Transformer hum

[andy]

I have an Audio Analogue Donizetti power amp and am getting a loud hum from the transformer. Very anoying when listening to a quite LP.

It is deffinately the transformer as i still get the hum when the pre amp and speakers are not connected.

The amp is sitting on spikes onto a slab of granite and my hi-fi has its own ring main so it is pretty well isolated from everything else.

Any ideas would be greatfully appreciated in resolving this sodding hum.....

thanks

[PinkFloyd]

Aug 5, 2009 21:25:56 GMT andy said:

I have an Audio Analogue Donizetti power amp and am getting a loud hum from the transformer. Very anoying when listening to a quite LP.

It is deffinately the transformer as i still get the hum when the pre amp and speakers are not connected.

The amp is sitting on spikes onto a slab of granite and my hi-fi has its own ring main so it is pretty well isolated from everything else.

Any ideas would be greatfully appreciated in resolving this sodding hum.....

thanks

Move it as far away from partnering equipment as possible... if this doesn't help you could remove the transformer, soak it in a bath of varnish for 48 hours then dry in a low bake oven for a couple of days.... that should cure the mechanical "buzz".

[andy]

Hi Pinky,
I have the amp as far away as i can from the pre-amp etc already.

Must admit that i had not thought of the varnish idea, i guess this helps to fill gaps in the windings?

[PinkFloyd]

Aug 6, 2009 9:08:12 GMT andy said:

i guess this helps to fill gaps in the windings?

Correct. yarchive.net/electr/60hz_noise.html

I'm sure there's a lot more about varnishing on the net, have a search.... it DOES work

[Deleted]

If you are spacing the equipment to avoid hum, remember the tranformers ( there's 2 of them, so plenty of varnish needed! ) are evenly spaced at the front of the amp.

[Deleted]

cjarchez said:

If you are spacing the equipment to avoid hum, remember the tranformers ( there's 2 of them, so plenty of varnish needed! ) are evenly spaced at the front of the amp.

You can't varnish toroidal transformers. First look for some mechanical reason like poor/loose mounting, or a steel top cover too close to the top of them.

SandyK

[robertkd]

Aug 6, 2009 12:39:25 GMT @cjarchez said:

If you are spacing the equipment to avoid hum, remember the tranformers ( there's 2 of them, so plenty of varnish needed! ) are evenly spaced at the front of the amp.

sorry but this is a classic example of dumb arse design

what idiot designed this ??

[PinkFloyd]

Aug 6, 2009 12:55:57 GMT @sandyk said:

cjarchez said:

If you are spacing the equipment to avoid hum, remember the tranformers ( there's 2 of them, so plenty of varnish needed! ) are evenly spaced at the front of the amp.

You can't varnish toroidal transformers. First look for some mechanical reason like poor/loose mounting, or a steel top cover too close to the top of them.

SandyK

I'm sorry, I didn't realise they were toroidals

[Deleted]

You may wish to give Nick at UKD a call to see if he has any experience of the fault. If you have the version in the photo he would have been the UK distributor for it.

I think I'm correct in saying he no longer distributes them (certainly not shown in his current web portfolio) and I have no idea who does now. However, he's a freindly and helpful guy so I'm sure if he has any insight he'll be willing to share.

[andy]

Sorry, deffinately torodial. will lift the lid and upload a photo later, i think the photo above is a much newer version than i have.

now where did i leave the camera?

[PinkFloyd]

sorry but this is a classic example of dumb arse design

what idiot designed this ??

Looks a bit arse over tit doesn't it? One would assume the logical approach would be to site the toroidals as close to the IEC inlet as possible.... not a mile away from it

[andy]

Right i have photos but cannot see how to load then to this forum, any help?

The base of the amp is as dead sounding as can be, the top plate rings a bit though so i have some sound deadening stuff and a granite slab to help that.

The transformers are mounted on a rubber pad with another rubber pad on top with the metal plate. The transformers are a little loose, i can turn them without to much effort, so i may need to tighten them up a bit.

[andy]

My version of the amp has the transformers at the front the same as the pic above but has a separate pcb along the left side that has fuses switch etc on it, this keeps the amps separate from the power IEC.

