I suddenly have a weird buzz issue; can someone help me solve the problem?

Hi Erik,

Thanks; I had also thought it might be the USB, so I checked on the BelCanto - it does, in fact, include galvanic isolation.

What do you mean by "pull the power out of your "clean" power section"?

Thanks,

Chris

Thanks czarivey,

Given Dennis' longtime success while he owned and ran Cary Audi and designed everything they made and sold amps, I'm sure he knows how to design and build a tube component without any issue.  At least I would certainly hope so.

However, your suggestion about the tubes would certainly be an easy fix.  Do you have any suggestion which tubes would be the likely culprits, i.e., signal tubes, rectifiers, voltage regulators?  Would it likely be tubes in the preamp or power amp?  I'm just trying to narrow down the options so I don't have to swap everything one-at-a-time.

Thanks so much,

Chris

Cary Audio, obviously, not Cary Audi, which would be a very different skillset 🙃

Thank you all for your suggestions.

So, I tried leaving everything connected as-is with the battery and inverter powering the Puritan, into which all components are plugged, as I'd really like to get this to work), but I powered on only the power amp with no ICs from the preamp. Silence (with subwoofer still plugged to wall socket and connected). So this rules out subwoofer and power amp, as well as all tubes in power amp.

I then connected and powered up the preamp and power amp, with nothing connected to the preamp's inputs - the buzzing returned. This rules out the Mac Mini, the BelCanto, and the DAC, as well as differing ground potentials between the components, as they were not connected (at least I think it rules these all out; please correct me if I am mistaken).

I swapped new signal tubes into the preamp - buzzing continues. I tried a new rectifier - buzzing continues. I did not try swapping the voltage regulator tubes, as I can't see why they would be the problem, but I could swap those if someone thinks they could be the issue. The preamp uses 01A tubes which, by definition, have to be from the 1920s or 1930s, because that is when that tube type was popular. I have read they can often be microphonic, but I am not sure if that could the issue and, if so, why swapping through 3 pairs of tubes made no difference.

Does anyone have any other thoughts?

Thanks so much to all of you for your help,

Chris

Thanks all, for the additional suggestions. @pennfootball71: I don't think it should be DC, because the Puritan has a DC blocker and because I'm running the system off a battery and pure sinew wave inverter. I have an old SS preamp that I can try, though, since the buzz/hum does not appear with just my tube power amp - that's a great idea!

@vinylshadow and @jriggy - I will try cheater plugs. I don't think it's a ground loop, as I installed cheater plugs on all components and the buzz/hum remained, but I did not try installing the cheater plug on one component at a time, so I will give that a try.

@jriggy: that's quite interesting about the weird interaction of your preamp and the Puritan, but that putting a cheater plug on your DAC solved it. I will do some testing with the cheater plugs one at a time. I'll also try plugging everything into just a piece of junk power strip in lieu of the Puritan and see what that yields.

Thanks!

Chris

@davidrolon: Interesting. My WiFi router is in another room, so that shouldn't be an issue, but I do have a fiber-to-ethernet converter sitting right behind the system. Could that be doing something?

Thanks,
Chris

So, I reconnected the system to the wall outlet; buzz/hum continues, even with nothing attached to the inputs of the preamp. What's even weirder, the hum/buzz changes as I turn the volume knob, even when the input selector is set to "mute", so there should be no output.  Does this help indicate what may be going on?

Thanks!

@jwillox - Thanks!  I don't have cable, though, so that's not the issue :-(

Hi BB,

Sorry for not better clarifying.  The volume of the hum increases as I increase the volume knob, i.e., turn it clockwise, even if the selector knob is set to "mute". if I get to about 2 o'clock, the hum is easily audible from across the room. If I turn the volume knob all the way down, there is no audible hum through the speakers.

Tapping my finger near the signal tube certainly produces some interesting results that are easily audible through the speakers, almost like the tubes are resonating with the tap of my finger on the chassis. Is this normal?

I tried three pairs of signal tubes, and the hum persists with all three pairs, so I am assuming it's not the tubes themselves causing the hum, unless all the signal tubes I bought are bad (which I suppose is possible, given the age of the 01A tubes). I have not yet tried the "tapping test" with the other sets of signal tubes, however.

I did try a cheater plug on the preamp, but as you predicted, this had no effect.

Any other tests I can do to figure out what's amiss?

Thanks so much,

Chris