Amplifier Noise

[TBL]

I bought a new (to me) power amp recently (Accuphase P-400) and I've just noticed how noisy it is. Fine when music playing and not audible from my normal sitting position, but definitely audible when within a few feet.

It's coming direct from the amp and is not a hum (like transformer hum) more of a mechanical type sound, I know that sounds odd but can't think how else to describe it. The noise is there even with nothing else connected.

Any ideas what it might be? and a possible solution

Cheers

Ian

[Reid Malenfant]

Sounds like it might be the transformer rattling due to loose windings ;) Solution would be new one, start saving your £10 notes in the piggy bank :rolleyes:

[jostber]

Could it be the fan noise that you're hearing?

http://audio-database.com/Accuphase-kensonic/amp/P-400-e.html

Maybe you can try to clean the fan to make it work optimally?

[TBL]

Sounds like it might be the transformer rattling due to loose windings ;) Solution would be new one, start saving your £10 notes in the piggy bank :rolleyes:


I do hope not that sounds too expensive for words.


Could it be the fan noise that you're hearing?

http://audio-database.com/Accuphase-kensonic/amp/P-400-e.html

Maybe you can try to clean the fan to make it work optimally?

That's a possibility (that sort of sound) I'm no electrician but I'll whip the cover off and take a look.

[Ali Tait]

If it is the transformer you try tightening it's fixing bolts.

[Reid Malenfant]

If it is the transformer you try tightening it's fixing bolts.
Unless it's a toroid ;) Yes I agree with Ali... If an EI transformer tighten it up :)

[The Grand Wazoo]

Nice amp!
It's not a toroid though

http://www.allegrosound.com/Accuphase_P-400.jpg

[DSJR]

Nice amp!
It's not a toroid though

http://www.allegrosound.com/Accuphase_P-400.jpg


:stalks:

[Marco]

Welcome back, Dave! :)

Marco.

[Butuz]

Wow thats some sexy internals!! It looks as if its got a 120 or 140mm fan fixed to the backplate i would be looking at that as first port ofncall. It could either be caked with dust and need a good clean, or the bearings could be on the way out so you would need a new fan.

Easiest way to test would be to unplug the fan and then try the amp for 5 mins see if the noise has gone.

Butuz

[Reid Malenfant]

Nice amp!
It's not a toroid though

http://www.allegrosound.com/Accuphase_P-400.jpg
My guess is that those big cans holding the transformers are also filled with potting compond to keep things quiet. I'm not sure how many of you are familiar with Quad 405 transformers which are similarly potted up, but as they age they can become noisy :(

I doubt you'll be able to to get to any bolts to tighten the laminations up...

This is probably not going to be good for your wallet, I just hope I'm wrong ;)

E2A:-Just spotted the cooling fan as per Butuz post, things may well be looking rosy once more :thumbsup:

[Ali Tait]

Aye, but if it is the trannies, it may be possible to remove the offending one and heat it enough to allow the compound to flow?
Agree it's more likely to be the fan though.

[Reid Malenfant]

I don't think the potting compound will unset itself no matter how much you heat it. It may be possible to dissolve the stuff & repot it though? :scratch:

Seen it done on PCBs previously ;)

[TBL]

Well, unplugged everything removed it from the rack and took the lid of. Plugged it back in and low and behold pretty much silent. There was a very low level of noise (hardly perceptible, but 99% certain it was the fan)

Connected everything back up and back in the rack (without cover) played a few tunes still nothing. I did blow out a few cobwebs with an air duster, but really quite clean.

Left it switched on for 5 hours and just been back to check, noise has increased and it is 100% the fan which is a relief. I do think some of it is that may rack is very solid (closed back) and confined and the noise is getting a bit of an echo which is making it sound louder than it actually is.

Anyway relief all round and I'm just going to live with it and make sure I always switch off to avoid wherever possible fan going into overdrive.

Thanks for the help guys.

Just as an aside the transformers are the square ones at the back but what are the 4 round ones each side, any ideas?

Cheers

[The Grand Wazoo]

Capacitors matey!

[Reid Malenfant]

The big cans at the side are some stonking great big computer grade capacitors ;)

If I was you I'd do something about giving it some more ventilation as that fan should only really be running when the amp is driving speakers hard. If it's running just sitting there then it's running miles too hot :eek:

Ah, just spotted it's an Accuphase... Could be class A then, it will run hot! Give it more ventilation, at least 5 - 6" of clearance above the thing & at least 3 or 4" on all sides if you want it to last.

