What is the acceptable range for in home voltage? Mine flucuates depending on the time of day from about 118 V to 122 V.

At what point should I be concerned about either damage to my Home Theater equipment or degredation in performance?

Your's is fine

you are fine - the change is due to load in your neighborhood. typically duringthe day voltage will be lower due to increased A/C demand. I would keep an eye for sudden changes like when the ac comes on or the refrig. they can indicate a problem.

I beleive Australia has a 6% tolerance in either direction. eg; 225v-255v I'm sure it would be similar for most of the world.

Your voltage looks fine but if you want to picky about it you can try UPS system. Not sure if it will improve the performance but it will protect you from brown outs or surges. And if you get a large enough one you can watch movies when the power goes out. :)

In the hamptons on summer fridays around 7-8pm when everyone and their brother arrives at their weekend home and cranks up the A/C, the voltage on the East End of Long Island can drop as low as 100VAC... Took us a while to find the problem with a customer's LCD projector, and finally nailed it when we stopped by on a Friday PM... Furman Stabilizer solved that one.

I am trying to isolate a buzzing problem with my power amplifier. It buzzes with varrying intensity and volume. It doesn't seem to be related to heat, temperature, or volume level. It also doesn't seem to be related to time of day. On occasion the amp is dead silent. The amp is a Rotel RMB - 1095 200 Watts per channel times 5.

I have talked with Rotel tech support and they have suggested that I look for high power usage appliances that might be causing the problem. I have 2 dedicated 20 amp circuits for my home theater and I turned off every breaker in the house with the exception of the home theater and I still get the buzz.

I've completely eliminated the possibility of a ground loop issue by disconnecting everything from the amp with the excpetion of the amps own power cord. The amp still buzzes. Besides, I don't get any buzz/hum coming from my speakers. Only the amp itself.

I also have my entire system connected to two Richard Gray RGPC 400 MKIIs. I have also tried plugging the amp directly into the wall. It still buzzes.

My next step will be to take it into the dealer where they can put it on the bench. I have a sneaking suspicion that when they put it on their bench it will be dead silent. I am also planning on bringing home a different amp from a different manufacture to see if it buzzes.

I plan to audtion the Parasound Halo A51 which has an encapsulated transformer which might make it a quieter amp. The Rotel does not have an encapsulated transformer. It's also possible that the Rotel's transformer might be loose and needs to be tightened up. There is a large bolt that goes through the center of the transformer. I will have to remove the cover in order to check the tightness of the bolt. I think I will let the dealer deal with that.

I purchased an inexpesnive electronic energy meter while I was in Canada which plugs into a wall outlet that monitors incoming voltage. As I mentioned, it flucuates between 118 and 122 V. Here's a link to the energy meter in case any ones interested.

[Link: upm-marketing.com]

Well.... Have I covered all angles and possibilities or is there something else I should check?

Usually if the amp itself is buzzing, it is the incoming power or a damaged transformer in the amp's power supply.

Since you have 2 dedicated 20A lines to the theater this is a long shot, but one way to truly check it off the list is to take the amp & preamp, and the RGPC directly to the service panel and plug them into the service outlet of the panel. Try it with and without the RGPC.

Another thing to check is where your breakers are located on the bus. It is not supposed to matter, but I know that it can. I like to have all circuits on the same phase and on adjacent spots on the bus inside the panel as high as possible.

I'm sure Larry and others can elaborate on why this matters.

If the amp still buzzes right off the panel, it can be something like a loose lamination on a transformer or a toroid that needs to be tightened down. Either way, it's a service issue at that point.

2nd Rick,

If it were a transformer issue wouldn't you think that the buzz would be there every single time I powered the amp on? Like I said in my post, on occasion the amp is dead silent.

Also, wouldn't my Denon 3805 which I am using as my Pre/Pro also buzz if it were the power coming into the the house.

If it is the power coming into the house what do you think it would cost to correct the problem? My house is fairly new. It was built in 1997.

In my area in UK the tolerance is +10% or -6% allowing a range from about 216v to 254v

I know this doesnt really help you!

Not necessarily, current draw does weird things with transformers. I have seen amps that are dead quiet until they are driven hard, and then they buzz and CONTINUE to buzz after the levels are brought back down...

