[sdiy] anti pop mosfets in minibrute

[Paulo Constantino]

Hilarious. They're labeled "anti plop"

In my experience, this sort of anit-pop feature is designed with depletion
mode FETs, which conduct to ground when there is no power. As soon as the
device powers up, the Gate turns off the FET, and the signal reaches the
output.

I learned about this feature the first time I repaired someone else's home
stereo equipment. The cheap solution was to just remove the FET. It had
failed such that it was conducting all the time, even when the Gate was
positive. I suppose it must have been a p-channel, but I don't remember. I
think that I later came back and installed the correct FET, just so the
owner would not get a 'pop' on the channel with the failed (and removed)
FET.

The Mini Brute schematic shows an enhancement mode FET, though, so the
schematic is already "wrong" in terms of what I would expect. Is this
designed to only mute the headphone output for a brief moment after the
power is turned off, and then the mute disengages once the capacitor is
drained?

Paul

On Sun, 28 Apr 2024, 10:15 Ingo Debus via Synth-diy, <
synth-diy at synth-diy.org> wrote:

>
>
> Am 25.04.2024 um 09:54 schrieb René Schmitz <synth at schmitzbits.de>:
>
> I would have used two NMOS in anti-series instead.
>
> What is also puzzling me: why are there two anti-pop circuits? The only
> reason for two series resistors (instead of just connecting both tip and
> ring via a single resistor to the amp output) I can think of is that
> there’s still some signal at the tip when a mono plug is inserted. But why
> two MOSFETs? Using a single resistor instead of R646/R647 and a single
> MOSFET would have done the trick too, no?
>
> Ingo
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