Musical Fidelity A5.5 hum?

[Unklechukar]

I just bought the Musical Fidelity A5.5 integrated, and am really enjoying listening to it--with the extra power and dynamics compared to my old integrated (the Pathos Classic One). However, I couldn't help noticing an audible hum coming from the transformer area of the unit (front left corner). It is not loud (and not audible while music is playing), but it is audible during silences. Is this normal for this integrated, or is there something wrong with it? I have never heard a hum like this with any of my other gear before, and don't know what to make of it. I hear the hum either with, or without using a PS Audio Quintessense filter. I've tried different outlets in my house, and even disconneted (and unplugged) the CD player, as well as the speakers without affecting the hum. Am I being too sensitive, or should I send the unit back on warranty? Please, anyone who owns or has listened to this integrated, let me know your experience.--Unklechukar

[audio amateur]

Can you hear it at your listening position? How far away is the amp from it?

[Feanor]

I just bought the Musical Fidelity A5.5 integrated, and am really enjoying listening to it--with the extra power and dynamics compared to my old integrated (the Pathos Classic One). However, I couldn't help noticing an audible hum coming from the transformer area of the unit (front left corner). It is not loud (and not audible while music is playing), but it is audible during silences. Is this normal for this integrated, or is there something wrong with it? I have never heard a hum like this with any of my other gear before, and don't know what to make of it. I hear the hum either with, or without using a PS Audio Quintessense filter. I've tried different outlets in my house, and even disconneted (and unplugged) the CD player, as well as the speakers without affecting the hum. Am I being too sensitive, or should I send the unit back on warranty? Please, anyone who owns or has listened to this integrated, let me know your experience.--Unklechukar

There is probably nothing wrong with your MF A5.5. This definitely sounds like a ground loop -- I've had the problem myself. I'm not too technical myself but as I understand, it's caused by small voltage difference between the grounds that you components are "seeing" -- grounds are often not exactly zero volts as we might hope. And most types of signal purifiers simply don't work to block these ground loops. The good news is that moderate humming of the transformer is usually harmless to the component.

There are a few possible solutions:

• Put all your components on one ground, in effect, power them all from the same power outlet.
• "Lift" the ground on the humming component, i.e. remove the third prong on your power cord, but, N.B. contact the component manufacturer to see is this is safe -- some makers strongly insist that you must leave the ground intact.
• Get a power conditioner of the type specifically design to reduce hum. Generally these are "isolation transformers". If I'm not mistaken, PS makes one or two such devices.
• The hum might becoming through the interconnect cable rather than the power cord; in that case there are devices that can be put at one end of the interconnect that will reduce the hum.

But note that not of these solutions will necessarily work 100%; more often hum will be reduced rather than eliminated. Note too that, e.g., an isolation transformer might reduce the hum in your amp but hum quite loudly itself -- this was my experience when I tried such a device.

[Kevio]

A ground loop causes a hum to come out of the speakers. The hum here is coming directly out of the amplifier. Probably the build of the power transformer is not as tight as it should be. This is audio equipment not a microwave oven. Get it replaced. If the replacement also hums, return it and buy something else. This is not something you need to put up with.

[blackraven]

Sounds like a ground loop! If you have a very long extension cord, try connecting the amp to it and plug it into an outlet on the other side of the house to make sure its on a different circuit. The Hum should go away if its a ground loop. The key is that it must be on a different circuit from the other outlets and especially from the refrigerator outlet.

You might need to go with a different amp to fix this problem. I have a Parasound A21 which has a ground loop switch and circuit to eliminate this problem.

[topspeed]

According to the OP, Kevio is right, this is not a grounding problem. The hum is coming from the amp, not the speakers.

Call the manufacturer and see if this is normal. If it is within spec, try placing the amp on some tiptoes or isoplats and see if that helps. Otherwise, have it replaced.

[blackraven]

Oops, I didnt catch that the hum was coming from the amp. Your right, its should not be a ground loop. Take the amp back and try it in the store.

