Aphex Channel noise after warming up

Hello everyone -

I purchase a used Aphex Channel to experiment with and am experiencing noise as the unit warms up. I tried uploading an mp3 of the noise, or lack thereof, right after powering on and then one and two hours later. The upload failed, so below is a dropbox link to the audio file.

https://www.dropbox.com/s/rtr9ln83sg...ex%20Noise.mp3

I've swapped cables and inserted a different mic pre-amp and the noise went away. At this point I'm confident the noise is coming from the Aphex Channel or some interaction between it and the other components. Any ideas on troubleshooting this? I'm planning to contact Aphex on Tuesday.

In case it helps, here is a diagram of the current wiring setup.
https://www.dropbox.com/s/fdikwyk1u2...o%20Wiring.pdf

Thanks for any help.
- Oliver

It's really hard to tell, but it could be a power supply issue.

Anyway to troubleshoot the power supply without opening it up? The Aphex Channel is plugged into my Furman M-8x^2, so power is conditioned.

Might be a ground loop. I've had a simular situation and used a ground loop isolator to remove it. It also could be a volume or gain turned up too high. Any gain that is too high raises the noise floor of electronic noise that is naturally present in all electronic audio equipment.

For what its worth I've had good results with Aphex customer/tech support.

Jace Nuzback
Product Specialist
APHEX
818-767-2929
jace@aphex.com

If it is ground loop or volume/gain related, would the noise be initially absent and then get noticeable over time without any changes? That's the symptom that is making me think it's internal as the tube and other components warm up. In the event it is a ground loop issue with the symptom I described, which ground loop isolator with XLR connections do you recommend? Thanks.

Dan - thanks for the contact. I'm crossing my fingers that it can be resolved without costly repair.

It doesn't sound like a ground loop to me, but it's not impossible. I'd forgotten that it has a tube. That's a possibility, or it could be the power supply. Again, it's hard to tell without being able to play with it in person.

Mike - Okay, thanks. I tried adjusting all the settings I could think of to isolate the issue, including turning the input gain all the way and the noise persisted. The one thing that reduced the noise a little was turning off the BB/EQ/AX.

I opened the chassis and nothing looks bad on the circuit board. I'll contact Aphex and buy a replacement tube to try.

I'd ask them about the problem before I ordered a new tube. There could be a known issue with the unit.

Hi Dan,

After not hearing back from techsupport@aphex.com this past week, I tried emailing jace@aphex.com and got a bounce notification back. Can you confirm the email address? Thanks.