Bassman Micro - My first build

Discussion in 'Shock Brother's DIY Amps' started by recoveryroom, Nov 8, 2018.

  1. sds1

    sds1 Tele-Afflicted

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    That store sells terminal strips -- catalog # 7281 and 7282.

    Those would get you solid offboard mounting points for your diode rectifier.
     
  2. recoveryroom

    recoveryroom TDPRI Member

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    Thank you, great idea. And I'll have extra turrets in case I damage any of them.
     
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  3. Dan Miller

    Dan Miller Tele-Meister

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    Late to the party, and sorry to hear that Watts is OOB, if that is true. I like their turrets.

    The proper drill bit for a Watts turret is a No. 32.

    FWIW, over the years, and working in many different media, I have found it helpful to acquire over the years, fractional, metric, numbered, and lettered drill bits.
     
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  4. recoveryroom

    recoveryroom TDPRI Member

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    I think I’m all set for the board and really appreciate the support from the community here, but keep an eye on this thread. :D

    There are a few things on the tube socket wiring I don’t understand, and I’ll be starting that after I wire the circuit board.

    There’s no doubt I’ll hit roadblocks when the soldering starts :eek:
     
  5. recoveryroom

    recoveryroom TDPRI Member

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    Here's the board with resistors and caps. Looks like I have an extra 56k, and I'm short a 100k 1.5 watt resistor.


    Putting the SS rectifier on a tag strip gives me more room on that side.


    [​IMG]
    [​IMG]
     
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  6. recoveryroom

    recoveryroom TDPRI Member

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    I tried to neaten up the layout a little. It looks like I need 2 100k 1.5 watt resistors. I can't see anything else missing except the diodes.


    A few questions:

    1. I'll get the 100k 1.5's, should I have any other resistors (or capacitors) on hand to tweek the circuit if I run into any issues with it's performance? or is that too broad to try to plan for?



    2. I intended to add the Neg Feedback mod, but the fact Rob removed it makes me wonder if I'm looking for trouble trying to incorporate it.


    Is the 15k NFB resistor mentioned below added to the circuit, or does it replace one on my board? Which one? Is this worth the effort? Is this too complicated for a first time builder?


    https://robrobinette.com/5F6A_Modifications.htm#3-Way_Negative_Feedback_Switch

    Here's some info from the Bassman Micro webpage

    Update: March 2017. I added a filter capacitor, made the choke mandatory and moved it to filter the entire amp to reduce the amp's hum level. I removed the feedback circuit because it encompassed too much of the amp and hurt the effectiveness of the tone stack.

    Note: the Negative Feedback NFB circuit has been deleted from the layout but if you do choose to use NFB I recommend a change to a 15k NFB resistor.




    3. I intend to add the SS/tube rectifier mod. Do I need 4 or 6 diodes? It looks like 2 on the tube socket and 4 on the board. Here's the Bill of Materials line item on the website in my op.

    Rectifier1, Rectifier2, Rectifier3, Rectifier4 OR Backup1, Backup2 1N4007 2 or 4 Diodes-- 4 Rectifier OR 2 Backup




    [​IMG]
     
    Last edited: Nov 25, 2018
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  7. robrob

    robrob Poster Extraordinaire Ad Free Member

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  8. recoveryroom

    recoveryroom TDPRI Member

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    Thanks Rob,

    So a 15k 1 1/2 watt resistor and maybe the 10k (1 1/2 watt) and 27k (1 1/2 watt) from your 5F6A NFB mod page? What would you recommend?





    This was mentioned earlier by sds1, it's a good idea. I'll get some tag strips for this, and the NFB circuit.
     
  9. sds1

    sds1 Tele-Afflicted

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    Well one setting on the 3-way NFB (Rob's preferred) is going to be no resistor at all (NFB off). So you only need 2 feedback resistors -- 15k (if you choose to go with Rob's recommendation) and some other.

    (I think I'm missing something though because I found that Rob initially had a 56k NFB resistor on this amp, but then he says he prefers no NFB. Using a 15k will allow MORE NFB signal to pass than 56k -- therefore further away from his preference of NO NFB so I don't quite understand how he ended up with 15k.)

    Given what Rob says here about the NFB encompassing too much circuit, I would not be surprised if you as well find that any amount of NFB to be too sterilizing. But I'll not discourage you from proceeding with this 3-way NFB mod because it's an excellent experiment and learning experience!

