2 off 250s or a pair of 135s

Nap 135 give 75W continuous over 70W and a transient handling of 500VA vs 400VA.
The nap 135 also have better signal earthing.

And that is what i guess im trying to flush out from the forum. In order to understand the theory I’d need to review the transformers in both the 250 and 135. It could be exactly the same transformer in both, or the 135 may just have the one set of slightly thicker secondary windings.
A lot of manufacturers use their part bins to create hybrid products. From memory the olive 180 was a 140 with a HC transformer in a bigger box- or something like that.
I need to start with swapping out the MF power amp for my 250.

All sorts of things find themselves becoming forum lore. Treat it with a pinch of salt! I suspect there has been confusion between (passive) biamping and biwiring. The latter is not good for Naim amps for the simple, well understood reason that doubling up on speaker cables upsets the inductance and capacitance to which Naim amps are sensitive.
People no doubt look down on passive biamping because it’s inferior to the active biamping for which Naim were well known, but that misses the point. Passive biamping is about quantity, not quality, by which I mean that it provides twice as much power which can be a big advantage if your speakers need it. Naim obviously don’t think it’s entirely bad, otherwise they wouldn’t put dedicated biamp outputs on some of their amps.

Personally I wouldn’t biamp because in addition to the the amp, you need an extra shelf, interconnect and pair of speaker cables. That’s too much clutter.


The advantage with Biamping is that you have one amp for the tweeters and one for the woofers in a two way" biwire" speaker system.

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IIRC, The 250 and 135 share the same PSU (transformer size etc) but as you say, the 135 PSU is just powering one channel rather than being shared between the two in the 250. The fan cooling allowed the 135 to drive harder and for longer, into difficult loads (typically Linn speakers of that era, namely Sara and Isobarik).

If you have a spare pair of 250s then it’s worth a try to compare to a single 250, but if you want the best (and your speakers are a more demanding load) then 135s are the way to go (serviced of course).

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Nap 135 (higher voltage) and give 75W continuous over 70W and a transient handling of 500VA vs 400VA.
The nap 135 also have better signal earthing.
But the Nap 250 can sound a little warmer than the Nap 135´s.

I would assume 135 or 350 mono are matched and aging in the same way. Buying two 250 stereo and use as mono must be challenging in getting left/right match perfectly. I would never do such at least.

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If you study the insides of the 250 and 135 you’ll see identical amplifier and regulator modules, and the same transformer / rectifier/ smoothing capacitors. So you might wonder why 135s sound different- even at low volume levels where the sharing of one primary power supply would have little negative effect. Look closely and you’ll see the grounding systems of both are very different though. In the 135 the main ground point is between the two large capacitors, while in the 250 it’s between the ‘speaker negative terminals. This is why they sound so different IMO :wink:


I’m not sure that it’s safe to run just one channel each on two NAP250s. The amp “expects” to be driving one speaker per channel, so you may make it unstable if you run just a single channel over any length of time.

Perhaps someone knowledgable such as @NeilS can confirm.

I have never had any problem using one channel on Nap 250,Nap 110,Nap 140,Nap 160

Yes it’s crucial that they are of the same age etc. :+1:

Well, good luck with that, although I can’t imagine why you would possibly want to do that with four separate amps!

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Technically no problem at all.

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I have done that, no problem.

There is no safety or instability issue in only running one channel Graham.

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You may be right, but I can’t see why you would want to do so. If you want a mono amp, chop in what you have and buy a pair of NAP 135s.

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As it happen I have two Nap 100 which I ran in such L + R configuration only.
No issues leaving other channel unused, and sounded great in my office setup.

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:+1:I did run four Nap 100´s using one channel in an active Snaxo 242 system, no problem.

Yes, no problem with only running one channel, but I would recommend using the dedicated L+R XLR cables - that way, the unused channel won’t be loading the input signal.



OK, Neil, thanks for that. My mistake!

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