Bolder Cable Co ELPAC Power Supply - Transformer Hum

msg · January 2023

I picked up this Bolder Cable Company modded ELPAC power supply from a member years ago that turned out to have a hum that's easily audible while listening.

I could find some way to hide/minimize it, but it's annoying, and I thought I'd take a look and see if there was anything going on inside potentially causing the hum. Nothing obvious jumps out.

@VR3 - can we talk about upgrading these caps to an external chassis or backpack?
I want to backpack everything.

So, you guys can see this wimpy little piece of foam on top of the transformer.

Question - maybe @SCompRacer, @ALL212, @mhardy6647 or anyone else: would it be unsafe to use a piece of Dynamat here? Was thinking that might draw down the hum.

What i really meant to ask though - duh - is what's the deal with transformer hum? Is it normal? Indicative of a problem?

Any testing I should be looking into?

I've tried this on several different circuits and also plugged into a PS Audio Humbuster that *completely* silenced the mechanical hum on a sub and an integrated amp. No effect on this.

msg · January 2023

heiney9 · January 2023

I had one of those when I got my first Squeezebox. I got lucky as mine didn't hum too loudly. My hum was the unit and it never came through the speakers. They were known to hum as various levels, but I don't recall them humming through the speakers. It made a noticeable difference in SQB performance.

To be clear mine wasn't modded by Boulder as far as I know. Maybe do a Google search, something's bound to come up in one of the various audio forums I would think. Or maybe look for a generic discussion about audio hum through a power supply.

Good luck

H9

P.s it's hard to tell what was modded about it. Maybe the rectifier and/or caps. Otherwise not much to it.

SeleniumFalcon · January 2023

So is the problem transformer lamination buzzing, or audible hum coming from the device that this supply powers?

mhardy6647 · January 2023

That's gonna be a hard one to fix if it is the lams singing.

Unless, e.g., wrapping the mains cord around a ferrite donut helped.

Could just be dodgy capacitors if its hum on the audio output of... whatever it's being used for.
Also could be induced, I guess... @msg IF it is hum on the audio (and not mechanical hum as @SeleniumFalcon mentioned): Have you tried moving the P/S around a little bit relative to... whatever other electrical gizmos are close to it? Changing its orientation in all three ordinary planes (x, y, and z) might be helpful (EDIT: one at a time, for troubleshooting/data gathering!). Also, plugging the AC mains into a separate outlet (separate house circuit ideally... big ol' extension cord in the hood?) might be helpful, too.

If it is the transformer singing, normally one would look for some weird reactive component riding on the AC input and quench it, or tighten down the screws holding the PT together a wee bit to quiet down the laminations. That transformer isn't built that way, though.

mhardy6647 · January 2023

Board's gotten toasty around that one active component (looks like it is labeled "D1"? Maybe a zener?). Maybe normal, but always a bit of a concern.
Stuff's packed pretty tight in there.
Kind of unsettling to see a place for a fuse that's unused.

Maybe there's a fusible link in the transformer, but... otherwise... well, I hope there's some protection against catastrophic failure in that gizmo!

EDIT: Is this thing housed in a cast metal box, or a plastic one? If the latter... well... seeing some sort of active components (regulators, I am guessing) using it for a "heat sink" is... ummm... well, not comforting!

Clipdat · January 2023

Swing it around and around by it's cable until it nearly reaches escape velocity, and then smack it upside the head of the schmuck who sold it to you.

msg · January 2023

SeleniumFalcon wrote: »

So is the problem transformer lamination buzzing, or audible hum coming from the device that this supply powers?

Hey Ken,
yes, to clarify, this hum/buzz is "mechanical", as they say? coming only from the power supply itself. It does not present in audio through the speakers.

Yeah Brock, this is configured for 5v for a SBT as well.

msg · January 2023

Hey Mark - yeah, I did the ole plastic rod stethoscope trick, even though I knew it was obviously the transformer. I placed the rod on the transformer's casing/bracket and there was vibe/sound coming through. Good point, you guys on if it's coming from the lams.

