[sdiy] Muting circuits for line out

[Mike Bryant]

Chapter 21 (well it was in edition 2) of Douglas Self's book on audio which should be on every audio engineer's shelf covers almost every way of muting a signal.  One of those should suit you.
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From: Synth-diy <synth-diy-bounces at synth-diy.org> on behalf of Benjamin Tremblay via Synth-diy <synth-diy at synth-diy.org>
Sent: 08 May 2025 13:56
To: synth-diy mailing list <synth-diy at synth-diy.org>
Subject: Re: [sdiy] Muting circuits for line out

The original design had the power switch on the volume knob. I suppose that was a way to mitigate this.
Benjamin Tremblay

On May 8, 2025, at 8:44 AM, Benjamin Tremblay <btremblay at me.com> wrote:

Oh wait, I suppose the patent is for an fm signal that has not yet been demodulated.
Benjamin Tremblay

On May 8, 2025, at 8:30 AM, Benjamin Tremblay <btremblay at me.com> wrote:


Hello,
I have this lovely Univox JR-5 rhythm machine I have modded with knobs to control the sound mix. The original circuit was high gain but impedance sensitive so it summed current, not voltage and was very
I added a simple op amp to handle the mix. When power is turned on there is a horrible thump that sounds like it is 100x too loud.
I have been looking for a simple muting circuit. When I was repairing a Roland MC-909 I saw the muting circuit was little more than a pair of BJTs shorting the signal path.
I also saw this novel patent which attenuates the signal without much voltage offset, maybe?
<https://patents.google.com/patent/US4288753A/en>
US4288753A - Muting circuit with operational amplifier - Google Patents<https://patents.google.com/patent/US4288753A/en>
patents.google.com<https://patents.google.com/patent/US4288753A/en>
<https://patents.google.com/patent/US4288753A/en>
<favicon.ico>

I really just need to prevent that initial thump. I’ll pick up a relay if that is best.

Is there an easier solid-state solution? I don’t mind adding another buffer stage at the output.

Benjamin Tremblay
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