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previous: R.G. 1.5% THD from a single FET gain sta... -- 10/25/1999 7:27 PM

Re: FET Electrical Performance

10/25/1999 9:06 PM
Scott	Re: FET Electrical Performance RG, Thanks for the info. This is pathetic performance compared to say a 12AX7, where you get a gain of 60 with less than 1% distortion, and if you were to use feedback to reduce the gain to 4, the distortion would be less than 0.1%. And at much higher output voltages. A study of the gain divided by distortion for various devices would be interesting - High gain and low distortion would give a large number. So how do you make a low distortion circuit with FETs? Use differential amplifiers to cancel the even harmonics? The open loop gain of the FET is already so low, applying negative feedback isn't really an option. I wanted to use the FET because of the high input impedance and the simplicity of the circuit, but it won't exactly provide a "clean" boost.

10/25/1999 9:06 PM

Scott

Re: FET Electrical Performance

RG,

Thanks for the info.

This is pathetic performance compared to say a 12AX7, where you get a gain of 60 with less than 1% distortion, and if you were to use feedback to reduce the gain to 4, the distortion would be less than 0.1%. And at much higher output voltages. A study of the gain divided by distortion for various devices would be interesting - High gain and low distortion would give a large number.

So how do you make a low distortion circuit with FETs? Use differential amplifiers to cancel the even harmonics? The open loop gain of the FET is already so low, applying negative feedback isn't really an option.

I wanted to use the FET because of the high input impedance and the simplicity of the circuit, but it won't exactly provide a "clean" boost.

Replies:

R.G. Well - the vacuum triode is the mos... -- 10/25/1999 9:31 PM