JohnRoberts

Re: JFET-based compressor question
« Reply #20 on: September 21, 2017, 07:37:21 PM »
John,
Thanks for reply.My bad. VCR2N.
http://www.vishay.com/docs/70293/70293.pdf
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.


http://www.cordellaudio.com/papers/thd_analyzer.pdf

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.

JR
Quote

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
John Roberts
http://circularscience.com
Tune it, or don't play it...


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