[groaninjock]

I've had my PSB M4U2 headphones for almost a year, and they've been great. I've been using them connected to a Fiio E17 portable amp, connected to an iPod Classic.
 
But today, after connecting them to a new Fostex HP-P1 headphone amplifier, there's no sound coming from the left earphone when the PSB M4U2 amplifier is switched on or the headphones are in noise cancelling mode.
 
I've tried the headphones with both OEM cables, with new batteries, and with several audio sources - iPod, iPod with both amps, Samsung phone - and the result is the same with all of them.
 
When the headphones are in passive mode, the sound is fine, but as soon as the switch is flicked, the sound is gone in the left ear.
Noise cancelling seems to be working, albeit with the missing sound issue in the left ear. Right ear seems to be fine.
 
Is it likely that I've blown something in the headphone by connecting them to the Fostex amp? Or can anyone think of another reason why I'm now encountering this problem?

 

[billybob_jcv]

It certainly seems like something in the active circuitry has gone awry. I think you are looking at PSB support issue.

 

[groaninjock]

Yeah, that's what I feared. I've contacted PSB support, see what they come back with. I'm not too optimistic though

 

[crimsonghost]

Yeah, that's what I feared. I've contacted PSB support, see what they come back with. I'm not too optimistic though

I have some M4U2 headphones also. They got damaged in an accident, so I'm looking to replace them with something, but the perfect replacement for the price doesn't seem to exist yet, or I'm not looking in the right places. I loved mine for years. Anyway, back to you. You said that you attach them to an external headphone amp? The amp that's built-in has been stellar for me. I'm curious as to why you add another amp between the headphones and the iPod. Is it possible that between the amp in the iPod, the external amp and the amp in the headphones that you're simply distorting the signal? That's honestly a shot in the dark. I'm more curious as to why you use a third amp in the setup, personally.