"Roy J. Tellason" wrote to "Thom Kouwenhoven" (03 Jan
03  04:06:29)
 --- on the topic of "I/F"

 TK> Aah...so you DO want a PWM-volume control with 4066s...then you nee
 TK> biasing indeed :-)

 RJT> That probably accounts for why my initial experimenting with this
 RJT> stuff,  before i got sidetracked into something else,  resulted in
 RJT> some horribly distorted signals.  :-)

 TK> Well...it can be done much easier...seen it done in a 1980 Marshall
 TK> JCM 800 Lead....pulling a signal to ground with a transistor via a
 TK> cap....no biasing no powersupply whatsoever....theoretically not
 TK> possible...but practically it worked perfect!

Let's see, a regular bipolar transistor might be used but usually for
switching on/off or pwm, so I believe it was probably a JFET. The thing
about a JFET is that between pinch-off and saturation the channel
resistance pretty much follows the voltage at the gate. It's actually a
pretty linear transfer curve within a certain range. I'd have to look
things up to find the actual equation but I recall looking at a graph
plotting the characteristic in an application for a Lowrey organ IIRC.

 Mike
 ****

... High Voltage Electronics:  Life's a glitch, then you fry.
--- Blue Wave/DOS v2.30