Right channel hum with volume pot maxed; goes away at 3/4 volume

[rogerfederer]

I recently bought a stereomour with a 2012 build date (signed by the builder!).  this may be a stereomour II, though I am not sure.

Issue: when I turn the volume pot all the way up i get a fairly loud buzz in the right channel (very efficient speakers).  If i back the volume pot off to 3/4 the buzz goes away even if i turn up the volume on the TVC i am using as a preamp in this rig (have been using the stereomour as a power amp only).

I have switched the tubes, deoxited the volume pot, and adjusted the hum pots.  Suggestions?  Yes, i could just leave the volume pot at 3/4, but 1. i might want to use it as an integrated, 2. i prefer the TVC volume control, 3. could be sign of a worse problem...

Many thanks in advance!

[Paul Birkeland]

I recently bought a stereomour with a 2012 build date (signed by the builder!).  this may be a stereomour II, though I am not sure.

Definitely a Stereomour 1.

Issue: when I turn the volume pot all the way up i get a fairly loud buzz in the right channel (very efficient speakers).  If i back the volume pot off to 3/4 the buzz goes away even if i turn up the volume on the TVC i am using as a preamp in this rig (have been using the stereomour as a power amp only).

Is the buzz present with the TVC plugged into the Stereomour?  Have you tried shorting plugs at the input of the Stereomour?  You may just be amplifying some noise that's being picked up outside of the Stereomour.

[Doc B.]

You may need to reflow ground connections, or you may have a bad cable.

[rogerfederer]

thanks for the response!

i have not had the hum problem before using the TVC in other systems and with other amps.  i also put another amp in the rig (instead of the stereomour) and did not have the right channel hum.

[rogerfederer]

thanks, doc!

happy to try reflowing the ground connections.  alas, i don't have the manual or the schematic.  i bet i can find them if you point me in the right direction...

[Paul Birkeland]

happy to try reflowing the ground connections.  alas, i don't have the manual or the schematic.  i bet i can find them if you point me in the right direction...

The seller of the built amp absolutely should have provided this for you. 

I would make a pair of shorting plugs.  If there is no noise with the volume pot all the way down, then you need to short a pair of the inputs and listen again to see if there's any noise. 

[2wo]

+1 on the shorting plug test. TVC's can be a little quirky...John

[rogerfederer]

OK, will try the shorting plug test today. 

[rogerfederer]

well, interesting results:
1. with both inputs shorted i get a low hum in both speakers; changing the volume pot does not vary the hum;
2. when i manipulate the volume pot quickly (with inputs shorted), i get a popping noise in the right channel;
3. when i switch to an input with a source (roon > streamer > DAC > TVC > amp) i get louder hum in right channel and none i can hear in left channel (volume pot on amp turned to max);
4. changing the TVC volume pot does not vary the hum in the right channel.

[2wo]

1, A certain amount of  residual hum is normal.
2, Then don't do that, seriously it might pay to inspect and reflow the connections at the pot. You might have a worn pot but if you turn it up to 100% and leave it, it is essentially out of the  Circuit anyway.
3, Try removing the TVC from the chain and controlling the volume with the amp pot or digitally with the DAC or software...John

[rogerfederer]

Thanks, 2wo

Will try the amp without the TVC this weekend

[rogerfederer]

i set the amp up with a tuner and some high efficiency speakers and the right channel buzz is gone.  great news! 

but also pretty mysterious; i but another amp in the rig with the TVC and no right channel buzz.  in other words, 2 other amps i tried in the TVC rig and no buzz.

i did notice that screws on the right output transformer were loose -- you could wiggle it -- so i tightened them down.  the screws on the other trafo were loose too, but not as loose.  could that have been the issue?

[Paul Birkeland]

i did notice that screws on the right output transformer were loose -- you could wiggle it -- so i tightened them down.  the screws on the other trafo were loose too, but not as loose.  could that have been the issue?

Plug it back in with the TVC and find out?

but also pretty mysterious; i but another amp in the rig with the TVC and no right channel buzz.  in other words, 2 other amps i tried in the TVC rig and no buzz.

If they are both solid state amps, this might not be all that surprising.

[rogerfederer]

the other 2 amps are tube amps.  will try the TVC rig again.

[rogerfederer]

put the amp back in the rig with the TVC and the loud right channel hum is gone!  must have been the loose trafo. 
thanks for all the advice!