Mains Hum from NAP 250.2

Generally Naim do not recommend the use of main's conditioners (and impacting the performance of power amps in particular is a major problem with them), just good quality non conditioning power strips. With this in mind, I have to ask:

1. If the 250 is plugged directly into the wall or a regular cheap power strip (not using the Isotek or the Sirius) does the problem persist?
2. Does the hum persist for more than 10 minutes after power on or does it slowly trail off to nothing (most common)?
3. Are there any speaker cables bunched up within 20cm of the 250 (such as underneith the rack)?

All I can say is that transformer hum varies from one 250 to the other, and of course it depends on the mains ('dirty' or not). My 250DR only hums very softly, but its 250.2 predecessor was louder. I found that there isn't much I could do on a humming unit (e.g., insulation mats around the transformer only help a little), however, I am using the DC blocker from HiFi collective on all naim gear, and this has a moderate calming effect.

Best,

Stefan

feeling_zen posted:

Generally Naim do not recommend the use of main's conditioners (and impacting the performance of power amps in particular is a major problem with them), just good quality non conditioning power strips. With this in mind, I have to ask:

1. If the 250 is plugged directly into the wall or a regular cheap power strip (not using the Isotek or the Sirius) does the problem persist?
2. Does the hum persist for more than 10 minutes after power on or does it slowly trail off to nothing (most common)?
3. Are there any speaker cables bunched up within 20cm of the 250 (such as underneith the rack)?

 

Hi Zen, the Syncro is supposed to balance the voltage, which initially worked instantly. The buzz stays on and the speaker cables naca5 are not near the amp. I am lost mate.

Hmm, I shouldn't think varied voltages would impact this too much. Naim have stated unofficially that the transformers used in their units have a tolerance of +/- 10% of stated voltage (I run 115V units but only get 103.9V from the wall). But I'm not telling you you ae wrong to use the Syncro, just that since they are not recommended, purely for troubleshooting can you take it out of the equation?

I feel your pain a bit. I know many have said that they have, and put up with a bit of hum on Naim gear but I never experienced a persistent hum on my gear or, back in the 90s working in the trade, any of the Naim boxes that went through the demonstration room. It would, quite frankly, drive me nuts.

I suppose you can also try different power outets in the house (obviously not practicle to hook up the rest of the gear) just to see if the symptoms are variable for location. Other than that, if the hum is audible from your listening position, it may be good to engage with you dealer now rather than after 3 pages of well intentioned forum speculation (or at least in parallel).

Hi Steve,  transformer hum is a fact of life with transformers, they all hum, irrespective of make or voltage  - even the so called "silent" ones.  

The first question is does the hum tone & volume change,  if it does its indicative of asymmetric distortion on the mains commonly called DC offset.  If the hum is unchanging constant,  you have most probably got a naturally noisy transformer. Second question is you have not answered Feeling Zen's  question "If the 250 is plugged directly into the wall .......  (not using the Isotek   or the Sirius) does the problem persist".  If powering the 250 through the IsoTek Evo 3 Syncro stops the hum its almost certain the  problem is DC Offset,  

The Evo 3 Syncro is not a power conditioner its only purpose is a DC blocking filter & apart from removing whatever asymmetric element is present on the power sine wave, it does not condition anything.   I have my own DC blocking filter & if anything it brings a positive SQ change.    

The Sirius power board however is a conditioner & has nothing in its design that will remove DC.  It has X&Y capacitors across LN&E & its these that are considered detrimental to SQ that Feeling Zen mentions.  I advise to temporarily remove it for the purpose of hum diagnostics - then when the hum issue is understood/fixed,  then the Sirus can go back & its SQ effects judged separately.

So the first thing I would do is answer the 2 questions & if the hum persists when powered via the Evo 3 Syncro,  then you have a naturally noisy transformer.

I've had 3 HCDR units. Two of which have been fine. The first however buzzed like a very buzzy thing...all the time.

G

Thanks all for your help, I really appreciate it. It's 9pm here now so I'll play around in the morning, but strangely I just went in to listen and the hum is all but gone! I wish I understood power as I wonder if I have "dirty mains" whatever that is.