Yes, the Corsair uses a Unijunction transistor (UJT) as
the sidetone, but there is an R-C low pass filter on the
output to clean up the waveform. Mine doesn't seem unduly
raucous, but it may depend on the response of individual headphones
and speakers, and of course, individual taste.
My sidetone is unmodified (I ami the original owner).
I would still look for an open capacitor or cold solder joint
in the sidetone filter.
One could always tack in more filtering, or replace the oscillator
completely with a phase-shift type.
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