Champ Micro build thread

Discussion in 'Shock Brother's DIY Amps' started by dotbot, Jan 18, 2019.

  1. dotbot

    dotbot TDPRI Member

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    Howdy shock bros.,

    I'm in the planning stages of my first amp build, which will be Rob Robinette's Champ Micro. I'm aiming for this rather than, say, a 5F1 kit because I like to build things from scratch and also I really like the idea of having both a volume and a master volume on this circuit. It's for use at home so the ~1W is ideal.

    Figured I'd start this thread as a place to share my progress.

    In contemplating this build I've been doing lots of reading, especially Rob Robinette's webpages and watching Uncle Doug on youtube. (Love me some Uncle Doug!) And, yes, before I start on the amp I will be making a light bulb limiter.

    I have a spreadsheet going with parts, prices, and sources for them. I'd like to keep the chassis relatively compact and either point-to-point wiring or using an eyelet board. It'll have just two tubes, 12AU7 and 12AY7, as I'll be using the diode rectifier option. I'll be making the cab myself and probably going with a 12" Weber as recommended.

    For the circuit, any thoughts on whether this board would work?

    Thanks for reading!
     
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  2. robrob

    robrob Poster Extraordinaire Ad Free Member

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    I hadn't seen those boards before, that should work great.
     
  3. dotbot

    dotbot TDPRI Member

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    Thanks, Rob! It's great to have your input. I had seen those B9A boards in one of your builds but, apparently, they're no longer available. Anyway, I'll order one of these 2 x 9-pin boards and we'll see how it goes.
     
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  4. dotbot

    dotbot TDPRI Member

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    Minor update: I ordered all of the parts today and constructed a light bulb limiter. With the long weekend and a blizzard coming, it will be a few days before I can get started on this. I guess I'll have time to clean the shop and shovel snow!
     
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  5. dotbot

    dotbot TDPRI Member

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    Progress! All of the parts have now arrived in 100 tiny plastic bags. Only things not shown here are the Weber speaker, which is in transit, and the cab, which does not exist yet. Just for fun I put the tubes into the board.

    I'll be checking all the little parts and getting started on the layout next. :)

    [​IMG]
     
  6. shortcircuit

    shortcircuit Tele-Meister

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    That's a big ol' power transformer to cram onto the chassis. I like it!
     
  7. dotbot

    dotbot TDPRI Member

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    Yes, indeed! Seeing it all together in front of me makes me skeptical that it will all fit in this chassis . . . I may end up "modifying" the circuit board to make everything fit. Anyway, this is going to be fun.
     
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  8. Prophetsnake

    Prophetsnake Tele-Meister Silver Supporter

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    That board looks super handy. How are you planning on mounting it to the chassis?
     
  9. dotbot

    dotbot TDPRI Member

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    Thanks! The board is pretty neat and would probably be quite useful for prototyping. It's becoming clear that this project will not fit into the chassis, though. Transformers and circuit board do fit but there is no room left for any kind of sane layout for the fuse, knobs, & switches. I will probably just go with a larger chassis but I want to finish the circuit board first. Then I'll draw a layout for the controls and decide on the right size of chassis.

    ...

    In other news, my brand new, beautiful speaker arrived in a shameful state. Double boxed and the outer box looked pristine so I was optimistic. Sadly the inner 12x12 box was really not supported inside the much larger outer box. The thing banged around inside there so badly that (a) it bent about 4 inches of the rim of the frame at a 45 degree angle and (b) the rim actually cut through two sides of the inner box. I mean, I was/am heartbroken. I've been in touch with the manufacturer and hope that they will do the right thing. That's a lot of someone's time and hardware, not to mention my $$$, to skimp on $0.50 of packing peanuts or whatever. :mad:
     
  10. dotbot

    dotbot TDPRI Member

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    Hi folks! It has been a while since my last post. I have been diligently working away on this project when I can find the time. I'm pretty happy with how it's going so far. For reference, here are the layout and schematic from @robrob

    [​IMG]
    [​IMG]


    Here's the circuit board as it stands today, no soldering has been done yet on any of the terminal, so please tell me if you see anything suspicious!

    Top:
    [​IMG]

    Bottom:
    [​IMG]
    Black wire in the lower left will connect V2 and B+1 to ground. Red wire off to the left connects the + on B+1 filter cap to the diode rectifier (not shown).

    Because of the tight confines of the terminal board, the V2 bypass cap and cathode resistor are nestled beneath the 47 uF filter cap.

    [​IMG]

    Again because of the tight confines, the V1A grid stopper (33K) is at bottom right in the top-down pic. The lead from the volume pot will come down to that corner, through the V1A grid stopper, and then to pin 2 on the 12AY7.

    Finally, here is a photo of the chassis. I had to abandon the little box I bought and replace it with a DIY sheet metal chassis, which looks homemade but has enough room to fit everything.
    [​IMG]

    One question for you all: The extra wires on the PT that I won't be using (brown, yellow, red+white stripe), how short can/should I cut them off?


    Anyway, that's where I'm at today and looking forward to the next steps.
     
  11. kleydejong

    kleydejong Tele-Holic

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    I think best practice would be to use a terminal strip or some other kind of physical connection so they're tied down securely and won't ever have opportunity to make contact. A PT bolt makes a good spot for this.

    I'll admit that I also have trimmed them, used individual heat shrink, and then zip tied them together.
     
