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balanced headphone protector

kevin gilmore

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This has been needed for a while.

For those with problematic DAC's that put out a bit of DC, and balanced headphone

amplifiers happy to amplify said DC and produce differential DC on the output...


This is the one case where ti kan's protection board does not work, unless

you want to use 2 of them.

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Do you have a schematic view you could post? I like the approach, comparators instead of Ti's summing amp. I see you used the same 1.6 Hz lowpass filter - I found this a little too sensitive on the epsilon12 and was getting a lot of false cutouts so I ended up lowering the cutoff to about .7 Hz and the gain on the summing amplifier from 10 to 5, which should make it cutout when it sees about 140 mV of DC offset. I'm not sure which did the trick as I did them at the same time.

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don't you mean Balanced Headphone "Protector"

oops, so i can't spell. I'll fix it later. Its not like its already etched

into a front panel. biggrin.png

We can adjust the comparator window as necessary, as well as the filter.

Ceramic caps up to 4.7uf in that lead spacing i believe.

Putting the thing in a small box with a female and male 4 pin xlr's on tails

plus a cheap wall brick should take care of those pesky massively overpowered

things from my friend in skokie that seems unable to comprehend DC servo's.

Edited by kevin gilmore
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I can't find the schematic. Seriously. I must have left it at home.

Will draw it up again and post soon.

here is a fresh version


For DC, it triggers on anything over +.5VDC and -.5 VDC

Detect time is 75 milliseconds.

For AC, at 20hz, it triggers on 5 VRMS.

Edited by kevin gilmore
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  • 3 years later...

Old thread, sorry: Kevin, do you have a schematic for the current version of this board?




EDIT: Oh, and some BoM-questions:


1) I assume the diodes are just standard 1N4148/1N914?

2) Is the 47uF cap supposed to be ceramic or similar since it hasn't got the same footprint as the electrolytics?

Edited by UFN
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See posts 14 and 15. I presume this is used like Amb's in that you put it between the amp output and the phones?


OK, you are right, but if you have a servo on the output ( I don't know if on other Dynahi versión has servo) when you add this board, you are duplicating the protection. Not?


Really, Is it necessary two protecction on the output?

Edited by jose
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