Ground loop hum? Part II (1 Viewer)

[AaronG]

Hi Guys,

A little while ago I installed a Bryston 9bst in my system and got a big hum http://www.hometheaterforum.com/htfo...readid=137334. After trying every remedy from everyone here I finally took the amp to Bryston where they revamped the grounding system to that of the newer sst line.
That got rid of 95% of the hum.

As the upgrade bug keeps biting, I've added a 3bsst to my system, and I've got a loud hum again.
This hum seems to be between the two amps. The mains (run by the 3b) are silent until I turn on the 9b. The rest of the speakers (in a 7.1 set up) have just the slight hum that was present from the 9b before.

I've tried having the amps plugged into the same circuit and different circuits, same outlet and different outlets on the same circuit, and same outlet via an extension cord.

Any thoughts?

Thanks,
Aaron

 

[MikeTz]

Aaron:

I'll see if the exorcist is taking new patients. Seriously, I have the same configuration as you, 9B and 3B, but my 9B runs the main 5 channels (front, center, sides). No hum, but I've spent a lot of time ensuring my house power and satellite cable are grounded properly (single point bond at the service box) and that all interconnect/speaker cable connections are tight. I'm sure after the last episode you have too. If you configure your set-up with the main 5 channels on the 9B and rears on the 3B does the loud hum appear on the rears?

MT

 

[AaronG]

Hi Mike!
Welcome back to my nightmare !

I'll try switching the 3b to the rear tomorrow-it's a little to late to keep playing.
I ended up having a retro night...Jaws-3D in STEREO!

Aaron

 

[AaronG]

Hi Guys,

Just some more info...
When I disconnect one of the interconnects between the Denon 3802 and the 3bsst (so there is only one connection between them) the hum goes away.

Mike,
I'll try moving the 3b to the back tonight.

Aaron

 

[MikeTz]

Aaron:

This sure sounds like the same symptoms that caused you to get your 9B upgraded to the SST configuration. Have you described this problem to Bryston? Since the 3B is in the SST configuration (and still under warranty) I wonder what they would advise.

MT

 

[AaronG]

Mike,

I emailed them last night, but haven't heard back from them (which is completely uncharacteristic of Bryston). If I don't hear back from them by Mon. afternoon I'll assume they didn't get my email and try again.

Aaron

 

[AaronG]

double post

 

[Mike Veroukis]

Is the 3802 and the 3bsst on the same circuit, or do they share the same ground? It seems there's a ground differential between the two. But it could also be one of the units hooked up to your receiver that's the problem.

What I would do is this:
Disconnect ALL wires from receiver except those that lead to the 3bsst that hums. This means no inputs at all and even disconnect any video cables. If there is still a hum the problem lies with one of those two units.

If the hum goes away when it's all stripped away, then start plugging inputs into your receiver one at a time and test for the hum each time. Eventually it will start to hum again and you'll know which input is causing the hum.

When tracking down a ground loop hum you basically need to strip things down and put them back together one at a time to isolate the problem. Once that's done it's usually not hard to fix it.

- Mike

 

[Jorge UF]

Do you have any video cable connected to the system in anyway? As in, is there a TV connected somehow to the system? I had a ground loop problem that was caused by the cable for my tv. ALso they sell something called a ground loop isolator that may help you. I think radio shack sells them.

 

[AaronG]

Hi Guys,

Thanks for the responses.
The hum is still there even with everything disconnected from the 3802 (I've even tried unplugging everything from the outlets including the 3802). The hum stays until I turn off the 9b.

Does anyone know why re-grounding the 9b the same way as the sst line worked for the hum before, and now that I've added a sst amp the hum is back?
The symptoms are exactly the same as when I first added the 9bst to my system.

Thanks,
Aaron

 

[Mike Veroukis]

Does anyone know why re-grounding the 9b the same way as the sst line worked for the hum before, and now that I've added a sst amp the hum is back?

So let me get this straight.... You kept the 9b and the 3b plugged in, but stripped the 3802 and even unplugged it from the outlet and the hum is there as long as the 9b is connected to the 3802. But if you disconnect the 9b from the 3802 the hum goes away??? What if you keep the 9b connected to the 3802 and disconnect the 3b (and any other amp you have)?

If the 9b hums when it's the only thing connected to the 3802 and the 3802 isn't even plugged in then I would say there's something serious wrong with your 9b.

Just an stab in the dark, but none of your speakers have any built in powered subs or anything, right?

Have you tried cheater plugs?

Anoither stab in the dark, but... how are the amps physically arranged? Is it possible that the case of the amp is acting as a ground, or could the wires themselves cause some grounding? Did you try different cables?

- Mike

 

[AaronG]

Mike,

The conflict seems to be between the 3b and the 9b.
The hum is there only when the 9b and the 3b are turned on. The hum is coming through the speakers attached to the 3b and it goes away if I turn off the 9b.

The 9b just came back from Bryston where they changed the grounding and gave it a clean bill of health.

I haven't tried removing the interconnects from the 9b while leaving it plugged in, so I guess that's next.

Speakers are passive (Paradigm Studio 60's, CC, ADP)

Cheater plug didn't work (also tried putting the two amps on different circuits)

Haven't tried new cables, but these are all new Acoustic Research cables (not the best, but should do the job)

Thanks,
Aaron

 

[Chu Gai]

Dumb question, but getting back to your original problem, do you recall if you'd bought or installed anything else at around the same time in your home? If so, you might want to either uplug or turn it off.

 

[AaronG]

Hi Chu,

I don't think there was anything new, but would it matter since the HT has it's own circuits (15amp for lights and recliners, and, 15amp for the AV equipment)?

Thanks,
Aaron

 

[Chu Gai]

yes, if the item in question was radiating noise via the air. myself, I don't have a real good handle on what's going on over there, and while Bryston has made good on the other amp, it's a damned vexing problem you've got there.

myself, I'd be looking to find the source of this problem and fix it there. However...and while i hate recommending products, there is a device used in the pro circles called the EbTech Hum eliminator. another gentlemen on this forum had a similar problem that was traced to his refrigerator of all things. Now for personal reasons he didn't wish to start futzing with the breakers and all that. The insertion of this device, which goes between the amp and preamp totally and completely eliminated any hum. He's running dead silent. If you're interested, i'd look in the phone book for any pro audio places...stores that carry electric guitars, amps, drums...someplace large. In the US, there's a a chain called Guitar Center but I don't think they're in Canada.

 

[Mark C.]

When I've run into this problem in the past, the only solution was to break down the entire system, piece by piece, and reassemble untl the hum returns. It's not easy; it's certainly time-consuming; but it works.

 

[AaronG]

Hi Guys,

I found the problem!

After several hours of plugging and unplugging, I found that it is the proximity of the two units that is causing the problem. If the 9b is turned on within 7' of the 3b, the speakers from the 3b start to hum.

My new problems are: 1. my rack is only 5' high, and, 2. the 3b and 9b can only be about 4' apart because of the length of my speaker wire (which is all in-wall).

Any ideas on how to get these two far enough apart?

Thanks,
Aaron

 

[Mike Veroukis]

You might wanna talk to Bryston about getting better shielding installed (if that's even possible). There's got to be a way to shield the two units.

- Mike

 

[Chu Gai]

Well I'd contact Bryston again and let them know what you're noticing. It almost seems as if the amp is generating EMI that's above and beyond allowable government mandated limits.

 

[AaronG]

Hi Guys,

The amps are going in to Bryston today for a check-up.
I'll let you know what happens.

Thanks,
Aaron