2. misc-audio
  3. 189628-17274

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

Hi all,

 

To provide some background, My system is as follows:

 

A “headless” Mac Mini as Roon core (my hands are tied with respect to using the MacMini, as I use Theoretica Physics BACCH4Mac cross-channel cancellation software/filtering to achieve "true" 3D sound, and this requires the player/streamer be a Mac device), outputting USB to a BelCanto RefLink USB-to-SPDIF converter, outputting SPDIF to a Mojo Audio Mystique v3+ DAC, which feeds a custom-built Dennis Had LP-2030 preamp, which outputs to a custom-built Dennis Had Inspire KT88 FireBottle SEP amplifier (max output, depending on tubes, is 12 WPC). Speakers are Coherent Audio GR-15 Neo Signatures.

 

All components are plugged into a Puritan PSM156 conditioner. I also have a GoldenEar Forcefield powered sub (amp is like 1200 watts) that is plugged directly into a dedicated outlet.

 

About a week ago, I became intrigued with the idea of powering my system completely off the grid, as even with the Puritan, I still noticed my system sounded markedly better on certain days and at certain times of day than others.  Also, there was some hum/buzz from the system, which I assumed was still AC-related, as it seemed worse at certain times of day than others.

 

I followed the guide from Ric Schultz here:

http://tweakaudio.com/EVS-2/Inverter_Power.html

 

All necessary components arrived, and I got them all hooked up.  Everything except the powered sub is plugged into the Puritan, which is now being fed by the Giandel inverter.

 

Interestingly, when I powered everything up, the previous hum noise is gone (yay!), and the sound is glorious when music is playing, but I now have a buzzing sound coming from my speakers (when nothing playing) that increases as I turn up the volume on my preamp. I tried installing cheater plugs on all components, lifting everything from ground, as I thought it could have something to do with the sub being plugged into the wall and the other components all going though the Puritan and the Giandel inverter, but this made no difference at all.

 

I would be very grateful for any advice/suggestions on what I can try.

 

One thing I noted is that the inverter is putting out 122 volts. I am wondering if the preamp is “unhappy” with this slightly high voltage and would prefer something closer to 115-118 volts, as read on another forum that this may be an issue and that one can test this by using a Variac, but I don’t know enough about electrical things to know whether it is a valid point or not, and I don’t know if I can plug a Variac into the inverter or not to test this possibility.

 

Thanks so much,

Chris

cporada
cporada OP
36 posts
 

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!

cporada OP
36 posts
 

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

jea48
4,294 posts
 

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"

You could try a ground cheater on the preamp but I doubt the problem is a ground loop.

Buzzing could be caused by a bad tube. Especially from this statement of yours.

What’s even weirder, the hum/buzz changes as I turn the volume knob, even when the input selector is set to "mute"

You don’t say if the volume level of the buzz increases and decreases as you turn the volume control knob up and down. Just a guess it doesn’t. A bad signal tube can cause a buzzing sound heard through the speakers. Two things to try. Tap quickly, firmly, on the chassis near each signal tube with your index or middle finger. Does the buzzing sound change with each tap of your finger? Another test is to use a wood pencil with an eraser and lightly tap on the glass envelope of each signal tube. Does the buzzing sound change with each tap on the tube?

 

BB

cporada OP
36 posts
 

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

garebear
1,062 posts
 

……lay off the gummies for awhile and see if that helps . 😎

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