NAD 3020 Transformer issue ( I did read alot of old treads )

[CHR]

Hey

I got a second hand NAD 3020 A from the Danish version of ebay, my plan was a full recap. Before i did the recap i plug it in, and the transformer was humming - I was going to do a full recap so I thought that it might help with humming.

After a full recap the amp sounds very nice, but the humming is still there! so i go and do some more online reading, and someone that suggested that the Diode bridges might be the source of the problem. But after I replaced the Diode bridges the humm is still there.

Then i read that tightening the mounting screws could resolve the issue - but i did not.

The humm / Buzz gets louder when the unit have played for 1 or 2 h.

Is this just the sound of an tranformer getting old ? or can anyone think of another reason?

If this it just the transformer can someone tell me what values VA and V i need? i know i will need to transformer to replace the dual transformer.

I hope someone can help me I love the 3020 but this hummm i driving me crazy! thanks in advance

 

[GrundigXpert]

If it is actually a mechanical vibration of the transformer (i.e. the hum does not come from the outputs), as a last chance I would try an old trick from the tube radio era: removing the transformer and sinking it in a can of transparent paint, like the paint that's used for boat wood. Hold it by the wires, let it dry for a couple of days, then sink it again. Before refitting, don't forget to remove the paint on the bottom around the screw holes, where it touches the chassis.

 

[CHR]

Ok... that is new one to me. Yes it is a mechanical vibration of the transformer there is no humm on the speakers. Will it work when the transformer is enclosed in metal ?

 

[GrundigXpert]

Ok... that is new one to me. Yes it is a mechanical vibration of the transformer there is no humm on the speakers. Will it work when the transformer is enclosed in metal ?

As the vibration is coming from the core, yes I would remove or at least open the 2 metal covers before the immersion.

 

[Goldie99]

I think you might struggle to get a suitable resin into the laminations of a NAD transformer, at least not without quite some deconstruction first.....

A couple of things that might possibly improve the situation:

Try to 'isolate' the transformer vibration from the chassis, I've used thin rubber washers on the mounting bolts before, and/or a thin sheet of rubber type material between the transformer & the chassis, to isolate the vibration, not the electrical contact.

Alternatively, and strange as it may seem, fitting a new set of feet to the amp could also help - the originals tend to get quite hard with age, and again transmit vibration very well. I had a somewhat similar problem last year, until I noticed the humming almost vanished if I lifted the amp off the rack... a new set of feet reduced the audible hum to an 'acceptable' level.

Neither option really addresses the problem 'at source', but they may be enough for now.

 

[62vauxhall]

Get another transformer? Considering the number of 3020's made, somebody parting one out can't be too uncommon.

 

[CHR]

Thanks for the tips that can to reduce the sound. But i will like to "solve" the problem by replace the transformer with a two new transformers. The problem is that the values of the output from the transformer, is not listet in the service manual. Does anyone know ?

 

[gasolin75]

Hej CHR nu skal du bare høre hvad jeg har fået at vide fra ARS i UK (response from ARS in UK)

I suspect that the hum you are hearing is being produced from the transformer/amplifier casing and not being heard as hum through the speakers with the audio? If so I'm afraid there is little that can be done as it is caused by the transformer windings resonating and being made more audible by the way the transformer is mounted and not due to any fault.

These amplifiers although of a very good electronic design were a low cost mechanical design which makes this problem worse in some examples. You might be able to reduce it by varying the tension of the mounting screws or even using thin rubber mounting pads between the transformer body and chassis but other than that there is nothing that can be done I'm afraid.

 

[avionic]

it is caused by the transformer windings resonating

Nej. It is loose laminations in the transformers iron core that are vibrating.

 

[Latvis]

Same here. This is a common problem. No wonder -no bolts!!!