Hello everybody.
This is my cuestion: can a Naim Nap 250 power amp work with 4 ohms speakers?.
It’s a vintage one with grey facsia.
Thanks to all and have a nice weekend.
The short answer is yes; the NAP250 should remain stable into any load, although protection may well kick in when you dip below 2 ohms.
Of course, a 4 ohm average rating for a speaker is just a part of the story; the load may well be highly reactive with peaks and troughs in the impedance.
Also bear in mind that the NAP250 will need to be in good fettle (a full service at least every 8-10 years is essential with a regulated amplifier) and you definitely should stick to Naim’s recommendation regarding speaker cabling (NACA5 or similar with SA8 plugs and of at least 3.5m length per channel - see FAQ on here).
What speakers are you considering here?
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Yes, you may gain on transients over an 8 ohm load and I doubt there will be a noticebale change in quality provided your 250 is in a good state of repair. Have fun.
I had a chrome bumper 250 and at the time used it with a pair of KEF 107s rated from memory at 4 ohms. No problems.
Hello to all and thank you very much for your answers.
Answering to your cuestions, the speakers I’m thinking on are a IMF Tls 50 Mk 1 (I blew a Quad 405 at its moment no knowing they were uncompatible).
And Richard, once again thanks a lot, yes, I use Naim Nac 5 speakers cable (3’5 meters long) but I also have at home a set of Linn K 20 (also 3’5 meters) that seems to be also compatible with Naim power amps, is it so?.
Thanks to all and enjoy saturday.
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Yes, the Linn K20 is fairly close to NACA4 and fine to use with Naim amps, subject to the usual requirements.
The Quad 405 absolutely hated low loads. It was really only happy on 8-15 ohm speakers, and even then you’d probably be better off with a 303 which sounded so much nicer…
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Great and thanks again. And what about the IMF?, what can I expect matching them with the Naim?.
I love the IMF, which I have always matched with Dynacos St 35 and Audio Innovations power amps and integrateds, and I also love the Naim power amps, always matched with Tannoy Berkeley.
And by the way, I’ve never owned and never or heard a Quad 303 but I have always loved the speed and clarity of the 405. A new search is starting … 
Worked well with my 4ohm Keilidhs for several years. I imagined there is many a NAP250 powering 4Ohm speakers out there. My 250 did trip a few times when pushed hard during those long hot summers (you know, the ones when Predators arrive from space to hunt humans), but only enough to motivate me to go for a pair of 135s. 
Remember the name (250) - that’s 250 watts total, 125 per channel… into 4 ohms!
The online specs claim it can be used down to 2 ohms.
Hi, please can you elaborate. I’m not very technical and I’m intrigued how this whole impedance stuff works.
I had TLS50 Mk II speakers from new back in 1975, chosen after auditioning 12 other speakers at similar price (equivalent to £2.5-£3k today), and they were wonderful - and my introduction and conversion to transmission line, from which I haven’t budged in three upgrades over the decades. (My son has my original speakers now.) However mine were 8ohm - were the Mk 1 4 ohm?
Transmission line speakers tend to benefit from high current capacity on transient, and low output impedance for grip on the bass drivers - though that may apply to most speakers! I learnt in time that amps like Amcron and Krell back in those days were regarded as best for those speakers, and more recently Bryston. I used first with a Sinclair bridged amp, then Radford HD250, and tgey sounded OK to me, though undoubtedly could have been better with better amps. I then upgraded the speakers to IMF’s top model (though older, and amps progressed.
How well the NAP 250 would manage them I have no idea, but for my current 4 ohm PMCs, which I know would appreciate peak power in excess of 500W for spirited playing, I wouldn’t be interested in trying anything below the 300, and have doubts as to how well it would manage compared to my Bryston. That said, Naim power amps have much greater peak current capability than their RMS power might suggest, so the 250 might acquit itself well, and better than th amps I used with tge Mk II, but that is only a guess.
Isobariks are a nominal 4ohm load. Many a 250 has been used with them. My father had one driving his first pair of Isobariks it would occasionally cut out when driven hard.
I still have that amp plus another two in my setup which I inherited from my dad. They are driving PMS Isobariks and have never given any problems.
My 9m old 250DR goes into Dynaudio Heritage Specials. Via 3m chord epic speaker cables. Sounds very nice. Amp doesn’t get hot. Comfortable listening between 8 & 9 0’clock on NAC 282 with SCDR. So no problems so far.
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The NAP250 would drive Isobariks fine but if pushed then they could have problems dissipating enough heat and then the thermal trip would be triggered. The “fix” was to give them plenty of space and air, going so far as to stand them upright on their sides and in extreme cases point a fan at the case. Naim, of course, then brought out the NAP135s which were based on the 250 but had extra cooling and an internal fan.
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Actually, the 250DR has been bench tested and found capable of more than 90W @ 8ohm and 160W @ 4ohms.
I think we are in violent agreement!
Well, as hard as I try, I can never get my 250 DR to get anything beyond mildly warm. Sad.
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Worth noting 4 Ohm speakers aren’t rare. They are everywhere. And amps a lot less capable that a 250 drive them. There are so many other factors that dictate how challenging 4 Ohms is.
Honestly, if in doubt and the dealer has no experience with the combination, I’d go by the speakers’ wattage guideline and if an amp (any amp) is in the upper half of that into 4 Ohms I’d not worry too much.
I can’t recall if my Kef 104.2 were 4 or 6 ohms but they sounded amazing with all the 250s I’ve owned over the years and they didn’t seem to have any problems driving them.
My first Naim system had a NAP 140 driving Dynaudio Contour standmounts - inefficient and a nominal 4Ohms.
It never broke sweat even when pushed (albeit within power limitation).