[Feanor]

A ground loop causes a hum to come out of the speakers. The hum here is coming directly out of the amplifier. Probably the build of the power transformer is not as tight as it should be. This is audio equipment not a microwave oven. Get it replaced. If the replacement also hums, return it and buy something else. This is not something you need to put up with.

I guess you'e the scientist. But I'm not sure the ground loop hum always results in hum throught the speakers.

In any case, lifting the ground is often recommended to remove transformer hum, for example, by Monarchy Audio in case their SM-70 Pro amps which I use. These amps definitely hum in my location unless I use "cheater", i.e. groundless, plugs.

Or some people have had satisfactory results stiffling hum by simply bolting down the transformer more tightly, or placing something like a denser rubbeer sheet between the transformer and the chassis.

[blackraven]

Here is some useful info- http://www.epanorama.net/documents/groundloop/

http://www.epanorama.net/documents/g...erhumming.html = other sources of hum besides ground loops

http://www.elo.utfsm.cl/~elo352/bibl...p%20basics.htm

http://www.chris-hofstede.nl/stories...age=ground.xml

[Unklechukar]

Thanks guys for your comments. I'm sure the hum is coming from the amp. It is barely audible at the listening position (about 6' away) during silences. It may be "normal" for this integrated, and really be no big deal--but i';m not sure. I will contact the manufacturer to see what they say.

[keepcoolmybabies]

Unklechukar,

I just bought the A5.5 and am having the same problem, although the hum my amp is producing might be a little louder. I can actually hear it from across the room. I've been told by a few people that there is probably an issue with the transformer. Are you contacting the importer (in New Jersey) or Musical Fidelity directly (in the UK)? Please post your findings.

Thank you.

[blackraven]

Sounds like wonderful quality control on MF's part!

[keepcoolmybabies]

No doubt, blackraven. Does anyone know if this is typical of Musical Fidelity?

[keepcoolmybabies]

Unklechukar, have you had any luck resolving the humming problem? Were you able to speak with the manufacturer? If so, what did they have to say about the issue? Did you figure out if the unit is defective or if this is just typical of their amplifiers?

[Glen B]

With two owners of the same amp reporting similar hum, it is possible that there coould be quality control problems with the product. At the same time, one possible culprit that I did not see anyone mention was DC offset on the AC power line. It could just be that the particular transformers used in the MF amps are susceptible to saturation from DC, even at a low level. I too am interested to know what the manufacturer has to say.

PS: Found a thread at HT Guide Forum on similar hum with the MF amp:

http://www.htguide.com/forum/showpos...&postcount=650

http://www.htguide.com/forum/showpos...&postcount=652

[markthis3]

I have the MF A5 and i have never experienced hum....it's really quiet. Previously
i had a Classe Cap 151 (a really good amp) and the person i sold to pointed
out the noise the Classe made. I never noticed it but the A5 is dead quiet and
i've been really pleased with it. Currently i'm pushing PBN Montana EPS2s
and a pair of Martin Logan Spires. The A5 matches very well with the
Montanas since it's a very detailed and lively amp. I think my old Classe
would have mated better with the Logans, but it's still a pretty good match.
The Classe is a little more subdued than the A5.....

[markthis3]

Correction....i do hear a slight hum from my A5....not from my listening
position but when i'm very close to the amp. No big deal as far as i'm
concerned.

I have the MF A5 and i have never experienced hum....it's really quiet. Previously
i had a Classe Cap 151 (a really good amp) and the person i sold to pointed
out the noise the Classe made. I never noticed it but the A5 is dead quiet and
i've been really pleased with it. Currently i'm pushing PBN Montana EPS2s
and a pair of Martin Logan Spires. The A5 matches very well with the
Montanas since it's a very detailed and lively amp. I think my old Classe
would have mated better with the Logans, but it's still a pretty good match.
The Classe is a little more subdued than the A5.....

