Mojotone VibroChamp Build

Discussion in 'The Squawk Box' started by Cjsinla, Nov 5, 2017.

  1. Cjsinla

    Cjsinla Premium Member

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    I decided to post a thread about my experience with the Mojotone VibroChamp kit. I went with the stock kit, no substitutions. The kit was shipped in two boxes. The first shipment included everything but the cabinet. Mojotone ships all the parts in clearly labeled boxes. This is a nice touch and helps speed up the assembly process.

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  2. Cjsinla

    Cjsinla Premium Member

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    The Mojotone VibroChamp kit does not come with an assembly manual and is not specifically meant for beginners. They do provide a layout diagram and a schematic.

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  3. Cjsinla

    Cjsinla Premium Member

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    This parts in the kit were of decent quality and came with American-made transformers. The speaker magnet was ceramic rather than alnico which i think might not be period correct. The chassis seemed to be pretty strong and durable.




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    Last edited: Nov 5, 2017
  4. Cjsinla

    Cjsinla Premium Member

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    The assembly of the board was pretty straightforward due to the way that the resistors and caps were labeled.

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  5. Cjsinla

    Cjsinla Premium Member

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    Mounting the board did require a little engineering. I had to drill holes through the board and case. Also, the screws that were supplied to attach the board to the case were a little on the short side. I ended up using self-tapping 1/2” sheet metal screws that I had laying around.

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  6. Cjsinla

    Cjsinla Premium Member

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    There was a couple of small problems during assembly. The wiring diagram showed an RCA jack for the speaker out but Mojotone had supplied 1/4” jack parts. For some reason a male RCA jack was supplied but I did call Mojotone and they sent me a female RCA jack to go with it.

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  7. Cjsinla

    Cjsinla Premium Member

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    Another problem that occurred was worse and took some help from @Leña_Costoso here on the forum to troubleshoot. The completed amp was squealing at all volume settings. It turned out that the 4 ohm tap from the OT was wired out of phase. The fix was to switch the yellow wire to the jack with the black wire that was soldered to ground. This pic shows the wiring to the jack and ground before they were switched.

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  8. Cjsinla

    Cjsinla Premium Member

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    The final piece of engineering was to drill holes in the cabinet so the the screws and straps could be put in place to bolt the chassis to the cabinet. There was no template supplied for that step, a minor annoyance. As a finishing touch i added a Fender logo to the grill.

    Overall impressions of the amp is that the VibroChamp sounds a lot like a tweed Champ but has more overhead and volume. It’s 7 watts compared to the 5 watt tweed version and those two watts make quite a difference. The VibroChamp still retains the nasal, sweet tone of the tweed Champ but has a little less grit and a little tighter bottom end. The vibrato works well but turning the speed and intensity knobs to zero cause a volume drop. Leaving the knobs on 2 and the pedal plugged in and turned off fixes the problem. This amp is a joy to play and I would recommend this kit to anyone.

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  9. guidothepimmp

    guidothepimmp Senior Member

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    excellent! congrats
     
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  10. Leña_Costoso

    Leña_Costoso Senior Member

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    Thank you for the kind words...
     
  11. Leña_Costoso

    Leña_Costoso Senior Member

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    Hey... btw, check the wiring on the intensity pot. If you have the center, and ungrounded end "reversed" for some reason, it will do just as you say with the volume decrease.
     
  12. Cjsinla

    Cjsinla Premium Member

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    I will check that and will also check the way that I have that part of the circuit grounded. It might be grounded to the back of that pot.
     
  13. Marshall & Moonshine

    Marshall & Moonshine Senior Member

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    That’s killer!
    I built my tweed Princeton as a 2x10 with a bigger OT and it’s a mid-sized stage beauty. They hit the sweet spot right on the nose.
    Nice work!
    I also got a bit of help with mine. I went with the original Fender schematic, which used a 1w cathode resistor on the 6v6. I think it was Don who predicted I’d get a few hours before it failed.
    Sure enough, I played one night (I needed it) and when I got home, it was discolored and blistering.
    Another member (Cygnus7, RIP) sent me a 5w resistor and bypass cap and it’s been strong ever since.
    The people here are a great resource. I love that this forum is small enough that we can actually get to know who the truly knowledgeable ones are, and there’s enough of them who are always happy to help.
     
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  14. bilbarstow

    bilbarstow Premium Member

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    Nice project, and I Agree with @Marshall & Moonshine, this is a great place to get help and advice.

    How high do you have to turn the volume to get the Tweedy tone ? (even a couple of watts can get too loud sometimes )
     
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  15. sonar

    sonar Senior Member

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    Congrats!

    My first build was a Vibro Champ, built for a practice amp. Still is my home amp these many years later. It resides in the living room for easy access. I did go with a Weber sig10 alnico wired at 8 ohms and have played around with the tremolo caps to decrease the speed.

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  16. Cjsinla

    Cjsinla Premium Member

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    These amps sound sweet at almost any volume, chime and sustain. You start to get some grit as well if you hit the strings hard. I usually play mine in the 7 to 8 volume range and get pretty good crunch with a Tele bridge pup. You could probably run it on less volume with P90’s and get good crunch as well.
     
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  17. Cjsinla

    Cjsinla Premium Member

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    Pretty sweet, I am on the lookout for one of those faceplates.
     
  18. Marshall & Moonshine

    Marshall & Moonshine Senior Member

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    Well, mine runs a little higher Voltage here and there, and with the larger (Allen OT “TO-11”, I think it is...) pushing two 10’s, it’s not a “crank in the bedroom” amp, but it gets into pretty great grind around 1/4-1/3 of the way up. After that it becomes a beast. I don’t use it more than halfway up because it compresses too much for my taste. The way I have it, it’s actually got enough clean volume for a mid-sized stage, if you use the volume knob and pick lighter. Not super loud cleans, but “not really distorted”, either. Kinda hard to describe, since all this stuff is relative.
    I play bluesrock, and its perfect for me.
     
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  19. bilbarstow

    bilbarstow Premium Member

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    Yeah, you guys are both right, it is a subjective thing. I like Fender sounds, and I am always looking for a good way to "get the goods" without having to absolutely blast the power, because I'm a strictly man cave player. I have a Fender Greta, and at ~2 watts, I can get pretty good Tweed style grind at a volume I can handle. But then it doesn't have much clean left. The old battle between headroom vs. Volume. I'm just trying to find that middle ground, and a small combo would fit that role perfectly for me. Maybe I just want to buy more gear ?
     
  20. Marshall & Moonshine

    Marshall & Moonshine Senior Member

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    I think a Tweed Princeton would definitely fit that bill, then. Hit it with a treble boost and you get a vintage Marshall-style grind to it.
    Definitely worth looking into. Maybe just do a 1x10. I really like the WGS 10” Veterans in mine. Low-ish sensitivity, something around 94dB.
    Here’s the link, and I think their description is very accurate.
    https://wgsusa.com/vet10#specs
     
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