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Naim NAXO bolt down trim pots

Discussion in 'classic' started by cctaylor, Apr 2, 2021.

  1. cctaylor

    cctaylor pfm Member

    Can anyone please help me identify the trim pots on my bolt down cased NAXO. This is a NAXO from 1977 used on an early Linn/Naim triamp system.
  2. DaveMc64

    DaveMc64 pfm Member

    Pete MB&D likes this.
  3. cctaylor

    cctaylor pfm Member

    Sorry I didn't make myself clear.

    I would like to know which of the 6 pots controls each of the six outputs.

    HF right & HF left
    Mid right & Mid left
    Bass right & Bass left
  4. DaveMc64

    DaveMc64 pfm Member

    Ah I see, sorry. I'm afraid I don't know that. If all else fails you should be able to trace the tracks from the output sockets to the individual boards.
  5. hp1

    hp1 pfm Member

    On the old naxo/snaxo the 50k trimmers could totally mute the input to the circuit so if you were to turn them all in one direction so they are all muted and then turn them back up one at time making notes as you go. If using naim amps be very wary of connecting/disconnecting the amp while its powered esp if connected to the hf units ,in fact dont connect them to anything until you know exactly where they go.
    The old naxo has 8 filter boards which need to be in the correct position on the main board ,check they are correct before anything.
  6. MJS

    MJS Technical Tinkerer

    Wow, these are so rare that I can't remember ever seeing one at the factory. I'm afraid you're going to have to work it out from the wiring.
  7. nobeone

    nobeone pfm Member

    Show a photo of the circuit and we can work it out I expect :) I shared a schematic of the later Olive NAXO here and an idea of the sectons on the PCB here, I have never seen a bolt down NAXO but my money is on the circuit changing little ...
  8. cctaylor

    cctaylor pfm Member

    @nobeone While the circuits are probably identical to the original NAXO. It is laid out in a similar way to an NAC12. It has a mother board with 8 daughter boards and 3 relay boards. I'll try posting a photo later.
  9. cctaylor

    cctaylor pfm Member

    [​IMG]Bolt Down NAXO by Cecil Taylor, on Flickr

    The six trim pots are across the top. At the front there are 2 groups of 2 then 4 individual boards each with their own trim pot.

    I suppose if I take out all the boards I can trace the tracks. I will need to very organised, the boards have no individual markings and are on identical PCBs, to ensure they go back where they started.
  10. nobeone

    nobeone pfm Member

    Hmm, well, it would seem to me we have, from left to right, a group of 4 vertical daughter boards for one channel (boards 1, 2, 3 and 4), then another group of 4 vertical daughter boards for the other channel (boards 5, 6, 7 and 8), then a group of 3 horizontal daughter boards with the output relays on (these are not very interesting so I will not mention them again). The boards in position 1 and 5 look similar, boards 2 and 6 look similar, boards 3 and 7 look similar, and boards 4 and 8 look similar. Hard to say why the pots are not symetrical with the cards, but again I would assume left to right that pots 1, 2 and 3 are for one channel, 4, 5 and 6 are the other channel. Logically boards 2 and 3, and boards 6 and 7 are the mid frequency filters, the bits missing in my NAXO 2-4 PCB photo I linked to earlier. So the question is whether cards 1 and 5 are low frequencies and 4 and 8 high frequencies, or vice versa.

    Rather than disturb the boards to trace the tracks, how about you don't :) if you did want to you could just pull board 1 and show both sides and I could (probably!) match it to one of the NAXO sections in the schematic. Alternatively:

    Kit Ryan gives a great run down on setting up a NAXO 3-6 here which you could follow, mark with a pencil the orientation as the pots are, then with the system playing use a nice plastic pot twiddler to get in there and and give it a go. Pot 1 will turn up/down the low/high frequencies on channel 1/2, have a listen, you will work it out! Once you know what pot 1 does you should be away. My total guess is the pots go:

    Pot 1 Low Channel 1
    Pot 2 Mid Channel 1
    Pot 3 High Channel 1
    Pot 4 Low Channel 2
    Pot 5 Mid Channel 2
    Pot 6 High Channel 2

