Is my active crossover faulty? Something is!

Please can somone with active system knowledge work through my reasoning below and see if they agree with my conclusion.

System boxes are NDS/555ps 252/Scap SNAXO/SCap 2 x250 SL2. Nothing new or different. All connections good, nothing been moved.

I have suddenly noticed some distortion which is quite frequency specific in the upper mid. More RH channel than LH. It equates to about the higher register of piano music and on a couple of specific tracks is very obvious. Much if the time it isn’t.

Thinking it was speaker related first I switch the RH and LH connections for both tweeter and main drivers. Same problem but more in LH channel now. So not an individual speaker.

Could be a 250; so swapped them over ie tweeter amp now main driver and vice versa. No different. Swapped just the SNAICs that connect to them around. Same. Not one of these either then.

Tried using alternate output from 252 ie switch from cd to tuner socket. No change. Not the pre amp unless it is across all outputs but see below.

Headphone amp run from 252 output sounded perfect; so not the NDS. Not the 252 either presumably.

My logic says this has to be the SNAXO or the SCap that powers it, the 252 PS or just possibly the (SL) cable from 252 PS to the SNAXO PS.

I have a non SL alternative to the active cable somewhere that I can swap in to test that.

So, any more ideas to help me take this further and attempt to refine which bit(s) I am going to have to send back. SNAXO seems the most likely to me but I’d like to be sure.



Hi Bruce,

Are your 250s olives?


Your tests seem logical and methodical, and I agree do seem to point to the Snaxo (though I don’t know what internally would be likely to fail), but odd to be both channels starting at same time. An additional check possibly worth trying is the channels one at a time: e.g. disconnect one speaker cable at amp and listen, then swap the cables over at amp (the other speaker connected, and first speaker disconnected. Then repeat with the other amp channel. Is it really both channels, or actually just one with distortion? If both, and started suddenly, it suggests something common to both channels, maybe the power supply, if only one then not the PS.

If it were me I would also use REW with measuring microphone and test with frequency sweeps at the same time as the above, and look at the distortion traces which will both help confirm and show where in the spectrum it is. Not sure whether it would assist, but it might.

Following your diagnosis seems to rule out a faulty or in need of service NAP250. It only really seems to leave the SNAXO itself.

Are you able to revert to passive operation and try each NAP250 in turn just to be sure?


I was also going to suggest running passive to confirm the Snaxo as the issue …

I had an issue with a 362 snaxo too not too long ago. I tried all various combinations to sort out a bass problem and ended up sending both snaxo and scdr back naim headquarter. Although naim did not find any apparent fault, upon return of the units and reinstatement the problem was settled. So yes, active systems can be quite tricky …

Thanks to all so far.

The 250s are olive.

I can probably set up passively; my ‘office system’ SBLs are using the SL2 crossovers and I think I have enough space behind them to set them up temporarily. At least I can double check each 250 alone in such a system.

If it is clearly an active problem then I am still not sure how I can define whether it is the SAXO or its PS. If it is only one channel (as suggested above) then I am not sure if that helps. I don’t have an unused PS I could try on the SNAXO. At least I could be sending only two boxes back not more.

Looks like a session of careful un-plugging and testing.

Happy days


Hi Bruce - You have two Supercaps so could you not swap them on the 252 if you test out the system in a passive configuration. Other than that, your friendly local dealer and a loan of a Supercap ( for the SNAXO) to fully isolate the issue may be in order - you’ll need to go through the dealer to get the faulty item back to Naim.


I could swap the PS over but if it is faulty then it won’t work OK on the 252 so I guess I would be no further.

It is a while since I had a local dealer relationship. I have bought most of my recent kit s/h or ex dem from a variety of sources.

I will report when I have tried the passive route. Might be a day or so; being retired now means I am so busy!


Well I am further forward now.

Same distortion running passively with both 250’s. Tried both cables too.

Swapped Scaps on the 252 in this configuration and problem is still there. Tried two different Burndy’s too.

All comes down to the 252 I think. Using a headphone amp off the 252 sounds perfect but I guess it might do. I think that proves it is not the NDS too. The problem not unique to the CD input though-sounds same when I connect the others. My last idea is to use my Qute as a pre-amp in the system. I can passively run one 250 in that configuration and check it sounds OK. I am trying to work out if I have a suitable cable to run the NDS into the Qute as a source to absolutely check it is not the NDS too.

Ho hum



Good work Bruce - looks like you’re getting there with the diagnostics,

Good work Bruce. Sounds like you’re narrowing it down nicely.

Ok, check this.

NDS analogue output enabled
2xRCA from NDS to Qute Analogue input
Qute pre out to one 250, passive to SL2

NDS stays as source, Qute now the pre. 252 out of the system. That should work?


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Total confusion

Qute as source and pre-amp driving one 250 passive. Distortion, all in RH channel.

Swap speaker cables over from 250. Now in LH channel. Definitely not the speaker.

Use the other 250, with the speaker cables connected the correct way around and the distortion is still the LH channel!!!

Note I’m using the same SNAIC in each set up.

This does not make sense at all. The source files are fine (headphone direct from Qute confirms). This is a fuzzy electrical distortion that is quite frequency specific. It is not a room issue. How can using two different amps connected identically make it swap channels?

Any suggestions before I go mad appreciated.

Hi Bruce that is rather confusing, the great thing about Naim boxes is at my age they are too heavy to throw out the window in this situation. Perhaps @Richard.Dane can fathom out what is happening after your latest test…most odd.

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Bruce, when did you last have your NAP250s serviced? I assume they were done together?


I am coming to the same conclusion

I did not buy them together, and I’ll have to check the service records with Naim.

In the passive system with just a Qute it has to be one or both of them that is faulty if the cables and speakers are fine. I cannot see any other explanation.


I’ve found that once past a certain age NAP250s can go off colour quite severely if not serviced, probably due to their regulated design, which makes sticking to the recommended service intervals pretty much mandatory on the big Naim amps. From what you describe, “a fuzzy electrical distortion that is quite frequency specific” that could definitely be something down to an amp needing a service.

Hopefully @NeilS will see your latest post and may have some ideas.

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Thanks. I have an ancient chrome bumper one in my office system I can swap in to try. Giving up for today, I am at risk of connecting them totally cockeyed having tried so many options.

What still confuses me is that both appear to have the same fault as running either in passive gives the same issue.

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Yes…the chances of them both having the same or similar fault, most odd. But perhaps they have been failing gradually and then just fell off a cliff edge…and hence you noticed.