Transformer Hum - Musical Fidelity 3.2

[ScooterMcTav]

Hello all,

New and unexciting development this evening.

When turning on my Musical Fidelity a3.2 this evening, I noticed an audible hum from the transformer. In the past, this unit has had no audible hum.

So, unplug inputs one by one, still hum. Remove speakers, still hum. Plug into single outlet dedicated socket, still hum.

Arrrgh!

I have a sneaking suspicion that the general response will be “take it to the shop”, though I don’t know anybody around here who even services MF!

Arrrgh!

Any ideas, or similar experiences?

 

[mbz]

Don't know MF anything. Only basic transformer knowledge.

The hum or closer to a buzz from a transformer usually indicates it's
working a bit harder or a breakdown of insulation between the laminates
You should do a basic health check on bias and dc offset. I assume the
amp is original or recapped to original specs, some people overdo the
main filters caps which put additional strain on transformer, rectifier,,,
If you have a DBT you could try and power it up on that to see if the bulb
remains bright.

Basically cause may be a larger current draw/early stages of failure or a
tired transformer, some try a dipping technique, I'll let them explain.

 

[Audi0]

Quick Google show 2 transformers. They both humming the same???

 

[Freddymac2]

I think you are wise to pursue this, I had a nice Tensor lamp on my TT, that started to hum more than usual and I just ignored it..... POOF!

 

[ScooterMcTav]

Yes Audi0, it does have the dual toroidal transformers, fed from the single power line.

I think I will need to plug it back in and try to listen if it is one side or the other.

mbz, this piece was introduced in 2003, so this particular set will have a max of 15 years on it, if not a few less. Odds are it hasn't been recapped, but then again, its caps should still be OK for its age (unless there was a defective one). Mind you, I could send it to MF in England for a refurb, but that will set me back the cost of replacing it.

But yes, there must be something putting additional strain on the transformers, and I did not check the DC offset. I bias my Jolida tube amp, but have never adjusted bias on a SS amp before.

Getting in touch with MF's Canadian distributor, they will look at it for $45, though with its weight, I'm looking at probably $100 round trip for it.

 

[mbz]

A 2003 amp should not need recapping. The bias and dc offset is more to get an idea of general health rather than point to root cause.
Do you have a service manual? I'd be surprised if the transformer was on the way out, again a 2003 amp. Maybe open it up and have a look
for any heat stressed resistors (power off/unplug). Options to remove some fuses or use freeze spray on some transistors to help identify the
path, need sm first to assess impact of taking that part "out of service"

 

[ScooterMcTav]

Well, strange things afoot.

I thought I would check dc offset, and then try throwing breakers in the house to see if any other circuits were introducing DC to the line.

Turn the integrated on, and dead silence. Zero hum. Just like it had been.

Check DC offset - not perfect but within tolerances (39 and 17 mv). So hook it back up and everything sounds great....and still no hum.

I am now somewhat curious as to if the unit had become a touch warm yesterday, and it had caused the hum. Or was there something semi conductive that had fallen into the unit, and the act of removing it, putting it in the basement, and bringing it back up knocked it loose.

But in good news I did find a local repair shop that is familiar with MF, and has reasonable rates.