GSSL add-on help thread

[lars on]

Thank's for answering,

@Paul : with heavy Drum and high threshold it seems to be differents ratio... Not very clear but more compression at 10:1 than 2:1...
@Scrip : my ratio connection is good and I know about the resistors. Mine are 120K because I have the THAT2181 VCA (reffering to Matt Fisher table).

Ok, now I plugged 1 SSC+Turbo according to the schematic attached and I still have a lot of distortion.
I know it's not ICs.

Any idea please ?

 

[lars on]

Any hint please ?

 

[Script]

Hard to hint. Approach by locating/eliminating.

You say that without the Turbo board  (i.e., classic gssl board is monoing stereo signal through 2 X 47K's) really everything worked fine?

Then, installing the SSC filter board
(I.e., monoing stereo signal at input of SSC filter board) everything is still fine?

(1)
You get distortion only in Turbo mode (i.e., without SSC filter boards in the path, which would have a 47K onboard)?

(2)
You get distortion also in Aarhus mode with SSC filter boards?

If (1) check for
- Solder blob shorting on Turbo board.
- 47K
- All T board traces for continuity.
- Wrong scaling resistor / component / component orientation somewhere on T board.

If (2) check
- Switch Aar/Oxf
- Wiring

 

[lars on]

Thank's Script.
I'll check again in that way.

 

[Script]

You have distortion when THR is at minimum?  You are driving the ICs too hot? Wrong resistor in audio path (output) IC feedback loops? Just a wild guess.

Try to eliminate/locate. Try to describe behaviour of unit in different configurations.

 

[lars on]

Ok today I restart from no Add-on.
I'll give news very soon.

 

[lars on]

So, no more distortion but... 

without any mod, the comp works.

With the Turbo, I send the left signal in and there is compression only on the right side.
No compression in the Turbo board.

With the test probe, on the Point 'C' of the TB there is not the good sound on the output 
Even if I change the frequency test, the output sound doesn't change.
I don't know how the signal from the Right path comes in the TB on which only the left signal is sent 

The other strange thing is that there is sound on PIN 1 of the VCA on Turbo board but not on the Main board's VCA.

I'm less lost than yesterday, I think... ???

 

[Script]

without any mod, the comp works.

OK. When sending a stereo signal into it, switch to a lot of compression  and then pan before unit. Doing so, the output compresses equally Land R and the stereo signal stays fully intact?
If so, your audio paths are fine and main board VCA works reasonably. Could verify using Keith's walkthrough.

With the Turbo, I send the left signal in and there is compression only on the right side.
No compression in the Turbo board.

What do you mean when saying compression only on right side? Only main board VCA yields compression? But TB does not? What you hear is stereo audio, correct?  And SSC filter board is not connected, correct?
If so, the T board ain't working. Either wiring is wrong or T board is faulty.

Right path comes in the TB on which only the left signal is sent 

Strange indeed. Audio into TB comes from main board audio path directly? Or from input junction on SSC filter board (where L and R get mono-summed)? Which would be wrong for your intended configuration, but explain the L and R swap.

The other strange thing is that there is sound on PIN 1 of the VCA on Turbo board but not on the Main board's VCA.

Now that is strange indeed.

A pure guess: in Oxford mode your switch does not send audio to the main board any longer?

-------
I'd start by either getting the TB for Oxford mode to work first (without the SCC!! ), or leaving the TB for now and focus on the SSC filter in Aarhus mode first (without the TB !!).

 

[lars on]

OK. When sending a stereo signal into it, switch to a lot of compression  and then pan before unit. Doing so, the output compresses equally Land R and the stereo signal stays fully intact?
If so, your audio paths are fine and main board VCA works reasonably. Could verify using Keith's walkthrough.

YES, Left and Right compresses equally. (More in the center than on the sides). No mods.

With the Keith test (silent input) I found :
TL074 of main board with no mods plugged.

DC PIN 1 = -192mV
        PIN 7 = 7.0 mV
AC (probes on each pins) = 0V

PIN 14 with ratio 2:1 = 226mV; 4:1 = 357mV; 10:1 = 392mV

What do you mean when saying compression only on right side? Only main board VCA yields compression? But TB does not? What you hear is stereo audio, correct?  And SSC filter board is not connected, correct?
If so, the T board ain't working. Either wiring is wrong or T board is faulty.

