useing a audio MosFET

Save Mart

Hi I would love to know the best way to use a MosFET in audio..
im trying to make something that can get an audio signal to stop
and go as I please... , but a good one to were theres no noise every
time I allow it to stop then go..

Thanks - Michael

Mike Green

I don't think you can do that with a simple MOSFET circuit. You will always get noise when you turn on or turn off an audio signal abruptly. Commercial audio amplifiers usually do this by using a variable gain amplifier, then rapidly (but not instantly) reducing or increasing the gain to/from zero.

Here's an article on Variable Gain Amplifiers: en.wikipedia.org/wiki/Variable-gain_amplifier

Save Mart

would it be a simple circut to make?...

Philldapill

You MIGHT be able to make a very simple version of a VGA, buy replacing a resistor in the circuit that determines the gain, with a small mosfet. As you apply a voltage to a mosfet gate, the resistance decreases until it reaches it's on state resistance(usually milliohms). You would want to do the reverse. Create a subcircuit that slowly charges/discharges a capacitor. This voltage on the capacitor would be what dictates the voltage on the gate. Changing the voltage on the capacitor will change the resistance of the mosfet, which changes the gain... That's the jist of a simple one, anyway.

scanlime

If you're analog-phobic, you could do this with a digital pot [noparse]:)[/noparse]