The 250 is well passed a service. I wouldn’t be connecting it to my speakers…
It sounds fine. Is there any evidence that an unserviced amp can damage speakers?
A regulated Naim amp like a 250 can ‘oscillate’ if one or more components have failed. This may well take out the speakers.
Regulated amps definitely need servicing within the recommended service period (8-10 years for the NAP250). Because a regulated amp is effectively two amps - where one regulates the other - at any point where components start to fall off spec over time, the resulting drop in performance is far more marked than with an unregulated design. At best, performance just goes south, but at worst it can sometimes get to the point where it could take out a driver if left too long.
Hi Kensalriser,
If none of your power supplies require a service, then it may be worth looking at a balanced power supply from someone like Airlink Transformers. My 555PS hummed loudly, the 135s and olive supercap quietly until I had an electrician install a BPS5120MP at the mains consumer end of the radial feed to the living room. This knocked out any asymmetric mains and allowed us to drop the voltage from 242V to 230V. The result was no more transformer hum and a sweeter sounding (i.e. less strident) system.
A call to Airlink may prove to be 10 minutes well spent, as they have quite a few UK customers with Naim music systems.
Hope this helps, BF
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I am considering a dedicated radial circuit as the consumer unit and meter are literally the other side of the wall from the hifi, so it should be a relatively straightforward job. But I don’t think there’s enough room to put in a big box. Were your boxes humming even on a dedicated radial?
Yes, especially the 555PS. Here’s a picture of the BPS as installed with the dedicated radial.
Airlink recommended either a 3kVA or 5kVA one for our installation, so we went for the bigger one.
Best regards, BF
On examining the humming problems a little more closely, I’ve concluded that the Supercap is just about tolerable and that the HDX hum is probably from the HDDs rather than the transformer, so just the nature of the beast.
The 250 is not tolerable, however. The noise from this is more of a granular, higher-pitched buzz. While playing around with the pre-amp inputs I noticed significant noise (including transformer hum) through the speakers on the phono and tuner stages which was most largely, though not completely resolved by plugging the 250 into a dedicated mains socket. I’m sure it’s usual for a phono stage to have some background noise (this is without a source connected) but is there a good reason the tuner stage should be noisy? The other line inputs are almost silent.
I will have the 250 serviced after the holidays, but as I’m not convinced that will solve the problem I imagine the next step will be a dedicated mains supply. Presumably this will entail a standalone consumer unit at the very least? I’d like to avoid Bluesfan’s bulky solution.
If the hum is caused by the quality of your incoming mains supply, eg if there is DC offset, a dedicated mains circuit will not help. It may improve things by better isolating the HiFi from the rest of your house mains circuits and the devices running on it.
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In my experience connecting a “dedicated mains supply” to the existing domestic consumer unit doesnt distance the supply sufficiently from the “noisy” existing consumer unit.
The incoming mains supply needs to be split after the meter, before the existing CU, and a dedicated consumer unit installed to provide mains power to the audio system.
This certainly reduces or eliminates transformer hum and improves SQ significantly.
This was the best sound for pound upgrade I ever made.
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Minded to try a DC blocker first as the cheapest and easiest option and take it from there.
The amp hierarchy is quite simple. From lowest to highest:
- Expensive
- More expensive
- Very expensive
- Bl00dy expensive
- You can’t afford the expense!
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When you get your new radial, put the 250 on the wall socket and run a decent mains block off the other socket. On the mains block first preamp, then analogue sources with digital last. This may reduce constant hum to a much lower level, but it can’t sort out incoming low quality AC. A good local earth rod may also help if you have PME. Always comply with local wiring regs.
Phil
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