[sdiy] Fet to short pedal input?

[Sean Ellis]

The current Korg synths still use BJTs for this as seen in the Prologue 8 service manual (which I just discovered!)


Https://www.manualslib.com/manual/2518830/Korg-Prologue-8.html?page=37<https://www.manualslib.com/manual/2518830/Korg-Prologue-8.html?page=37>

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From: Synth-diy <synth-diy-bounces at synth-diy.org> on behalf of Mattias Rickardsson <mr at analogue.org>
Sent: Friday, 28 November 2025 10:20 PM
To: brianw <brianw at audiobanshee.com>
Cc: synth-diy at synth-diy.org <synth-diy at synth-diy.org>
Subject: Re: [sdiy] Fet to short pedal input?

On Fri, 28 Nov 2025 at 22:12, brianw <brianw at audiobanshee.com<mailto:brianw at audiobanshee.com>> wrote:
On Nov 28, 2025, at 2:09 AM, Roman Sowa <modular at go2.pl<mailto:modular at go2.pl>> wrote:

> BTW, BJTs are most commonly used everywhere for muting output jacks during powerup or whatever other reasons, because it works so much better than FET in this application

I've only ever seen FET used for muting. In particular, I've seen depletion mode N-FET used because they conduct (to ground, in a mute circuit) when no voltage is applied to the gate. How would a BJT remain in saturation mode when all power is lost to the device?

I'd call this usecase "muting" (with big wavy rabbit ears around it) where the output clicks just need to become less loud, not necessarily silent. Here I've seen and used BJTs.
For real muting, where the signal needs to be muted for real, I've seen and used FETs and CMOS switches/muxes. :-)

/mr
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