Gssl 2180 vca calibration

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Sallivan

Member
Joined
Nov 8, 2010
Messages
24
Hello, I haven't a distortion analyzer, so I decided to build a Gssl whit 2180 BL vca.

I read this :

http://diy.fischerworks.com/gssl_vca.shtml

but there aren't two values :
1) 100k ratio adjustment , I think is the same of the 2181, so replace it whit 122 k resistor.
2) 2x 47k the summing network.. I don't know if I have to change that resistors whit two 120k.......
3) Also I would like to have 10 db of gain reduction I know there is something to change... maybe the 1K resistor closed to 1M...

I built 1 gssl unit whit 2181 lb in the past, but without  analyzer, it was little bit distorted...
Can you hlep me please :)!

 
All the 2180 series (a,b,c) are pre trimmed... the A has less distortion than B.
In any any case I have to replace some values of resistors  :-\
There is someone who built the ssl clone whit 2180 vcas? Any suggestions?
Thanks!!
 
Sallivan said:
1) 100k ratio adjustment , I think is the same of the 2181, so replace it whit 122 k resistor.
2) 2x 47k the summing network.. I don't know if I have to change that resistors whit two 120k.......
In terms of control law (dB/V, port impedance) the 218x series and the 215x series are identical, so there should be no difference. However, the 218X are better trimmed for distortion, so they need less voltage range on their symmetry adjust pin, so the resistor coming from the trimmer can be of higher value, giving more resolution for manual trimming, but if you use a pre-trimmed version, it is irrelevant.
3) Also I would like to have 10 db of gain reduction I know there is something to change... maybe the 1K resistor closed to 1M...
I don't understand your question; GR is the result of the signal being above threshold and depends on the compression ratio; it is not something you can predetermine. Or do you mean you want to reduce the overall gain of the unit by 10dB? In taht case you may use the gain control or alter the value of the FB resistor in the i/v converter (the opamp that recives signal from the VCA). [/quote] I built 1 gssl unit whit 2181 lb in the past, but without  analyzer, it was little bit distorted... [/quote] Even grossly misadjusted, a Blackmer VCA will have thd below 0.2%, so I doubt that's what you hear. Remember that compression IS distortion, particularly at low frequencies, where the detector output has fluctuations.
 

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