hello everybody

at first say hello to you and thanks for your Attention to the electronic .
i have a problem about AGC circuit . i use this circuit but it is not work
correctly .



the output has many noise that is not normal and i dont know what
to do . . . !


of course i use 2SK0301 instead of BFW10 and use bc640 instead of bc558 .

so whats your suggestion to me ?

im waiting for your answer .

 

Hello,

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Bertus

 

NE5534 looks like a better op-amp.
I can't see much wrong with your transistor choices, as long as you check the DC operating point of the NPN.
But I don't like the time constant on the gate of the j-fet. That puppy is set for about 10MHz and it should be a lot slower, so look at the 1K and the 0.1uf to see about slowing it down.
http://www.mouser.com/Semiconductor...v7emuSGgjdhptZ1yvde3fZ1yv9hj3SGT&Ns=Pricing|0

 

i think that this problem occur because the 2SK0301 or any jfet dont have Linear performance about voltage
this problem cause when the voltage of the gain rises up as a Specified voltage the Rds of jfet decreas not lineary

so the Challenge is to make a Linear electrical resistance

HOW TO MAKE IT ?

 

The input stage bias has no feedback so it depends upon a particular transistor gain for proper operation, which is a poor design.
If the bias is off you will get a lot of distortion.
What is the DC voltage at the collector of the BC548 transistor?

And a 741 is a lousy op amp for audio circuits.

 

The AGC low pass filter has a corner frequency of 1.6 kHz so the nonlinear effects of the JFET pass right through as audio. Increase the capacitor on the gate to 10 uf or higher and that might fix things up.

The JFET has a maximum pinch-off voltage of -8 volts. Depending upon the individual JFET you may need a higher negative power supply voltage in order to obtain the full dynamic range of the AGC.