[TBL]

The amp is switchable and I'm not running it in class A. It's not running hot, so either the fan is designed to run full time (it starts the moment the amp is turned on from cold) or the sensor is not working.

I know what your saying about ventilation but moving it outside the rack is not really an option. I'll keep checking the temperature and if it looks like it is getting too hot I would change the amp rather than the rack.

[bobbasrah]

The amp is switchable and I'm not running it in class A. It's not running hot, so either the fan is designed to run full time (it starts the moment the amp is turned on from cold) or the sensor is not working.

I know what your saying about ventilation but moving it outside the rack is not really an option. I'll keep checking the temperature and if it looks like it is getting too hot I would change the amp rather than the rack.

Noise could be from fan bearings failing, crud clipping the blades, resonance on the cabinet, etc.. Unbolt the fan from the case and have a look and listen with the power on, turning the fan up/down/around/etc to see if you can induce and feel or hear the cause.
If the fan is at all mechanically faulty, change it. The fixing points/bolt centres and electrical connectors are usually standard dsktop computer types, and so long as the airflow and voltage are the same you can unplug/unbolt and switch the fan for a multitude of options.
eg - Noctua make a larger dia fan which bolt centres are for a smaller diameter fan, shifting the same airflow at lower rpm. ie You can upgrade the fan CFM if your location warrants it.

All my fans (Noctua, Scythe, etc) are inherently quiet low rpm types mounted on rubber pull throughs rather than bolts as a further safeguard against case resonance. They are effectively silent running right up close.

If the amp's location is constrained, you can always consider assisting airflow from the underside of the casing with a thin Scythe or similar or allowing/forcing airflow through the shelf perhaps?
:cool:

[MartinT]

The fan may be configured to run silently at all times and speed up when the amp heats up. That may explain the noisiness after a period of running. It shouldn't be too difficult to source a replacement fan, although I usually take them apart and re-lubricate the bearings as fans fail all the time on PCs and rack mount equipment. Lubrication (light machine oil) often gives them a new lease of life.

[TBL]

I am now sure it is just the echo effect from the rack increasing the fan noise. As soon as I bring the amp forward the noise level drops to almost nothing, so I don't think a new fan would help. I have given it a lubrication squirt as well as an air dust.

As I said now I know It's not a serious fault I'm happy to live with what in effect is only a very minor issue and only noticeable when up close ie changing a disk. Other than that I would never hear it. My initial concern was that it was a problem that needed urgent attention.

[jandl100]

Yep, sticking an even slightly noisy component in an enclosed space can drastically increase the perceived level of noise.

Sounds like the amp is AOK. :)

[The Grand Wazoo]

So now you've got that sorted tell us how the amp sounds!

[TBL]

So now you've got that sorted tell us how the amp sounds!


That's not as easy as it might sound, I've gone from

Luxman SQ-38u integrated
Luxman D-38u CD Player

to

Accuphase C-222 Pre Amp
Accuphase P-400 Power Amp
Accuphase DP-60 CD Player

A fairly wholesale change current to 30 year old, Tubes to solid state, 30w to 200w & integrated to pre/power. It all couldn't be further apart.

So all I can do is give an overall view of the system and I think most people would admit that the Luxman set-up was a fairly decent combo that most would be happy to give house room. One person even called me barking mad to even consider changing.

But the end result is I'm 110% glad I did. My speakers are a very easy load to drive and 30w certainly did them proud but 200w of solid state oomh just brings so much more the bass is deeper & tighter The treble is much better contained and gone is the occasional tizz I got from the luxman. For sheer slam and attack there is a significant improvement. But by far the biggest and best improvement which was a surprise to me is in the sound stage/presentation. What a difference I wont say night and day but not far from it.

My only slight grumbles would be no remote for the pre. The Headphone out is not quite as good as the Luxman (but the phono stage is better, I think) Other than that I am a very happy bunny indeed, especially as I sold the luxman kit for £3,900 and paid under £3,000 for the Accuphase. The only question now is how do I spend the leftover £1,000

[Ali Tait]

Buy more music!