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mravlcax 12th November 2007 09:32 PM

OPA2134 buffered
 
I have made buffered headphone amp with opa2134 opamp! Well the sound is great and everything but there is one problem. When I turn on or off the switch amp makes that nasty bum in headphones which is not very good. Any suggestions what could be wrong??

It is battery powered (2x9V) it has 2000uF per one voltage rail and the scheme is from here http://www.raymondaudio.nl/projects/...7/ampschem.pdf and instead of 1,5uF input capacitor I have 2,2uF and gain is down to 5.7!

Greating Ales

Minion 12th November 2007 09:36 PM

Maybe you need a soft start circuit?

Nordic 12th November 2007 09:43 PM

It is pretty normal, and normally not dangerous....
See if putting a small 100nf cap over the swich helps at all...

mravlcax 12th November 2007 09:53 PM

It is dual switch for negative and positive rail and I have 100nF over caps from rail to GND.

Nordic do you mean to attach it like this (the cap in red circle)??

http://shrani.si/t/C/1a/3BeYSLEf/untitled.jpg

And thanks for your replies!

Greatings

Nordic 13th November 2007 06:12 AM

yep

mravlcax 13th November 2007 04:20 PM

I was experimenting today and I works fine with 470uF, the can barely be heard so this is good!

Tnx nordic for your suggestion

And here are the pics of the headphone amp!

http://shrani.si/t/w/c7/2tc5enZW/dsc03534.jpg

http://shrani.si/t/E/VZ/3U8UokRp/dsc03546.jpg

Nordic 13th November 2007 06:23 PM

I'm glad... at least your experiments are going better than mine today... fried a small inductor this afternoon.... man! What a lot of smoke... it also killed the parallel resistor, which I don't have a spare for in my parts... Oh well, tommorrow is another day.

I am surprised you needed susch a big cap.. would have thought a few pf to nf would be enough.. but if it works :)

mravlcax 13th November 2007 06:43 PM

Well take a day off and just relax, it helps belive me and the best thing is to think it over ;)

Nordic 13th November 2007 06:50 PM

Baaaaaaaaaaaaaaah just no time... I'm relaxing a bit by reading DIYAUDIO... I allready wound new stronger inductors... but heh the amp I'm testing is osscilateing just a little.... every 10 minutes I get the urge to go unscrew it, and look for the problem... But so far I am manageing to resist. Not to mention I took on some web projects that will keep me busy for 3 weeks again today... Jeez I should realy get a job again... its just so much less work when you have a boss.

PS, very cool build... I like everything except the toggle switch... too 1965, and always gets bumped into on position when noone is looking... keep an eye open maybe for a small round rocker switch, it would look neato.

mravlcax 13th November 2007 08:52 PM

Well the toggle switch was the only one laying around and having 6 pins, about the rocker switch I will think about it, if I'll get small enough I'll stuff it in :D

BTW I like the fact that you like it!

Greatings Aleč


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