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Help!! Loud hum after adding new Amp...  

post #1 of 13
2/25/02 at 7:59pm
Thread Starter 
I just added a Sherbourn 5/1500A to my system. I'm now having a humming problem, but I'm not sure if its a problem with my electrical or the amp. Let me explain what's happening...

I have two lamps on different outlets, each are also on a different outlet as the Sherbourn. When I put either of these two lamps on the lowest setting (these lamps have two positions) I hear a loud hum from the Sherbourn. If I turn the lamps to the second setting the hum stops. I have a third lamp that is on the same outlet as the Monster HTS-3500 to which the Sherbourn is connected and no matter which setting it is on there is no hum from the Sherbourn. So, my question is, is this a problem with the Sherbourn or my electrical? How can I get rid of the hum if it is my elctrical and not the Sherbourn?

What makes this weirder is that when I was testing the Sherbourn I noticed the hum. While I was testing it the Sherbourn was plugged directly into the wall. It was then that I realized it only hummed when one of the lamps was on low. I then tried plugging the Sherbourn into the HTS-3500 and the hum went away no matter what the lamps were set at. I thought that was the end of it... but, when I put the Sherbourn in my rack, the humming came back even though it was connected in the same way.

Ok, and one final oddity... now my TV speakers hum when playing through my Tivo (cable) and my satellite Tivo. This never happened before. The only difference is the Sherbourn (I did disconnect everything when putting the Sherbourn in, but reconnected it all in the same way... I realize something may have happened when doing this, but I double and triple checked all connections). Just to see if it was the Sherbourn causing the problem, I disconnected the Sherbourn from the HTS-3500 so it was plugged into nothing. The TV speakers still hum. Why would this just start?!?!?! It has nothing to do with the Sherbourn since it wasn't plugged into anything.

Thanks for any help!!

Jeff

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post #2 of 13
2/25/02 at 8:23pm
Not sure if this will help but -
I did own a Lexicon DC-1 and had it close to my TV (Tube 36 inch). But by moving it away from the TV by about 3 feet the hum stopped. It appears you may be having a similiar problem?
post #3 of 13
2/25/02 at 11:03pm
Thread Starter 
Well, when I was testing the amp it was just as close to the TV as it is now. It was only in front of it rather than to the side. In fact, it was directly in front of the speakers.

Moving the amp is not an option unfortunatly.

Jeff
post #4 of 13
2/26/02 at 4:01am
It may be a ground loop hum. If the electrical plug has three prongs try a two prong adaptor. I have never had this but I have read this is a problem sometimes.

TedO
post #5 of 13
2/26/02 at 5:49am
Are these halogen lamps?

They often cause electical noise if they are all on the same circuit, which it sounds like it is. If you can, dedicate one circuit to your HT setup and make sure everything is plugged into your Monster HTS.

Also set your HTS and amp closer to the ground so that the noise is less noticible. This also isolates the power cords going to the HTS from other cables. Somtimes just rearranging the order of your components makes a big difference. Try to keep your speaker cables away from cords and video cables as this will add to the ground loop problem. I also found that well isolated, dirctional cables (grounded at one end) do help keep electrical noise from passing from one component to another.

Is your Tivo connected to the HTS or directly into the wall?
post #6 of 13
2/26/02 at 5:53am
Ohh, do not use a cheater plug for anything going into the HTS, it will void the warranty and is a potential fire hazard.
post #7 of 13
2/26/02 at 7:29am
I had a terrible hum after connecting my big amp. After much work and expense, an electrician had to reground one of the circuits (I'd had two new 20-amp in-phase circuits installed to handle the HT system). It made absolutely NO sense to him, but it was the only way to eliminate the hum. He'd already traced all the wires, etc. and nothing was wrong. Fortunately, this expense was covered as they'd done the original work. The really weird thing was that all the fixes he initially tried lowered the hum to the point where none of the 3 men involved could hear it, but I could hear it two rooms away! Once one circuit was regrounded, the hum disappeared.
Leslie
post #8 of 13
2/26/02 at 9:31am
Jeff wrote:
"I have two lamps on different outlets, each are also on a different outlet as the Sherbourn. When I put either of these two lamps on the lowest setting (these lamps have two positions) I hear a loud hum from the Sherbourn. If I turn the lamps to the second setting the hum stops."

