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XEN SHPP -- Simple Headphone Protection
XEN SHPP -- Simple Headphone Protection
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Old 8th June 2016, 03:42 PM   #1
EUVL is offline EUVL  Europe
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Default 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%20SHPP%20V1.pdf


Patrick

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File Type: jpg 160607 SHPP Proto1 Top.JPG (284.4 KB, 1107 views)
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Old 16th June 2016, 09:07 PM   #2
00940 is offline 00940  Belgium
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Nice compact board.

One question though: what's the trigger delay when there's a real problem like the output going to rail voltages ?
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Old 17th June 2016, 06:01 AM   #3
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3s, as already mentioned in the article.
Also mentioned in the article is how it can be changed to suit individual needs.

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Old 17th June 2016, 09:05 AM   #4
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3s is for a 80mV offset. A quick sim gives 30ms for a sudden 5V offset, which is fine.
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Old 17th June 2016, 11:00 AM   #5
EUVL is offline EUVL  Europe
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Yes, speed increases with offset amplitude.


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Old 21st September 2016, 06:40 AM   #6
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Installed in one of my high power headamps.


Patrick

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Old 21st September 2016, 07:13 AM   #7
jan.didden is offline jan.didden  Europe
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Nice!
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Old 21st September 2016, 08:58 AM   #8
SamAnytime is offline SamAnytime  India
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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.
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Old 21st September 2016, 09:34 AM   #9
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Well spotted.

Can add a diode before R5 and another after the emiiter of Q2.
And then increase the gain by 2.


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Old 21st September 2016, 10:44 AM   #10
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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.


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