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Nap 135 help: self-muting and fan adjustment

Discussion in 'd.i.y.' started by hifiaf, Jul 27, 2020.

  1. hifiaf

    hifiaf pfm Member

    Tonight I recapped the fan boards, replaced the VBE tant on the amp boards (which I may have fouled previously), replaced the zener diodes on the reg boards, and de/resoldered all the connection to the XLRs. Also checked all my interconnects to make sure they're not mixing signal and ground.

    I also checked the values on the over-amperage trim pots. The "good" amp has both of its pots set to 258 ohms (I got two identical readings and one 0 reading in the three possible pin positions). The "bad" amp had its pots at 220 and 240 respectively. I tried my best to get them to 258, but they wouldn't go that high. They would go from zero (all the way in) to 220 or 240 (halfway) and then back to zero as you backed them off completely. This may indicate a problem with the pots, or with my way of taking readings, or with the very concept of trying to take readings with them in circuit... In any case, I just put them back where they were initially.

    I'll test the amps out tomorrow and see if any of this has made a difference!
  2. colasblue

    colasblue pfm Member

    This just gets weirder and weirder!

    So you switch off and it immediately cuts back in until the PS drains down?

    That's not a regs board trip sir! The regs board trip normally needs 15 minutes of power down to reset.

    The thermal cutout cuts the mains input but clearly the PS is still charging so it can't be that either.

    There is no mechanism inside the normal 135 that could make it behave in this way.

    Bottom line - the amp is ON

    Something is interrupting the signal.

    If you switch the 135's over does the fault follow the amps or does it stay on the same channel?

    You might also sensibly check that no spurious voltage or signal is appearing at the amp's input which might upset the source somehow.

    The fact that it suddenly works when you isolate the amp from the mains may be indicative of a voltage offset problem caused by a failed coupling cap somewhere.
  3. hifiaf

    hifiaf pfm Member

    I've tied my hands in terms of checking different channels on different amps, since I've only got one XLR input on each amp, one for the left, one for right.

    Hmm, maybe the next thing to check out is the relay in my 32.5. I recently switched all the cards over to Ryan Sound Labs, except the relay, which is original.

    Another thing possibly worth noting: the left channel, which is the one that cuts out, also has some very faint radio breakthrough that I haven't been able to sort out (this was one of the reasons I got the RSL cards). I've changed interconnects, speaker cables, disconnected all sources, tried swapping the speakers... but it's still there.

    My preamp power supply is a Snaps that has been upgraded with 2 Avondale TRP-2s. I've set the voltage to 25V on both rails, which is what the RSL cards like.
  4. Tom Bonjour

    Tom Bonjour pfm Member

    If you can change the amps left for right, that will really help narrow this down. I am guessing that the problem will stay in the same channel. But it's just a guess. This is certainly a very puzzling problem.
  5. colasblue

    colasblue pfm Member

    Could be a job for a couple of bent paperclips!
  6. hifiaf

    hifiaf pfm Member

    I'm onto my fifth straight LP with no interruptions. I've been putting off writing this update for fear I'd jinx the streak I'm on -- but now I've done it, so we'll see what happens :)
  7. Gervais Cote

    Gervais Cote Predator

    That’s good news !
    If I may ask, can you eventually describe the sound of these big babies in comparison with your previous amplifier..............they are definitely on my wish list...........:)
  8. hifiaf

    hifiaf pfm Member

    I definitely will, @Gervais Cote. I have a freshly recapped Nait 2 and a CB 110 with an Avondale PSU to compare them against, and am planning one of my usual over-the-top shootouts in the near future. I did have the Nait 2 in the system yesterday, and (true to its reputation) it wasn't a million miles from the 32.5/Snaps/135 -- just a touch of harshness around the edges and a little less control of the bass, and it did get ragged at truly high volumes, but with the efficient NS-1000Ms it was fine up to reasonable levels. Of course that's a total apples-and-oranges comparison... it would be nice to get someone to bring a 250 or a 160 over to compare it to (anyone in Toronto, you're welcome!)

    8 hours of continuous listening and still no self-muting...

    Thanks for all your help, everyone. Let's hope hope the streak continues! (Every time a producer decides to move the action to the right channel my heart skips a beat, but so far it's just been in the mix :))
  9. Gervais Cote

    Gervais Cote Predator

    I had Nait 1, I now have a lightly modified NAP 110, an original NAP 160 BD and a more recent NAP 250.2 .........but I live in Montreal, not Toronto !
    Surprisingly, I always come back to the 160 even after giving the others a long trial. I can’t explain what it is, maybe the 160 is kind of magic..........
    Anyway, your comments will be more than enough to give us a good idea as you will be comparing McIntosh apples to Cortland apples IMO ! :D

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