Most likely the lower light setting is achieved by placing a diode in series with the light bulbs. This results in a lower voltage to the bulbs and therefore less light. HOWEVER, the BIG problem is that it causes a very unsymmetrical ac current and therefore a DC offset in the ac line which can cause transformer cores in equipment to go into saturation and hum or buzz mechanically. It might also result in hum being heard from the speakers.

It is not a good idea to use such lamps at all when trying to achieve a very low noise in your system unless you leave them on the high setting.
post #9 of 13
2/26/02 at 9:49am
Thread Starter 
Thanks for all the replies!!!

MaxC Wrote:

"Are these halogen lamps?"
One is and one isn't

"Ohh, do not use a cheater plug for anything going into the HTS, it will void the warranty and is a potential fire hazard."

Is that the same as the two pronged plug mentioned above or is that something else?

Oscar Neundorfer wrote:
"It might also result in hum being heard from the speakers."

The speakers on my TV hum regardless if the lamps are on or off. The TV speaker hum is actually the most annoying part since it happens all the time. I can at least control the Sherbourn hum.

The main thing I wanted to know is if it's the Sherbourn or my electrical since I'm still in the demo period for the Sherbourn. It sounds like it is the electrical and that the Sherbourn is more sensitive than my reciever... correct?

Thanks again!

jeff
post #10 of 13
2/26/02 at 11:55am
Quote:
s that the same as the two pronged plug mentioned above or is that something else?
Yes, and I have used it in the past for my sub (on a seperate wall outlet), but I just wanted remind you that Monster specifically states that use of a cheater plug will void any warranty if plugged into the HTS. Feel free to try it if your lamps are three prong and not plugged into the HTS.

I believe your problem is with the electricity and not the amp. You may even be able to hear a difference in your HTS when the lamps are turned on. They tend to emit a low hum and mine gets noticibly louder when I turn on my halogen lamp, however, since I live in an apt, I cannot dedicate a circuit to my HT setup, plus my apt is probably poorly grounded.:(

Your problem could be due to bad grounding, your cable TV, or cords/cables that are not well isolated. How is your Tivo hooked up? With the TV, the problem would be due to the cable, which can cause a ground loop hum if other cords are too close to it and not shielded. This may explain why your amp hummed once you put it next to the TV.
post #11 of 13
2/27/02 at 6:52am
Jeff wrote:
"The main thing I wanted to know is if it's the Sherbourn or my electrical since I'm still in the demo period for the Sherbourn. It sounds like it is the electrical and that the Sherbourn is more sensitive than my reciever... correct? "

I am guessing about the Sherbourn, but my guess is that it has a fairly large transformer, quite possibly a toroid type. (Toroids are more prone to saturation from a dc current component on the AC line). Larger high power transformers have low resistance windings to avoid limiting the current, and this low resistance along with a dc current component on the AC line makes the core easier to saturate.

Smaller transformers with higher resistance windings are not as likely to saturate, and EI core transformers are also not as easy to saturate.

At SMART, we make our own transformers, mostly toroids, and we have done all we know how to do to reduce the noise from core saturation due to dc on the line. Our cores are epoxy impregnated, and some of the transformers have a epoxy plug in the middle (the "donut hole" of the toroid) to attempt to reduce noise. Even this is only somewhat effective. The best thing is to provide the purest electrical supply you can get, and keep distortion-creating equipment (like your lamps) on totally separate circuits. I cannot over-emphasize the importance of proper power distribution and especially proper grounding for high quality sound systems.
post #12 of 13
2/27/02 at 3:46pm
It's possible that you have the hum because of your cable TV connection. When I first hooked up my ATI 1505 amp, I had a strong hum thru the speakers. For what ever reason, my pervious amp was not affected by this ground problem.
To eliminate it, I took two 300 ohm converters (you can buy them for a dollar), and attached the spade lug end of 1 converter to one spade luge of the other converter. Then did the same to the other 2 spades.
You take the TV Cable From the wall, screw it on one end of the attached converters, then using another length of cable, screw one end into the other end of the converters and then into your TV.
This breaks the ground loop.
post #13 of 13
2/27/02 at 4:10pm
I had the same hum when i hooked up my rotel 1095 amp, I found it to be the cable tv cable try and unhook it and see what happens. the dealer says the fix is a line conditioner. good luck
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