Hum coming from my amp

tcrossma

I have an intermittent hum coming from my amp. I've never had a ground-loop hum in any of my systems, but this is what I envisioned one of them to sound like. But the hum is coming from the amp itself and not the speakers.

The odd thing is that it'll disappear for days at a time, and then all of a sudden it might come back.

The amp is a Belles Reference 150A - 2 channel amp.

Is this a bad sign that there's something wrong with the amp?

george daniel

So the sound is coming from the amp? Not thru the speaks? Have you opened it up? That was'nt much help was it,, I'd call Belles,, the only time that I've called,,I spoke to David himself,, quite helpfull,actually,,good luck.

Early B.

Try a couple of simple things first, like switching cables (RCA and speaker and power cord) one at a time.

tcrossma

The sound is coming from the amp itself, yes. During these times there is a slight bit of extra hum coming from the speakers as well, but the amp is usually very quiet in terms of speaker hum.

I was wondering if it might be a power conditioning problem -- I don't have this on a dedicated circuit.

I'll try cables next time it happens, but the problem is that it's intermittent. If I shut the amp off, it probably will not have the hum when I power it up so it's difficult to diagnose since I can't unplug cables with it on (can I?).

I'll call if I have to, although I guess I just feel a little odd about calling for support on something that I bought used...

george daniel

I bought mine from an a'gon seller,,Mr. Belles supports his gear,,period--call .. Worst case senario,, you may have to send it in,,good luck.

TNRabbit

If it's humming, teach it the WORDS, man!!


Seriously, I have A Sunfire Signature amp that does the same thing; always has. No sonic effect, so I don't worry about it.

bikezappa

Are you saying that if the speakers are disconnected you hear a hum from the amp?

If so then something is not tight or fastened correctly in the amp. Try pushing on the amp cover or moving it to see if you can increase or decrease the hum.

tcrossma

I don't know if the hum occurs without the speakers connected or not, but the hum itself is definitely coming from the amp. It's not a "rattle" type of hum -- it sounds a lot like speaker hum, only louder. The hum does not change when I turn up the volume.

I'll try and diagnose it a bit more over the weekend and see if I can make heads or tails of it. Thanks guys.

Ricardo

Toroidal hum; you might have some DC in your AC. I had this, and the PS Adudio humbuster will kill it. They show up in Audiogon every now and then.

http://www.psaudio.com/products/humbustermoreinfo.asp

tcrossma

Thanks Ricardo. Would adding a dedicated AC outlet solve this? It's been on my "to-do" list for quite a long time anyway, so this might just be what it takes to get me moving on that project

Ricardo

tcrossma wrote: »

Thanks Ricardo. Would adding a dedicated AC outlet solve this? It's been on my "to-do" list for quite a long time anyway, so this might just be what it takes to get me moving on that project

It did not work for me, but it all depends on where the "noise" is coming from.

dracoskeeper

I would definitely run a dedicated circuit especially if you are not sure what else is on the same line. I had intermittent hums on both my old 2-channel system and my HT setup even when using the Panamax but once I ran dedicated 20 amp circuits (w/ground) and Hubbell outlets did a little cable management/separation all is quiet.

unc2701

Is the power transformer toroidal? or EI?

unc2701

Nevermind: toroidal. EI transformers have a bad habit of developing mechanical hum. Toroidal ones can do it, too, but not as frequently.

Anyhow, if it's actually coming from the unit, swaping IC, speaker cables and power cords isn't going to fix it (well, power cord, maybe, but the existing one would have to be REALLY bad).

I'd put money on the noise coming from the transformer- this can be caused by voltage fluctuations or just the transformer aging. Make sure that the bolt holding it in is nice & tight- put your hand on it and see if you can feel vibrations.

Ricardo

The Belles has a toroidal.

unc2701

Yeah, found that. I think Ricardo is right- DC on the AC line will saturate a toroidal & make it hum. The PS audio device will take care of it, or just google DC blocking circuit- it's a fairly simple circuit, just a little hairy since you're working with mains voltage.

