-=> Mike Ross said to Thom Kouwenhoven
 -=> about "I/F" on 01-03-03  09:06.....

 MR> thing about a JFET is that between pinch-off and saturation the channel
 MR> resistance pretty much follows the voltage at the gate. It's actually

Actually the voltage betwen the gate and the channel. And since
the channel has the audio on one end and ground on the other in
an application like this, there is a small amount of audio
component in the gate-channel voltage, if the gate is fed with
pure DC. This causes the resistance of the channel to vary during
the cycle of the audio signal, causing distortion.

This can be overcome to some extent by adding part of the audio
signal on the drain to the DC on the gate. The proportion is
about 50%, but for critical applications the amount of audio is
adjusted by a potentiometer for minimum distortion.

One of the best ways to achieve this is to tap some of the audio
from the drain via the trimming pot to feed an emitter follower
transistor or a voltage follower op amp. The storage or timing or
bypass capacitor on the gate is then returned to the output of
this follower stage instead of going to ground.

From Greg Mayman, in beautiful Adelaide, South Australia

... Free the Indianapolis 500.
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