advertisement


Naim NAP250 Advice

imarks

imarks

Ian Marks
Hi

After a recent power cycle my system came up with distortion in one channel (NAC102/HiCap/NAP250). I eliminated my source as it was fine through my Nait2 and after a bit of mucking around I've isolated it to the NAP250 as when I connect a Squeezebox directly to the NAP250 I still hear the distortion.

The distortion sounds a bit like crunch or overdrive that you get from a guitar amp so I'm guessing it's clipping. At low volumes the distortion seems to follow the pulse of the music i.e. comes and goes with bass drum/bass gutar notes but at higher volumes it's distorted all the time. Could it be the regulator board? If not any ideas for likely things to look for?

As far as I know the amp has never been serviced so it's probably long overdue a re-cap. Anyone know the current going rate for a re-cap or a rough idea of the cost of parts to do it myself?

I'm considering taking a look myself. I'm pretty sure I could replace capacitors but don't have much in the way of test kit so diagnosing the fault if it isn't just a re-cap might be more difficult. To take the sleeve off is it a simple matter of unscrewing the 4 feet and the six allen head bolts on the bottom of the amp and sliding the inards out?

Thanks
--Ian
 
Personally, I'd get it serviced by Naim through a dealer, especially if you're not experienced at this kind of thing and it will come back sounding better too.
 
Yep, classic NAP250 needing a service symptoms. It's currently an RF oscillator and playing havoc with any music you put through it. If you do nothing else just change the 4 10uF capacitors on the output of the power supply board. That'll fix it while you consider other options.
 
Recapping a 250 requires a medium to highly skilled technician so just make sure you’re okay before proceeding.
If it’s more than 10 years old and played a lot of music, it’s probably due for a full recap.
 
Replacing 4 x 10uF Philips or equv 10uF/63Vdc axial electrolytic capacitors is very, very simple though. Through-hole parts that are unique on the board - anyone can do it.

And it will solve 90% + of sim reported issues with a NAP250 or NAp135. These parts are stability critical- and yet cook-out first.

Also - very very cheap DIY to change! After which if symptoms persist - look elsewhere.
 
Thanks for all the replies.

I'm going to have a go at changing the 4 10uF electrolytics as Martin said they are cheap and looking at some images I found online I can't see them being too difficult to change. Would there be any point in going for a higher voltage rating? 160v are readily available. Just thinking if they are the usually the first to fry then maybe higher voltage rating would improve longevity.
 
Hmm I would wait for a kind fish to suggest a known good replacement rather than just picking a much higher voltage part. The issue, I fear, is higher voltage parts will tend to have a lower ESR, and that may be exactly what you don't want here. I am not saying I know, just saying I know there is more to it that just voltage rating :)
 
imarks said:
Thanks for all the replies.

I'm going to have a go at changing the 4 10uF electrolytics as Martin said they are cheap and looking at some images I found online I can't see them being too difficult to change. Would there be any point in going for a higher voltage rating? 160v are readily available. Just thinking if they are the usually the first to fry then maybe higher voltage rating would improve longevity.
Click to expand...
Generally speaking, each and every capacitors in a Naim amplifier have been sized an optimum way at the factory so I would stay with same capacitance and same voltage or just go up on voltage but just a little bit to stick to the original Naim sound.
Tantalum caps fail short when they get to the end of their life so they have to be replaced on a regular basis anyway as they cause a lot of damage when they die. For an amplifier that plays music loud every day, the caps need to be changed every 10 years.
My favorite tantalum capacitors are the Kemet series 356 but something else similar will work fine as well.
Make sure you identify the polarity before removing any of these to avoid any damage when powering the amp!
 
Gervais Cote said:
each and every capacitors in a Naim amplifier have been sized an optimum way at the factory
Click to expand...

Hey I am no Naim basher, not at all, but let us be honest, these 250 regulator caps are not optimal in any sense of the word I recognise, then there are the XPS caps with no voltage margin, shall we start a list?
 
I have a pair of 250s, one that was serviced by Naim in 2016. The other one I serviced myself by changing all tantalums and the four electrolytics on the regulator board. I didn't have any particular brand of components in mind but I used a combination of AVX for the tants and Nichicon for the electrolytics because they're a trusted quality make. I think it cost me less than £50 in parts.

I cannot tell any difference between the two amps sonically so I'm not convinced there is anything magical about the Naim choice of components.
 