    Anyhow, since this all a matter of personal taste I think a fun exercise for you here would be to use 15k as recommended, and then temporarily clip in say a 7.2k (half) and then a 27k (double) and see which one you think is a better option for your 3-way switch. Then solder that one in permanent.
     
  10. robrob

    robrob Poster Extraordinaire Ad Free Member

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    Yes, those would be good values

    I worked with a Bassman Micro builder that really liked the 15k NFB resistor and after doing more tests I ended up agreeing with him. The original NFB loop was too big. Ideally, injecting the NFB at the phase inverter grid (we must use a cap in the NFB loop here) would be the best option but I haven't gotten around to trying and tuning that setup.
     
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  11. King Fan

    King Fan Friend of Leo's

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    Yow. I have trouble keeping up on re-stringing my guitars. Can you imagine Rob trying to update all his web pages? This is good stuff right here, and from the source.
     
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  12. recoveryroom

    recoveryroom TDPRI Member

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    Yeah, when I was researching this project, I was a little hesitant to go with something like this for my first build, but Rob’s website convinced me he really knows fenders and the bassman.
     
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  13. recoveryroom

    recoveryroom TDPRI Member

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    Here's my board, a neighbor helped make the turret tool over the weekend. I was able to move around a block of wood to keep the board level and stable. Three decent taps with a hammer.


    Some of the turrets are a little loose, but they all seem like they're secure so I don't think they'll ever come out. Any reason to worry about this? Should I try retapping or is that likely to damage them? I have a few extra but probably not enough.




    [​IMG]
    [​IMG]
     
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  14. sds1

    sds1 Tele-Afflicted

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    I think a turret with tiny bit of wobble is OK, but you be the judge.

    If you hit it with the hammer again it may very well tighten up. If you hit too much or too hard the turret will split. When it splits it is still useful, it just sucks that it split. I suppose worst case you'll lose a turret and let the rest go.

    You could go either way. See how bad it bothers you. :)
     
  15. recoveryroom

    recoveryroom TDPRI Member

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    Thx, I think I'll go with it as is. Most are tight, a few I can turn, and a couple wobble a bit.
     
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  16. recoveryroom

    recoveryroom TDPRI Member

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    I picked up most all of what I need. Turns out I have enough 100k's, I didn't have the two 100 ohm .5's for V3 tube. Btw, I mentioned 1 1/2 watt resisters in an earlier post but I meant 1/2 watt.


    I'm not sure how to set up the terminal strips for the ss rectifier and neg feedback mod.


    Here's a pic, with


    - two strips placed next to where the ss rect mod diodes would have been on the board. Do I need two strips or can it be done with one?


    - and, two strips near the speaker jack and where I'll drill a hole for the mini neg feedback switch. Rob's mod recommends the switch near the jack. Same thing, two strips or can I do this with one?


    I picked up 2 4 lug and 2 6 lug strips.


    [​IMG]
     
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  17. robrob

    robrob Poster Extraordinaire Ad Free Member

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    Do it like this. If you want to relocate the switch then use a terminal strip in place of the switch, then connect the tag strip to the switch using two wires.

    [​IMG]
     
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  18. recoveryroom

    recoveryroom TDPRI Member

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    Thanks Rob, I see this on your website. And it looks like I can use the existing hole, on the back of the chassis near the rectifier socket, for the switch.
     
  19. recoveryroom

    recoveryroom TDPRI Member

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    I think the last layout issue for me is how to integrate the neg feedback circuit and switch.


    I have 2 switches I think I can use:

    one is a Philmore 30-10044 mini SPDT and I'd need to drill a hole near the speaker jack for it

    the other is a normal size GardnerBender GSW13 and I can use an existing hole next to the speaker for it


    I'd like to use the larger switch if there's no impact on the output.





    Working this mod into the Micro Bassman layout isn't clicking with me yet. It sounded earlier like a terminal strip(s) would be a way to do this, but I'm not seeing how :cry:




    Here's Rob's 5F6A mod


    [​IMG]
     
  20. tvas22

    tvas22 Tele-Meister

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    I will be following this closely.. I’ve just ordered everything but the transformers for my own micro bassman build (putting it in a Princeton reverb chassis). Built a champ last year, but still very much a beginner. This thread already has a bunch of useful info!
     
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