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FET Audio Mute

I'm trying to design a simple audio mute using a fet but I can't seem to get it to function properly. (Actually this is essentially equivalent to what I'm trying to do... So I need help on this specific method and not some other method which might be easier(such as just a switch)). The audio signal is is < 2V p-p.

Essentially audio signal passes through a enhanced n-mosfet connect to source. The drain goes into a load which is what ever load the would have been connected to it in the first place.

The base of the fet is connected to -5V. The gate is connected to a STDP switch that selects -5V or +5V for turning on and off the fet.

The circuit does work but the signal is extremely attenuated. Its about 1/10 of what it should be. If I double the supply voltage then I can half the attenuation. I just want the fet to pass the signal completely(with almost no attenuation) or completely turn it off(effectively).

Is there something I'm missing? I thought that a fet could essentially act as a voltage controlled switch? So whats wrong with my circuit? I've posted a schematic in binaries.

Thanks, Jon

Reply to
Jon Slaughter
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Use a jfet.

Graham

Reply to
Eeyore

The audio signal

I always watch your posts with interest because it looks like you and I are attempting to design similar things. Is your mute circuit for a guitar by chance?

Have you tried connecting both the input and the output to the source? Then when you switch the MOSFET on, it will conduct the signal to ground.

Reply to
tempus fugit

lol. Well, its not really for a guitar mute but it is something for a guitar. For a guitar mute I just use a switch.

I'm not sure I follow.

Ultimately I'm going to use an audio analog switching ic but I want to understand the basic idea first but can't get it to work. Well, its working but its attenuating the signal way to much. (so its not acting like a switch but more like a resistor)

Jon

Reply to
Jon Slaughter

to get

what

some

signal

to

have

STDP

about 1/10

the

almost

essentially act

posted

Maybe you should use a circuit designed by a broadcast engineer - he should know what he is talking about...

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Reply to
Ross Herbert

SNIP

Sorry, that was the wrong link. This is the one I meant to post.

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Reply to
Ross Herbert

Thanks for that Ross. I'm still in the process of trying to implement JFETs to bypass a string of effects and this could be a big help, although if anyone has a way to configure the JFET switch to act as a SPDT or DPDT relay, that'd be even better.

Reply to
tempus fugit

What are you trying to do with this circuit?

have

I've successfully done what you're trying to do here with a CMOS switch IC. Instead of running your signal through the MOSFET, just connect both your signal input and output to node 1 in your diagram. When you apply voltage to close the MOSFET switch, the signal will pass through the MOSFET to ground, thus muting the output. When the switch is opened again, the signal will be audible again since there is no longer a path to ground to mute it.

Reply to
tempus fugit

Oh, I think I see what your saying. You mean that instead of having the signal pass through the fet you have the fet ground the signal at that point?

Reply to
Jon Slaughter

Exactly. You also don't have to worry about altering your signal since it doesn't actually pass through any extra silicon (if that's a concern).

Reply to
tempus fugit

Yeah. Only thing I'm worried about is that for a guitar the ground is sorta "floating"? Else it seems like a good idea... although for my specific application I actually need the signal to go through the fet because I need to disconnect the audio completely from the circuit(grounding at a point might cause some problems although maybe can be fixed other ways). The main issue I think is that I want to try to use some ic's and not go discrete because the application requires a ton of "switches".

I ordered some analog switches though and maybe these will work for now.

Jon

Reply to
Jon Slaughter

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