Add DBX 202C VCA to new gssl

[Jitter]

Hi friends.

I wanna build a GSSL with the 202C vca in place of the ThatCorp VCA.
The rev of pcb is this https://pcbgrinder.com/index.php?route=product/product&path=59_60&product_id=59

I’m confused with the info in the official Gssl post of grupdiy.
I need help.

Simply, I wanna know what are the correct components, the place and values that I need change or replace in the ggsl boards to add a 202C VCA.
If it is possible the correct steps for calibration.
I was consulting the docs in Gyraf web, but my confusion is the same.

Regards

 

[RuudNL]

In my opinion the only thing you have to do is omit the components in the  DBX202 emulation circuit (NE5534+THAT2181 and components). The main circuit shows the connections to a 'real'  DBX202.

 

[Jitter]

Thanks, I think the same, but in post of groupdiy says and talk about change resistor values on input and output of VCA, trim era, etc. All is very confused.

 

[Apache5]

I think there are changes in impedance of the diferent models and the resistors arround must be diferent depends on model of vca. There are diferences betwen control signal too. DBX202c (goldcan) is 50mV/dB and the dbx202 (black can) is 6mV/dB. I dont know what is suposed to be the one in the gssl circuit,  You can see and example of how to adapt one control to other on page 7 of the attached pdf...

 

[Jitter]

Finally I decided place a pair of Igor Quad VCA pcb on place of 2181C circuit.
The question is the same,
The changes for add this Quad VCA on place of single 2281c, have the same requeriments as insert a pair of Gold Cans?

 

[Apache5]

2181s has 6mV/dB control. You must see at schem of igors quad vca if there is a correction on the control  voltage or not.  It seems to me that gssl uses 50mV/dB control. On gssl schematic you can see an emulation circuit for a that2150 that is 6mV/dB and the circuit corrects that. For input resistor  the that2002  that uses 4 x2181s, uses 6k04 on input and  7k32 on out (with te ne5532)... you can see that info on pdf that I posted before but dont know if its the same with the igor quad...

 

[Jitter]

The schematic of Igor Quad VCA is this.
The circuit have a 50mv/db correction via 832r.

Is correct?
What values need modified on te main board?

 

[Apache5]

50mV/db is the same that on GSSL, right. I think,  if you are using the 20K resistors on vca inputs like on quad vca schem,  that you need to jumper 15K* vca input resistor on gssl schematic and put a 5K resistor instead of 15K resistor on the NE5532 next VCA.  See atached pdf about paralleling vcas...  hope it helps

 

[Jitter]

A lot of thanks for your reply!

If I am understanding you and I am understanding the notes and their reasoning, the idea is this that I contribute in the drawing.
It is ok?

 

[Apache5]

That seems fine to me but thinking on it maybe would be more "conservative" to maintain the 15K on the 5532s and put a 10K on the input resistor instead of a jumper. With that you have unity gain (10k+5K on input and 15K on output).  I'm not sure what would be the performance difernce inbetween these two arrangements... both must have unity gain.

 

[Jitter]

Ok, thanks.
But in the ** of notes says 27k instead of 15k for unit gain on input, considering the quad vca schematic and to get the unit gain... Will be correct put another resistor in place of 10k as you say?
By example, 7k(input in Main ssl board) + 20k (on each input vca of quad pcb).

Or I’m wrong?

 

[Apache5]

well... as I understand quad vca has 5K input impedance if you put 20K input resistors in each 2181 in the quad vca. You have 4 x  20K in parallel that's the 5K input impedance. All  you need is to has the same resistance at input as you have on the output 5532 to be in the unity gain.  I sayd 15K on output 5532 because is the value in GSSL schematic.  wiht that 15k on output you need to add the 10K on input to have 15K like in the output.