Hum question

[dcmo]

I just bought a new amp and now have a hum in my speakers, as well as the componets making an electrical (synthesizerish for a lack of descriptive words) sound when initially turning them on. I unhooked the dish cable and roof-top cable from their source, and unplugged the power cables from all the different componets (tv also) but the problem remains. One thing I didn't do is unplug the RCA cables from the amp, can I safely (for the amp and speakers) have these unplugged and still turn on the amp. Also is there any damage being done to anything in the time being because of this problem? Thanks for your help!

[Guest BobG]

You're not damaging anything, but the problem is annoying. You have a ground loop (I'll bet dollars to donuts). It's caused by the ground from either your satellite dish or TV antenna/cable. You likely have 3 prong AC cord on at least one of your system components which is providing another path to ground and this creates current flow on the ground side of your audio patch cords.

Do a search on this forum for "ground loop" or "hum problems". There are solutions. A ground isolator will do the trick. One kind for TV Cable and antenna and a second, different kind for your satellite dish.

[dcmo]

The thing is I disconnected the satellite cable from the satellite, the roof-top antenna cable from the antenna, and I also unplugged all the componets from the surge protector. What I can't remember is if the cables and power plugs were undone at the same time when I tested the amp. Also can I unplug the RCA cables from the amp, and then power it up with only the speaker wires connected to it or will this cause damage to the amp or speakers? Thanks.

[Guest BobG]

Take a reductionist approach to solving this problem. Start by connecting only the most basic parts of the system. Amp and speakers. Check for hum. If it's present then 99% it's a problem with the amp as speakers don't create any sound on thier own. Start without your surge suppressors.

Next, hook up a single source component; say the DVD player. Check for hum. Continue like this untill everything is connected. Hook up any device that has a ground or three prong AC cord LAST. This includes your TV Cable, Rooftop Antenna and Satellite Dish. Somewhere in your system you have multiple grounds and this is almost certainly the cause of your problem.

[dcmo]

When you say only have the amp and speakers connected, you do mean to have the RCA cables unconnected right. And when I do start hooking things back in, wouldn't the pre-pro (receiver in my case) be the first thing to put back in and then start putting back in the single source componets. Also what would cause the componets to make that electrical sounding sound when turning them on. Thanks.

[SCOOTERDOG]

Wow! I am going thru the same thing. It is a ground loop problem just like I am having. This weekend will attack the suspected problem and report back.

scooter

[D-MAN]

I have an amp that has a ground problem. The answer was a 2-prong adaptor at the wall outlet for the amp.

Now it's quiet as a mouse at idle.

DM

[Guest BobG]

Step 1 Connect power amp to speakers with speaker wire - check for hum

Step 2 Connect the Pre/Pro to the power amp via standard patch cord - check for hum

Step 3 Add a single source component via standard patch cord - check for hum

I don't have an explanation for the turn on noise you mention.

I do NOT suggest "cheater plugs" though they are expedient. They are also potentially dangerous. Good to test for ground loop as the cause of the problem but not worth leaving in permanently.

[SteelerFan]

I used to have a hum in my system I couldn't cure no what I tried until a forum member suggested I try some RCA to XLR cables between my preamp and amp. That finally did the trick.

[dcmo]

Okay, so this is what I did Bob. I disconnected the RCA cables from the amp, so only the speaker cables were attached. Then I unplugged all the other componets so that the only thing connected to the outlet (all componets were without power except for the sub which I forgot to unplug. It is plugged into another outlet which is on a different circuit, but was left connected into the receiver) was the amp which I bypassed the surge protector for and plugged directly into the outlet. I left the dish and roof-top cables alone, which I figured wouldn't hurt (disconnected them last night without any difference) as they were running into the satellite box which was without power. All this being said there is still a hum (at the same volume) without anything being connected, or any items (save the sub cable) near the amp with any power. So am I looking at the amp being the actual cause of the hum, or is it possible the hum is being picked up thru the electrical circuit, or is one of the componets (irregardless of it having any power) creating the problem just by being in the same vicinity. Thanks for your help.

[jpm]

Like D-man said. Try a 2 prong adaptor on the amp's 3 prong power cord.

