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Naim Nap 135 Servicing thread

Discussion in 'reference' started by colasblue, Nov 23, 2014.

  1. colasblue

    colasblue pfm Member

    Ok here it is – the long awaited Naim Nap135 servicing thread.

    The warning part:

    In order to properly service a power amplifier you will need to have it fully powered up some of the time with the covers off and test equipment connected. Unless you are 100% confident that you are fully competent to do this then DON’T, leave it to the experts. There will be potential exposure to mains voltages which can be lethal, and certain components (large capacitors) can explode if connected incorrectly.

    Some new speakers have moved in with me and two pairs of 135’s just wasn’t enough so I had to set about getting a third pair as closely matched to the ones I’ve already got as I could, and preferably at bottom dollar in order to try them out. Actually a big "Thank You" is due to Richard at Naimly Linn/In Tune for being willing to indulge my uncertainties here. He let me try them out on a sale or return basis. I was a bit worried that those sideways firing bass drivers would upset my turntable collection but actually they're fine.


    The ideals in decreasing order of importance are are:-

    H&F traffos
    CAD drawn amp boards
    CAD drawn regs boards

    Ebay to the rescue


    and for when the ebay link is long dead just the photo


    I thought I’d done OK but in fact the pictures didn’t really do the amps justice, they were actually pretty minty and clearly little used – so much so that the 28 year old heatsink compound was still moist and not at all discoloured.

    I got 2 out of the three ideals, but the regs boards are a slightly earlier layout than on my other two pairs.

    So I try them out passively on my SBL’s and actually they are fine, don’t really need servicing at all apart from the fact that their sonic signature is slightly different to the other pairs I have, probably due to component differences. The only minor thing is that one of the XLR’s has a slightly loose earth conection.

    Putting them into the 6 pack though revealed issues. Initially I tried them on tweeters and things didn’t seem quite as good as they should be, which was confirmed by switching them to bass which was a lot better. None the less I decided to match up the components with my other amps in the expectation of greater synergy.

    So I’m starting with something pretty good.


    Judging by how little dust was inside those fans had never been on!

    The BoM


    There are:-

    4x22000uF 63V Kendeil caps
    4x47uF Evox Rifa MMK (big thank you to Martin Clark for supplying these)
    2x 470uF 63V Panasonic NHG series
    2x 47uF 50V Panasonic NHG series
    4x 47uF 50V Elna Silmic II
    4x 10uF 63V Panasonic NHG series
    6x 10uF 35V AVX tantalum bead
    2x 47uF 10v Kemet tantalum bead
    4x 3K3 2W metal film resistor.
    4x BZX79-C10 10v Zener diode (Fairchild)
    4x Neutrik plastic body chassis mount silver plated female XLR socket
    8x Rubber foot (from Malvern Audio)

    The BoM is my own and is chosen to match the other 4 135’s in my collection. It’s all good but obviously other people will have their own views on what’s best.

    Equipment required:-

    Set of allen keys
    Posidrive screwdriver
    Piano wire cutters
    box spanners (or other) for cap bolts
    snipe nose pliers
    soldering iron
    desolder pump
    Digital (or analogue) multimeter.

    Now first some safety, so the next thing I did was properly insulate the mains switch in accordance with modern safety standards. The material used is just some big heatshrink sliced open.


    Next thing I needed to do was check that the fan board actually works. To do this mark the position of the preset with a pencil or felt pen and then with the amp powered up turn it up and see if the fan starts. If it does (and mine did) all is good. If not you have a fan board fault to diagnose and fix.


    Once done put the preset back to its original setting.

    Next the big stuff so amp off for a few minutes and before starting and just to be safe make sure the caps are fully discharged by shorting with an insulated screwdriver.


    Do this to each cap in turn.

    Next the disassembly.

    Remove the board wiring loom by steadying the board with one hand and pulling directly upwards on each connector with a pair of pliers in turn with the other. Only pull! Don’t be tempted to wiggle since that will likely as not break the connectors off of the PCB giving you another little repair job to sort out!


    Then turn the amp upside down and undo the four allen bolts that hold the heatsink to the chassis.


    Lift and separate!


    Next thing I did was take out the old res caps caps. It’s a lot easier if you take off the air inlet cover, which is secured by two self tapping screws.


    That gives better access to the “U” clamp nuts. Clamp off, caps off, loom out of the way and that gives best access to the XLR sockets. You wouldn’t normally change these but I noticed one of mine was a bit iffy.


    Neatly replaced by new ones.


    New caps on (take care to get them the right way round!)


    And you can then put that bit back together and move on to the board servicing.


    I started with the fan board.


