Signal interference - troubleshoot

I was getting this loud noise from both speakers when I unmuted my phonostage (ARC PH-3 SE). It sounded like a Geiger Counter, different than the ground noise. This only happens when I switch source on my preamp (ARC LS-25) to phono, and when I unmute my phonostage.

After doing some testing, I was able to isolate the issue to be inside the preamp. Somehow the signal from the DAC was causing this noise in the analog playback.

I had changed out the cartridge, cartridge lead, phono cable, and it is still there. I had connected both the DAC and the phonostage to different input jacks, and the noise is still there. I tried a different DAC and the noise is still there.

I can listen to digital source without any issue. But to listen to analog, it seems that I would have to either unplug the DAC from the preamp, or unplug the power of the DAC completely (putting it on standby doesn't work.)

This problem just developed over the weekend. It has never been an issue. What could be the cause of it????

Thanks in advance,

Few different ways, but you need to define what you want to do:

1. Sending unit to ARC

2. DIY... Normally Audio Research tech specialists are capable to give you information where you need to look for failures and sell you necessary parts so you can replace them yourself. I can also help ID-ing bad components and other DIY guidance.

3. Local repair specialist if available.

What you're describing is common problem in built-in stages that pick up the noise from line componets due to their very high sensitivity OR have a bad tube.

1. Before examining circuit components, I would HIGHLY recommend inspecting the solder joints around all RCA plugs inside the preamp box.

2. Try to replace phonostage tubes(ARC definitely will help you ID them if you can't) that are in most cases inexpensive or buy inexpensive ones first to test if the problem dissapears.

3. If the problem still there, you'll have to examine PCB solder joints and circuit components mainly ones that isolate ground and power supply(see DIY).