Author Topic: Power supply help please...  (Read 709 times)

Offline HAL

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Re: Power supply help please...
« Reply #15 on: May 14, 2021, 04:55:55 AM »
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.

Offline tmazz

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Re: Power supply help please...
« Reply #16 on: May 14, 2021, 07:37:50 AM »
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...

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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Offline rollo

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Re: Power supply help please...
« Reply #17 on: May 14, 2021, 10:01:23 AM »
  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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Offline Barry (NJ)

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Re: Power supply help please...
« Reply #18 on: May 14, 2021, 04:37:53 PM »
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...

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Audio Alchemy PSU150 by Barry, on Flickr
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Offline HAL

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Re: Power supply help please...
« Reply #19 on: May 14, 2021, 04:52:51 PM »
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!

Offline Barry (NJ)

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Re: Power supply help please...
« Reply #20 on: May 14, 2021, 05:08:52 PM »
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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Offline Folsom

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Re: Power supply help please...
« Reply #21 on: May 14, 2021, 06:23:18 PM »
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.