how do i identify ground loop hum ?
dose the hum come and go or slowly pulsate ?
and where do you hear it from ? (speakers/amp)

i have a slow hum that comes and goes (1-3 times a minute)(creeps in and out) and it comes from the amp not the speakers ...... is this ground loop hum ?

HELP
Supertom

Supertom...is the hum coming directly from the amplifier itself? Does the unit continue to hum if you remove all input and output cables from the amp? (Please do this with the power OFF!)

My friend's computer makes noises very similar to your amp. In her case it's a bad power supply fan. If there's no fan in your amp...and the hum is indeed coming from inside the amplifier itself...the problem may be a loose lamination or winding on the power transformer.

Ground loop hum is something you would hear coming from the speakers.

BobZoom

As BobZoom says, ground loop is generally produced by the speakers. It's also more commonly a continuous sound. It is possible for ground loops to produce hum in an amplifier itself (there have been cases reported of this happening with Model 200 and Model 2200 amps ). There are no fans in the Model 7500, so this noise is most likely coming from the transformer. If it's pulsing, I'd suspect something like a compressor or other piece of equipment elsewhere in the house producing the problem (similar to the hum that can be produced by dimmers). The best place to start may be to go through the standard ground loop search (disconnect everything in the system and slowly add each connection back, checking after each one to see if the hum is tied to that connection), although I'd start by simply unhooking everything from the amp except for power. If the hum is present when just power is connected, I'd try connecting it to a different outlet, then try looking around the house for possible noise generators (unplug the fridge, turn off the AC, turn off lights).

I had the same issue when I hooked up my 7700. Seemed like it was a hum that came and went from the Amp. I tried unhooking everyhting and it was still there. I added a Panamax stage 4 power conditioner and it went away. Been perfect ever since.

Hello Tom,

What you are describing sounds like mechanical hum from the transformer which is usually caused by something external to the amp, it's rare to have a faulty transformer. It's something we never see with these amps.

Use a heavy extension cord to plug the amp into several different circuits throughout your home. You should eventually come across an outlet where it no longer hums. If the problem ceases to exist with another outlet then there is most likely too much current draw. A textbook symptom of inadequate power with an amp using a toriodal transformer is that it will hum from the chassis if there is a voltage sag. Sometimes it's not the voltage, it's DC offset voltage across the AC line. Unfortunately this is tough to pinpoint, the only way to verify whether it's the amp or environment is to physically move the amp to another location. Obviously this is the last course of troubleshooting but it's sometimes necessary. It's probably nothing to worry about and you should be able to pinpoint the problem using the extension cord tecnique. It could be something as simple as a halogen lamp on the same circuit. During troubleshooting try to think of anything sharing an outlet in that room however benign you may think it is, dimmer switches, heater, any appliance, etc. I should add that we've had a few amps sent in for mechanical hum and to the best of my knowledge none have exhibited hum in our test environment. Please be syre to contact me if you have any questions or need to troubleshoot further.

HELLO STEVE:

After using the above extension cord tecnique i found the hum went away.
So i think ill just add a seperate 20 amp circuit just for the amp .... it worked but only if thats
all that was connected into that Plug as soon as i add ANYTHING Else (EX:990) the Hum would return
so i just run it (AMP) without sharing the outlet .... so far so good

Now just the other day while listening to music (not that it matters but low volume) and working around the house my wife turns on the hair dryer in the bath room and slowly the sound disappears
and the HUM returns (turning the hair dryer off everything returns to noraml)

Is that AMP drawing that much current that i can't run it in MY HOUSE ??? (I really don't want to return it) but i'am a little confused about what i should do and what my options are

am i right to say that if the ONLY thing running in my home is the 990 and 7500 and CD player that i SHOULD not have any problems because there the only things using Current ?

Hair dryers, vacuums, and refrigerator compressors are all significant electrical loads that can do odd things to your house power. If the bathroom circuit is related to the amp's circuit (same leg of the house service, for example) then there could be some weird interaction. Do you have any sort of power conditioner? Something like that (such as a Belkin PureAv PF30 or PureAV PF40 ) could help cope with the noise/trash being dumped onto the house wiring by devices like the hair dryer.

hey GONK i have connected to all other equipment on a separate plug a Monster Cable HTS850 but not the amp .... the amp is on its own 20a circuit
and its own plug if i plug all my A/V + AMP into HTS850 and then into my new 20a circuit i get the HUM again (is this really a case of not enough power in my house ???) can i test something ?
PS:never had anything like this with my last System Yamaha/Cinpro which i just sold

anyway thanks for your HELP
SUpertom

You could try putting the amp on the HTS850 by itself and connecting to the dedicated circuit, then run the hair dryer to see what happens. It wouldn't cost you anything but time.

My old house (roughly 1000 square feet, built in 1954) originally had only a 60A electrical service. When I set out to install a stacked washer/dryer a few months after I moved in (the existing dryer was in a closet on the back porch), I needed a new 208V outlet. There was no way to add the new circuit with the existing service, so I had it yanked down and a 200A service installed. If you've recently had an extra 20A circuit installed, I suspect that you are not in the same position that I was then, but you could ask the electrician who put it in what size the existing service is.

Hum usually isn't caused by a lack of power! It is caused by other things, ground loops, etc.
It sounds to me when you plug your amp into the extension cord you are putting it on a separate phase, (most houses have 2 phases of 120 volts apiece), than your other equipment. When the electrician installs the new outlet make sure he keeps the new outlet on the same phase as the extensiojn cord. Jim

Hullguy,

I've experienced similar problems with my Anthem Statement amplifier, but I've not been able to isolate the problem. All I know is that the degree of hum is not consistent. I've yet to try the extension chord method.

This house was built in 61, with a 60amp service, but was updated to a 100 amp, in 85. Most of the breakers are on the upper rail. When you say that Supertom should be sure to have the new outlet installed on the same phase as the extension chord outlet, what exactly do you mean?

Also, my amp doesn't have a ground lead, but has a binding post for grounding. I grounded the amp to the grounding post in the main box. However, given that when there's a problem, the excess load is dumped to ground, I'm thinking this could actually harm my amp and have reconsidered grounding it to a nearby water pipe. Is this a good idea?

Any and all information, appreciated.

thanks,

John