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When you hear stuff without signal

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#1

Hum in the HT. The 50-60Hz is only in some speakers. My HT uses a Dectet and otherwise almost entirely basic power cables. The hum is only in a few speakers …not all. I feel like I removed the hum from some, but then it went to others. I’ve done some isolating but hear it with everything unplugged (though rca connectors still connected) except the amp. I only have one three pronged thing in the mix. It’s not unbearable, but I hear it and don’t like it.

Additionally, I’m hearing what was explained to me as wifi in my phono tube stages. It’s a bleep and a bloop sound. My tubes are exposed and not under cages. Do I need cages? My router is probably 30 ft away.

#2

Can’t speculate about the hum. But, I too had clicks, bleeps and other strangeness in not just a tube phono stage (a Herron Audio phono stage), but every other phono stage I had in my system tube or SS. After upwards of two years of sheer frustration, I finally traced it to garbage that was being emitted onto the mains by powerline ethernet devices. The junk being emitted on the mains was so intense it got through my power conditioner. No idea whatsoever whether that is your problem, but I assure you you hurt nothing by disconnecting any and all computer gear you may have plugged into the same circuit as your phono stage. For me the elimination of the unbelievably annoying problem was instantaneous, I mean those gremlins were absolutely, positively zapped and I’ve had no issues since with any phono stage in my system.

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#3

Hard to say without knowing how you’ve got everything wired. The most basic test is unplugging everything but the speakers and amplifier power.

If plugging in the RCA causes hum, there’s a ground difference between the two devices connected by RCA.

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#4

Thanks, Vee and owlsalum.

The RCAs to be unplugged are from a Denon processor and are channel outputs to a McIntosh MC257 amp. Anyway. I will always keep going forward.

It’s clear my tubes are acting as little antennae. I’m also hearing a similar sound in bluetooth headphones, so do think there is something to the wifi theory. I ordered a Hammond cage/enclosure from digikey to see how much that helps. The router is a good 20 feet from the tubes…both in a huge multi-room area.

#5

Kinda crazy…I touched my phono tube amp aluminum case, and all that unwanted, unexpected noise goes away. A cage arrived today too, and it definitely changes a few things when I’m putting it over the tubes, but I guess I hadn’t played around with keeping my hand on the case. Dramatic change in what I’m hearing. Is this a sign that my house ground is insufficient?

#6

Possibly. It could also mean your amp is more sensitive to ground imbalances.

Can you lift the ground off your tube amp? Lifting ground will cause any current leakage to leave through other devices.

Another thing to test for is whether the chassis is charged. Touch an edge and see if it sends a charge into your hand. That’s a telltale sign of an improperly done ground. Likely neutral and ground are bonded at the outlet.

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#7

See Footnote 1 to Stereophile’s new Wilson Audio SabrinaX review. Link on the Stereophile splash page. I kid you not, I thought about this post the moment I saw that footnote. First time I’ve ever encountered a professional report of hum coupled to an unconnected loudspeaker. But there it is.

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#8

Hmmm…

“ Footnote 1: One anomaly I found when I unpacked the SabrinaX was that even with the loudspeaker not connected to an amplifier, I could hear a very low-level hum coming from the midrange unit. The level of this hum varied with the position in the room and the orientation of the loudspeaker. The hum frequencies were primarily 180Hz and 300Hz. All I can conjecture is that the iron, steel, or ferrite core of an inductor in the midrange crossover circuit was picking up the hum field from my home’s AC wiring. When the speaker is connected to an amplifier, the latter’s very low output impedance should damp the hum. This is more a curiosity than a concern.”