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Old 15th Sep 2020, 5:52 pm   #1
RobustReviews
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Default NAD 3020 Chassis Buzz

Hello all,

I have a beloved NAD 3020 (original 80s model) with a tremendous buzz coming from the transformer. There's negligible (about 1-2mV)DC component across the secondary (or the primary for that matter) and I've moved it between two homes as well as my office and the symptoms are identical so I'm satisfied it's not mains referred.

I recently serviced the unit and all relevant electrolytic caps were replaced as well as a full scheme of tweaks etc, none of which had any impact on the buzz. The rectifier diodes were also checked and nothing was found untoward.

I'm pained to dispose of it as it was the pride-and-joy of a late friend and it serves musically perfectly, every day but the buzz is just getting worse and worse.

Potential diagnostic factor is that the buzz gets worse the longer the unit is on, starting faintly and turning in to a din noticeable above the music after an hour or two. For clarity this isn't being imposed on to the output signal, it's the physical amplifier casing buzzing.

Before I just isolate the transformer from the chassis with blocks of rubber, any suggestions of components that could be breaking down? I'm no expert here.

Cheers,RR
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Old 15th Sep 2020, 6:49 pm   #2
Craig Sawyers
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Default Re: NAD 3020 Chassis Buzz

Buzzing transformers are more common than you might think. Caused by loose windings mainly, although core magnetostriction plays a role. I have a fan cooled 600WPC professional power amp with a monster toroid - that buzzes like a hornet.

And the Quad 405 had such a problem with buzzing mains transformers that they replaced them free of charge.

Even high end amps suffer from this. At one stage I had an Audio Research valved power amp. I put it on the bottom shelf of the rack, because it was a hernia weight. I was then tormented by a hum from my record deck - but only when the stylus was on the record. The mains transformer in the amp was vibrating the entire rack.

You could have the transformer re-wound. There is someone on this forum that offers that service. Or it may be that the existing transformer could be vacuum impregnated with varnish to shut it up.

The NAD 3020 is a classic, very well thought of at the time, and well worth saving.

Good luck!

Craig
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Old 15th Sep 2020, 6:55 pm   #3
Bazz4CQJ
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Default Re: NAD 3020 Chassis Buzz

I've owned a 3020 since the mid-1980's and that too is beloved! Although there have been threads about NAD units on here from time to time, I certainly don't recall anything like this. I've never had the covers off mine.

Any chance you could post a picture of the transformer and its surroundings? Have you noticed how warm / hot the transformer runs?

B
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Old 15th Sep 2020, 7:20 pm   #4
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Default Re: NAD 3020 Chassis Buzz

I've come across one 3020 that had some buzzing from the transformer, but it was largely just mechanical. Tightening the mounting bolts, and fitting some new rubber feet to the amp, instead of the age hardened plastic originals, entirely resolved it.

In the worst case, depending upon which exact version of the 3020 you have, I may have a spare transformer available from a parts unit I bought a couple of years ago.

Alan
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Old 15th Sep 2020, 7:30 pm   #5
GrimJosef
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Default Re: NAD 3020 Chassis Buzz

Mechanically isolating the transformer can help. There is a well-known buzzing issue with the mains transformer in the legendary Dynaco Stereo70 for example (worse in the UK because the transformer was designed for 60Hz) and the people who currently supply Stereo70 spares actually have an isolation mounting kit as a stock item ! If it were an EI transformer then you could also try tightening the lamination clamp bolts. But it isn't.

As it happens I've had a customer here this afternoon to listen to buzz from a pair of amps which have had after-market outboard HT supplies fitted (he bought them, I wired them up). He's taken the system away, content that he can barely hear any buzz. But I could name other customers who would be sucking their teeth over it.

As well as isolating the transformer you could also look at damping the chassis (high-Q resonators can seriously raise volume levels - ask any songbird ). I had to apply a fair amount of SilentCoat deadening mat https://www.silentcoat.co.uk/collections/silent-coat to the lid of one of my customer's power supplies to quieten it. It's not super-cheap. But it is a purpose-designed product for this application. In my experience so far it sticks like the proverbial poo-to-a-blanket, and it's designed to stay stuck close(ish) to hot car exhausts, so it can be used in warm places. That said, one face is aluminium foil-clad so it needs to be reliable if it is hanging above high-voltage electronics.

Cheers,

GJ
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Old 15th Sep 2020, 8:02 pm   #6
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Default Re: NAD 3020 Chassis Buzz

Do a search for "nad 3020 transformer buzz" to see that this problem is not unique.

This one identifies loose laminations as the cause of buzz, getting worse as the unit warms up, with photos https://audiokarma.org/forums/index....treads.781582/

I'm sure Ed Dinning could wind one for you that would not buzz. Or buy a cheap junker 3020 and swap transformers - and hope that the replacement one scavenged doesn't have the same problem.

Craig
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Old 15th Sep 2020, 8:10 pm   #7
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Default Re: NAD 3020 Chassis Buzz

Did I say cheap junker? Just checked sold auctions on eBay for the 3020 - anything up to £320, with most in the £80 to £150 bracket.

Yeesh!

Craig
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Old 16th Sep 2020, 7:45 pm   #8
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Default Re: NAD 3020 Chassis Buzz

Cheers all.

I expect delamination having read the symptoms.

Unfortunately the dynasty of the ex-wife and family is very much that of the custom, low-volume transformer business but.... well... I'm "not on the Christmas card list."

I believe (hazy memories) that something akin to yacht varnish was used for dipping transformers at their factory but we're going back a few years now.
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Old 16th Sep 2020, 8:38 pm   #9
Michael.N.
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Default Re: NAD 3020 Chassis Buzz

A while ago I came across some guy on Utube who had a radio transformer that was buzzing excessively. The layers had delaminated somewhat. I think he used glue and some G clamps. Don't know which glue. Maybe superglue? - if it can tolerate the heat/warmth that the transformer reaches. It's certainly thin enough to get between laminations.
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Old 16th Sep 2020, 8:42 pm   #10
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Default Re: NAD 3020 Chassis Buzz

This guy

https://www.youtube.com/watch?v=dtOwewfqucI
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