[sdiy] headphone driver for synths

Gordonjcp gordonjcp at gjcp.net
Sun Aug 29 12:49:53 CEST 2021

On Wed, Aug 25, 2021 at 11:35:56AM +0100, Gordonjcp wrote:
> My standard headphone amp is basically a ripoff of the headphone amp used in the Kurzweil K2000 and countless others (E-Mu ESI springs to mind) with an opamp driving a complementary pair of small transistors.  I used a TL071 (or TL072 for stereo) and BC548/BC558, because it's what I've got great big poly tubs of in the workshop.
> I've built hundreds of these amps and never had one fail.

And indeed here it is.  This particular circuit (and its accompanying PCB, not shown but available on request) was used for adding a headset output to a Motorola Mototrbo radio, independent of the loudspeaker and its volume control.  The muting tranny was necessary because of the high level of noise on the line output with no signal, and also served to tame the loud "CHIRRUP!" of the talk permit tone when you key the microphone - just enough bleed through the muting circuit.

This was loud enough into a standard 32 ohm "walkman" type headphone to be actually painful at full chat, and certainly more than adequate for closed-back headphones in a noisy environment.

The amp itself is practically noiseless, at least into my Beyer DT100s, and sounds pretty good and clean.

It is, as previously mentioned, shamelessly stolen from the Kurzweil K2000 service manual.  If you're going to steal, steal the best you can.


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