of the diodes again - all good. Replaced THAT 2180 on turbo board - no difference. I also compared all the components of the turbo board with the sidechain of the main board. Everything is the same and the values of the resistors are also identical, so no broken resistor or something similar.

Search gssl help thread for maybe also "47u" "u47" and "6u8" capacitor orientation
I understood that The original board schematic has the 6u8 in parallel with the 750K and the .47U in parallel with the 91K. Whereas the redrawn schematic (Gyraf) has them the other way around. Should I swap these now because I soldered them as described in the schematic by gyraf ???? I'm confused because I don't think that Gyraf was wrong, because it works for others too, or does the turbo modification play a role here?

Search gssl help thread as well as "latch" or "latching".
If I understand correctly, the latching problem often occurs when the voltage regulator (7815) has problems with the output (mostly too low voltage). I measure 22 volts at the input of the voltage regulator and 15 volts at the output, so everything is good, as far as I can judge.
This is what the stand looks like so far. The problem with the needle persists. A few tips for further troubleshooting would be really good, so that I can narrow down the sources of error. Where should I look further for your opinion?
 

Harpo

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Both boards, i.e. main and turbo, show a value of plus / minus 12 V, so everything is ok.
Double check for steady +/-12VDC again with makeup-gain in both CW and CCW settings in order to exclude a wrong hooked up bypass switch.

Check that the side chain input is connected up OK (audio in on one channel with 0 DC offset) arriving at pin 1 of the 2181. Your main board should only have the other channel feeding in for permanent turbo. Check the input levels are similar on pin 1 of the equivalent 2181 on the main board.

Both boards have a value of 0.001 V, so everything is correct, but I use 2180 B VCA's, which shouldn't play a role in this case.

Measuring voltage at the VCA pins 1 or 8 doesn't make much sense, as the VCA is a current-in/current-out device, not a voltage-in/voltage-out device.
Compare VAC input voltages again at the other side of the input resistors (opposite of the resistor leg that connects to VCA-pin1).

... However, I only get negative values when I hold the red measuring tip to the ground and the black to the pin. Normally the black measuring tip should be used for measurements on the ground, right? I'm a bit confused now, because it could also be the mistake, right?
Black wire probe connects to the multimeters COM-port with probe tip pointing to reference voltage of the tested device, most often 0V.
Red wire probe connects to the multimeters V/Ohm/...-port with probe tip pointing to a spot you want to measure the voltage value in respect to the black wire probe reference voltage. Depending on multimeter setting you get an unsigned AC or a signed DC voltage readout in respect to reference voltage.
Since the difference are in the mV range, I don't know now whether that is still ok or not.
The THAT218x VCAs come with a 6mV/dB control law, so little differences might matter.
 

Script

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It could of course be a short. if there is a short, it should be on the turbo board because the compressor works perfectly without mods, right? Or is my reasoning wrong?
Did you also measure the diodes on the Turbo board? No need to desolder them. Can do in place. -- This should reveal a dead diode. Do the same with all diodes on the main board.

Could also measure all resistors on the Turbo board and compare to values of corresponding ones on the main board. Whatever those values are (cos resistors are interacting with surrounding components), they should read the same, as the Turbo board is an exact copy of the main board sidechain, it only looks different -- This should reveal faulty solder joints.

Since the difference are in the mV range, I don't know now whether that is still ok or not.
I'd say your readings at 4:1 look somewhat off. I'd check the voltages of all ratios (with threshold CW and CCW) and check the diode in the ratio network in particular.

Should I swap these now because I soldered them as described in
The release timing caps. The position shouldn't make your needle jump. I'd check for orientation of the caps. Those tantalums have a plus and minus, but at least on older boards the silkscreen was hard to read (as are the plus signs on those caps).

And yes, could also check for steady 15V and 12V when running audio through the unit.
 

babaorum

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Check 100R on main board. For Turbo installation, the 100R does not lift one leg off the board (unlike the 47K).
Yes I just soldered on the existing 100 R without pull it.
Pull THAT on Turbo board. Could measure with multimeter set to 'Diode'. Between pins one and two (Input and Ec+) you should get a reading. Between pins 7 and 8 (V+ and Output) you should get none.
It's the reverse here ... I have 1.678V between 7 and 8 and 0V between 1 and 2 ... in total bypass and I have none for both 1/2 and 7/8 in turbo.
Maybe you would like tell with a signal in input ?
 
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Script

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Identifying input pin 1 of THAT VCA.

--Reading in pic not accurate, cos cheapest of helper metres.--

(Also just checked on a replaced 'DBX1252' (Singapore), which give 0.6V.)
 

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