Power supply help please...

Barry (NJ) · February 10, 2021, 12:54:14 PM

So, I love my Audio Alchemy OM-150 amplifiers, but there is a small problem, hum/buzz. The power supplies have a mechanical hum/buzz that makes its way to the speakers. I was wondering if I could add a filter of some type, to the DC after the rectifier, to prevent this transmission. The power supply looks extremely simple, and there is 93.5V DC coming out of the bridge rectifier diode. There is a good amount of room on the other side of the transformer, about 4" x 4" x 3", for capacitors and such, if needed. Thanks for any input and guidance.

Audio Alchemy PSU150 by Barry, on Flickr

HAL · February 10, 2021, 05:26:46 PM

If you are hearing hum/buzz in the speakers, most likely it is the power supply caps are drying out and need replacing.

A good person to ask is Dusty Vawter at CI Audio as he was at Audio Alchemy when they were made.

Good luck.

Folsom · February 11, 2021, 09:59:10 AM

The DC side is not where I'd be looking.

Try a HumX first.

Barry (NJ) · February 12, 2021, 05:14:37 PM

Quote from: HAL on February 10, 2021, 05:26:46 PM
If you are hearing hum/buzz in the speakers, most likely it is the power supply caps are drying out and need replacing.

A good person to ask is Dusty Vawter at CI Audio as he was at Audio Alchemy when they were made.

Good luck.

Dusty wasn't really involved with the amps, I'd traded emails with him some time ago on it, and I had the caps replaced in one of the amps a few years ago by a local technician, sadly it didn't help.

Quote from: Folsom on February 11, 2021, 09:59:10 AM
The DC side is not where I'd be looking.

Try a HumX first.

Between the amp and wall I've tried similar from AVA, a Belkin Power Conditioner, even floating the ground on the power cable, and none were effective. I've also run an uninterrupted dedicated line from the main box to my equipment. The sound is definitely coming from the transformers, it is clearly audible when you're very near the amps, and the same can be heard near the speakers.

Folsom · February 12, 2021, 08:07:58 PM

In that cause you have to stop it from vibrating, perhaps with rubber footers. Otherwise replace the transformer.

Forget about a filter to get rid of it, won't work.

P.I. · February 12, 2021, 11:27:56 PM

Quote from: Folsom on February 12, 2021, 08:07:58 PM
In that cause you have to stop it from vibrating, perhaps with rubber footers. Otherwise replace the transformer.

Forget about a filter to get rid of it, won't work.

+1

Barry (NJ) · February 13, 2021, 04:05:37 AM

Thanks guys.
Would something like this work?
Seems to put out 90V DC without a transformer(?)

HAL · February 13, 2021, 06:17:00 AM

The link only shows a rectifier and caps, not a new power transformer as suggested.

You might ask Peter Madnick as he was possibly involved in the AA amp design. He is with ELAC USA now, so that might be a way to contact him.

tmazz · February 13, 2021, 07:58:06 AM

If you are getting a mechanical buzz from the transformer that would be caused by physical vibrations. Why don't you try placing a brick on top of the transformer and see if the extra weight damps the vibrations. Vibrating transformers can be the result of some DC on you incoming power line. PS Audio at one time made a device called the Humbuster that filtered that out and from what I remember reading about it, did a good job of reducing transformer buzz. Unfortunately they have been out of production for a while now and are not easy to find on the used market.

Also, try just plugging the amp into an outlet in a different part of the house (or even a different outlet in the same room, if it is on a different breaker) to at least see if the problem is coming right out of the wall. No need to connect anything up, just listen to see if the transformer buzzed when plugged into a different breaker.

But that aside, I don't see how a mechanical transformer buzz would make its way to the electrical signal going to your speakers to produce a buzz there. Do you have access to a scope so you can take a look at what the PS output looks like? You make actually have two separate problems.

P.I. · February 13, 2021, 09:25:41 AM

What Tom said. You can try one of these, too:

https://emotiva.com/products/cmx-2

_Scotty_ · February 13, 2021, 10:21:51 AM

Hi Barry, sometimes a power transformer will be sensitive to the polarity of the incoming AC power and quieter when connected to the AC one way more than the other with respect to hot and neutral. You could try reversing the polarity of the AC connections inside the case.
This may reduce volume of the hum or it may make it louder you won't know until you try it. The power supply caps may also be a little microphonic but this is usually only a problem with signal coupling caps and not power supply caps.
Other than that I got nothin'.
Scotty.

Response Audio · May 11, 2021, 03:57:56 PM

Any update on this? Haven't been here in a while due to being busy. I have thoughts if it hasn't yet been figured out.

tmazz · May 11, 2021, 05:01:31 PM

Barry sometimes physical transformer hum can be caused by a small amount of DC voltage piggybacking on your AC mains.

iFi just introduced a DC blocking device that might help if this is the cause of your problem. It is only $99. You can get them on Amazon and if you are a Prime member you get free returns so if it doesn't solve the problem you can get your money back.

https://ifi-audio.com/products/dc-blocker/

Barry (NJ) · May 13, 2021, 10:59:02 PM

Quote from: Response Audio on May 11, 2021, 03:57:56 PMAny update on this? Haven't been here in a while due to being busy. I have thoughts if it hasn't yet been figured out.

No solution yet, kind of resigned to living with it for now, but I'm more than willing to listen and try something new!

Barry (NJ) · May 13, 2021, 11:04:50 PM

Quote from: tmazz on May 11, 2021, 05:01:31 PM
Barry sometimes physical transformer hum can be caused by a small amount of DC voltage piggybacking on your AC mains.

iFi just introduced a DC blocking device that might help if this is the cause of your problem. It is only $99. You can get them on Amazon and if you are a Prime member you get free returns so if it doesn't solve the problem you can get your money back.

https://ifi-audio.com/products/dc-blocker/

May be worth a shot, as I do have Prime, but I do have the AVA DC Blocker... https://avahifi.com/products/humdinger-dc-line-blocker
and it didn't help...