[tim79b]

Hi all
 
First post here, but I’ve been lurking for the last few weeks digesting information…
I am very new to the DIY audio thing, and I have just finished building a cMoy headphone amp from the instructions at http://www.tangentsoft.net, and yesterday tried to add a little tweak by putting on a DC power jack.
 
I have added the jack by using a SPDT switch which, in one direction closes the battery powered circuit, and in the other direction is either off, or on wall power if the AC-DC Adaptor is plugged in, as shown in the circuit sketch (only the power section of the circuit is shown here). The adaptor I am using I this one - http://www.jaycar.com.au/productView.asp?ID=MP3147
 
The problem is that, whenever I have the DC adaptor plugged in, I get no sound from the amp (but the power LED does light up), and the opamp chip gets really hot. If I switch to battery power and the adaptor is plugged in, I still get no sound, but the opamp runs at normal temp.
 
I finished late last night, so haven’t had a chance to do any testing yet (beyond checking that the polarities on the dc jack are correct), but wanted to see if anyone could think of any obvious causes, or had any specific advice on what I should be checking…
 
Thanks in advance for your help.
 
Tim

 

[wakibaki]

What opamp is it, i.e. is it rated for a continuous short circuit?
 
Post a good picture of both sides of the board.
 
w

 

[tim79b]

Hi all...
 
resolved the issue - just needed to insulate the DC Jack from the metal case the amp board was in...a little carefully placed heatshrink and a couple of rubber o-rings I had around and it works perfectly!
 
I don't understand the reasoning behind this causing the op-amp to heat up, but it seems to have resolved the issue (the amp is sitting by me right now, happily playing on dc power...)
 
Thanks All!!