Annoying hum in poweramp transformer

I got an annoying hum in my poweramps tranformer. The poweramp is fed by a P5 and connected on the HC outlet.

The hum starts in about 20 minutes when the P5 is warmed up. The P5’s total charge is about 300 watt. The input harmonics is around 2,3 and output 0,1. The hum is only audible on low listening levels or when music stopped playing.

The most annoying thing is when the hum increases and decreases in seconds.

My guess would be a little DC out of the P5.

The poweramp is a Classe CA2300 and there’s no hum when it is connected straight in to the wall.

I already installed the latest P5 firmware.

Is this a known problem?

Is there something I can try or does the P5 need some service?

Thanks in advance!


Do you happen to have the P5 set to output multiwave?

At the moment it is, but it also happens while sinewave is selected.

I must say the transformer in the poweramp is pretty big so I always could hear it when I come close to it.

But now it’s louder and I can hear it anywhere in the room.

Frustrating. All transformers make some noise, but it should not be a distraction.

i immediately think ground loop. I suggest disconnecting other pieces one by one until the noise goes away. My guess is there is something creating a ground voltage differential. These can be hard to track down.

An easy quick start is to disconnect the interconnects to the amp and unplug everything else from the P5 and see if you still get noise.

Yes that is a good point I have to try that, but I would suspect the hum would be there as soon as things are powered up and not when things got warmed up. At the moment I feed the poweramp through another filter. There’s more rest in the music and no hum in the room.

When the poweramp is fed through the P5 there is a bit more power in the music, so I like that part.

On the other hand the P5 fans are cooling the unit constantly which makes a little simmer audible at the same level as the hum.

Now the P5 is charched at 70 watts feeding the PWD the Pre-amp and the CD player the fans are dead quiet.

I’d check with PSA with respect to the fan. I do not expect the P5 to need cooling with a 300 watt load.

Well maybe it needs a bit more room. The fans aren’t cooling at full speed, but they make more noise than lets say two laptop’s!

Attached files

@wijnand my P5 (230v version) is also having fans on after few minutes i turn on my amp (P5 shows about 15% usage (around 150watt). i have plenty of space for p5 to breathe, but room temperature about 26-27’C in these summer days…

I also have a hum from amp and headphone amp power supplies, i have to check if it’s there also directly to wall… I also can hear differences in SQ during different parts of the day, which I though should not happen with the P5 :frowning:

@Paul / @bob / @dennis Is there any easy way how to find out if my P5 is working OK? I think there could be eventually more people with the same issues, I even guess some may not notice this (as I realised and verified it only after some time)…



Does your equipment hum from the start or when the P5 is warmed up?

When your fans start cooling do you hear a soft simmer of the fans or just a soft fan noise?

I’m curious too if others notice when they have this issues, but I guess they will.

wijnand hmm, i just wanted to reproduce the transformer hum and its gone for now. i will watch it more closely and let you know. the P5 is on now for several days and amps are turned on for few hours now…

regarding the noise from fan - it is the bearing noise i would say, not the airflow noise :frowning:

it’s quiet, but can be heard during night when it’s quiet from my listening position (about 3 meters from the P5) - what helped a tiny bit was to put p5 into other shelf of my rack so there is another shelf over the P5 about 3cm above the P5. But I can still hear it :confused:

Any ideas if I can replace this fan by myself? I mean if it’s standard size and power like in PCs? I would buy some very quiet one to replace original…

Hi maniac,

Yes indead bearing noise could be it. I sit about 3,5meters from the P5 and can hear it during daytime and even when music play softly. I would say as loud as an older 3,5 inch harddrive.

I wonder if the original fan’s should create any noise like this. If not maybe it can be replaced by an original one.

I opened a ticket, just in case!


I used to have a CA2300 and I had the same problem, even into the wall. The hum would come and go, but was loud enough to be bothersome from 15 feet away. Here’s what I learned: the CA2300 does not have a DC filter as the CA2200 did and the result is that, in some houses, this allows the huge tordial transformer to emanate this rather obnoxious hummmmm. ~X(

I talked to the folks at Classe and they said they would retro- fit the unit with a filter because other users, particularly those in Europe,have experienced the issue. If your unit is under warranty, this is done free of charge. Unfortunately, you’ll have to ship your unit back to the factory or convince them to convince a dealer to do it in the field. I didn’t want to ship mine, so I moved on to another amp. These amps are easily damaged (I 've seen two destroyed in transit) so I’d insist on them palet shipping it. Your hum may not be as bad as mine was. Pity the CT2300 owner because there is NO fix for that unit.

Sorry you’re experiencing this.


Might contact PSA and inquire if a Humbuster 3 outlet might help DC transformer noise.


Well that is interesting, but I would expect the P5 to be free of DC.

My unit CA2300 is 2 years old so probably it not under warranty anymore.

Shipping the unit back to Canada would probably take weeks or months, so that’s not an option.

And indeed the amp is to havy and will be easely damaged when it’s dropped.

Have you found a better amp in the same pricerange?

Maybe a Humbuster like rrwwss suggested, or maybe a power DC X-Terminator could solve the problem.


I have heard that a humbuster works in some situations and it would definitely be worth a try. I know that Classe’s warranty is at least three years, btw. Given your distance they might be able to arrange the retro-fit locally. I believe Van Alstine (the famous amplifier designer) also sells something similar to the humbuster because his amps are prone to this issue as well.

I hesitate to make amplifier recommendations because there are so many variables. I found a mint condition Conrad Johnson Premier 350SA that bests the 2300 by some margin. There a number of reviews on the web, particularly Jeff Dorgay’s review in Tone Audio. It’s a legendary amplifier and couldn’t be made today for less than $15k. The problem is that the 350’s are equally difficult to transport without damage. There’s one for sale on audiogon right now if you want to inquire further.

Hope this helps.

vhiner1 said: Van Alstine (the famous amplifier designer) also sells something similar to the humbuster

He does, indeed. At $125 this is well worth trying.

Well that is a better price the DC X-terminator plus of Kemp is 695€!


I was just curious which amp was for you a good replacement. I don’t have plans yet to replace my amp.

When I feed the amp through my old filter unit there’s no annoying hum, but maybe the P5 is to expensive to only feed the pre-amp and the PWD for audio. I hope I can feed the poweramp through the P5 soon too!

If you can’t find a humbuster 3, here is a cheap alternative.


The 2300 is a very fine amplifier and it will not be easy to find a better one for the money if it comes to that. I hope you find a good solution.