Bassman Micro/Hammond 125B OT 16 ohm hookup question.

Discussion in 'Shock Brother's DIY Amps' started by Bitsleftover, Feb 27, 2020.

  1. Bitsleftover

    Bitsleftover Tele-Meister

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    Hi, Im planning my bassman micro build and I’d like to add either a speaker impedance selector or multiple jacks for 8&16 ohm speakers.
    What is the best way to attack this?

    Ive looked into it but don’t have the confidence to jump in without asking you guys to double check first if that’s ok?

    The Hammond data sheet doesn’t specify 16 ohms, the closest is 15ohms.
    15 ohms output would require connecting lugs 1&4 to give 21.5K, or lugs 4&6 to give 24K(15ohms)

    (Rob specifies 22.4k for 8ohm speaker @ lugs 2&4)

    Is that close enough?

    To hook up would I just connect both output jack tips to lug 4, then one jacks sleeve to jack 2 and the other jack sleeve to 1 or 6 (depending on the answer to above)?

    As always, thank you for your time and patience with my noob questions.

    Cheers
    Mick


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  2. Bitsleftover

    Bitsleftover Tele-Meister

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    [​IMG]


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  3. dan40

    dan40 Tele-Afflicted

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    If I remember correctly, you can only hook up one speaker tap with that OT. It does not allow the use of both 8 and 16 ohm options unless you rewire for different plate loads.

    I ended up using this OT in my Micro build that allows for multiple speaker taps without changing the plate load. It sounds great in my build and many other members here have reported good results with this brand.

    http://rover.ebay.com/rover/1/711-5...0001&campid=5338148343&icep_item=164068571385

    https://www.musicalpowersupplies.com/products/
     
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  4. Bitsleftover

    Bitsleftover Tele-Meister

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    Thank you Dan, I’ve already got the Hammond so I’ll stick with that I think.


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  5. robrob

    robrob Poster Extraordinaire Ad Free Member

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    You need to use the #4 wire for the sleeve (ground) for the two jacks, then the other two wires to the jack tips. You can't use a shorting jack for either speaker jack.
     
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  6. dan40

    dan40 Tele-Afflicted

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    @robrob ...will that OT allow the use of both the 8 and 16 ohm taps while still keeping the desired 22k plate load?
     
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  7. Bitsleftover

    Bitsleftover Tele-Meister

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    Brilliant!
    Thank you sir. Much appreciated.
    Mick



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  8. Meteorman

    Meteorman Tele-Holic

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    Since I'm almost at this point in my build, I'll jump in for some clarity - on the 125B OT, are the secondaries interchangeable at the output jack ? Or is there some polarity to worry about ?
     
  9. robrob

    robrob Poster Extraordinaire Ad Free Member

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    No polarity to worry about.

    Be sure and use the 8 ohm jack tip for the NFB source.
     
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  10. robrob

    robrob Poster Extraordinaire Ad Free Member

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    Yes, when wired as I describe above.
     
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