Help with a compressor circuit

[Robin Maillot]

hello I am currently designing a compressor circuit for a project in class. I wanted to be able to play on the attack, realease, ratio and threshold hence the variable resistors. The input is on the right then there is a full wave rectifier portion, then I convert that into an almost direct voltage that is proportional to the amplitude of the source. Then the problem is when I try and use this to control the JFET as a voltage controled resistance nothing happens and the output is the same as the source. Any comments would be helpful cause I don't really understand the JFET and how to use it properly, thank you

 

[JimB]

Your FET is operating directly on the output of the op-amp OA1.
That output will be low impedance and the FET will have no effect.
Try putting a resistor between the output of OA1 and the FET. Try a 10k resistor to start with.

JimB

 

[Robin Maillot]

Thx, I just tried that and now the only effect noticable is the one from the new resistance. I checked that the JFET works by imposing different values of R1 and looking at the results so it is working, but no matter what amplitude I put on the source the attenuation remains proportional, which is really frustrating.

 

[audioguru]

I agree that the Jfet should be fed audio through a resistor. Then the Jfet can attenuate the signal.

A Jfet produces horrible distortion when attenuating a sound level that is higher than about 20mV. Usually half the drain signal is fed to the gate which reduces the distortion a lot and allows a level of about 100mV. But then the voltage divider charges the coupling capacitor slowly which results in a slow attack time.

Don't you want the attack time to be as short as is possible so that beginning loud sounds do not come blasting through (and are waiting until the attack time is finished)?

Your circuit has opamp OA7 which does nothing and can be replaced by a piece of wire.
Your resistor R19 has a value much too low.

Here is a fast peak limiter project that can be used as a compressor: **broken link removed**

 

[audioguru]

Thx, I just tried that and now the only effect noticable is the one from the new resistance. I checked that the JFET works by imposing different values of R1 and looking at the results so it is working, but no matter what amplitude I put on the source the attenuation remains proportional, which is really frustrating.

Your R14 and R16 attenuate the DC control signal to the gate of the Jfet. Then the Jfet is not controlled by the signal level.

 

[alexzender]

how to fit compressor circuit into fridge?

 

[audioguru]

how to fit compressor circuit into fridge?

A fridge has a mechanical compressor that compresses the fluid or gas so that when the compression is released then it cools.

An audio compressor cuts the amplitude of loud signals and expands the amplitude of not loud signals so that their levels are almost the same.

 

[audioguru]

how to fit compressor circuit into fridge?

A fridge has a mechanical compressor that compresses the fluid or gas so that when the compression is released then it cools.

An audio compressor cuts the amplitude of loud signals and expands the amplitude of not loud signals so that their levels are almost the same.