Also, if you are only using the receiver as a pre-pro, you are only using that power supply at a fraction of it's capability so it may not freak out.


That means very little... A loose wire nut, a loose set screw on a breaker or on a bus bar, receptacles wired with the push-in terminals instead of the screw terminals, etc., etc... Time really has nothing to do with it.
If you have a friend that is handy with electricity, they could help you go down the list and double check the connections on your circuits.
(if you aren't comfortable poking around inside a service panel, shut off the main breaker and consider buying an insulated screwdriver)

It just may be that nothing you have plugged into that receptacle tried to draw as much current from that circuit until you used the amplifier.

Don't assume anything and just follow the normal procedure for isolating the possible causes.

I learned a long time ago that I don't need to understand every how or why a component acts odd when I am troubleshooting... I just need to know how to isolate the offender and get it out.

You will drive yourself crazy trying to speculate why this happened or trying to relate another components performance or whatever.

Also, voltage measurements are meaningless unless they are done under load.

What is the voltage drop (high vs. low) at full load with the HT cranked??

Seek out Larry Fine's email and send this thread to him. He should be able to think of something we haven't.


Or perhaps motorized devices, such as refrigerators or freezers, even at the neighbors' houses. They also use your local pole transformer.

If something is sucking power repeatedly at some particular phase of the 60 Hz cycle, it could deform the sine wave you should be getting. A deformed sine wave is a sine wave with overtones. Overtones can make a transformer sing when pure 60 Hz does not. A refrigerator would come on at random times of day and night.


Excellent troubleshooting.


Excellent logic, too. A ground loop is so unbelievably subtle compared to whatever would make a transformer sing!


If you have a power waveform problem, it will indeed be silent at their place. Hope that it sings.


That is a crap shoot -- even if you have a waveform problem, there is no sort of guarantee that any other amp will have a problem with it. If it does, well, then you definitely have a power problem!


I kind of doubt that it is the mounting bolt, but it could be. I did not know it, but get from your description that the power transformer is a toroid, which are less prone to singing than standard flat-plate transformers!


That voltage range is essentially rock steady. You have nothing to be concerned about there.


Yeah, you want to see if you can put the amp on the other phase of your power at a time when it sings. Actually, that makes me think -- if it is singing and you unplug it and reconnect it, does it reliably keep singing, shut up, or randomly sing? Please let us know....

Anyway, about the other phase. Let's say something is on one phase of your power line and is screwing up the waveform. The other phase might be fine.

On most power panels (again, I bow to Larry Fine if he has something to add), the odd numbered breakers are on one phase, the even on the other. It could also be that the breakers on the left are on one phase, those on the right, on the other phase. DANGER WILL ROBINSON: removing the cover from the panel and checking voltages can tell you which is which; email me for more details.

Anyway, if the amp sings on one phase but not on the other, you have effectively eliminated the amp as the problem.

Anywhere in this process, you could (risk your LIFE if you don't know what you are doing and) use an oscilloscope to look at the waveform of the 120 VAC. You should see a clean sine wave if the amp is not buzzing, and I am betting you will see a funky one if the amp is buzzing.

Yes. It is a toroidal transformer.

I have tried unplugging the amp while it was buzzing and then plugging it back in again. It still buzzes.

I also tried plugging the amp into a different outlet which is on a different breaker. Whether or not it's on the same of different phase I don't know.

One other odd thing.... Sometimes when I power on the amp and it goes through it's test phase and all 5 status lights come on momentarily it will Buzzzzzzzzzzz quite aggressively immediately after power on and then when the lights go off it still buzzes but not quite as loud.

Other times when you power it on the status lights will light and then go off and the amp will be dead silent for about 5 or 10 seconds. Then it starts to buzz gradually until it reaches it's peak. This usually takes about 10 to 15 seconds total before it reaches it's peak buzz. I suspect that this has something to do with Rotel's "current absorbers" which supposedly minimize turn on surges.

Of course when the amp is dead silent I never hear this "scaling/increasing" buzz at power on.

Well, it sounds like your amp is damaged....

Have you had any storm or surge damage to anything else in your house?? VCRs and alarm clocks are notorious for "taking the hit" on smaller surges, but sometimes bigger devices like amps sustain some damage as well.

Have you tried the service outlet on the panel with and w/o the RGPC??