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Quad 34 MM load

Discussion in 'd.i.y.' started by chartz, Sep 4, 2019.

  1. chartz

    chartz pfm Member

    Please please! Tell us more!
     
  2. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    Oh OK then...
    For MM (all part numbers refer to schematic in post 25):

    C12,13 = 100uF (on MM input board) Observe polarity.

    R34 = 82K

    C27 = 10uF

    If you want to bring the slight treble boost down to something more correct make C21 150pF

    It's a pretty weird design overall...

    For MC:

    C12,13 = 2200uF (on MC input board) Observe polarity.

    R34 = 82K

    C27 = 10uF

    C18 = 220uF

    Some of these values may seem counter intuitive in some ways.. or at least odd, but they are correct in sim and I have very little doubt that they will work in practice.

    Do all or non of the above mods! There are some strange interactions, which I've taken care of.... I hope:)
     
  3. chartz

    chartz pfm Member

    Thanks!
    So you keep the 2.2 µF?
     
  4. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    Just seen this.. you must have posted whilst I was adding to my post above.... please read further comments above..

    For MM you can keep the 2.2uF but for MC it needs to be 220uF. However if you make it 220uF then this should be fine with either. If only MM is to be used then the 2.2uF could be made a film type for a further possible tiny improvement. If you do the other mods for MC but leave the 2.2uF in place there will be a big bass peak before it then rolls off pretty quick... hence my comments about do all or non of the mods...
     
  5. davidsrsb

    davidsrsb pfm Member

    These values work on my simulator and the 2u2 is no longer sensitive.
    Now there is no warp filter at all
     
  6. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    That was my intention.

    If you do a sim for the MC case you will find the reasons why I specified 220uF to replace the 2.2uF... but yes it ceases to be that sensitive in the MM case:)

    You can however, as I said earlier, fit the 220uF as a default and it will work fine with either...for those with MM and MC boards, but the changes on the individual input boards should still be done. 6.3V electrolytics should suffice but use the best you can get, particularly for the ones changed on the input boards.
     
  7. davidsrsb

    davidsrsb pfm Member

    I like to see a warp filter, but less intrusive than Quads. A roll off below 10Hz is more sensible to keep group delay nasties out of the way.
     
  8. chartz

    chartz pfm Member

    Jez, could you re-calculate to get a cut below say 15 Hz?

    I tried the no-rumble filter option but the bass panels of the ESLs flap badly on warps. Not good.

    How about 4.7 µF for C12 and C13?
     
  9. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    Sorry but no. I never use rumble filters and find them to be always deleterious to sound quality. I've never had a problem without them and have used ESL's before with phono stages without rumble filters without problem, including with power amps that go all the way down... unlike the Quad ones!
    One of the mods I do on the Arkless 640P is to remove the rumble filter altogether and several have used these with ESL's without issues.
     
  10. chartz

    chartz pfm Member

    Ok then.
     
  11. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    For anyone wanting these mods but not a DIYer I will carry them out for £50 plus postage. Several further mods also available. PM me for details.
     
  12. chartz

    chartz pfm Member

    Something odd Jez, replacing the 470 nF with 10 µF (Nichicon Muse) and C12/ C13 alone restored treble level and detail (and bass, amazing effect on ESLs!). Can you explain?
     
  13. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    They have no effect on the treble but I would expect the effects to carry up to the lower midrange and could therefore give the impression of better treble and detail just by "bringing it all into focus"... It's an odd thing but improvements at one end of the spectrum sometimes give the impression of improvements at the other end!
    I would expect considerably better bass, especially in terms of bass "slam" and "texture"/"timbre" and improved dynamics.
    You should change the resistor as well for the full effect! This is important. As I hinted up thread this is a rather odd phono stage design...
    Original R34 is 56K and you need to change this to 82K. If you have a pair of 27K to hand you could add these is series if you have no 82K in stock.

    I have further mods for it in terms of power supply upgrades and op amp upgrades but I'll see if there's any interest from potential paying customers before deciding whether to publish these for DIY use.
     
  14. chartz

    chartz pfm Member

    Good idea! No 82k in stock but I think I do have 27k. I'll report later.
     
  15. davidsrsb

    davidsrsb pfm Member

    C12, C13 and C18 all 4u7
    R34 = 75k
    Gives a steep cutoff below 10Hz
     
  16. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    ... leaving most of the warp frequencies to pass through...

    I've always said that the warp frequencies are so close to the lowest bass that we want to reproduce that it's not really possible to adequately remove the warps without spoiling the sound... hence I never put such filters on any of the phono stages I design and always remove them from those I modify.
     
  17. davidsrsb

    davidsrsb pfm Member

    I agree that it is not possible to filter out the higher warp components, but at least we don't need to amplify the effects of an off-centre record
     
  18. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    Good luck finding that cartridge that's flat to 0.56Hz :D
     
  19. davidsrsb

    davidsrsb pfm Member

    It is fortunate that they are not, as an all too common 2mm peak to peak centre error would be embedding your drivers in the walls.
     
  20. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    Any results yet?
     

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