Circuit O' The Day : A headphone output buffer. - diyAudio
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Circuit O' The Day : A headphone output buffer.

Posted 28th May 2013 at 12:24 AM by rjm
Updated 28th May 2013 at 12:08 PM by rjm

Experimental : For Research Use Only

It's bring-your-own-voltage-gain. This output stage is a unity gain buffer. A sort of diamond-buffer-meets-sziklai-pair hybrid. It lets the driver pair bias the output pair without the complexity of an additional bias network, but, unlike the basic diamond buffer, the output pair can have a much higher bias current than the drivers.

LTspice file attached, if you'd like to play along.

*****

I did my best to shut my eyes and design this just by messing about in LTSpice from the starting idea of a "level-shifted-complementary-sziklai-pair" (i.e. mirrored J-Mo mk II), but I see now a shout-out to 47 Labs is due as the 0247 Treasure uses the same stage.

Ah well, I guess my neat idea isn't new after all.

*****

The general performance is in the order of 0.01% THD for 50 mW / 16-300 ohms at 100 mA bias though the output pair. I've been trying to tweak the values, but the circuit appears to have a very broad optimization curve. As long as there is plenty of current running though the output transistors the actual component values don't matter very much.
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