transformer hum

lennie trystero · « **on:** 22 Jan 2019, 06:21 pm »

Hi all - I'm a relative novice around here, so forgive me if this is stupid, or convoluted, or whatever. Over the last few years I've been assembling a system mostly made up of pieces made by a local builder (45 amp, 01a preamp, Cg3-based phono stage). It sounds fantastic on the Tannoys, but some of the transformers are really buzzing. I read around a bit, ending up buying a Humdinger DC line blocker from Audio Van Alstine that made a slight improvement, but not as much as I was hoping for. This is in addition to a passive power conditioner by Running Springs Audio (the "Elgar").

Recently bought an old PS Audio P500 and... the hum vanished. I was able to buy it cheap because it maxed out at 150W -- I was warned by the seller -- and sure enough, after a couple days, it blew out the fuses on my equipment and shut itself down for good. (My system, it turns out, was drawing a bit less 200W total).

PS Audio is willing to rebuild it for $700 plus whatever shipping ends up costing, let's say another $150 or so. Here's my question: is there a better way to spend that money to eliminate, or at least really reduce, the transformer hum? Like, three Humdingers in series? Or whatever?

Thanks for any guidance.

FullRangeMan · « **Reply #1 on:** 22 Jan 2019, 06:34 pm »

Dont spend nothing before discover the hum origin and reasons.
Transformer hum can have machanical origin too aside parasitic induction between windings etc, you need an expert to examine this transformer or amp.

jsm71 · « **Reply #2 on:** 22 Jan 2019, 09:34 pm »

Transformers can be tricky, especially if they are hand wound as most are. Have you talked to your local builder, from whom you bought the unit?

Speedskater · « **Reply #3 on:** 22 Jan 2019, 10:35 pm »

Have you checked your AC line voltage? High line voltage with respect to what the transformer was designed for, can cause buzz.
In the past, I have replaced the thru-bolts with stainless steel hardware so that I could tighten the plates tighter.

RDavidson · « **Reply #4 on:** 22 Jan 2019, 10:38 pm »

Maybe first step would be installation of a dedicated power line to your audio system outlet

lennie trystero · « **Reply #5 on:** 23 Jan 2019, 01:22 am »

Thanks, all. A dedicated power line would be cool, but given that it's a Manhattan apartment, probably not an option... line voltage varies between 121-124, so nothing too out of the ordinary.

And for what it's worth, the output transformers, which were hand-wound by Dave Slagle, are dead silent. It's the other one (power transformer? input transformer?) that seems to be the problem. Maybe I'll try experimenting with fasteners etc to see what happens.

FullRangeMan · « **Reply #6 on:** 23 Jan 2019, 01:29 am »

What are the input voltage the power transformer are expecting?

RDavidson · « **Reply #7 on:** 23 Jan 2019, 01:42 am »

Getting a dedicated line is about noise reduction, not just consistent voltage. The line would be isolated from shared lines that things like your refrigerator are very likely running on. I understand you can't install a dedicated line, just helping you understand the full benefit. As an experiment, you can temporarily unplug your fridge and other noisy appliances and see if it helps. It may point you toward a solution, perhaps power isolation / regeneration devices.

Speedskater · « **Reply #8 on:** 23 Jan 2019, 04:02 am »

Quote from: RDavidson on 22 Jan 2019, 10:38 pm

Maybe first step would be installation of a dedicated power line to your audio system outlet

Far (very far) from the first step!
Why would you think that a dedicated power line is a solution to an diagnosed problem?

Mark Korda · « **Reply #9 on:** 23 Jan 2019, 04:43 am »

I tried lots of things to reduce a hum from a real nice Dyna 70. I noticed the power transformer had missing hardware. You can see there was a hole for a center bolt. Dynaco may have neglected that bolt for cost reasons. I put a wooden shiv from the hardware store for a fix and it reduces the hum dramatically. Speedskater is on to something. I've also removed a dimmer and installed the Emotiva hum buster power bar.
Another thing I do is lay a cast iron 5 pound York barbell weight on the cage with great results...take care ..Mark Korda

RDavidson · « **Reply #10 on:** 23 Jan 2019, 02:37 pm »

Quote from: Speedskater on 23 Jan 2019, 04:02 am

Far (very far) from the first step!
Why would you think that a dedicated power line is a solution to an diagnosed problem?

I don't think it's a diagnosed problem. That's why the OP is asking for things to look into. To prevent derailing the thread, because the OP cannot install a dedicated line anyway, I won't ask you to explain or otherwise be helpful.

borism · « **Reply #11 on:** 23 Jan 2019, 02:57 pm »

To me it looks as if Speedskater misspelled and meant "undiagnosed".

RDavidson · « **Reply #12 on:** 23 Jan 2019, 05:12 pm »

Perhaps...but some folks here have extensive history of being condescending and unhelpful. I'll leave it at that.

JohnR · « **Reply #13 on:** 23 Jan 2019, 06:00 pm »

Quote from: lennie trystero on 22 Jan 2019, 06:21 pm

Here's my question: is there a better way to spend that money to eliminate, or at least really reduce, the transformer hum?

You should ask the person who built it about the power transformers he used. They may be vintage units that should really be run at 110V or lower, or maybe they are underspecced (or not generously overspecced) for the filament load.

belle harbor · « **Reply #14 on:** 23 Jan 2019, 09:05 pm »

Sometimes simply tightening the bolts which hold the bells to the laminations will eliminate the buzzing. Also check to see if there are fiber washers under the heads of the bolts and nuts. If someone removed them, buy some and replace them.

lennie trystero · « **Reply #15 on:** 23 Jan 2019, 09:09 pm »

More thanks. Seems to be that the problem is both diagnosed and undiagnosed, given that the hum vanished when I plugged it into the PS Audio P500. In other words, I have a solution available, was just hoping to get by without spending all the money.

I'll open up the amp this evening and have a look at specs and especially mounting hardware. It would be brilliant if I could fix it with a quick trip to the hardware store.

Oddly difficult to find 2A slow-blow fuses in New York City these days.

belle harbor · « **Reply #16 on:** 23 Jan 2019, 10:31 pm »

This may help you:

https://www.homedepot.com/p/Cooper-Bussmann-MDL-Series-2-Amp-Silver-Electronic-Fuses-2-Pack-BP-MDL-2/100115560

It appears to be in stock at this location.

lennie trystero · « **Reply #17 on:** 23 Jan 2019, 11:01 pm »

That’s my Home Depot alright. Went there on Monday and they told they didn’t have any.... guess I was misinformed

FullRangeMan · « **Reply #18 on:** 24 Jan 2019, 11:19 am »

Quote from: belle harbor on 23 Jan 2019, 10:31 pm

This may help you:

https://www.homedepot.com/p/Cooper-Bussmann-MDL-Series-2-Amp-Silver-Electronic-Fuses-2-Pack-BP-MDL-2/100115560

It appears to be in stock at this location.

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RDavidson · « **Reply #19 on:** 24 Jan 2019, 02:49 pm »

Maybe check nearby electronics sales / repair places?