Vishay 10uF/ 63Vdc at Rapid Electronics, a perfect drop-in.o for about £1 each:

https://www.rapidonline.com/vishay-2222-021-38109-10-f-20-63v-axial-electrolytic-capacitor-49-2166

ETA: extract from the linked datasheet for this case size/value:
Useful life at 40 degC ... 70 000 h

- or about 8 years if left continuously powered-up.

Now you see why Naim used to recommend servicing at 7 year intervals, matching their original recommendation these amps were left on. It's not magic - nor marketing foo.
 
nobeone said:
Hey I am no Naim basher, not at all, but let us be honest, these 250 regulator caps are not optimal in any sense of the word I recognise, then there are the XPS caps with no voltage margin, shall we start a list?
Click to expand...
Well, I must admit that if you have a power supply capacitor rated at 40 volts in a circuit running at 37 volts, the margin is rather low. I would then go to 50 or even 63 volts if the ESR and physical dimensions are about the same.
I quite often replaced some 40 volts caps with 80 volts due to the size and availability, especially in Hicaps and they work perfectly fine.
 
martin clark said:
Vishay 10uF/ 63Vdc at Rapid Electronics, a perfect drop-in.o for about £1 each:

https://www.rapidonline.com/vishay-2222-021-38109-10-f-20-63v-axial-electrolytic-capacitor-49-2166

ETA: extract from the linked datasheet for this case size/value:
Useful life at 40 degC ... 70 000 h

- or about 8 years if left continuously powered-up.

Now you see why Naim used to recommend servicing at 7 year intervals, matching their original recommendation these amps were left on. It's not magic - nor marketing foo.
Click to expand...

Thanks for the link Martin, I wasn't aware of Rapid. I almost bought the stuff I needed from RS yesterday but held off as they were out of stock on a couple of items.

I'm thinking it would be sensible to clean off all the existing heatsink compound and apply new. Is that correct? If so do I need any particular type?

--Ian
 
imarks said:
Thanks for the link Martin, I wasn't aware of Rapid. I almost bought the stuff I needed from RS yesterday but held off as they were out of stock on a couple of items.

I'm thinking it would be sensible to clean off all the existing heatsink compound and apply new. Is that correct? If so do I need any particular type?

--Ian
Click to expand...
Heatsink compound? You're just changing some caps aren't you?
 
Yes he is, but you've got to remove the NAPA amp board from the chassis to do it and the heatsink is held to the chassis by 2 screws and a smear of thermal paste between heatsink and chassis!
 
jpk said:
These caps need enough ESR, I used 100V Vishay 138 AML series.
Click to expand...

Just to be clear - ESR in sufficient quants / the right range isn't a problem with small axial electrolytics.
I've used those I linked in several fixes for friends 250/135s, and no problem yet with any. And as you say, 63 or 100v rating is fine.
 
It lives!

I'd like to say a big thank you to everone who offered advice on this, particularly Martin and MJS without whose help I wouldn't have had the confidence to fix my amp.

A couple of things worth mentioning incase anyone happens on this thread in the future:
  1. The capacitors linked to by Martin up thread are fine, they're a good fit mechanically and once put back together it sounded like new.
  2. Getting the case off was quite difficult (for me anyway). The 4 feet unscrewed easily enough but the 6 x 4.5mm allen head bolts which hold the outer sleeve to the sledge/heatsinks and transformer were extremely tight and I worried a little that I might damage something by removing them. However they all gave-in in the end and came out. When I re-fitted the case I tightened them up as much as I could easily do using a regular 'L' shaped allen key levering on the longer part of the key.
  3. There are 5 connectors going to each regulator PCB these are push fit but care is needed when removing them as the PCB is only supported at the heatsink end and it's quite easy to bend (or possibly) break the PCB if you don't support it whilst un-plugging the connectors. Replacing the connectors afterward requires similar care and each connector give a quiet but discernable click as it goes fully home.
  4. The regulator PCBs need to be removed from the sledge. The PCBs and heatsinks are held on with a further 4 x 1.5mm allen headed screws (these were not particularly tight). Once removed the Heatsink may need a little coaxing to pull it away from the heatsink compound.
  5. Removal and replacing the capacitors is easy although care should be taken to get them the right way round. I've highlighted the capacitors that I changed in the attached photo, note that the one on the left is +ve to the top where as the other is +ve to the bottom of the image.
  6. I didn't replace the heatsink compound. As MJS said Naim use a lot of the stuff and there was more than enough left on the sledge and heatsink to just move it around a bit before re-seating. It's horrid messy stuff though :(
 
Last edited:
You must log in or register to reply here.


advertisement


Back
Top