Did you ever get a resolution to this? I'm freaked because I came home one day to find all the lights on the front of my FF400 half lit up. I pulled the adapter jack out of the back and put it back in and the jack seemed to be working only intermittently as I played with it (My FF has been sitting in my rack since the day I bought it a few years ago and hasn't moved). After playing with it for about a minute the jack seemed to be stable again and everything appeared normal at first but I then realized I had no audio output. It was exactly as you described... I switched to bus power (which I've never even used before) and everything is fine but when I go back to adapter power there is no sound output to my monitors or headphone out. It's recognized by my pc and I can see working audio meters in my players or daw but no sound. I updated my firmware and driver but it didn't change anything. I don't know what to do. This happened out of the blue one day while I was out. I'm running off bus power for now but I need to resolve this because there's obviously something wrong. Is it just maybe the adapter?... I hope so, I don't think it's still under warranty and I can't afford to have it fixed... more importantly I can't afford to be without an audio interface if I have to ship it for repair.

Jeff, thanks for replying. So you think it sounds like the power adapter and not something internal where the jack plugs in? If so can I order one to Canada through you? Was trying to find a way to test with another of the same adapter but anyone I know around here with a FF has the 800 and they told me it doesn't use one.

ok great, thanks.

tsjah, thanks for letting me know. I tested out my adapter last night and, like yours, it seems to be fine so now I'm worried. I mean, I can use the FF400 with bus power for now but that's not the point, there's obviously something wrong with the unit. Being in Canada I think I'd have to send it to Synthax USA but then I'm without an interface for who knows how long? Can't afford shipping and repairs right now anyway. Pretty bummed about this.

Matthias, you might be right. I thought my 12v test device was working properly when I tried to power it from the RME adapter but I just tested it again after reading your reply and although it appears to function it only functions for about a second and the dies. The green LED on the jack of the RME supply dies at that point as well. When I initially tested this last night I thought I just wasn't holding my bare wire tightly enough against the barrel and that was why it was cutting out... apparently not. So I guess there is still hope, I will buy and try a new adapter on the FF400. Wish me luck

One question...

Will an output current of 1.5A be enough? There are plenty here for me to choose at that rating but 2A devices are harder to find, out of stock or are expensive unless I order one from China. The ones I'm looking at are all regulated and some even have overload protection (100 - 240vac input and 12v output)

Ok, thanks. Will report my results.

tsjah...

... that's great, man. I hope that's all my issue is as well. Am trying to find time to go get an adapter today but I'm stuck here in front of the computer researching some stuff I want to buy over the next few days with the black friday sales going on. Will try to make it out today if I can, the place is clear across town.

EDIT
I have a 5v 4A output adapter lying around... just tried that one as I remember reading here that the adapter can be 5v to ? and I still have the same problem. On bus power everthing is fine... I can play something for example in my media player, close the palyer, flip the switch to adapter power, start up my player with the same file and although I can see meters in totalmix on "Playback" and "Output" there is no sound. When I close the player and switch back over to bus power I get the windows bleep bleep indicating a device has been plugged in... I don't get the bleep bleep when switching back to adapter power.

Just picked up a 12v 1500mA switching non-regulated supply from my local surplus store for $5 and all is well! I was worried when I first switched over to it from bus power because I didn't hear the Windows "bleep bleep" that I always hear when when I switch from external dc to firewire bus power... but I fired up some audio into my player and I  have audio! I guess the bleep bleep is just a firewire and usb thing in Windows. Anyway, everything is working now, I'll get a better regulated supply soon with over-voltage and over-current protection for $15-$20.

Thanks guys.

Eschatologist... glad to hear it, man. I'm glad I found this thread too. Seems these adapters will eventually fail but at least they are cheap to replace. I see you're in Canada... MRO Electronics here in Edmonton has the supplies... regulated and over-voltage/over-current protected. You can find them on ebay from China as well but get regulated ones.

I think the 2A ones at MRO were out of stock when I looked a couple of days ago but there are 1.5A amp ones in stock I think. I seem to remember Calgary had some of the ones Edmonton didn't... it shows the stock in the listings. If you just want to try a cheap unregulated one right away to assess the problem Princess Auto has a 1500mA (1.5A) supply in the surplus section for 5 bucks right now if you have one near you. It's just a single cord adapter, not the 2 piece like the RME but it is a 12v switching supply. RME support says 1.5A is fine. I think the FF only draws an amp.