Question Massive buzzing coming from Pro-ject Phono Box USB

fidothe

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I have a setup that worked fine for a couple of years, with an Onkyo TX-NR414 Receiver connected to various bits and bobs by HDMI, and a Rega Planar II connected via a Pro-Ject Phono Box USB (the Onkyo has no phono preamp). The Onkyo is connected on to a TV via its HDMI output.

Six or seven months after I made the last change to the system (adding a PS4 via HDMI) the system started to develop a hum which would appear after 20 minutes or so of being plugged in. It would start quiet and get louder and louder. After a while the time between switching on the receiver and hearing hum got shorter and shorter, until it appeared almost immediately.

After much faffing about (including replacing the Onkyo after they recalled it) and disconnecting things in turn, it turns out that it's the Phono Box. If I connect the Phono Box and power it, I get the buzz. Disconnect it and the buzz stops. Connecting the turntable makes no difference at all. If I switch the box from MM to MC the buzz changes noticeably (MC is much louder and choppier)

So, my question is - is this an earth loop or other too-many-things-plugged-in problem, or is something (either the PSU or the phono box itself) broken?

The Onkyo has a two-pin unearthed plug, as does everything else plugged into the system. The Phono Box has a little external DC power supply, also unearthed.

If it's not a ground loop is there a sensible way to tell if it's the PSU or the box itself that's faulty?

Thanks! (All suggestions gratefully received...)
 
Is the hum present all the time, or only when you're switched to the input the Pro-Ject is connected to?
 
All the time, across all inputs, as long as the Phono Box is connected and powered.
 
So, I took the Phono Box and its PSU into a local hifi dealer (the very nice phonophono in Kreuzberg) who hooked it up to an amp to see if it buzzes outside my electrical system. It does, so it looks like it's just a broken Phono Box rather than anything more complex. The fix: a nice new Rega Fono Mini A2D.
 

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