Re: JFET-based compressor question
« Reply #20 on: September 21, 2017, 07:37:21 PM »
Thanks for reply.My bad. VCR2N.
Yes - that's what I meant. Heard it used that way, just never learned how to spell it ::)

I'm familiar with that concept about total noise being dominated by preceding stages, but I was wondering if that might still mean lower total noise in a cascaded  topology?  Please correct me if I'm wrong here, but if the first JFET attenuator and recovery amp stage has much lower noise (because the series resistor - maybe 3K ish - and the JFET resistance is much lower) and then that signal, including  the noise added by the first stage recovery amp, is attenuated by  the second series resistor - again 3K ish - and JFET resistance which also has a much lower resistance than the classic design, couldn't the overall aggregate signal/noise end up being lower? Maybe something other than a equal recovery gain in each stage?

Might there be additional virtues if the two cascaded stages had their own side chain with a fairly low gain reduction range (maybe 10 db ish apiece), in terms of smoothing gain recovery and "prettier" sounding abrupt gain reduction transients? Seems like I remember something about Dolby C doing something along that line somewhere in the deeper recesses of my mind ;D

I searched for  the Cordell AGC, but not sure I found what you are referring to. What I came up with was an oscillator using a JFET to adjust the gain of the Wien Bridge oscillator in a variable audio sine wave oscillator circuit as an improvement over the old light bulb trick .  Looks like it handled maybe 6db maximum attenuation.

page 6 of the PDF 39 of the original Audio article.

sorry if you don't like it. I did.   BUT I don't like distortion.


I have played around some with THAT VCAs, and have appreciated their wide range of attenuation and gain, and maybe I should just concentrate on developing a compressor circuit around them.  Best practice is best practice. 

I think what attracts me to the JFET as a voltage-controlled resistor in a voltage divider as a gain element is the impression that the JFET overload behavior might have a desirable character or sonic signature, ...which might or might not pan out.

Again, thanks to all for the stimulating discussion.

mr coffee
Visit to hear what properly "cleared" drums sound like.

mr coffee

Re: JFET-based compressor question
« Reply #21 on: September 23, 2017, 06:21:16 PM »
Wow - thanks for all the stimulating  discussion and ideas.

Multistage - abbeyroad d'enfer your analysis is always so pertinent and practical. Much food for thought!

VCA + JFET distortionizer.  Serendipity is always cool, isn't it? If it wasn't cool it wouldn't be serendipitous... 8)

John - Thanks much for the reprint of the Cordell THD - I had never seen it. Worth Studying for a good while!

Again, much gratitude for the stimulating discussion.

mr coffee