[Deleted]

While you suss how to upload piccys here's the other versions of the original Donizetti.





PS Link to uploading photos explanation
rockgrotto.proboards.com/index.cgi?board=q&action=display&thread=2184&page=1#22565

[andy]

i appear to have a hybrid of those two, i have the power board from the lower larger pic and the transformers from the smaller top pic.

[andy]

Right, decided to have a chat with my neighbor and got some 'O' ring rubber washers. Re-seated the torodial's with new washers and added some dynamat deadening to the chassis.
All is sounding a whole lot better, i realise that the hum will never go, but it is very nearly gone.

Also tweeked the torodial on the pre-amp as well and added a load of dynamat to the lid as it rung like a bell, popped a granite tile to the top to finish it off.

Chris Rea now sounds great again!

[jonclancy]

Agree with the trafo damping. I have some toroids that are really quiet, but still faintly hum when I had them on a wooden board for testing. A cocktail stick under one side cured that, but compliant damping is the way to go IMO.

Nice one, Andy!

Jon

[PinkFloyd]

I don't see any reason "why" you can't dip a toroid in a varnish bath for a few days.... strip off the polythene, dip the toroid in a bath, dry in a low bake oven for a few days, re-wrap with some insulating tape...... etc.

[Deleted]

Aug 7, 2009 22:23:02 GMT PinkFloyd said:

I don't see any reason "why" you can't dip a toroid in a varnish bath for a few days.... strip off the polythene, dip the toroid in a bath, dry in a low bake oven for a few days, re-wrap with some insulating tape...... etc.

What sort of temperature can the insulation on the captive primary and secondary tails withstand? (in the oven)

[PinkFloyd]

Aug 7, 2009 22:43:19 GMT @cjarchez said:

Aug 7, 2009 22:23:02 GMT PinkFloyd said:

I don't see any reason "why" you can't dip a toroid in a varnish bath for a few days.... strip off the polythene, dip the toroid in a bath, dry in a low bake oven for a few days, re-wrap with some insulating tape...... etc.

What sort of temperature can the insulation on the captive primary and secondary tails withstand? (in the oven)

"low bake".... you are looking to set the oven to around 60C - 70C or thereabouts ;D.... the "tails" should be able to withstand that

[Deleted]

Aug 7, 2009 22:23:02 GMT PinkFloyd said:

I don't see any reason "why" you can't dip a toroid in a varnish bath for a few days.... strip off the polythene, dip the toroid in a bath, dry in a low bake oven for a few days, re-wrap with some insulating tape...... etc.

Mike
Of course it's doable, if you know what you are doing, but it's not something for the faint hearted, and if not done properly could result in a damaged transformer.
Are you going to post a pictorial on how to do it properly ?
Alex

[andy]

It does look as though the transformers have already been dipped as the braided output cables have got a lot of varnish on adn are 'painted' into the braid.
I dont know many transformer makers that would braid the output cables and then dip everything.

[rickcr42]

there is a damn good chance you are looking in the wrong direction for the cause-mechanical-because this sounds like a classic case of "DC" on the AC Mains line which would cause the very "buzzing" you describe.

The process is simple.Once you have eliminated one set of possibles,mechanical buzz,via physical isolation methods such as rubber grommets between the chassis and the trafos yet the problem is still there then you need to eliminate a DC voltage rider as the culprit by adding a "DC Blocker" at the mains inlet (do a google using terms such as "DC on AC","DC Blocker".Etc )

[andy]

just seen this Rick,
I live in the country, so the mains is quite clean-ish. The amp is on its own spur from the fuse board as well, it is only my hi-fi that is on this cable.
I use a slightly filtered 6way mains cable as well.

will check google tonight, thanks

Andy

[PinkFloyd]

My latest batch of Pinkie transformers have been "dipped" in a varnish "bath"..... they used to spray them with varnish but there was still a bit of "buzz" as the varnish hadn't fully penetrated the laminations..... I haven't heard them yet (they are delayed due to the "snow") but am assured the varnish "dip" has made them TOTALLY silent