ShinAce

unc2701 wrote: »

Yeah, found that. I think Ricardo is right- DC on the AC line will saturate a toroidal & make it hum. The PS audio device will take care of it, or just google DC blocking circuit- it's a fairly simple circuit, just a little hairy since you're working with mains voltage.

I was gonna add the same advice. Check the transformer in the amp.

tcrossma

Anything I need to be careful of when I open the amp up and check the transformer? Do these things hold onto power when they are unplugged or anything?

unc2701

The capacitors will hold power for a little while, but most designs will drain as long as you have your speakers hooked up... but the toroidal can still hum w/ DC voltage even if everything is tight.

DC blocking circuit and discussion here:
link

(note that he's feeding the output to a transformer to get balanced power as well)

HB27

Outside interference can also be a problem. I've got a DeWalt cordless drill/screwdriver that when it's charging it will give me a hum in my system. Not even on the same breaker but I'm sure the grounds are all tied together. Freaky thing I almost never caught. I was listening to music and changing batteries on the charger and the hum went away when I pulled one battery out and the hum came back when I installed the other battery back in the charger. It's the only cordless I have that does this. I've seen some weird problems.
Hope it's something simple for you instead of the amp

TNRabbit

Also realize that rheostat controls (dimmer switches) in your house is NOTORIOUSLY bad for causing hum like this.

lakesailor

I would first try plugging the amp into different locations in the house and see if the hum is consistent. Also you can try unplugging all other items on the same circuit to hear if this has any effect. Trial and error is usually the best way to find the cause. Once you know the cause it can be easier to find the solution.

tcrossma

I had been under the impression that other household devices (dimmer switches and whatnot) would cause hum through the speakers. I guess I never realized it could cause a hum in the device itself.

After reading some of the DC related posts in this thread it certainly seems that DC on the line can cause the transformer to hum inside the unit itself.

I don't think I'm too keen on spending $299 for that hum buster device. This weekend I'll try and narrow it down by switching outlets and/or circuits. It would help matters if the hum was consistent instead of coming and going like it does.

Thanks for all the replies guys.

unc2701

One last thing to try. It could be that the transformer's EM field is vibrating something in the case. Loosen the bolt on the tranny and slowly rotate the orientation of the transformer as much as the wires will allow & see if this impacts the noise. My money is on DC since it's intermittent, but you never know.

Face

It's not a true fix, but may quiet things down.
http://www.partsconnexion.com/catalog/dampingmaterials_isofeet.html
Last item on the page.

bikezappa

The hum sound like it's mechanical and the transformer is the problem as other have said.

Based on what you have told us it's not electric switches.

Open up the cover and wait for it to hum and carefully locate the hum by touch.

I like the idea of loose transformer bolts someone said.

tcrossma

bikezappa wrote: »

The hum sound like it's mechanical and the transformer is the problem as other have said.

Based on what you have told us it's not electric switches.

Open up the cover and wait for it to hum and carefully locate the hum by touch.

I like the idea of loose transformer bolts someone said.

Ok, I could do that. But is there anything dangerous to touch in there? I've never opened an amp before...

bikezappa

HB27 wrote: »

Outside interference can also be a problem. I've got a DeWalt cordless drill/screwdriver that when it's charging it will give me a hum in my system. Not even on the same breaker but I'm sure the grounds are all tied together. Freaky thing I almost never caught. I was listening to music and changing batteries on the charger and the hum went away when I pulled one battery out and the hum came back when I installed the other battery back in the charger. It's the only cordless I have that does this. I've seen some weird problems.
Hope it's something simple for you instead of the amp

Wow, Finally someone with the same problem.

I finally determined that my battery charging cordless drill was causing static interffernce with my FM tuner. I spend weeks trying to locate it.

I was shocked to find that unplugging the charger stopped the static ticking every 2 seconds on my tuner.

Solution was to just find a different location/plug for battery charger.

bikezappa

tcrossma wrote: »

Ok, I could do that. But is there anything dangerous to touch in there? I've never opened an amp before...

The safest way is to use a section of wood to push on the transformer and any other locations.

Do this while the amp is on and huming.