Bassman Micro Stupid Questions

Discussion in 'Shock Brother's DIY Amps' started by Bitsleftover, Jan 4, 2020.

  1. Bitsleftover

    Bitsleftover Tele-Meister

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    Hi,
    Hopefully one of you knowledgable guys can answer these noob questions about the Robrob Bassman Micro...
    1/ I’m thinking of adding reverb. But I notice the effects loop (which is my usual placement cue) is straight after V1, not after V2 and the treble cap as I’d expect?
    2/ The write up says the MV acts as an effect send, but the schematic looks like a general amp and effects level control?
    3/ Ive ordered the 370aX power transformer, but I’d love to squeeze and extra0.3A out of it each for reverb and tremolo?
    I guess I could go SS tremolo and 1 tube reverb, Or SS reverb and use the tube for tremolo.
    Any views/opinions?


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    Last edited: Jan 5, 2020
  2. drneilmb

    drneilmb TDPRI Member

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    1. What I see on https://robrobinette.com/Bassman_Micro.htm is that the "effects loop" is specified after the wiper of the "Pre MV" pot which comes after V2 and the treble pot. Are you seeing a different schematic?

    2. The effects send is the "Pre MV" pot which allows you to control how much signal is being sent out into your effects before they come back into the power amp. The "MV" pot comes after the LTP phase inverter and changes the volume in the power amp stage.

    3. If you are adding reverb and tremolo, then you are designing your own amp (in my opinion). If you want to do that, then you should choose an appropriate power transformer that matches the needs of your amp. If you need more heater current for that design, there are standalone filament transformers that could be added, e.g. Hammond 266 series.
     
  3. Bitsleftover

    Bitsleftover Tele-Meister

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    Thanks DrNeilmb,
    I must be completely misreading something?
    What you describe is what I expected to see.
    But I’m looking at the orange wire from the wiper of the Bright Volume Pot to the effects Send/ Return jacks which goes on to the 270k V2a Grid Stopper.
    Good point regarding the H266 series. That could be the ideal solution.
    [​IMG]


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  4. tvas22

    tvas22 Tele-Meister Silver Supporter

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    Rob rob moved the effects loop after my build - I had issues putting reverb in.

    It worked better after the move, but the SS reverb on his site had impedance issues I could only figure out by putting a buffer in beforehand. I used a SHO style boost/buffer, and even with the mixing resistor bypassed the boost has to be full up for the amp level to be the same with the reverb engaged compared to bypassed. The SHO is powered using the 16v for the reverb.

    I will say, it sounded fine with the boost in so I just left it and gave up with the puzzle. My gut tells me that you would have more success with the one tube reverb (although I am currently having trouble with a one tube reverb in a build).
     
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  5. drneilmb

    drneilmb TDPRI Member

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    That layout does not match this schematic. That sometimes happens with Rob and everyone else who publishes both.

    Bassman_Micro_LTP_Schematic_small.png

    The schematic makes much more sense to me than the layout portion you showed.

    Maybe @robrob will appear to help resolve the confusion.

    -Neil
     
  6. Paul-T

    Paul-T Tele-Meister

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    So you needed the boost in the second location, or the first? Do you have a link for the build?
     
  7. tvas22

    tvas22 Tele-Meister Silver Supporter

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    https://www.tdpri.com/threads/second-amp-build-bassman-micro.911917/page-2

    This was my build, not actually that much info in here really.

    Looking back at his Bassman Micro page, I built the version with the cathodyne phase inverter, and used the effects loop from the volume pot, as shown in the current layout pic for that version. I still needed to go from the effects loop -> buffer/boost -> reverb -> effects loop for it to work (although I didn’t wire in the jacks for the loop in the end).

    You can see how it was when I started building it here: https://web.archive.org/web/20170701191203/https://robrobinette.com/Bassman_Micro.htm
     
  8. robrob

    robrob Poster Extraordinaire Ad Free Member

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    Since the passive FX loop in the Bassman Micro is so simple I didn't draw it on the schematic.

    Adding reverb to an amp is not a simple mod and I've had many communications with people having difficulty making it work. I recommend if you want tube and spring reverb then build an existing design or be ready to do a lot of re-design and tweaking.
     
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  9. Bitsleftover

    Bitsleftover Tele-Meister

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    Thank you for your help


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  10. Bitsleftover

    Bitsleftover Tele-Meister

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    Thank you for your advice Rob. After a lot of reading and a lot of research, I think I am ready to do a lot of re-design and a lot of tweaking.
    I’ve begun designing a build.
    It’s a “Marshall Plexi Micro”. All the best bits of the classic Marshalls
    It’s based upon your Robrob Bassman Micro, but with a Marshall twist .
    I’ve taken the Bassman Micro LTP design.
    Made it a standard 4 hole parallel input design preamp.
    Then added the Tube/SS rectifier mod to give a JTM/1962 bluesbreaker option.
    A rear panel switch to split the V1 cathode for a JTM/SLP option.
    I’m thinking I’ll add a rear panel switch to go from 56k slope and 220p treble cap to 33k slope and 470k cap.
    Maybe a switchable .68 bypass cap an V2A
    And a 3 way -ve feedback switch.
    If I can find a way to drop the bright coupling cap from 0.022 to O.0022 it might help a lot.
    I’ve had quite a bit of success adding one tube reverb and I’ve been experimenting with a solid state tremolo design to further explore the British Bluesbreaker route
    The beauty is I can pretty much build the Bassman Micro then mod it from there!
    Most of the parts have been delivered.
    I should really start a new build thread. I spent the afternoon drilling a tube-town chasssis


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  11. Nickfl

    Nickfl Tele-Afflicted

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    Blackface type tube reverb is going to make it a totally different amp, and not in a good way IMO. Buy, or better yet build, yourself a reverb pedal instead and just plug it into the effects loop when the mood strikes you.
     
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