WDKEL84 Transformer Hum

[Chivvyp]

Hi,

Finally sorted out the various build problems that I had (thanks WAD for the replacement valve) and spent the weekend listening.

Sound quality is fine with minimal hum through the speakers but there's an annoying mechanical hum from the mains transformer which is quite obtrusive during quiet passages in the music (I'm sat about 3 m from the amp).

This is my first valve amp so I'm not sure if this is this a fault / problem that can be fixed or is it something that you have to learn to live with with these amps.

Regards

Pete

[Cobblers]

Kel84 is apparently a low hum design. I do not know whether this applies to the literal mechanical transformer hum or just lack of noise fed back through speakers.

The audible mechanical transformer hum is the most significant weakness of most good tube amp's I feel.

I have never heard hum through the speakers with any of the valve amp's I have used, and frankly if this required my ear to be at the speaker it would not bother me in the least.

Listeners lucky enough to have large to medium size rooms never have to suffer this, or even realise it is there. Certainly it should not be a problem for them (their only problem is having speakers good enough and sensitive enough to drive a large room, especially at high volumes).

Probably your best bet is to try different placement for the amp within the room. This can make a considerable difference, just as placement of the speakers can bolster certain frequencies. Light weight resonant surfaces cannot help either.

Rubber grommet mountings etc for the mains transformer do not work. I suspect you would need a very much more expensive design with careful design of transformer laminations etc to eradicate most of this.

Your kel84 is a modern quality design with small but quality transformers, I expect it is one of the quietest designs out there.

If on the other hand the amp is making a real din (motorboating) this would a fault within the amp.

[Chivvyp]

Hi,

Certainly not motorboarding, just a permanent Hum / Buzz from the transformer. You can feel an accompanying vibration with a finger on the cover.

The tx is mounted on rubber grommets. Should the bolts be screwed down tight or loosely, does it make any difference to the noise?

Regards

Pete

[Cobblers]

The TX rubber grommets should be there, but they don't eliminate noise within the transformer itself, merely reduce resonances in the chassis .

Tightening the bolts could tune the resonance to your taste i.e least offensive. They should not be loose, that's for sure.

I do not think you should be able to feel the vibration.

[systemx]

When you assembled the amp, did you remember to put the white "top hat" inserts into the mains transformer gromets? they prevent the rubber from being over compressed and are inserted from the top of the chassis.

[Chivvyp]

I definately fitted them. Not sure from memory if I put them in from the top or the bottom. I'll have to check tonight.

Regards

Pete

[Mark]

Hi Chivvyp,

I have a KEL84 and I can only hear the Mains TX hum with my ear 2-3 inchs from it. Yours shouldn't be making that much noise !

Systemx is right - the nylon inserts are to stop the rubber grommets being over-compressed. However, I took mine out in a microphony hunt (don't ask !) and never got round to putting them back,and I've never noticed the difference.

Did you remember to earth one of the TX bolts. It won't stop mechanical hum, but it might reduce electrical hum (but it might only be a safety earth).

Edit : Just read your post again and thought about it some more. Try loosening the TX bolts, but make sure there is enough thread in the nuts before you turn the amp over to stop the TX falling out. Also try waggling or tapping the TAX gently in-situ - re-aligning it slightly may break the path of the energy from the TX to the chassis.

Regards

Mark

[Phil Y]

Hello Pete,
I have an 'old' KEL84 which buzzed quite badly when new but mounting the transformer on rubber grommets (the TX was mounted hard to chassis originally which acts like a sound board) shut it up almost completely. If your amp is a new one it has a bigger(quieter) transformer and the mounting kit which were introduced to cure this once quite common problem with the KEL84. If your TX is mounted correctly it sounds like you may have a noisy one. Mine can only be heard if you are within about 15cm in a quiet room. If it does turn out to be a TX problem i'm sure WD will exchange it for you.

Regards, Phil.

[Chivvyp]

Hi,

The top hat inserts are fitted correctly from the top through the grommets. I loosened the bolts and gave it all a jiggle and retightened. Still getting the buzz from the transformer (not from the speakers) so I don't think it's the way it was sitting on the case.

Not sure if it's relevant but I noticed that the hum only starts when the led changes from green to orange. I guess that means it's the HT circuit that's the cause of the problem? And it's only when under load?

Regards

Pete

[systemx]

Yes sounds like a doggy mains transformer. Have a word with WD and see if they will send a replacement.