    I changed the two axial electrolytics and the two 10uF tants. Tants like for like, electrolytics replaced by Panasonic NHG series (47uF and 470uF) which are radial rather than axial. No big deal IMHO. Tants have their positive leg identified on the case and on new ones the positive leg is usually slightly longer. Old axial caps usually have the negative end identified by a bar (ring). New radial caps have the negative leg identified by a stripe on the can and with new ones the positive leg is usually longer.


    Next the amp board, which is going to be a bit of fun, since there’s no way those MMK’s are going to fit in the space left by the original tant right?

    So here goes. First the SoA components. Now you see them


    Now you don’t (and yes I know I could have removed a further two redundant resistors before anybody shouts).


    Next change the VBE bypass tant (47uf small blue one), the input tant (10uF red one) and remove the feedback tant (100uF big blue one). The VBE tant may have caused a novice some issues since its markings were virtually invisible, making polarity identification difficult.


    Now no PFM thread would be complete without a bit of bodging, so here’s how to bodge a pair of 47uF gigantic MMK’s into the space left by that larger blue tant (of course if you were doing the service by the book you either replace the 100uF tant like for like, or fit two 47uF tants in parallel which requires you to scrape down the legs to fit two into one set of holes. Note that really is what Naim do these days since 100uF tants tend to go leaky).

    Solder a wire into the hole nearest the heatsink and another one sticking out from where the rear ground tag is.


    Solder a leg of the first MMK to the vertical wire



    Give it some support by sticking the other side to the edge of the PCB with some hot melt glue, stick another MMK to it, solder the two middle legs to the stalk and connect the far leg to the first with a wire link.


    Now on to the reg board.


    Firstly what I’m not doing and what you probably shouldn’t touch either! I’m not going to adjust or reset the overcurrent trip. This job is beyond the typical DIYer since it needs a pulse generator, scope and dummy load test resistors to complete it. There is no reason to expect the factory setting to drift much so unless there’s obviously something wrong (eg preset hanging off or broken) then it’s best left alone. The trip is set by the two presets furthest from the heatsink. Best to just not touch them at all. If disaster occurs then the correct value is about half way between the two extremes of the preset.

    Things normally changed are the 3k3 resistors nearest the heatsink, the four caps and the two zener diodes. I didn’t really expect the resistors and diodes to need changing on this amp but they’re inexpensive so better safe than sorry. Old 250’s sometimes have composition resistors here whose value can drift, but mine had the look of metal film, and sure enough values were spot on.


    I foolishly bought 2W replacements and wish I’d stuck with the original 1W spec since the new ones were a bit of a tight fit!

    I replaced all of the axial caps, the 10uF blue ones with Panasonic NHG series and eth 47uF gold ones with Elna Silmic II’s. Note on my board Naim had used polarised caps so the correct orientation of replacements was easily identified. On later boards they used non polar gold caps (either RoE or SLCE). In those cases the new caps always go in the same orientation as on my board for the same relative position. Another clue is that Naim always put the plastic bung of a non polar cap at the positive end so far as I’ve ever observed (but don’t rely on that). If in doubt check the polarity by measuring with the amp powered up. I also replaced the two zener diodes (note the new ones are orange)


    Now before you put it all back together it’s worth having one last check over the backs of the boards to make sure you haven’t made any “extra” connections that shouldn’t be there. On some of the older hand drawn boards some of the soldering is particularly fiddly with lots of unconnected components in very close proximity (particularly the regs boards on my amps). Note I cleaned the holes on the amp boards to make refitting the SOA circuitry easy if it’s ever required.


    Now it can be reassembled and set up.

    Obviously if the amp’s previous life had been a little harder and the heatsink goo was hardened or discoloured I would have de-soldered and re-seated the power transistors with new compound or all in one insulators in addition to what I’ve done above, but there really was no point in doing that in this case.

    First set the voltages on the regulator board. The easy way to do this is connect the negative lead of a DVM to the earth bar between the caps, and probe the two output connectors of the regs board with the other end. The voltages are set by the two presets nearest the heatsink, one for V+ and one for V- nearest their respective terminals. Obviously the amp has to be on to do this and should have no input or load connected. If there are any big bangs or blue smoke at this point then you’ve definitely done something wrong!

    You want +39.2V and -39.8V



    Next setting the quiescent current.

    I'm using the "Avondale" method with values for an amp board with SoA circuitry removed for which the amp board power consumption is 36 to 38 mA when correctly aligned.. If you want to keep the SoA circuitry in then the current required is a little higher and on the only samples I have I've measured it as about 42 mA to allow for the extra consumption.

