This could well be daft but here goes.

I’ve got a headphone amp that works perfectly (24v dc from wall wart, not earthed) and a small mixer that also works perfectly.

For some reason I decided to connect the headphone amp to the mixer’s tape out (via rca) and it works fine.

The weird thing is that the amp is now always on – irrespective of what it’s on/off switch says.

If I disconnect the RCA leads from it then it turns off / on. Or connect something else to it via rca – all fine – the switch works again.

So its not a big deal, but I’m just curious whats up, and given that something’s wrong – why is it all still “working” perfectly. Any ideas?

Ive got the multimeter out but not sure what to check next.

Quite common: http://www.diyaudio.com/forums/parts/136636-dc-voltage-rca-output.html

Does your mixer have XLR inputs with phantom power?

Thanks footflaps: I’d not even considered that! So I should see DC on the tape out’s from the mixer I guess.

dave – yep: the xlrs are shared with rca’s (via simple adapters) on channel 1/2 that are connected to the computers soundcard. I’ve no idea if they’re powered (and no user manual).

#Edit : it’s one of these:

#Edit 2: The meter shows 0v dc on the rca tape outs and a happily fluctuating 0.0 – 0.3v ac depending on tunes.

#Edit 3: Is there any way the amp could be switched on neutral and the mixer is providing an earth or something? I’ve just tried a bench psu and its doing the same so dont think its related to the wart.

Edit Shoulda read all the thread! 🙂

No worries trampus – you got me metering the shared inputs anyway – which was worth checking.