[Guest BobG]

If you have hum with ONLY the power amp connected via speaker wire to your speakers, there is a problem with the amp. I don't see any list of components in your system, but if you are using high sensitivity speakers (like Klipschorns, La Scalas, Belles, Heresys, RF-7s) then you may be hearing the residual noise in your power amp. Rereading your initial post does not make me think that.

Go ahead and try a 3 to 2 prong adaptor but just as a test. If this does get rid of the hum, then I'd have the amp checked and also have the electrical circuit into which it's plugged checked. A power amp should not create audible hum when connected to a pair of speakers unless you place your ear very close to the speaker.

The only other suggestion I would make is to test this (amp connected Only to speakers) with shorted inputs on the amp. Do this by (with the amp off at first) plug in a pair of patch cords to the L and R inputs. Then (and this is a bit tough to explain) on the other end of that patch cord, kind of jam the L plug into the R plug by putting the center pin of one between the center pin and outer ring on the other. You could also do this by putting conductive material (aluminum foid, paper clip etc.) between the pin and ring on each L and R RCA connector. Then turn on the power amp and see if the hum is still there. What this does is eliminate any outside source of interference from being picked up by the power amp. I've seen a few very odd situations where radio frequency interference gets into a system and causes odd noises including hum.

Let us know the results of these tests. Sorry this is such a frustrating process but when you're done, it will have been worth it.

[dcmo]

So would Radio Shack be a good place to pick up a 3 to 2 prong? On the other test I don't have a designated L&R input, it is a 7 channel amplifier with the recommendation of using the center 3 inputs for the LRC channels. Would any 2 channels work for this test? My speakers are RF7's, RC7, RS7's, RSW15, and I am using D-9's as my back surround. Thanks.

[Gliderguy]

May I ask what Amp your are using? RMB 1095 by any chance? Oops, I see 7 channel, not a 1095.

How loud is your hum? How close do you need to be to hear it?

Is it 60Hz?

Can it be described as hiss?

Do you have the noise in every speaker?

Does it increase in volume when you turn your preamp up?

[dcmo]

The hum isn't too loud, but I can hear it at low level listening and quite clearly with no signal being input. I don't need to be close at all to hear it, all I have to do is be in my seating position which is 12 ft from the front speakers and about 10 from the back. The hum is definitely lower in frequency, although I don't know if it's 60 hz or not. It's not hiss, and is present in all speakers. The hum level is steady, increase in the volume control knob has no effect on it.

[Guest BobG]

Try any two speakers and any two channels of the amp for this test. I suggest Front Left and Right just because.

[dcmo]

Well I didn't even get the chance to try the 3 to 2 prong adaptor. I talked with Jerry with Gemstone, and he sent me a new one right out on the chance it is the amp. Guess we will find out whether it was the amp or the electrical circuit. I do have to say it was wonderful customer service on his and Gemstone's part. For those who wanted a write-up on the Gemstone, all I can say is be patient until I can get the new one in. My receiver (Pioneer VSX53TX which I am going to have to use as my pre-pro for quite some time as the kitty is dry now) has an EQ section (5 different frequencies cablibrated) on the automatic set-up, and my guess is the hum is being picked up when it is being ran. I don't know what kind of effect it is having, but it would seem to me it would have an effect somewhat (how great or small I don't know). Anyway my new amp should be here next week, so I might be able to post something on it next weekend. Keep in mind though I have no reference point to judge it against, having never heard any of the better amps (other than my receiver and I would hardly rank that in there).

[Bret_Salyer]

So, did you resolve your problem?

[dcmo]

Yes the probelm has been resolved. Jerry from Gemstone sent me out a new one, which upon hooking up showed no signs of a hum. He said the previous amp probably hadn't traveled very well, and it cost me nothing to send the other one back. I'm still not ready to write (or attempt to write) what I think about the Gemstone, I really need to AB (it's a good thing I have banana plugs on it now, or ABing it would never happen) it against what is unfortunately only a receiver but that is all I have to compare it against. I will say it sounds great, the surround has never been better, and the volume is sweet.

[Guest BobG]

Seems like I failed to think of the most likely cause of your problem - a defective component. In any case, thanks for letting us know the hum is gone. Give us a report on the sound of the amp once you've had a while to listen.