Switched Audio Attenuator

Is it possible to get a 16 step attenuator from 4 SPST switches and resistors and have infinite attenuation (or close to it) as one of the steps?

I want to simulate a volume pot so this needs to be logarithmic.

I'm thinking something like this, but am not sure about values, or even if the idea will work:

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- Mike

Yes. No.

You are going to control this with a PIC ? Then use PIC logic outputs as the switches to the ground.

The THD is going to be at the order of 0.1% or so. There will be audible clicks when switching gains. The gain accuracy is going to be poor.

Better solution is with the switches in the feedback of non-inverting opamp, but it won't fix the clicks.

Vladimir Vassilevsky DSP and Mixed Signal Design Consultant

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Thanks for your reply, Vladimir.

The uC is an ATMega8, but I was planning to feed it from a 4094 I could probably use uC port pins directly if there was a major advantage.

I have used a port pin in the past to mute audio in the past but it was important, IIRC, that the peak audio voltage never exceeded Vcc or below

0V to avoid clipping. This was using a AT1200, so more modern chips might behave differently.

Small clicks and THD of 0.1% won't be a problem.

Won't that only be capable of a minimum gain of 1? Maybe I'm not understanding what you are suggesting.

Ideally, I want a gain range of 0 to 1, but can work with a different maximum.

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- Mike

I just found a very cheap volume control IC that will do the job, so problem solved.

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- Mike