I don't know much about electrics, so I'm not inclined to go poking around too much with this thing powered on. Unless someone here tells me it's okay, and that I should be standing in water or something while I do it. you know because water will buffer the shock, isolating me a bit from ground.

I do wonder about trying to upgrade some bits!
Kinda got a hankerin' to do some SOLEdering.

mhardy6647 · January 2023

Mechanical noise probably means either the laminations in the power transformer are loose or the transformer is being electromagnetically stressed. I don't think either would be easy to fix, although a complete refresh of the components in the thing might help.
Not much "there" there.

EDIT: Actually, I wonder if the lams are bolted together under that electrostatic shield?

Here's what a more substantial power (filament) transformer looks like, for comparison

The screw heads are the bolts that hold the laminations together -- they can be gently tightened, but it's a little like lug nuts. The tightening needs to result in equal torque, and they can be too tight.

Clipdat · January 2023

I suggest you do this with it:

VR3 · January 2023

Change those 3 caps to these guys!

ALL212 · January 2023

Out of the box attempt if the coils are loose.

Heat with a heat gun but not hot - just warm.

Add hot glue.

Kinda last ditch…

mhardy6647 · January 2023

One thing that will make a transformer or a choke hummmmm can be too much current draw downstream. @msg if you have an IR thermometer (or, even better, a thermal imaging camera) check the components for temperaure. Those heat-sinked semiconductors are meant to get warm,maybe even hot, but not excessively so. Also, e.g., a 'bad' electrolytic filter capacitor can get warm if its ESR is higher than it should be. Filter caps shouldn't get warm. Might give some insight into the matter if the mechanical hum is due to an operational flaw.

heiney9 · January 2023

IIRC, these when new weren't expensive. So perhaps the transformer is just at it's end of life. They didn't become expensive until people started using them for Squeeze Boxes, then the market went up.

IIRC, I paid like $110 shipped for mine. That was about 14 years ago, and it was a used one then as they were discontinued before that.

This hum was a problem 14 years ago. Like I said mine made some mechanical noise but it never really interfered with music listening.

Good luck

H9

mhardy6647 · January 2023

Transformers last approximately forever (to a very good approximation) unless they're defective or employed too close to their limits. Numerous 60 to 70 year old PTs here that are just fine (even at today's higher line voltages... which does stress them).

heiney9 · January 2023

Yes, they should last a long time. My point was since these were not that expensive, I'm sure the transformers were not that good, like in a Dynaco amp.

There are lots of cheaper made transformers out there, especially in these types of power supplies. We're not talking about a vintage piece of audio gear.

H9

treitz3 · January 2023

It's a defective transformer. There are tricks to reduce the hum but I wouldn't bother. They usually do not last.

Tom

msg · January 2023

Okay then. Thanks Tom.

Clipdat wrote: »

it is. I'm gathering these things weren't that great to begin with.
Guess I got ripped off.

msg · January 2023

Oh, you meant the fixes don't last! lol

mhardy6647 · January 2023

msg wrote: »

Okay then. Thanks Tom.

Clipdat wrote: »

it is. I'm gathering these things weren't that great to begin with.
Guess I got ripped off.

It looks like something I would build. That's not a good thing.

If you know the secondary voltage of the transformer (which can be measured) it could be replaced -- but the replacement would have to physically fit. It's probably an off-the-shelf PT, though -- heck, it might even have a mfg. part number on it that could be searched for a replacement from Mouser, Digi-Key, Allied, Jameco, or your other favorite sparky parts vendor.

Plus, I wouldn't just assume that there's not something else making the PT unhappy...

What is the voltage and current output rating of that P/S @msg ?

SCompRacer · January 2023

Apologies! Found my polk emails in the spam folder.

I recalled seeing an old 2007 thread at Audio Circle about the WM220-1.

https://www.audiocircle.com/index.php?topic=38842.0

Wayne said way back then "We have been getting a couple of these power supplies through the shop that have a mechanical hum. This is likely caused by the plates in the transformer vibrating.....I am not aware of any other transformer that would fit except for another ELPAC WM220-1."

What are you powering with it, using 5v or 12v?

Bolder Cable Co ELPAC Power Supply - Transformer Hum

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