AudioNervosa
Systemic Development => Amplification and Preamplification => Topic started by: Barry (NJ) on February 10, 2021, 12:54:14 PM
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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.
(https://live.staticflickr.com/65535/50929759043_a0682d1190_c.jpg) (https://flic.kr/p/2kAujZR)
Audio Alchemy PSU150 (https://flic.kr/p/2kAujZR) by Barry (https://www.flickr.com/photos/20967309@N06/), on Flickr
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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.
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The DC side is not where I'd be looking.
Try a HumX first.
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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.
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 (https://avahifi.com/products/humdinger-dc-line-blocker), a Belkin Power Conditioner (https://www.belkin.com/us/support-product?pid=01t80000001JNnTAAW), 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.
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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.
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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
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Thanks guys.
Would something like this (https://www.electronics-lab.com/project/dual-90v10a-unregulated-power-supply/) work?
Seems to put out 90V DC without a transformer(?)
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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.
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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.
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What Tom said. You can try one of these, too:
https://emotiva.com/products/cmx-2
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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.
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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.
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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/
(https://ifi-audio.com/wp-content/uploads/2020/10/blocker-plugged-in-768x576.jpg)
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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.
No solution yet, kind of resigned to living with it for now, but I'm more than willing to listen and try something new!
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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/
(https://ifi-audio.com/wp-content/uploads/2020/10/blocker-plugged-in-768x576.jpg)
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...
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Do you still have the hum/buzz from the speakers when the amp has no inputs and powered on with the speakers connected? If you have shorting RCA plugs you can put those on the amp inputs. It should be disconnected from all other equipment for the check. If it still gives hum/buzz through the speakers it is the amp power supply. At that age, probably the power supply caps or others in the amp itself.
Hum/buzz coming via the speakers as OP noted is either a possible ground loop, or power supply noise. Removing the amp inputs will isolate all other grounds.
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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/
(https://ifi-audio.com/wp-content/uploads/2020/10/blocker-plugged-in-768x576.jpg)
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...
From what I can see in the write up that AVA unit does the same thing as the new ifi, so if that didn't help I doubt the ifi would be any different.
I think Rich has the right idea. If you totally isolate the amp from the rest of the system and it still hums that pretty much points t the amp itself ass the source of the problem. (Of course if you want to be belt and suspenders sure you can hook up another set of speakers to the isolated amp and if it hums through different speakers then the amp is definitely the culprit. )
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Curious. Were any new devices installed in system that may have introduced a Hum ? I take it this is a recent thing.
charles
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Thank you to all who have commented, I do appreciate your input!
Do you still have the hum/buzz from the speakers when the amp has no inputs and powered on with the speakers connected? If you have shorting RCA plugs you can put those on the amp inputs. It should be disconnected from all other equipment for the check. If it still gives hum/buzz through the speakers it is the amp power supply. At that age, probably the power supply caps or others in the amp itself.
Hum/buzz coming via the speakers as OP noted is either a possible ground loop, or power supply noise. Removing the amp inputs will isolate all other grounds.
There is noise from the amps when nothing is connected to them.
There is noise from the amps when they are muted, which prevents any signal from reaching the output stage.
There is noise from the transformers when not connected to the amps.
Curious. Were any new devices installed in system that may have introduced a Hum ? I take it this is a recent thing.
charles
No, not really recent, and no new devices, and the equipment is now on a dedicated line, unbroken between the outlet and the main breaker box.
The issue was present prior to the dedicated line, it was an attempt at silencing the noise...
Here's a look inside...
(https://live.staticflickr.com/65535/51179441213_dddd9c35cd_b.jpg) (https://flic.kr/p/2kYy1NR)
Audio Alchemy OM150 (https://flic.kr/p/2kYy1NR) by Barry (https://www.flickr.com/photos/20967309@N06/), on Flickr
(https://live.staticflickr.com/65535/50929759043_a0682d1190_c.jpg) (https://flic.kr/p/2kAujZR)
Audio Alchemy PSU150 (https://flic.kr/p/2kAujZR) by Barry (https://www.flickr.com/photos/20967309@N06/), on Flickr
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Do you hear the noise through the speakers as audio signal as well? If so, then it is the power supply.
The pictures of the power supply caps look like some of them have bulging tops. Those are possible signs of out-gassing from electrolytic caps going bad. The date codes are from 1994. Those are 27 years old and most likely ready for replacement. The mechanical noise is the transformer trying to produce a lot of current trying to feed power supply caps that are low impedance internally.
An amp tech can check them and replace if needed. If they fail it will be a big mess.
Good luck!
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Do you hear the noise through the speakers as audio signal as well? If so, then it is the power supply.
The pictures of the power supply caps look like some of them have bulging tops. Those are possible signs of out-gassing from electrolytic caps going bad. The date codes are from 1994. Those are 27 years old and most likely ready for replacement. The mechanical noise is the transformer trying to produce a lot of current trying to feed power supply caps that are low impedance internally.
An amp tech can check them and replace if needed. If they fail it will be a big mess.
Good luck!
Thanks, I'll try to find someone local to bring the amp to.
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I have an ifi Ground Defender and results of sound quality on DAC were not desirable. I have yet to AB with my HumX I use in another location.