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Schematic for Walter Woods 2 Channel MI 100-8?

Discussion in 'Amps and Cabs [BG]' started by purrsuader, Nov 15, 2018.


  1. purrsuader

    purrsuader

    Oct 18, 2013
    Hey all. I have a 2 Channel WW MI 100-8 that needs some work. I've scoured the internet for a schematic and haven't had any luck. The closest I've come is the 1 channel version. Thanks to the TB poster for that one. Does anyone have a schematic for the 2 channel version or know where I can find one? Thanks!
     

    Attached Files:

  2. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    What part of the amp specifically? There is some information that can be gleaned from the 1975 patent that might be helpful.
     
  3. purrsuader

    purrsuader

    Oct 18, 2013
    No sound from Channel 1. Channel 2 works fine.
     
  4. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    PM me with your e-mail address and I will try to help you. Do you have a scope and signal generator?
     
  5. beans-on-toast

    beans-on-toast Supporting Member

    Aug 7, 2008
    You have to trace the signal through channel 1 from the input with a probe. This can be done by a tech without a schematic if necessary.

    Start with a visual inspection. Look for any areas of distress in the channel 1 circuitry.
     
  6. beans-on-toast

    beans-on-toast Supporting Member

    Aug 7, 2008
    Not the same model but built like a tank.

    BB37C04A-998E-4F81-9284-64DAE365DA20.
     
  7. purrsuader

    purrsuader

    Oct 18, 2013
    Thanks for the offer of assistance, agedhorse, but I'm not feeling confident in servicing this myself. I don't have a scope or signal generator. I did a visual inspection of the circuit board and didn't see anything obviously amiss. I contacted a tech and it looks like I'll be able to have him look at it on Saturday. I was asking for a schematic because I read that early versions of the MI 100-8 like mine came with a schematic folded up inside the amp and was hoping a member had one. Mine is missing. Hopefully the tech will be able to track down the issue without one.
     
  8. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    Have your tech e-mail me if he needs help.

    Your amp used a kind of unique "fetlington" type emulated op-amp. It's a pretty cute and novel circuit but not very good performance by today's standards. Even Walter moved onto true op-amps with later products.

    There's actually a lot of thought that went into these amps IMO, Walter was very ahead of the times with the SMPS, doing an SMPS now is much simpler and more cookbook. Even when I designed my last SMPS, I was able to use more off the shelf type parts and today it's even more straight forward (except the EMC rules are MUCH tougher than in the "good 'ol days").
     
    Passinwind likes this.
  9. beans-on-toast

    beans-on-toast Supporting Member

    Aug 7, 2008
    As was mentioned the patent has a schematic which can be used in a general way.

    US3860876A - Musical apparatus - Google Patents

    There’s a hand drawn schematic for one of the revisions here. There are three file links on the left for different sections of the amp.

    Walter Woods PowerSupply

    Here is the preamp one. Even if it isn’t the same as your amp, your tech may find it helpful.


    85EF4856-4976-4430-AEF9-A2BFD234CFB4.
     
  10. interp

    interp Supporting Member

    Apr 14, 2005
    Garmisch, Germany
  11. Oldtimer

    Oldtimer Supporting Member

    May 4, 2002
    New Mexico
    Is it possible it is as simple as a bad "Channel Select" switch? Also, if I remember correctly, my 1982 M100-8 has a schematic folded up inside!
     

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