Musical Fidelity a5.5

Hi...
Ive just purchased an MF a5.5 amplifier and love the sound ,however there's a rather loud humming from the rear left of the unit where the power lead is fixed.The hum can be heard from my sitting position which is about 8 ft away from the amp.The pitch of the hum changes frequently and it can get quite annoying in a quiet room.Is this normal for this amplifier?.I wanted this to replace a primare i30 which just didn't gel with the speakers as i would have liked.The MF is much more to my liking musically with my speakers but the hum is spoiling the "party" quite a bit for me.The hum is there even when there's nothing connected to the amp.Ive also tried plugging the amp in different power points with same result.This is the only amp ive had that makes such a racket.Is this down to poor quality internals somewhere ,or have i just got a dud?.The Hifi dealer said they would take it back and compare it to another ,but after searching hifi forums i see that others have complained about the hum in the a5.5.Im not sure what to do at this point.I know there are some MF experienced people here so maybe they can shed some light on this issue?
thanks in advance
ellison

 

p.m. me
nando

 

Hi Ellison,

If if it is new, take it back to the dealer and either;

a) Get it fixed
b) Swap it for a new one or
c) Get your money back.

By law these are your consumer right if something doesn't work as intended.


SCIDB

 

Thanks both for replies.Theres a two year guaranteee on it so im not unduly worried.Im going to leave it for a few weeks then reevaluate if the hum is going to be a problem.
ellison

 

good to talk to you, hope i helped,
regards nando.

 

Hi nando..
Yes..thank you for your help.Bartletts have arranged to pick it up on monday so that was nice and quick.Back to the primare for a few weeks i guess
ellison

 

If its obviously wrong I wouldn't delay too long.

 

After a few weeks Ive just recieved the MF a5.5 back.Musical fidelity says the amp noise is within spec and they cant find anything wrong with it and Bartletts hifi say the same.However plugging it in at home once again results in a mains/earth type sounding noise that alters pitch and loudness.Note this is from the amp and not the speakers.I can hear this noise quite loudly 8ft away.Ive turned off every other electrical thing in the house and still get it.Ive tried different mains leads and still the noise is present.No other hifi equipment in my home makes any such noise.A friends has suggested using a ferrite ring on the mains lead.Does anyone have any experience of these and whether they would help?.
tia
ellison

 

I have installed 2 Earth Spikes in my garden then attached one to the chassis of my hifi gear and one to the mains earth of my feed socket. This has helped a great deal with my amp buzz. Might be an idea for you.

http://www.russandrews.com/article-8.-Poor-Noisy-Earth-pgearth.htm

 

Hi Chris..
I havent tried that yet because i assumed that was for earth loop hum that would be heard through the speakers.The amp makes the hum noise without anything connected to it at all.The noise also changes frequency and seems to get louder and quieter.Either MF and Bartletts are deaf or theres something wrong with my mains or theres some sort of interference (radio?) that the A5.5 is picking up but my other hifi equipment (amps included) are not.
ellison

 

maybe i think you got an earth loop,
nando.

 

Hi nando..
Im not sure.The g/f plugged a hair dryer in upstairs and thats affecting the amp too.The hum/hiss gets considerably louder from the amp (not the speakers).The tone of the hum/hiss changes all the time and also the volume of the hum/hiss.Is that earth loop or radio interference?
ellison

 

you have a problem with your mains i thinks!
nando.

 

That had occured to me however ,i have a primare i30 ,a rotel ra1062,an arcam dvd player,a nad tuner ,a sansui tuner ,2 CA cd players ,a humax pvr ,2 tvs ,plus all the normal kitchen appliances and none of them produce any noise or hum (even when the hairdryers on) except the A5.5 ,so my logic leads me to believe that the A5.5 is not shielded adequatley somehow.A friend of the family suggested using ferrite clamps on the mains lead.Have you had any experience of using these nando?
tia
ellison

 

Can you take the amp round to someone else's house to see if it still makes the sound on their mains?

 

Hi..
Yes i took it over my parents house ,and tried it and its still the same.My sister and brother in law happened to be there on a short visit ,and the brother in law who has some experience in electronics reckons its the transformer and he doesnt think a ferrite ring would help much with the hum and change of frequency of the hum.He said without comparing it with another a5.5 its hard to tell whether they are all like that.In any case ,i think ill ring MF and ask them if they actually tested the transformer or just put their ear to it.
ellison