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interesting insight into late 70s Mutron III's

Discussion in 'Effects [BG]' started by Roscoe East, Jan 18, 2014.

  1. Roscoe East

    Roscoe East

    Aug 22, 2011
    Mike Beigel just posted this on his Facebook feed, I thought it was pretty fascinating and worth sharing:


    BETWEEN 1978 and 1980.

    By the time ARP was making Mu-Tron IIIs, I was already out in my own (Beigel Sound Lab) consulting and product design business again, and i never paid much attention to the ARP Mu-Tron products. (They are the Mu-Tron III products WITH the AC line cords, and labeled as produced by Mu-Tron INC. (not Musitronics Corp. which made them from 1972 to 1978.

    Last night (January 17) while working with my colleague Richard Lingenberg on some new product design work, we got to talking about the ARP (Mu-Tron INC) units, and I got a BIG and DISAPPOINTING surprise. I had always figured that they were competent enough to make the product the way I had originally designed it, but that was WRONG.

    To make this brief, Richard (who gets all my Mu-Tron Vintage repair work and his own repair work from other sources) has fixed up and calibrated a lot of these ARP units.

    Apparently they changed the inside POWER SUPPLY VOLTAGE but in doing so, they apparently DID NOT UNDERSTAND to change some component values that were designed for the ORIGINAL power supply voltage.

    What Richard noticed about (ALL?) the ARP units coming in for repair, was that the FREQUENCY SWEEP was WAY TOO HIGH.
    And also that the DOWN DRIVE never really worked to drive the filter down "all the way" as it was supposed to.
    Both of these symptoms had to do with changing the power supply voltage but not compensating for the change by changing ALSO some very critical component values.

    So Richard (who knows what a Musitronics Mu-Tron III unit SHOULD sound like), changed the offending parts values and recalibrated the SWEEP range and DOWN DRIVE to what they were designed to be.

    I never knew about this before, and am sharing it now.

    if you have an ARP Mu-Tron III and don't like the way it sounds or works, now you know why.

    if you want it to be fixed (even though it's not officially "broken"
    and recalibrated, please send me a note at <info at mu-tron dot ORG (NOT .com), and I will forward the information to Richard, who will contact you and give you a quotation on fixing the parts values and re-calibrating it to the frequency sweep range of the original factory Musitronics Mu-Tron Calibration.

    (But if you are perfectly happy with your ARP-Mu-Tron unit, then by all means USE IT AS IS. Richard also noticed enough variation in the calibration of the ARP units that it's just possible ttyat YOUR vintage ARP-MuTron III unit is accidentally calibrated "just fine".

    There weren't all that many ARP units made, but I thought it appropriate to inform the owners of these vintage (and AUTHORIZED by Musitronics Corp) i.e. LEGITIMATE reissues, that there might be issues with the units that (I) didn't know till last night.

    Mike Beigel