    There is an alternative (and arguably more reliable) method based on measuring the voltage across the emitter resistors which I will describe as an addendum. Not all meters will have a range suitable for that method though.

    Turn the amp off again and let its caps run down and reconfigure the DVM for milliamps. Lift the “U” shaped positive feed from the regs board to the amp board and connect up the DVM in its place.

    Turn the amp on and leave for a few minutes. Once settled adjust the preset on the amp board to get between 36 and 38 mA. Then leave it to settle again. Keep doing it until it sticks at a value between the range indefinitely (could take a while).


    Finally check the DC offset at the speaker terminals and also that there’s not much AC (ideally there should be no AC but some 135’s and 250’s hum slightly with no input connected. If that’s the case then short your input to ground and do it again). Note some (most?) meters will register DC when in fact there’s only AC present. Anything under 50mV is fine.


    Then turn it off, put the case back on and it’s theoretically good to go, but you should probably soak test it by leaving it on without actually connecting it up to your prized speakers or preamp for a day just to make sure nothing bad happens!

    And did I achieve the improved synergy I was hoping for by doing this you ask? Well I reckon so actually!


    The more "official" Naim method for setting the quiescent current.

    Since an alternative thread has appeared on PFM extolling the virtues of the official factory method, and I happen to have acquired another olive pair of 135's to completely match my 6 pack and hence I am returning the CB pair to more or less factory spec for sale, I thought I'd have a look at the alternative method.

    So I set up my incoming pair of 135's as described above and then compare the result with the factory method, which is to measure the voltage across both emitter resistors and set it to 7.0 mV. This method seems to be the same for all amps except the Nait 2 which needs 7.2 mV The details are in the other thread(http://www.pinkfishmedia.net/forum/showthread.php?t=83253)

    Anyway it seems that both methods are at least reasonably equivalent since without doing any tweaking this is what I got.


    And just to confirm exactly where to connect the test probes (which I don't think is clear on the other thread)


    In aligning the outgoing pair which now have the SoA circuitry reinstated I found that the "Avondale" approach needs to be adjusted slightly to allow for the consumption of the SoA circuit, and if you don't do that you only get about 4.6V - which is a bit low.
  2. Pete MB&D

    Pete MB&D Pete Maddex, the one and only!

    Nicely done.

    Just a couple of things why no film cap on the input? and don't those yellow wires to the thermal trip carry AC? aren't they a bit close to the feedback cap?

  3. colasblue

    colasblue pfm Member

    Not much point using one film cap here when both my 82 and Snaxo are stuffed full of coupling tants! Maybe when I'm in the mood for changing about 30+ tants in one go I'll think about it.

    Yes those yellow wires do carry the AC to the thermal trip. That's actually their normal position in the 135's and it doesn't show but there is quite a bit of clearance between the MMK's casing and the bottom of the chassis so I'm not too worried about either accidental contacts or induced hum. I could have taped them a little further south I suppose.
  4. peterm

    peterm pfm Member

    Thanks for that useful thread, I've just serviced my 250 with a comprehensive kit from Avondale but if you'll forgive a question that must have been answered long ago where does the +39.2/ -39.8 volts come from? I set my regs to +/- 40, as per Les W's instructions. I've seen the lower voltages mentioned before but what's the reason for the different values on +ve and -ve rails, have I done it wrong?
  5. colasblue

    colasblue pfm Member

    It actually doesn't make much difference. The 0.6V difference is the diode junction drop on silicon devices and setting things up like that just means that if the amp clips it does it symmetrically.

    In theory you can jack the voltages up a bit for slightly more oomph into reasonably high impedance speakers (up to 44v is perfectly fine and I have a pair of nap clone boards running at that voltage in my PC amp) or reduce it a bit to protect electrostatics such as Quad ESL63's.
  6. peterm

    peterm pfm Member

    Many thanks for that! As you may have guessed I'm a bit new to delving inside my naims (but I don't think it's sacreligious like some people do - I've read lots of pfm posts in search of enlightenment over the last few years and have learnt a lot without having much to contribute of my own!) Since I'm running SBLs at a volume dictated by my wife and 4 dogs who "don't like it so loud" I think I'm probably in safe territory so won't open the amps up again, just yet!
  7. colasblue

    colasblue pfm Member

    Any more comments?

    I'm guessing it's mostly good since nobody is telling me I've done anything horribly wrong.

    If not then perhaps one of the mods can move the thread into reference.
  8. flashgo

    flashgo DIY Practitioner

    I did a similar service on my CB135s. The improvement over a 250 was more than I expected, and I've always wondered if the 135s could be pushed further. Replace the Kendeils with CAP-6's or the Naim boards with Avondales?