[guanaco]

I had a similar problem some years ago with my Quad 707 Amp. It seems that the coil was not tightened enough and there had been a small rotation around the central nut during transportation. It took me some time to unscrew the nut/bolt, rotate the coil into several positions until the hum finally -almost- disappeard.

[Audionirvana]

Not a ground loop problem, as I just checked my A5.5 and I have no hum. So I would have it repaired or if it is new, then exchange it.

So far the sound differences between the A5 and A5.5 are different, also the volume control is more linear and it doesn't jump around as much when using the remote as the A5 did.

[lamont2769]

I've got a MF A5 that has the same humming trannie. It's not loose, checked that. Sometimes the intensity changes- gets louder, other times soft sounding. Doesn't effect the music and not related to the output. Of course when I bring it to the dealer or my mechanic it's quiet.... perhaps related to my other equipment? I never disconnected everything to see if it stopped. Right now it's in the shop getting checked for the trannie noise and some other mods. Maybe others with this problem can disconnect their equipment and speaker loads to see if it's quiet??? Any ideas for this annoying problem?

[Glen B]

I've got a MF A5 that has the same humming trannie. It's not loose, checked that. Sometimes the intensity changes- gets louder, other times soft sounding. Doesn't effect the music and not related to the output. Of course when I bring it to the dealer or my mechanic it's quiet.... perhaps related to my other equipment? I never disconnected everything to see if it stopped. Right now it's in the shop getting checked for the trannie noise and some other mods. Maybe others with this problem can disconnect their equipment and speaker loads to see if it's quiet??? Any ideas for this annoying problem?

As I mentioned in post #15 above, DC on the power line is a possible cause of mechanical hum, especially since the amp was quiet at the dealer. I have experienced transformer hum problems from DC myself and helped others cure the problem with simple, inexpensive DIY DC blockers. http://forum.audiogon.com/cgi-bin/fr...enflup&23&4#23 DC offset could come from inside your home or a neighbor's house that is fed from the same power company transformer. I have experienced both.

To isolate a possible source of DC, start by turning off every circuit in the house except the one your amp is plugged into. Make sure no other device but the amp is plugged into that circuit. If the amp still hums, it is possible the source of DC is from a neighbor's house. If all is quiet, turn on each breaker one at a time and see if you get any hum.

[lamont2769]

I think I've solved the noisey trannie. I noticed on their website that Musical Fidelity offered some upgrades to the A5. Looks good but I don't want to send the unit to England, so I found someone local to do the same mods and hopefully fix the hum from the trans. If you look at the list of upgrades MF offers some of them refer to the trans- "noise belly band on trans" & "realign power trans". The tech that did my work pulled the trans out and set it on some isloating material and isolated the hold-down nut also. He also put on a copper belly band and glued the windings. No noise for about a month now! He also did a list of other mods- I'm very happy.

[mr_macgee]

I bought a demo A5.5 in Feb.'10 that was never used.

I will first say that I have been very happy with the music coming out of this amp, it was very different sounding to my other amps but I just keep playing music more and more now with it and that's what it's all about. But don't get me started about the built-in usb dac sounding terrible compared to a decent outboard dac. That's for another thread.

The sound coming out of the amp comes and goes, at first it was very silent then after about a week of hard playing it began. It's quite loud for me as it's in my bedroom and I'm 11 feet away. When it happens in the evening I have to turn it off and I really hate that.

It doesn't always happen I could go a week or more with complete silent bliss or it happens every night for a week. Other wise it's very quiet.

It is the transformer physically making the noise. There's a couple reasons why it's making sounds. It could be a badly made transformer or the mounting & assembly is sub par and needs to be improved or both. (A toroidal transformer can sometimes create strong magnetic fields which will change the shape of the core, creating sound emitting from it).

Either way, the best thing is to isolate the existing transformer or replace it. I was not impressed with the craftsmanship to say the least when I looked inside. But it does sound very nice except when I'm sleeping.

Going through your house chasing the source of the problem triggering the noise could help but MF should have designed and assembled a better amp so it won't be so effected by bad electricity. I have had many good amps in my room that do not do this, not even close.