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Mojotone Studio One

Discussion in 'DIY Amp Forum' started by LarsN, Aug 2, 2019.

  1. LarsN

    LarsN Strat-Talker

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    Not much to report yet, but my next DIY Amp project is about to begin. This will be the third amplifier kit I've tackled, and it's the one I'm most excited about.

    I love that cranked Marshall sound but don't think I'll ever be playing anywhere bigger than my home, so a 50 or 100w head is just too much. The Mojotone Studio One seems to be a great way to get those sounds, without needing hearing protection.

    [​IMG]
     
  2. TangerineDog

    TangerineDog Senior Stratmaster

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    Shallow me... first thought: that looks absolutely gorgeous!
    Be sure to post a sound check ;)

    Also, how likely, do you reckon, is it for someone like me (adequately adept with a soldering iron and at installing new lamps) to electrocute himself when building a kit like that?
     
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  3. vid1900

    vid1900 Senior Stratmaster

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    If you can solder, you can build an amp kit.

    It's 1930s rocket science
     
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  4. LarsN

    LarsN Strat-Talker

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    Super easy honestly. The Mojotone 5E3 kit (which was my second amp build and posted in this forum) includes a lot more in depth instructions making it a very easy project. The Studio One kit includes a circuit diagram, and a full size rendered drawing of what it should look like, but otherwise no instructions.

    If you can read a diagram and solder I'd dive in and build whatever amp you want to play. If not you might consider starting with one of the Level 1 Kits like the Tweed Champ 5F1

    @vid1900 is 100% accurate. We're playing around with what was state of the art in the first half of the 20th century.
     
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  5. Triple Jim

    Triple Jim Senior Stratmaster

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    My preference is the Princeton 5F2-A. It's essentially the same as the Champ, but with a tone control, which is a very effective treble control.
     
  6. StratoMutt

    StratoMutt Strat-Talker

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    I will be watching this develop ...check the values of the parts!

    Yes, the Studio One is for real. Plenty loud for me - quite dramatic at full volume. SO MUCH gain on tap.
     
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  7. LarsN

    LarsN Strat-Talker

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    Well It's assembled. I get ZERO output from the speaker though on either channel.

    Voltages measured at the test points are written in blue.
    [​IMG]
     
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  8. LarsN

    LarsN Strat-Talker

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    They are all a little bit low, but I noticed the same thing on my tweed, and it sounds fine. I figure none of these are exactly "precision" devices.
     
  9. LarsN

    LarsN Strat-Talker

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    I found it frustrating that the turret board provided didn't have the exact same layout as the drawing. If you look at the left side of the drawing you have the two yellow 22nF caps. next to the 500pF cap, and all those turrets are in a straight line. If you look at the image of my actual board you'll see some of those are drawn up to the middle of the board.

    [​IMG]



    I also found it frustrating that in at least two places the gap between turrets was wider than the legs of the components intended to bridge them.
    for example the 1.5Kohm resistor and capacitor on the right edge of the board. I ended up soldering an additional leg to the end of the component to make it long enough to bridge the gap.
    [​IMG]


    Finally the polarized caps paired with resistors to bridge turret gaps (again like the one on the right above, and the one in the middle of this photo.) should have been the caps with two ends like the yellow models, rather than with both legs sticking out the bottom since they aren't being mounted into a circuit board. That's just poor component selection on Mojotone's part in my opinion.
    [​IMG]
     
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  10. LarsN

    LarsN Strat-Talker

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    This kit may make for a fantastic amplifier once I've got it working, but as a kit I'm far less impressed with this one than I was the 5E3 I built first.
     
  11. StratoMutt

    StratoMutt Strat-Talker

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    The turret board is not well laid out. Almost as if they had their trainees do the punch-outs.

    I had the same trouble with the too short leads. I just improvised.

    Your observed voltages were quite similar to mine.
     
    Last edited: Aug 7, 2019
  12. StratoMutt

    StratoMutt Strat-Talker

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    Did you happen to use lead free solder?
     
  13. LarsN

    LarsN Strat-Talker

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    Yeah, I used 2.0% Silver Solder
     
  14. StratoMutt

    StratoMutt Strat-Talker

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    Yeah, I thought ... I could see by the way the solder did not want to stick to the pots. Does not look like rosin core either.

    Old timey 60 / 40 rosin core is the stuff to use. I'll venture a guess you have a wonky solder joint or two.

    See the way the solder flattened out on the pots and grabbed the ground wire? Those are small blobs of solder.

    upload_2019-8-7_19-27-0.png
     
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  15. LarsN

    LarsN Strat-Talker

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    While I'm waiting for Mojotone to get back to me, I guess I'll put the iron on every joint, get it nice and molten, and put a little more in each one for good measure.

    I should order some old school 60/40 rosin core (and by some I mean a box of it.)
     
  16. StratoMutt

    StratoMutt Strat-Talker

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    I'd redo with 60 / 40 - PM sent. ;)

    From what I have read, you may need to de-solder some or all of the joints as 60 / 40 and lead free are not compatible.

    Someone here should confirm or expand upon that. I've never tried to mix the two.

    At the very least get some rosin to sure up the existing joints with the lead free. Even lead free will flow better with rosin.
     
  17. Robins

    Robins Dr. von Loudster Strat-Talk Supporter

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    No output at all?
    Did you used the channel switching PBC?
    If so disconnected it and check again. Wire the amp without using the switching.

    All the best,
    Robin
     
  18. LarsN

    LarsN Strat-Talker

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    No output at all with either channel position. I'm not sure what I would have to move to completely remove the channel switching PCB from the signal path.

    It can't be as simple as disconnecting the Shielded gray wire, and two blue wires wouldn't I need to connect the gray wire to somewhere?
     
  19. StratoMutt

    StratoMutt Strat-Talker

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    There is a lot going through the switch PCB. Have no idea why, but it does work quite well once you get the bugs worked out.

    Removing it from the circuit for troubleshooting does not seem that easy. That was my first inkling as well. I was wrong.
     
  20. Robins

    Robins Dr. von Loudster Strat-Talk Supporter

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    The grey one is the clean channel signal.
    The dirty channel signal is coming from the treble pot going into the master volume pot.
    The blue cable from relay PCB going to the 22nF cap is the PI input going into the power tubes (signal input - power section).

    All the best,
    Robin
     
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