No more SSC connected for now, only the TB. I mean when I pan Left the signal before, I see on the meter that there is no Gain Reduction. (wich is the side which goes to the TB). And I hear that is not compressed at Left. I measured it at the output  as well which confirm it.

Strange indeed. Audio into TB comes from main board audio path directly? Or from input junction on SSC filter board (where L and R get mono-summed)? Which would be wrong for your intended configuration, but explain the L and R swap.

The left signal goes to the TB directly after the 47K of the main board through a switch. (Exactly like Expat Audio instructions said).

A pure guess: in Oxford mode your switch does not send audio to the main board any longer?

No.

I'd start by either getting the TB for Oxford mode to work first (without the SCC!! ), or leaving the TB for now and focus on the SSC filter in Aarhus mode first (without the TB !!).

With only SSC board everything seems to work fine.
I focus with the TB only without the SSC.

So I go ahead with voltages test on TL074 and checking the TB problems.

 

[lars on]

Found !!!  ;D

After re-drawing the TB schematic...
Again big troubles because of nothing very serious...

It was a cutted track on the TB between R18 and C4.
A piece of the track was missing.

Thank you very much Script for your help !

Now I have a working TB with more compression on the sides than the middle, good !
I'll make the Keith test with silent input to compare the two TL074, to see.

For now I see less compression in Turbo mode than GSSL mode when switching ? something like 5db less.
Don't know why.

Next step : plugging the SSC + TB

 

[Script]

Fabulous

From memory only (!), your Pin14 voltage looks about right.

You sum L&R on the input of one SSC filter board for Aarhus mode? If so, change the two 10K's on the SSC board input to 20K's to scale down the signals, i.e. sum the signals through 2x20K. Could swap out the 10K resistors on the board or put before the input another 10K per channel in series.

Two mono signals , when summed,lead to buildup of up to 6dB, which in turn leads to a hotter SC signal and thus more compression (roughly the 5dB you see).

 

[lars on]

The difference of 5 db happen without the SSC.
Now my signal schematic is that.

I'd like to find this 5db loss source before to go ahead.

 

[Script]

Just remember the 10K to 20K when inserting the SSC filter board.

Oh, and the SSC board replaces both 47Ks for summing...

 

[lars on]

You sum L&R on the input of one SSC filter board for Aarhus mode? If so, change the two 10K's on the SSC board input to 20K's to scale down the signals, i.e. sum the signals through 2x20K. Could swap out the 10K resistors on the board or put before the input another 10K per channel in series.

There is already the 2x20K  on the SSC input (printed on). 
Now I have an equal compression level with each modes ! That good !

Two mono signals , when summed,lead to buildup of up to 6dB, which in turn leads to a hotter SC signal and thus more compression (roughly the 5dB you see).

Of course, I should have guessed.

Do you think it's  usefull to plug a second SSC ?

 

[Script]

Now I have an equal compression level with each modes ! That good !

Stupendous 

Do you think it's  usefull to plug a second SSC ?

Only you can know...
------------
Just being curious. In the end, you figured out where the distortion came from? Was it the broken trace on the Turbo board?

 

[lars on]

Oh yes I forgot to mention that.

It was a stupid splash of pewter on the TB between Point 'C' and S/C CV.
Under the header, well hidden !

And one more thing.
For those who search for this, I attach the wiring for Stereo/Mono sidechain.

 

[Script]

Short hidden under a header? Douw, the worst kind.. ...

Do you think it's  usefull to plug a second SSC ?

Only if you feel the desire to SC-filter also in Turbo mode. Could design / add your own filters.

 

[lars on]

Douw, the worst kind.. ...

One week for this 

Only if you feel the desire to SC-filter also in Turbo mode. Could design / add your own filters.

I'll leave it like that for now.

 

[lars on]

Hi every one,

Today I've noticed something strange with my comp.

There is one SSC and one turbo board switchable.

When I'm in turbo mode and the threshold full counter clockwise and only in ratio 2:1 the needle of the db meter is jumping around 4db compression but no noise can be heard.

Any suggestion is very welcome.

Thank's !!

 

[Dynamex1]

Hi Guys,

my first post here and i have a question:

Is there any source in Europe, where i can get the CRC, Turbo and VU Meter Driver PCB´s ?
I know that Expat Audio offers them, but shipping is ~ 50% of the price for the Boards.

If there is no other Source, i will buy from Expat, but maybe someone knows another one ?


Christian