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previous: Scott RG,Thanks for the i... -- 10/25/1999 9:06 PM

Re: FET Electrical Performance

10/25/1999 9:31 PM
R.G.	Re: FET Electrical Performance Well - the vacuum triode is the most linear open loop amplifying device ever invented, so having a FET come close is actually a compliment. The only way to get lower than a triode's distortion is to use linearizing feedback. The study of gain versus distortion by device was done long ago, and the triode won. Some salient points: You probably can't hear the FET's distortion at 1.5%, being purely square-law distortion as it is. In that way the JFET resembles the triode in having primarily second order. The human ear is very tolerant of that. You might try the JFET and see how it sounds, not how it measures. Many people have built JFET gain stages and like them very much for guitar use. To get lower distortion with anything, you up the gain and apply feedback. There are some JFET/bipolar transistor pair circuits that can give open loop gains of around 4000 and closed loop distortion well under 0.1%. For "clean boost", you have a couple of options. You can go with the JFET and see if you like the sound anyway. You can use a JFET/transistor pair and feedback, or use a JFET input opamp.

10/25/1999 9:31 PM

R.G.

Re: FET Electrical Performance

Well - the vacuum triode is the most linear open loop amplifying device ever invented, so having a FET come close is actually a compliment.

The only way to get lower than a triode's distortion is to use linearizing feedback. The study of gain versus distortion by device was done long ago, and the triode won.

Some salient points: You probably can't hear the FET's distortion at 1.5%, being purely square-law distortion as it is. In that way the JFET resembles the triode in having primarily second order. The human ear is very tolerant of that. You might try the JFET and see how it sounds, not how it measures. Many people have built JFET gain stages and like them very much for guitar use.

To get lower distortion with anything, you up the gain and apply feedback. There are some JFET/bipolar transistor pair circuits that can give open loop gains of around 4000 and closed loop distortion well under 0.1%.

For "clean boost", you have a couple of options. You can go with the JFET and see if you like the sound anyway. You can use a JFET/transistor pair and feedback, or use a JFET input opamp.

Replies:

Scott q{For "clean boost", you have a cou... -- 10/25/1999 9:52 PM