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Audible transformer Hum

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Audible transformer Hum

Postby Jumpeyspyder » Fri Jul 13, 2018 12:00 am

Hi All,
I've just purchased a 80s vintage DDL rack from ebay at a very reasonable price - not a classic but has real knobs to twiddle and no menus!

Sadly, the power chord is missing insulation where it joins the back of the rack unit (probably, I can replace it without any fuss) but was not mentioned in description.

More worryingly there is an audible buzz when the unit is switched on (Not connected to anything - I'm assuming it's the mains transformer) and I can even feel vibration by touch through the rack case!

I've not pluged any audio through this thing yet (suspect it will be fine)

Should I be concerned about this?
is there a safe fix for old tranformers?

I'd like to hear some neutral opinions, thanks!
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Re: Audible transformer Hum

Postby James Perrett » Fri Jul 13, 2018 12:19 am

Is this a Digitech unit by any chance? I have one with a very loud transformer hum but it only happens when the metal cover is on. With the cover removed it is quiet. It looks like they tried to silence it by gluing some foam to the transformer but it doesn't really help.
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Re: Audible transformer Hum

Postby Jumpeyspyder » Fri Jul 13, 2018 12:36 am

Its an 8 bit peavey (low specs even for 80 s standards (prob more for live use than recording )

I've seen some stuff on 't' interweb about pouring superglue or shellac to stabilise a buzzy Transformer ?
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Re: Audible transformer Hum

Postby resistorman » Fri Jul 13, 2018 3:41 am

If the transformer isn't getting hot, then it may be just a noisy transformer... I've had a few in my life. Look for any signs of excessive current draw like overheated parts and circuit board discoloration.
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Re: Audible transformer Hum

Postby ef37a » Fri Jul 13, 2018 6:21 am

A great deal depends upon the type of construction of the transformer.

If it is fully encapsulated or a toroid there is little you can do but replace it. If of the 'thru-bolted frame' style then torqueing up the bolts should help (do this when the traff is hot but disse'd from mains of course!)

Many low power, sub around 20VA, traffs are of 'clamp' construction and the same principle applies, squeezing the laminations but these are trickier to do. I used to mash them in a BIG Mother engineer's vice but that can need another pair of hands if it is not practical to get the transformer out. Could try Mole Grips?

Do not use any old encapsulating gloop in there. Can be a way but get the right potting compound first.

Pictures?

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