XEN SHPP -- Simple Headphone Protection

With dynamic headphone now getting more and more expensive,
and the many high bias class A amplifiers around, including two from us,
it is perhaps a good idea to have a protection circuit for headphones.

The difference to a loudspeaker protection is of course the lower trigger voltage level (e.g. +/-80mV DC).
This requires a different treatment for the DC sensing stage.
Here is our solutions.
Works first time as intended. ;)

http://xen-audio.com/documents/SHPP/XEN SHPP V1.pdf




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    160607 SHPP Proto1 Top.JPG
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2016-07-25 8:33 am
I agree - nice!.

I notice that when the output of the opamp is at the negative rail, the base-emitter of Q1 is reverse biased to almost the -ve rail voltage. Those intending to modify this design for use with higher rail voltages should keep this in mind, as the reverse breakdown voltage of the base-emitter junction is not very high.
According to
Integrated Analog-To-Digital and Digital-To-Analog Converters
Rudy J. van de Plassche
Section 9.2.1

The Veb junction can be used a Zener diode when reversed bias current is limited to <1mA.
So we can actually simply change R5, R6 to 10k intead of 1.5k.


Yes it can but is very noisy. Some equipment uses reverse-biased e-b as a noise source...
BTW regards from Jacco, I just met him in Turnhout. ;-)