Humming NAP250...

Hi Top Cat, Ive had a new 250 for a couple of months that hums just like yours. It seems to get worse at night. All my reference series kit seems to hum to a certain extent, especially when I place my ear on the outer case, but the 250 is the worst no doubt due to that massive transformer. I don't care about it any more, the music sounds too good and no hum comes from the speakers. When I notice it from time to time I just think of how much power a transformer of that size is caple of sending to my Allaes.

Enjoy your 250, it's a beautiful musical instrument!

Mario.

This is what the Naim Audio owners manual has to say on the subject.


The transformers in the amplifiers and power supplies may sometimes make a mechanical noise caused by distortion of the mains (house currant). Naim transformers are large in size and have large gauge secondary windings, making them quite sensitive to this distortion. A separate spur from your consumer unit for your Hi-Fi system can often reduce the effect, while also giving an overall improvement in sound quality, but it may be necessary to take account of mechanical transformer noise when siting your equipment.

Thanks, guys. I'd have thought a dedicated CU and spurs would have isolated the system from any other 'regular ring main' noise.

Has anyone tried putting any of those isotek or Russ Andrews silencing things next to fridges and so on to see if that helps? Did it?

Turning the music up isn't really an option. Even at highish volumes, my turntable's vinyl noise is at a lower perceived level than the transformer hum. Not good.

However, otherwise all else is well. ANy other suggestions for minimising the hum gratefully appreciated.

John

TC '..'
"Sun went down in honey. Moon came up in wine. Stars were spinnin' dizzy, Lord, the band kept us so busy we forgot about the time."

John

I too can confirm the hum on the new 250 and that it is affected in my case by my kitchen appliances (washing machine, tumble dryer etc.). Since I don't have a dedicated spur that probably does'nt help

It is not as noticeable as time goes by because indeed the music takes control.

Also based on my experience and a few others that have commented the new 250 sounds great straight out of the box for up to 48 hours then it all goes away and you start wondering where the great sound went.
You then have to be patient as it burns in for at least a couple of weeks after which the great sound starts to return and continues to get better even a month or more after switch on.I think also the hum reduces aswell.

So don't panic if this happens to you just keep playing away and it will all come with time.

regards
GEOFF

Hi Geoff,

Some misunderstanding - my 250 isn't a new one - it's new to me (as I've never owned one before) but it's a 1998 vintage olive 250 (along with matching 82 and an almost unused 2000 HiCap from Naim themselves - still sealed!)

Point taken, however - what's good for the goose, and all that...

John

TC '..'
"Sun went down in honey. Moon came up in wine. Stars were spinnin' dizzy, Lord, the band kept us so busy we forgot about the time."

top cat:

can you try the following:

(a) plug the 250 into its OWN spur

(b) plug everything into ONE spur (any of them)

and see/hear what happens.

i have mains hum from my power components in my system, but not enough to bother me.

if your hum is "excessive", with a multiple spur arrangement, which is supposed to isolate (so we are told) mains distortion from the 250 from other components, then perhaps, in your case, this multispur is not delivering.

anyway, try the above and please let us know. the 250 is a trully great amp and thoughts of mains hum shouldnt really distract from its great musical ability. i think one of my 250's in the active duet is a 1998 vintage too -- sounds great. as i say, i have hum too, (twice the amount in fact!!) but it really doesnt get in the way.


enjoy

ken

If you are unlucky enough to live in an area with a really bad mains supply then no amount of separate spurs are going to help, have you considered moving?

I have 6 dedicated spurs, dedicated earth rod, 250, 82, Supercap, CDSII, XPS and sometimes quite distracting hum.

I have one of the Russ Andrews silencer thingies next to the fridge. Cannot really say whether or not it made any difference. Must do a test sometime.

My system however sounds great. When it is playing I don't hear any hum.

Not what you want to hear; but you are at the mercy of your local supply.

A separate spur won't cure it, if the distortion is coming from outside your home.

Naim are aware of the problem and strive to make new transformers quieter. They've tried compliantly mounting the transformer, but it compromises the performance of the amplifier.

My 135's used to make a hell of a racket. The local supply company eventually overhauled the system and renewed some cabling etc:

THAT cured the problem.

It's a waste of time complaining to your supply company - as long as your supply is within set voltage limits, they will say it's OK.

Good luck.

Hi again. Finally got broadband at home, makes all the difference, eh?

Anyway, I'm off for Christmas now, and so I've finally had a chance to crank the system and also to hear what it sounds like during the day. Oddly enough, there's almost no hum at all right now, and I've made sure that (knowing the neighbours are out) I've put plenty of heat into that amp by whacking the volume up to around midday. In a moderate sized room, into 90db 4 ohm speakers, that's *loud* - far louder than my DNM ever managed (but then, it was only 23wpc).

Overnight, the sound has opened up a little more - definitely better than it was on Wednesday, say, and I'm hoping that it keeps improving!

John

TC '..'
"Sun went down in honey. Moon came up in wine. Stars were spinnin' dizzy, Lord, the band kept us so busy we forgot about the time."

TC

you've got all manner of flash spurs.... how's your EARTH? That's more important than the spurs.

HTH

Rico - SM/Mullet Audio

PS - congrats on your new acquisitions. Now, if only you could move the DNM's...

Its a long shot but it may be worth checking the allen head screw that holds the transformer to the case, i had a noisy CD5 which was "improved" by having this tightened by my dealer Robert Ritchie. He suggested this.
I know it wont cure bad mains but the torque may affect resonance.

David

quote:

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you've got all manner of flash spurs.... how's your EARTH? That's more important than the spurs.

---

Not as good as the spurs, I admit. We (my sparkie F-I-L and I) went for the easier option, leaving dedicated earth spikes for later when we replace a large portion of lead water pipe next summer. We had planned to do that this summer past, but other priorities took over.

One thing that I wondered about was using the lead pipe as a kind of 'earth rod' in itself. Don't know if it would be of any use, can't remember whether lead is as good as copper for conductivity (brain is mush, too much Christmas excess!).

quote:

---

PS - congrats on your new acquisitions. Now, if only you could move the DNM's...

---

Yep, they're not so easy to shift. A damned shame, 'cause apart from not being as powerful as the 250, the PA3^S is a somewhat more musical amplifier. That said, the 250 has revealed that the PA3^S wasn't really beefy enough for my speakers and room, missing out a bit on the deepest stuff, and there's a sense of weight that the DNM couldn't deliver. Excellent amp though the PA3^S unquestionably is - my Naim dealer rates it at the same level as the 500 in many ways - the 250 probably ticks more boxes for me right now.

As to what to do with the preamp, I'm using the 3B Primus's phono stage in preference to the 82's K-boards right now - it just sounds better, it's quieter, faster and more detailed.

However, add a 52 and/or a SC and I'm sure that changes.

Enjoying what the old Naim is doing, it's warming up nicely and I think it's safe to admit I am now a Naim convert*.

John

* admittedly, I think my Naim plays second fiddle to the DNM in a number of ways (mainly round earth it has to be said), but overall I think the Naim sound will win me round comprehensively over time. Still think the DNM is a classic amp, but then if a buyer comes along they'll get a bargain of an amp with some fantastic qualities... meantime, back to the Naim!

TC '..'
"Sun went down in honey. Moon came up in wine. Stars were spinnin' dizzy, Lord, the band kept us so busy we forgot about the time."

Replacing the wall plugs & sockets with high quality items from a firm called HMS reduced the hum levels in my 250.

Regards Robert