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Audio amplifier output problem

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northumber82

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Hello, I'm here again.

This is the audio amplifier structure:
Immagine.png

This is the output of a 1kHz sine wave:
WhatsApp Image 2018-06-11 at 21.32.56.jpeg

Do not care about it doubled, it's my phone that can't do a decent photo in the exact moment, because the signal generatore pulses and it's not continue.

There is a strange distortion in the low part of the wave. Whats the problem? The double-transistor bias? (I've already corrected the bias resistors). Or the unmatched transistors of all the amplifier?
 

Without trying to analyze your 4000 transistor circuit, it looks like you've got some clipping. Do you see this with lower amplitudes?
 

Yes, I see the same distortion. Seems the point of work is not correct
 

How much is your supply voltage? The FETs could have totally different threshold voltages compared to the model, with lower supply that can cause a problem like this maybe.
And I would try to decrease values of R19 to R21. Those seem to be a limiter thing.
 
Last edited:

Dual Power supply +-30V, 5A max. The I have to deacrease the CFP differential resistances?
 

I don't know what you are calling CFP differential resistances, sorry.
 

Yeah, those. And max voltage on R1,R2,R7,R8 should be less than 0.6V to keep the cascoded portion in normal active region. If you posted a schematic with component values it would have been easier to say more I think.
 

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