I have run into an issue with an year old NC 250, connected to an 222 with npx 300, feeding my lovely Sonus Faber Olympica Nova 3. A few days ago I had a little party and I was listening at one moment to a few songs at higher volume. The maximum volume is set to 70 in the system setting, and I was turning to 90-95 in the 222. At one moment, the music faded very much, the power button on my 250 started to blink. I was not aware what is going on, not having this problem until now. After a few seconds, the music came back to normal, but after another minute, the music faded again. Then I touched the 250 and it was very hot in the left side. I stopped the unit but it was too late, the highs on the left speaker broke (hope the crossovers are ok, I will check them).
My dealer was funny, he told me that this is a unit for HiFi listening and not for high level listening. I usually listen at 70-75 dB, but sometimes I like to go higher, especially around friends at a glass of wine.
Iām still waiting for an opinion from Naim Tech, the dealer will send the unit to service (unfortunately in other country as we donāt have locally).
I think is a faulty unit, I didān get the chance to check at the time at least if the fan was working, but I donāt think is normal this behavior.
The high volume was for a few songs, at a level which at the time looks like it could go higher. The room is 35 sqm.
I now regret a little for not using my McIntosch with the SF, but I like the Naim and keep it in my main system.
I use NACA5 cable speakers, Chord Signatura jumpers on SF. The 250 is in a rack with pretty good air flow.
One thing to further investigate, sometimes I have some relay clicks on standby, I suspect the DC in the circuit, as I have solar panels. I intended to buy a DC blocker to see if it fixes the issue.
One more thing, in standby, the 250 is a little warm on the left side, I donāt know if itās normal.
I believe your speakers are pretty sensitive (90db?). I just canāt imagine turning my 222 up to 90. It would be incredibly loud. So Iām not that surprised your NC250 overheated and cut out to save itself. I believe this is by design.
from the Colloms/Stereophile NC250 review
Continuously working beyond the rated power will cause a low-noise cooling fan to turn on, after that a temporary thermal shutdown. (Naim calls the amplifier āparty-proof.ā) Reset is automatic. The amplifier runs cool at modest power, barely warm to the touch and better for the environment.
I guess the shutdown means the unit is working as intended? As far as I know Iāve never got the cooling fan on my 250 to come on.
Iād imagine playing at this level would also put thermal stress on the speaker drivers (and resistors in the crossover?) and lead to increased resistance seen by the amp.
How did the system sound after it had all cooled down?
You said āthe highs on the left side brokeā. What do you mean by that? Do you mean that there was distortion, or did the tweeters stop working but mid and bass continued?
I canāt comment on the volume setting as I donāt understand how you can set a maximum setting of 70 then play at 90, and those numbers are meaningless to me having no familiarity with the 222).
The output transistors, which dissipate heat, are off center and more to the left hand side. Youād expect the left hand side of the amplifier to be hotter than the right.
As IB has mentioned, it sounds like the protection mode of the amp was triggered so probably working normally. Itās possible that a driver failure or crossover issue on the speaker may have caused the issue. But it could also have been the amp. Or an issue with the cabling, or.. Best get your dealer to check over the amp - if it checks out OK then itās probably one of the other possibilities as the most likely cause.
Of course the amp should protect itself, but as I said, I donāt abuse my equipment, but 2-3 times per year I listen for letās say half an hour, at higher volumes. I just didnāt think that this kind of equipment is not able to sustain a few minutes of high volume, I still believe there must be something with my unit.
At least in my setup, the volume was high, but not incredible high. Thatās why I keep my max volume at 70, to not have my kids turn it too high and to broke somethingā¦I did it instead.
Iāve turned it on in the morning, the sound seemed to be ok, but without the left tweeter, I didnāt test it any longer as I was angry.
At least the thermal protection would have protect my tweeter also, I rather repair the 250 than the SFs.
This is precisely why I found my chrome bumper 250 not fit for purpose - every time I had a party it wimped out. I traded for 135s and it solved the problem and I now have a Nova which is also capable, probably due to class D amp technology.
I would have thought Naim would have fixed this on the NC range - maybe they should put a āNo partiesā sticker on the vulnerable models to warn people.
The NC250 now has additional fan cooling so shouldnāt have the same issue as earlier 250s (which only relied on passive cooling via the casework) with their thermal limiter cutting in too soon when driven really hard.
I could be completely wrong, but the symptoms described above suggest a case of amplifier clipping where, for a short time, the power amplifier is overdriven resulting in the bass/mid frequency sinewaves being clipped and moved by the crossover into the high frequency range and blowing the tweeter. A few years ago this was a fairly common issue though I have not heard of it for a while. If this is the case then the three possible solutions to prevent further occurrences are:
Listen at lower volumes
Get higher efficiency speakers
Use a more powerful amplifier
I hope this gets resolved to your satisfaction soon.
Itās an expensive lesson, but Iām afraid to say your dealer is correct when he says that domestic hi-fi units (bar sources) arenāt designed to play music at what one might call PA levels. Naim amps have protection circuits built-in (as already discussed), but āspeakers donāt have such protections, and blown āspeaker drivers are often the result of over-driving. This has been reported on here several times.
I strongly suspect your 250 is OK. My (non-fan) 250 would shut down when driving 4-ohm Dynaudio āspeakers at medium/high volume after c.15 minutes, as it got very hot.
Please take this the right way, but you have to understand how amplifiers and āspeakers interact. Itās akin to over-revving a car engine. Something will give.
What utter rubbish! Its an amplifier - abuse it and it will protect itself (like any output-protected amplifier, PA or āHiFiā). Now, abuse the system and you may damage it elsewhere - like blowing a tweeter , which appears to be what has happened.
Unfortunately, it sounds to me like the amplifier and/or speaker system were pushed too far. The 250 gave warning signs (the lowering of output) but was then āaskedā to continue. It is certainly possible that the amplifier clipped, which damaged the tweeter. It is also possible that something in the speaker that failed was giving up under thermal stress which dramatically altered its impedance curve etc. thus causing the amplifier to get hot. I suspect that the 250 could be fine, alas something in one of the speakers is not.
Regarding the point that the dealer made, although both the amplifier and the speakers will have significant headroom for normal listening, neither are designed for sustained high-level output in the same way that a dedicated PA system is. This is why products such as the Crown series of amplifiers exist - relatively inexpensive power designed for operating at sustained high volume. Itās the same with the speakers - PA speakers are designed for wide dispersion high level sound output - the SFs are not. Are PA speakers HiFi - no, usually not, but critical listening is not really a concern at sustained party levels.
For the record, I used to work with a 20,000 watt PA system that used Chevin Audio amplifiers and Martin Audio top boxes/sub boxes for the main PA in addition to a 6000 watt amp system for monitors. It was equipped with compressors and thermal management to prevent failure. IIRC it also ran off a 16 amp 3 phase supply. It went ridiculously loud and ākickedā like a mule when setup correctly. It was not so good for listening for musical subtleties, inner detail and soundstage placement.
Spot on advice. Your dealer should be able to drive your amp at high power into a dummy load and check out everything is ok. I use high power dummy load to test my 1kW amplifier. The dummy load is oil cooled . Your dealer might not go that extreme, but will be able to check out as Richard says non the less. Our amplifiers here are not high power in the grand scheme of things.
My bet itās the speaker driver/cross over, cabling relatedā¦ but Iāll keep further speculations to myself.
. Your dealer might not go that extreme, but will be able to check out as Richard says non the less. Our amplifiers here are not high power in the grand scheme of things.