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Naim NA322/3 replacement capacitor for cartridge loading

Discussion in 'audio' started by GordonM, Jan 13, 2022.

  1. GordonM

    GordonM Member

    I have a Naim NAC62 with NA322/3 MM phono boards and have come to the conclusion that the standard cartridge loading of 470pF is the cause of a long standing bright sound from my LP12 /Ittok / Goldring 2200 cart. The loading for the G2200 should be 100 - 200 pF. The arm is correctly set up.

    Everything has been recently serviced and I'm super pleased with the sound of the system as a whole otherwise.

    I had a brief email exchange with Les at Avondale about possible replacement cards. He said just change C3.
    (They don't make 322 replacements). Didn't want to pester him further so thought I'd ask here.

    Problem is I don't know what type or make C3 is. Have done a search of PFM but couldn't find the answer.

    If I've identified it correctly it looks like maybe a polystyrene?

    Can anyone here enlighten me.

  2. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    Prob polystyrene yes but really doesn't matter what type or make is used as all will be fine in that capacitance range.
  3. MJS

    MJS Technical Tinkerer

    onlyconnect and nobeone like this.
  4. GordonM

    GordonM Member

    That's the one I thought it was. So polystyrene then. Thanks.

    I don't listen to vinyl that much so didn't really want to fork out for Neil Jadman or Ryan Sound boards if a simple cap change suffices.

    I'll order a pair today and post a reply once fitted.
    Mynamemynaim likes this.
  5. coredump

    coredump Press <ALT-F4> to continue.

    Another vote for polystyrene caps; did that mod myself a few years ago and never looked back.
  6. coredump

    coredump Press <ALT-F4> to continue.

    Someone has a serious anger issue.
  7. stuwils

    stuwils pfm Member

    If it sounds bright already then will decreasing the capacitance not actually make it slightly brighter? I seem to recall the ortofon Vms20e was often fitted with a fixed 210pf device called the cap210 which was intended to smooth out a slight lift in the top end. or have I got it wrong?
    It may be down to other factors rather than the minimal impact of capacitance loading.

  8. coredump

    coredump Press <ALT-F4> to continue.

    I guess that depends, among other factors, what "brightness" means to the listener. Werner wrote a nice article on MM cartridge loading.
  9. Craig B

    Craig B Re:trophile

    Yes, with decreasing capacitance comes both increased frequency and amplitude of the resonant peak. With increased capacitance comes reduced resonant frequency as well as reduced amplitude, therefore, the foothills of a given reduced frequency/amplitude peak can fill-in the response dip that typically starts above 1kHz, while at the same time taking the ensuing HF peak down to a more comfortable level.

    The thing to remember with CAP210 was that is was an optional solution for MkII version VMS cartridges, released at a time when the Japanese major electronics manufacturers had previously begun lowering the fixed input capacitance of their phono sections by roughly half. The majors weren't typically publishing phono input capacitance during the 1970s, however, a scan of the relevant service manual schematics indicates a correlation between this trend and the growing inclusion of OEM audio-technica MM cartridges with their turntables. As with Shure, Ortofon's F/FF/M derived VMS models had been specified to work best into circa 47-50kOhm and 400pF from the start. IOWs, the inherent electrical rolloff of their coils needed the extra capacitance in order to 'fill-in and flatten' what would otherwise be a greater mid-range roll-off with a much higher amplitude HF peak above.

    Ideally, with MM cartridges, the ability to independently adjust both impedance (which acts purely as a peak amplitude control*) and capacitance would allow more precise control than either can in isolation. Unfortunately, these days, few MM stages allow for any adjustment, let alone both impedance and capacitance.

    [image credit: Pioneer Electronic Corp, SA-9500II Operating Instructions]

    * Although there exists a lower impedance limit which, if crossed, leads to audible HF ringing.
    dan m likes this.
  10. GordonM

    GordonM Member

    So fitted the 100pF caps and the brightness (peakyness) has gone. Now sounds very balanced.

    Unexpectedly the slight sibilance I got on some records has almost gone as well.
    Just a hint of breaking into sibilance now. On the edge so to speak.

    Is it possible that the electrical loading affects the mechanical loading on the cantilever as well?

    Increasing the tracking weight from 1.7 to 1.8g has almost eliminated it completely. (only did this after listening to a few albums).

    I note that the Neil Jadman boards come with 100pF loading as standard.
    The Ryan Sound boards are user configurable from 0 to 367pF.

    Maybe try 80pF at some point as they are cheap and easy to fit but will give the 100s a chance to settle.
    Craig B and coredump like this.

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