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  12. dotbot

    dotbot TDPRI Member

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    Update: We have sound!

    I finished the wiring today and then I followed @robrob's startup guidelines. Everything went according to plan so I decided to roll the dice and power up. I did this with headphones in as I haven't wired the speaker yet.

    Here's what it looks like as of tonight
    [​IMG]
    underside of the circuit board
    [​IMG]
    The red wire is not interfering with the tube at all. This is just the way it lies when it's upright.

    I was using my kids' headphones so the sound quality was not phenomenal. I'm sure it will sound much better through the Weber (of which an unmolested version arrived a couple of days ago).

    I was doing this all through the light bulb limiter, couldn't resist a photo of that, in the dark, :D.
    [​IMG]

    I didn't play very long but I did try all the features and it was truly a unique experience. This is my first amp build and I still can't quite believe that it works!

    When I get up the nerve to plug it straight into the wall, I'll report voltages for anyone who is interested.

    I still have a long way to go on this with cabinet, speaker, and finishing touches but today was a big milestone.

    Huge thanks to @robrob for sharing this design with all of us.
     
  13. robrob

    robrob Poster Extraordinaire Ad Free Member

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    Congrats on bringing it to life. Yes, headphones don't do it justice. It will sound much better through a proper guitar amp speaker.
     
  14. dotbot

    dotbot TDPRI Member

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    I decided to measure the voltages under direct wall power in case anyone else builds this fine amp and wants to have another set of numbers to compare with @robrob's.

    My wall voltage is 121V, FWIW. PT output 293V AC, all other numbers are DC. Numbers in parentheses are listed on the Champ Micro webpage under "Measured Voltages". Rob's numbers in parentheses.

    B+1: 394V (399V)
    B+2: 279V (304V)
    V1A plate (pin1): 133.2V (150V)
    V1A cathode (pin3): 2.19V (2.3V)
    V1B plate (pin6): 134.5V (146V)
    V1B cathode (pin8): 2.12V (2.4V)
    V2 plates (pins 1+6): 390V (390V)
    V2 cathodes (pins 3+8): 12.78V (11.75V)

    My numbers are within about 10% and always a bit low.
     
  15. Lynxtrap

    Lynxtrap Tele-Holic

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    Great!
    Two things though. Those resistors and the wire on the underside of the board, and the rectifier hanging free like that.
    I would not feel comfortable with those solutions.
     
  16. dotbot

    dotbot TDPRI Member

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    Good, good. Thanks for the feedback!

    This is my first build so I have a lot to learn about what are good and bad practices. This will likely be installed in the orientation shown in the photos.

    What would make you uncomfortable with these items and how would you improve them:

    - the wire and resistors under the circuit board?

    - the diode rectifiers?
     
  17. Lynxtrap

    Lynxtrap Tele-Holic

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    Basically, these components /circuit points are ones we don't want to short to chassis! In a worst case scenario, that could happen the way you mounted them.

    Amps get hauled in and out of cars, thrown around on stage, topple out of car seats and lord knows what. If not by you, then buy your buddy who loans it, the guy you sell it to in ten years or your cousin's toddler, you know... One day gravity might strike and B+ hits the chassis with a flash.

    I would prefer to have the rectifier diodes soldered firmly on a board.

    The resistors I'd either want on the upside of the board, or if you really have to have them on the underside, all wrapped in shrink tape.
    Another option is insulation on the bottom of the chassis, like a rubber mat (mouse pad might do), under the card.

    There are those solder tag strips that could be used if you're out of space or turrets.
     
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  18. dotbot

    dotbot TDPRI Member

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    Wow! It's been a month since my last post. Time flies. I haven't disappeared but I've had some travel for work.

    I've finished the chassis and started working on the cabinet. I'll post some pictures of my progress this weekend.
     
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  19. Fatknuckle

    Fatknuckle Tele-Holic

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    That little chassis looked a bit problematic. I like your layout and setup on the new chassis. Interesting little project!
     
  20. dotbot

    dotbot TDPRI Member

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    Well, for the time being I'd say this amp is done. It still needs a handle and I have a bit of hum that I'd like to reduce or remove. There is another thread with some discussion of this so I have hope.

    I am totally happy with the result! The tone is what I was hoping for, nice and clean at low volume but can get some dirt when it's cranked -- and I won't get yelled at for being too loud. I've been having fun playing around with the options (see below). The speaker wire has enough length that I can build another amp as a head and use the same cab. Now that I've been bit by the bug, I've definitely got my eye on another Micro.

    The cabinet is nothing fancy. It's made from some 1x12 pine and finished with shellac. It will not be going to any gigs and, if it gets hit with a beer bottle or "groupie's undies", I have only myself to blame.
    [​IMG] [​IMG]

    From left to right:
    1. Boost switch. This is a DPDT with the normal and double boost mod.
    2. Guitar input
    3. NFB switch
    4. Speaker jack
    5. Headphone jack
    6. Master Volume
    7. Volume
    8. Light (purple!)
    9. On/Off
    10. Fuse

    I really need to put some labels on! I'm also thinking about making a nicer backplate to go around the chassis. This one looks kinda hokey.
    [​IMG] [​IMG]
    The speaker baffle held on by wingnuts is something I saw on one of Uncle Doug's build videos. It's sturdy and also makes taking the speaker and baffle out a breeze. In the end, the whole package weighs 24 lbs.
     
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