    I hope that helps, apologies if the suck it and see approach is teaching Grandma to suck eggs.
  11. hp1

    hp1 pfm Member

    The front 4 boards look like the band pass section for the mid range as they have one pot per pair if boards.
  12. nobeone

    nobeone pfm Member

    That would explain the pot arrangement, but the boards don't look right for that, by which I mean board 1 and 3 look superficially similar but one has a 2200pf where the other has a 1000pf and boards 2 and 4 don't look similar?
  13. hp1

    hp1 pfm Member

    All the board connector positions are the same so its very easy to fit them in the wrong position, in the pic some look wrong to me.
  14. nobeone

    nobeone pfm Member

    True, so, question to @cctaylor is this working as it stands? I mean if hp1 is right then the boards are in the wrong positions and it would be working oddly at best. I think hp1 guess is:

    Pot 1 Mid Channel 1 or 2
    Pot 2 Mid Channel 2 or 1
    Pot 3 Low or High Channel 1 or 2
    Pot 4 Low or High Channel 2 or 1
    Pot 5 High or Low Channel 1 or 2
    Pot 6 High or Low Channel 2 or 1

    I can't see a way round this other than sharing photos of front of boards 1 to 4 to see if we can work out which board is which section of a NAXO and tracing the wiring and the motherboard ... unless of course somebody else with a working bolt down NAXO 3-6 pops up!
  15. DaveMc64

    DaveMc64 pfm Member

    Looking at the photos, the boards are arranged type L-1234, R-1234, left to right.
    Looking at the tracks coming from the trim pots, left to right:
    pot 1 feeds board L1;
    pot 2 feeds board L3;
    pot 3 feeds board L4;
    pot 4 feeds board R1;
    pot 5 feeds board R3;
    pot 6 feeds board R4;

    Given the one big polyester cap on boards L4 and R4 I would guess they are the filters for the bass section so trim pots 3 & 6 for Bass.
    From the tracks it looks like boards L2&3 and R2&3 are linked (diagonal trace between boards but see below) so these are probably mid section so trim pots 2 & 5 for Mid.
    Leaving boards L1 and R1 fed from trim pots 1 & 4 for Treble.

    That would be my best guess at this point.

    The other possibility is that boards L1&2 and R1&2 are linked (difficult to tell from photo) which would make trim pots 1 and 4 the mid trimmers. First scenario above seems more logical though.
    nobeone likes this.
  16. nobeone

    nobeone pfm Member

    I think you are probably right :) looking at the tracks from the pots to the boards does resolve the slightly uncomfortable difference between the similar boards and the pots. It is also logical that the big old Noel Edmonds Swap Shop of a cap is for the bass.

    Looking at the pot positions, pots 1 and 4 look set to about the same, pots 2 and 5 about the same, and pots 3 and 6 about the same ...
  17. Martin M

    Martin M Crueller than April

    Hi, why not first mark the current trim pot positions with a felt tip (dot at the current point for example) and then just turn each pot up and down while listening to music or white noise? Mark the result on a piece of paper and put in the NAXO's box? Seems easier than tracing tracks.
  18. nobeone

    nobeone pfm Member

    I think because a decent idea before you start of what you are likely to find is helpful and may reduce confusion, at least that was the idea. I did also suggest having a go ...

  19. cctaylor

    cctaylor pfm Member

    Thanks for all your suggestions. I'll not be doing anything until I've fitted the new tweeters. I may need to adjust the settings to suit as they are a bit more sensitive than the originals

    I will update this thread with my findings.
  20. cctaylor

    cctaylor pfm Member

    While checking the boards and taking photos of them I must have failed to put board 5 in correctly and lost the treble on the left speaker so the lid had to come off again. I took the opportunity to do some investigating.

    After some careful board pulling of boards 1, 4, 5 and 8 I established the following:

    From the front:

    Board 1 Right HF
    Board 2 & 3 Right Mid band pass
    Board 4 Right Bass
    Board 5 Left HF
    Boards 6 & 7 Left Mid band pass
    Board 8 Left Bass

    This would logically make the trim-pots as follows:

    1 Right HF
    2 Right Mid
    3 Right Bass
    4 Left HF
    5 Left Mid
    6Left Bass

    This matches the suggestion from @DaveMc64

    Thanks everyone for your help.

    PS tweeters just been delivered, just need to steel myself to fit them.
    nobeone, wylton and DaveMc64 like this.

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