BeePre hum

[joepiecuch]

After several years of reliable performance, my BeePre has suddenly developed a VERY loud 120 Hz hum. It takes about 2 hours of warmup to manifest and is unrelated to volume and source settings and input connections. I expect this is a call for reflowing joints starting with grounds, but suggestions for other approaches are welcome. An odd, possibly irrelevant (but maybe not) bit of info is that both times it's happened it has coincided with the heat in the room being on. And when the heat is on, my mains voltage drops to about 112. But when the heat shuts off the hum stays. Thoughts?

[Paul Birkeland]

How is your line voltage?

[joepiecuch]

Normally it's 120; that gets checked every time I'm wiring a kit transformer. This morning, when the hum was bad, it was 112. Right now, the heat is running and I'm showing 117. But the heat's been turned on since October and this just started yesterday, so it's not all that clear cut.

[joepiecuch]

I'm inclined to think the heat thing in itself was a coincidence and red herring. It's turned off this afternoon; after about 90 minutes of warm up the hum showed up. Line voltage is 117. The hum goes in and out, sometimes fading, sometimes quickly. It's more of a buzz than a hum at it's loudest. Sometimes it's both channels, sometimes one or the other. It's annoying!

[Paul Birkeland]

I suspect you may just be fighting line voltage variations.  112V is not enough line voltage for a BeePre 1 to work properly. To get around this, you can use a small boost box with a 12V CT transformer so you can get +6 and +12V options during the times when your line voltage sags, or you can look into a regenerator.  BeePre 2 is not nearly so sensitive and won't have these issues either.

-PB

[joepiecuch]

Really loud right now and I'm seeing 113.6V.

[joepiecuch]

Will an on-line UPS serve the purpose?

[Paul Birkeland]

No, a UPS provides power when there's no line voltage.  Somewhere around 117-118V is what I remember being the minimum amount you really want for things to work properly.

[joepiecuch]

By 'online' I meant a double inverter UPS; they've gotten cheaper, but I see they're still pricey.

[Paul Birkeland]

If you can have one kick on for small deviations, it's possible.  Do keep in mind that UPS batteries have to be refreshed periodically, so the difference in price between a UPS and a regenerator may get gobble up by the first round of battery replacement. 

[joepiecuch]

Thanks!

[joepiecuch]

Line voltage back to ≈122 last night and this morning; no oppressive hum.