Single Knob Compressor (Schematic enclosed).

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abbey road d enfer said:
... and the FET has no distortion compensation on its gate; both tend to indicate that low distortion was not a major concern in the design.
Or it's not needed because the FET is operated at such a low level being connected (almost) directly to the inverting input.

This reminds me of this EDN article:

  Op Amp And Two JFETs Form A Voltage-Controlled Amplifier

which is missing figures but the circuit looks like this:

qtby3.png
 
squarewave said:
Or it's not needed because the FET is operated at such a low level being connected (almost) directly to the inverting input.
The level here on the FET is not too different than in the more common non-inverting topology (ca. -30dBu), so the distortion should be about the same as that of the non-inverting topology without compensation.

Op Amp And Two JFETs Form A Voltage-Controlled Amplifier
Well, no distortion figure is published. Admittedly, at unity gain (where both legs are balanced) there is some distortion compensation happening but in a compressor it's always used with gain. And the noise gain of the stage is very high (about 40dB at unity gain) resulting in poor noise performance.
 
80hinhiding said:
I've not used a Yamaha mixer or their one knob compressor, or the Behringer but I'm curious are these similar to DBX 160X compressors, and the SSL Channel Dynamics at least in their compression behaviour/perceived tone?

https://www.youtube.com/watch?v=YpOZcaT3txM
 
80hinhiding said:
Thanks, I found that video yesterday actually.  From what I heard I felt this one knob compressor isn't something I'd likely use but I wanted some more opinions.. in a musical context.  I've only used the dbx 160x on kick drum or bass and I'm even on the fence about those applications but it works.

I'm on the lookout for a stripped down tube compressor with a little more control than one knob.

Adam

I use a knob compressor for filler tracks, which pops out a couple of times during a performance, and aren't as important as the main tracks. It's adequate, and I don't have to resort to a full blown compressor. I've built this Yamaha one knob compressor in a 16 channel configuration in a 1U box just for that purpose. Alternatively, I also use the Waves One Knob Compressor plugin.
 
Hello,

(bad English - sorry)

now I´ve found all the transistors and chips to buy. But there are new questions. Can you help?

In the electronic shematic for the Yamaha there are 2 transistors typed 2SC2412K. For this transistors are 3 differences possible for their hFE-values: type "Q" for hFE 120-270, type "R" for 180-390, and type "S" for 270-560. In the Yamaha-shematic there I can not find the differences for this transistors. Can you say me, please, wich type (Q, R, S) I have to use?
Hope, you can understand my "English" ;-)

Maxi22
 
Maxi22 said:
Hello,

(bad English - sorry)

now I´ve found all the transistors and chips to buy. But there are new questions. Can you help?

In the electronic shematic for the Yamaha there are 2 transistors typed 2SC2412K. For this transistors are 3 differences possible for their hFE-values: type "Q" for hFE 120-270, type "R" for 180-390, and type "S" for 270-560. In the Yamaha-shematic there I can not find the differences for this transistors. Can you say me, please, wich type (Q, R, S) I have to use?
Hope, you can understand my "English" ;-)

Maxi22
I am not sure which schematic you are referring to but the bipolar transistors are generally performing general purpose functions where beta (HFE) is not critical.  Picking the middle range should be safe, but all will probably work.

JR
 
Maxi 22 wrote :
'' I need the compressor not for recording, but only for talkback-mic ''
I would suggest you to have look at the talkback mic amp and compressor circuit  of the Studer 169 console.
Deceptively simple and works perfectly.
Best,
Guy
 

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