Musicman output jack, 4 prongs really necessary?

Discussion in 'Pickups & Electronics [BG]' started by HalfManHalfBass, Jan 6, 2009.

  1. HalfManHalfBass


    Jan 21, 2003
    (I posted this question at the end of another existing thread, but rather fear it will be overlooked, due to the original thread's title being somewhat unrelated. Therefore please excuse me and accept my advance apologies if I have violated some rule about 'double posting', I mean no offence. Thank you.)

    Does anyone here know if the Musicman 4 prong jack socket, can be changed out for a standard 3 prong stereo switchcraft type?

    It appears to me that Musicman wire their plug like this:

    1) The black negative battery wire directly to the circuit.

    2) The red positive wire from the battery is split in two with each half wired to a special separate terminal on jack socket. When the guitar lead is plugged in, these two halves meet together and power the circuit.

    Is it not possible instead to wire it like this?;

    1) The red positive battery wire directly to the circuit board.

    2) The black negative battery wire to the third prong of standard switchcraft stereo jack? Like all other active basses are!

    This means that only 3 terminals would be needed and not four.

    I can only think Musicman do it their way to prevent the audio negative and positive leads ever sharing battery power terminals, (i.e. the audio and power paths are completely separate).

    But is this truly necessary with their circuit? It makes finding replacement jack sockets a real pain! Many thanks, Rob.
  2. kraigo


    Jun 21, 2007
    Minneapolis, MN
    Typical active basses use TRS jacks for input. The battery isn't used until the ring and sleeve prongs are shorted by the standard instrument TS plug. Perhaps that's what you're seeing.

    bassdude51 likes this.
  3. The80thAction

    The80thAction Guest

    Jan 16, 2016
    Can I bump this question?

    I am currently trying to do this to my '92 MM SR myself.

    MY question is - Where exactly on the circuit board do I connect the red positive 9V battery wire?

    What I would loove to see is a little step by step instruction onn how to do this. I've had MM output jacks has crap out on me twice now and I am in need of an alternative.

    I know I've seen @walterw post about this, I just need some clarity.

  4. Hopkins

    Hopkins Supporting Member Commercial User

    Nov 17, 2010
    Houston Tx
    Owner/Builder @Hopkins Guitars
    I see no reason at all that you couldn't switch the battery negative vs the positive. There is no need to solder anything to the board, just solder the two positives on the switch together.
  5. walterw

    walterw Supportive Fender Commercial User

    Feb 20, 2009
    yep! the red wire from the battery clip gets jumped right to the red wire leading to the preamp.

    the one black wire that's coming from the 9V clip negative will go to the ring terminal of the new regular TRS jack, while all those other black ground wires go to the sleeve terminal on that jack.

    the one tradeoff (and my guess as to why MM wired their basses this way) is that plugging into the revised jack setup while the amp is on will lead to some power-up noise through the system; thing is, you shouldn't be plugging/unplugging while the amp is hot anyway, that's amateur hour.
    Geri O likes this.
  6. Geri O

    Geri O Endorsing Artist, Mike Lull Guitars and Basses Gold Supporting Member

    Sep 6, 2013
    Florence, MS
    Since the MM OP jack came up, I'm wondering if Walter or anyone else knows if the MMs came with the usual Switchcraft TRS connector at any point. All the ones I've seen and poked around inside (5 total) had the long barrel-type OP jack. This last 2005 SR5 I bought came with the Switchcraft (NOT Witchcraft, damn auto-correct!) jack and I had to go in and repair a messy solder job on this jack a week after I got it and the bass died due to a signal wire breaking away from the lug on the jack. It took some doing to get those lugs squeezed down to fit inside the connector hole. I had finished the job when I realized that this doesn't appear to be the correct jack.

    What's really stupid on my part is that almost 2 years ago, I bought 3 of those barrel-type OP jacks, one to repair a friend's SR5 jack (because the local GC couldn't get the order right), and a couple of spares. I TOTALLY forgot about the two remaining barrel jacks in my parts drawer. ARRGGHH. I plan to replace that Switchcraft (don't do it!) jack one of these days
  7. walterw

    walterw Supportive Fender Commercial User

    Feb 20, 2009
    i've never seen that!

    they've all had the plastic "black box" jacks with a separate isolated "make" connection to engage the 9V+ to the pre when you plugged in.

    supposedly the very early MMs used a regular mono jack and just wired the preamp to be on all the time, figuring the battery life was still long enough for it not to be a problem.
  8. The80thAction

    The80thAction Guest

    Jan 16, 2016
    Ah, you see, that makes almost too much sense. No wonder I couldn't find an available port on the circuit board. Thanks
  9. The80thAction

    The80thAction Guest

    Jan 16, 2016
    Thank you for this! I should be up and running in no time.
  10. Geri O

    Geri O Endorsing Artist, Mike Lull Guitars and Basses Gold Supporting Member

    Sep 6, 2013
    Florence, MS
    I went back and looked at those replacement jacks that I bought from EBMM.

    I'm convinced that drugs are being slipped into my coffee in the morning somehow. Well, I'd like to blame it on that and not the fact that I may be losing my mind...:help:

    You are correct. They are all the black box type you mentioned. I have no idea where I got the idea that the jacks were the barrel type. I really don't. And yes, all the MMs I've poked around under the hood had these black box jacks. Sorry for the confusion. I probably better double-check my schedule today, I have two gigs!

    I have a 1979 Stingray sitting here that I'm kinda baby-sitting for a friend, who's been traveling a good bit (not music-related). We are having to replace the preamp in it, so I'm gonna have a look at the jack in that one. The original finish has already been stripped off of the instrument down to the natural wood, so he's not too concerned with keeping the bass original for value's sake.

    Here's the jacks I got from MM parts department...


    Now where is that schedule!!:D
  11. Dilligas

    Dilligas Guest

    Oct 20, 2012
    Smithtown, New York
    I know this is an old thread but was looking for a replacement jack for my SR & found this thread so I called MM. They answered on the first ring & I was able to order the part directly from them. The total was $11 including shipping. AAAAAAAAA++++++++ for them, amazing customer service!
  12. selowitch

    selowitch Supporting Member

    Aug 6, 2005
    Rockville MD
    Ernie Ball Music Man sent me this diagram which some of you may find helpful:

    Aloe and coves like this.
  13. coves

    coves Supporting Member

    Exactly what I needed. The original output jack on my MM Classic kept cutting out on me. Thanks for posting @selowitch
    selowitch likes this.
  14. tadawson


    Aug 24, 2005
    Lewisville, TX
    FWIW, I just had to replace the jack on an early Bongo, and it was 3 lead . . . The replacement was 4, so apparently MM has used both over the years