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mw0uzo
05-31-2011, 11:05 AM
Ok, I have a selection of components and want to make an analogue switch that will turn on or off line level audio.

The circuit needs to work and have the minimum of components. Input and output is line level audio, enable is 5V active high.

Devices available
J310 N channel JFET
2N7000 MOSFET
Standard NPN BJT eg 2sc1815 or bc547.

Help!
NQ6U
05-31-2011, 12:09 PM
Okay, I'm sticking my neck out here because you probably know more about this stuff than I do but I think that for audio frequencies, the JFET or MOSFET might be overkill.
mw0uzo
05-31-2011, 12:27 PM
Okay, I'm sticking my neck out here because you probably know more about this stuff than I do but I think that for audio frequencies, the JFET or MOSFET might be overkill.

Doesn't matter, all that matters is its the simplest circuit with as few components as possible.
mw0uzo
05-31-2011, 04:40 PM
Tried a jfet, switched on via a 4.7k resistor. Almost worked, but was distorted. Perhaps a small amount of positive bias will work properly?
HUGH
06-01-2011, 06:21 AM
ANALOG DEVICES ADGxxx series of ICs or INTERSIL DG411-413 are analogue switches. I'm using these already so I suggest trying these, you don't need any extra components.
mw0uzo
06-01-2011, 08:06 AM
Ok I think I've done it with a JFET.

Three resistors, 1 jfet.

22k pulldown resistors to Gnd from Drain and Source.
100k gate discharge resistor from Gate to Gnd.
Audio in to Drain.
Audio out from Source.
5V on signal directly to Gate.
W1GUH
06-02-2011, 01:39 PM
Doesn't matter, all that matters is its the simplest circuit with as few components as possible.

You can twist two wires together to turn on and undo them to turn off. That's zero components.
NQ6U
06-02-2011, 02:26 PM
If you used a bipolar transistor, couldn't you do it with just two resistors?
N8YX
06-02-2011, 04:53 PM
CD4066 CMOS switch. 4 channels; 60dB minimum isolation between input/output lines and adjacent channels. One 14-pin DIP.
N1LAF
06-05-2011, 07:44 AM
Untested, but should do the trick....

http://paulfelgate.com/hamisland/analogswitch.jpg

5 Volt switch input will cause the MOSFET to fully conduct, dropping Line Out to ground. Audio voltage is now dropped across R2. R1 keeps the MOSFET inactive when not connected to voltage source, and may be omitted.
mw0uzo
06-05-2011, 04:25 PM
Thanks for the suggestions :)

I'm making a CTCSS squelch box for an echolink node. Will post some pics.