    The fan on one of my 135s comes on more than the other and stays on long after the music's ended. Any advice on how to set the sensitivity of the fans? Given the monster heat sinks, the fan doesn't seem really necessary.
  9. stackowax

    stackowax pfm Member

    What brand of XLR sockets did you use?
  10. colasblue

    colasblue pfm Member

    I have had the problem of fans being a little inconsistent between amps, though not with this pair.

    The only way you can easily sort it is to get the amps hot enough so that the fans come on with the covers off and the pots easily accessible. When I had SBL's my technique was to put the offending amps on bass and play "clocks" by coldplay at high volume on repeat for a while, and observe from the other side of the patio doors to protect my delicate ears (This only works if you think one of the amps fan setting is about right). Once both fans are on you then wait for the amps to cool down a bit and as the "good" amp's fan starts to slow down you adjust the pot on the "bad" amp to match the speeds. You can repeat that proces a couple of times during the cooldown process if necessary.

    I suspect there is a more scientific way to do it if you know some correct parameters, but the above worked for me.
  11. colasblue

    colasblue pfm Member

    New XLR sockets were Neutrik. The originals were Re-an and are no longer manufactured. The cut-out is standardised so any brand ought to fit.

    I suspect 135's could go further, and in fact Les is happy to mod them so he must think so too. My view on that though is that it's better to build an amp from scratch than modify something and devalue it in the process. My 135's can be returned to "stock 3rd party service + recognised upgrades" very easily by replacing the MMK's with tants and possibly my choices of some of the lytics with Nichicon Axials.
  12. hp1

    hp1 pfm Member

    Nice work there.

    Naim now fit deltron xlr sockets btw.
  13. diybry

    diybry pfm Member

    What an excellent post for an apprentice bodger like me!!!
    I've a couple of questions:
    I have recapped my CB 250 using an Avondale kit, but have only replaced the main smoothing caps and the reg board caps (I think the Philips ones which tend to dry out?), also the resistors which were a little scorched.
    So I've not replaced any tants.
    (I have implemented the 'MOJO' mod as per Mr Tibbs-a huge improvement!)
    My Questions are:
    1) Is replacing the tants like for like likely to improve SQ?- I had it in my mind that the tants don't deteriorate
    2) Can you describe the changes the MMK's make to the sound? It seems that availability of these is even worse than the possibility of my listening to any music during Eastenders, so is there any viable alternative I could use?
    Thanks again for an excellent post
  14. colasblue

    colasblue pfm Member

    The jury is out on replacing tants. Naim always do, but I'm not convinced they deteriorate provided they always remain in correct polarity. Trouble is that the VBE bypass one and feedback one don't always remain in correct polarity. Also tants Naim used in the early days , particularly the STC yellow ones, possibly weren't very good in the first place and I've usually found improvements through replacing those. I've never found any improvement as a result of replacing one of those big red ones though.

    What tants do in the feedback position is add a particular type of colouration to the sound which makes it sound (for want of a better adjective) a little more "organic" in the sense of as opposed to "synthetic". A lot of people like that and it is part of the "Naim sound" which results in significant controversy over what is "best" here. A fair few people who have switched to film caps have found they didn't like the result.
  15. Pete MB&D

    Pete MB&D Pete Maddex, the one and only!

    And a fair few replaced all the tants in the signal line with films and found they did like the result :D

  16. colasblue

    colasblue pfm Member

    No they don't, at least not to old 135's and 250's since Deltron only make diecast panel sockets and Naim only use nylon bodied ones.
  17. Barrie

    Barrie veteran member

    nice thread
  18. mmaatt

    mmaatt pfm Member

    Naim fitted a metal XLR socket to my CB 250 when it was serviced in 2004 (and completely rewired).

    Excellent thread though, should be in the ref section.

  19. colasblue

    colasblue pfm Member

    Did it originally have a metal socket or was that a change? Some older units used metal XLR's with a different cut-out so they have to stay that way.

    They certainly used to replace some other early metal ones with plastic and there certainly seems to be some sonic benefit in so doing. They also make a point of using fully plastic bodied XLR plugs. It's the same eddy current issue as surrounds the discussion of Eichmann bullet plugs and WBT Nexgen phono sockets (and for that matter the HiLine), though no huge amounts of extra money are required to have plastic XLR's.

    Can't see why they'd do a U-turn in 2004 for servicing the older kit since placcy sockets of good quality are readily available.
  20. mmaatt

    mmaatt pfm Member

    Interesting, maybe my recollection is wrong and they left the original socket in place. It does seem odd given that they said they replaced sockets and did a full rewire they didn't change the XLR socket to the nylon version.


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