Posted by kelley pace on October 29, 2003 at 13:08:53:
In Reply to: Circuit design posted by Roy on October 29, 2003 at 03:01:45:
Roy,
For the moment, I can't remember all the terms associated with FETs, and so I will use tube terms (eg. grid for gate) and leave it to others to transpose (shows how rusty I am).
I would connect a gridto the + terminal of the music input, and connect the anode to a resistor which goes to ground (- term). The anode resistor is large enough to cut off the tube (read FET) in the absence of no signal. There is a plate resistor connected to the plate, and the other end is connected to a large cap to ground (this smooths the current). Also, the plate resistor and capacitor are connected to one end of a relay primary. The other end of the relay primary is connected to the B+. This relay also has a time delay built in to promote smoothing of its behavior. The relay secondary swiches in parallel or series a resistor to reduce the bias. Positive signals on the input will be detected, filtered into DC at the plate, and trip the relay which will cause the relay to open and increase the bias to normal levels when listening.
I am sure someone can do better than this.