XEN SHPP -- Simple Headphone Protection

[EUVL]

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


Patrick

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[00940]

Nice compact board.

One question though: what's the trigger delay when there's a real problem like the output going to rail voltages ?

 

[EUVL]

3s, as already mentioned in the article.
Also mentioned in the article is how it can be changed to suit individual needs.

Patrick

 

[00940]

3s is for a 80mV offset. A quick sim gives 30ms for a sudden 5V offset, which is fine.

 

[EUVL]

Yes, speed increases with offset amplitude.


Patrick

 

[EUVL]

Installed in one of my high power headamps.


Patrick

.

 

[jan.didden]

Nice!

 

[SamAnytime]

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.

 

[EUVL]

Well spotted.

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


Patrick

 

[EUVL]

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.


Patrick

 

[jan.didden]

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.


Patrick

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. ;-)

Jan

 

[EUVL]

But in this case noise does not matter.
It is only discrete logic switching.




Patrick

 

[RollE2k]

Patrick: is it possible to buy these boards from you?

 

[EUVL]

In principle yes.
Need to check if someone has time to send to you.


Thanks for your interest,
Patrick

 

[RollE2k]

In principle yes.
Need to check if someone has time to send to you.


Thanks for your interest,
Patrick

Great, let me know as soon as you have an answer. I would be interested in to-92 sinks at the same time also if possible.

 

[EUVL]

Heat sinks out of stock.
We shall only restock when we have other GBs to serve.
Too much work and margin too low.

Sorry.


Thank you for your interest in any case,
Patrick

 

[Morde]

Hi Patrick.

Do have these headphone protection boards available now? I would like to use one with UTHAiM...

 

[EUVL]

Can you see whether you can organise a GB and take 10~20 pieces, all ship to you ?
Sending just one is A LOT of work.


Patrick

 

[dabore84]

I'm also in for couple of boards.

 

[EUVL]

Please open a new thread for Group Buy and post there only.


Thx,
Patrick