Ground loops..hums and tube amps

ohbythebay

ohbythebay

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So we know certain tube amps can be susceptible to hums...ground loops etc. And I am just trying to understand something. I gather some hum can be caused by associated components on the same line with different ground potential (not sure if that's the term but...)

Okay, so if you used a device like this
Amazon.com: Furman PL-8C 15 Amp, Advanced Level Power Conditioning, SMP, EVS, LiFT, 9 Outlets, Pullout LED Lights, Isolated Outlet Banks: Musical Instruments

That should eliminate hum or noise coming from your power yes?

But can an amp STILL have hum caused by its transformers, circuits, etc. even if it is being fed clean power ?

I ask because on my right channel I have never completely eliminated the hum in the right channel. It is very very low (have to put my ear right there) but the level channel is dead quiet..very slight tube rush.

Being OCD, would love to eliminate that last 1% but I am NOT willing to delve into the electronics of the Velleman again. I am lucky I got it as far as I did originally after 2 months work, much research and some real crazy solder and re-solder skills.

So electronic experts, what say ye ?
 
ohbythebay said:
So we know certain tube amps can be susceptible to hums...ground loops etc. And I am just trying to understand something. I gather some hum can be caused by associated components on the same line with different ground potential (not sure if that's the term but...)

Okay, so if you used a device like this
Amazon.com: Furman PL-8C 15 Amp, Advanced Level Power Conditioning, SMP, EVS, LiFT, 9 Outlets, Pullout LED Lights, Isolated Outlet Banks: Musical Instruments

That should eliminate hum or noise coming from your power yes?

But can an amp STILL have hum caused by its transformers, circuits, etc. even if it is being fed clean power ?

I ask because on my right channel I have never completely eliminated the hum in the right channel. It is very very low (have to put my ear right there) but the level channel is dead quiet..very slight tube rush.

Being OCD, would love to eliminate that last 1% but I am NOT willing to delve into the electronics of the Velleman again. I am lucky I got it as far as I did originally after 2 months work, much research and some real crazy solder and re-solder skills.

So electronic experts, what say ye ?
Click to expand...

Have you tried swapping your IC's from left to right channel before the amp? Maybe you have a noisy tube on one channel of the amp???
 
Rob,

When I first hooked up my CJ gear, I used multiple outlets. I had a hum that was driving me crazy. After doing a little experimentation and talking to CJ service, it was recommended that I run everything from the same outlet. Once everything was put on the same circuit, DEAD QUIET! I was stunned. My OCD kicks in because I always thought more outlets and power headroom is better but I am well under the power consumption for a 20 amp outlet with my CJ gear so I worry no more.
 
Thanks for the input guys...after several hours this morning, I have gone back to where I was which was 99.578% hum free (really it is just an OCD thing with my ear to the speaker. The fact that it took me several months originally to get there about a year ago (much pain, much sweat, much soldering, having technical get together's with the Velleman on an oscilloscope as the patient)...it is a miracle it works.

And works well indeed. Anyone who ever owned one, worked on it, hated it..but the sound is awesome. Plenty of tube power at 90wpc. very tailorable with the input tubes. I love it...it had design flaws which have been fixed with the exception of 3 HONKING big torroidal trannies that sit emitting gamma rays at everything in its path..its a wonder I don't get FM on the damn thing...LOL..and all caged in behind a reflective chrome plate that may as well be a target mirror for a laser. Seriously, have you ever gone near a tube amp and had all your metal drawn to it like the force under the island in Lost ? Okay..just kidding.

I love my amp..she works fine, I am just OCD> Obsessively Compulsive & Determined...:exciting:

148584_550619564953510_1710044483_n.jpg


77120_636861239662675_98676529_n.jpg
 
Its a sandwich maker...You butter the bread, put in cheese, lay it on the tubes. Makes nice little toasty circles, flip over, do the same.

The chrome is for easy cleanup....LOL
 
I hate ground loops. The first thing I do to trace the root of the problem is to run the power amp hooked up to the speakers without the preamp connected (the interconnect has to be unplugged). If the power amp hums still, the issue is with the power amp. If it disappears, its one of the sources, or the preamp. In a majority of the cases I've encountered, the culprit is usually the cable TV point.

I almost chucked a Cary SLI-80 out of the window trying to trace a hum problem. Swapping the input tubes didn't help, the hum stubbornly remained on one channel. Suspecting a problem with a coupling cap or local decoupling cap, I sent the amp in to a well trusted tech that does work for most of the retailers over here. We had a discussion on the source of the hum, and he guessed it was a solder point or routing of the cables. I asked whether it could be a power tube, but he thought not. He asked whether I swapped the power tubes from right to left. I said I did, but the hum remained there.

After many days of silence, he called me excitedly to tell me that he traced the fault. It was a certain power tube. The Cary requires matched pairs of power tubes, as it only has one bias pot adjustment per channel. Certain combinations resulted in hum, some didn't. I bought a new matched pair of tubes - problem solved. I also kicked myself for many months of trouble shooting but failing to pick this up. Not saying that this is the problem here, but thought that this info might be useful.
 
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