Adding Cut Control To Trainwreck Express Clone

Discussion in 'The Workbench' started by johnfv, Jan 24, 2019.

  1. johnfv

    johnfv Well-Known Member

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    I'm a novice with mods, am making some tone tweaks to my TW Express clone - trying to tame the gain/clipping and brightness a bit. I've already made good progress by tweaking various resistor values. I want to try adding a Vox style cut control, my question for the amp build experts is this: how important is the location of a cut pot for minimizing noise? Can I put it on the back panel or is that asking for trouble? Experienced advice/suggestions appreciated.

    My amp is a Ceriatone, here is the layout. I intend to keep the presence as is (and mine has a PPIMV on the front panel next to presence). There is plenty of space on the back panel away from the output section.
    [​IMG]

    I'm planning to base the cut on Robinette's layout (I do not intend to attach the pot casing to ground/rail but again appreciate advice on this):
    [​IMG]

    Thanks in advance!
     
  2. Adieu

    Adieu Well-Known Member

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    If location turns out to be unimportant, you COULD go concentric-stacked.... dual 250k pot should be an easy to find part, so Treble EQ would be a potential placement

    PS note: might LOOK sorta like a balance pot, but not the same thing.... independent shafts not single shaft needed
     
  3. johnfv

    johnfv Well-Known Member

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    Interesting idea about the concentric pot but on the Express, none of the other pots are 250K. I'm hoping someone has real world experience with placement on the cut control, if nothing else I'll do some trial and error. I could make room on the front panel if I really need to...
     
  4. ampmadscientist

    ampmadscientist Well-Known Member

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    What schematic are you using for treble cut?
     
  5. Adieu

    Adieu Well-Known Member

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    Seems you can cannibalize other pots and cobble together what you need:

    http://www.tdpri.com/threads/fender-cts-concentric-pot-anatomy.436859/
     
  6. mickeydg5

    mickeydg5 Well-Known Member VIP Member

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    That "Cut Control" in pink is a PPIMV circuit. So are you going to have two PPIMV controls?
     
  7. Guitar-Rocker

    Guitar-Rocker Well-Known Member

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    The Rob Robinette Cut doesn't appear to use a dual pot (nor does Kens pages showing a cut diagram). I think there is confusion of "Cut" versus "Master" in this discussion.

    Use a piece of 2 conductor shielded cable, locate the pot where it is best utilized. Only ground the shield at one end. Isolate the shield on the other end of the cable. ValveStorm sells 2c with shield cable.
     
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  8. Guitar-Rocker

    Guitar-Rocker Well-Known Member

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    John, If you wish to keep your PPIMV and add a "Cut control" then scroll all the way down to the bottom of Rob's page, click on the Trainwreck link. There is a diagram there, again way down in those pages, of a cut... plus a type 3 master PPIMV. See if that is what you may have in mind.


    [​IMG]
     
  9. johnfv

    johnfv Well-Known Member

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    Thanks for all the info Terry. It does currently have a dual pot PPIMV, I was thinking I could also do the cut? I realize they both go to the same location, I was hoping that it could work with both. Maybe I would need to do it more like this (Nik's DZ30)?
    [​IMG]
     
  10. johnfv

    johnfv Well-Known Member

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    I'm no expert but I thought the capacitor is what makes it a cut?
     
  11. johnfv

    johnfv Well-Known Member

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    I don't have the parts yet but I think I will try (via alligator clips) adding the 250k pot/.0047 cap combo at the power tube grid leak location and see what happens... Unless you guys talk me out of it :)
     
  12. johan.b

    johan.b Well-Known Member

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    Look at the vox ac30 schematic. It's just after the p.i.
     
  13. Guitar-Rocker

    Guitar-Rocker Well-Known Member

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    I'd say go the DZ route.
     
  14. mickeydg5

    mickeydg5 Well-Known Member VIP Member

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    Yes it is a PPIMV type circuit with a adjustable frequency shelf cutoff due to the incorporated capacitor. It cuts frequency starting from the upper range.

    Lower capacitor values will not cut as deep.
     
  15. johnfv

    johnfv Well-Known Member

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    So I added the Cut to the TW Express (just like in Robinette's diagram). It works perfectly, in addition to the presence and PPIMV. I tested with alligator clips first (of course) and when satisfied I put it on the back panel - NO noise issues. I did twist the wires like the ones that were going from the PPIMV to the output tubes and I ran my wires in the same location. Dunno it that helped anything but I am *very* pleased with the results. Since I play a lot of Fender guitars, having a cut control to tame the high end is awesome. I very well may be adding a cut control to other amps. Maybe I'll post some pics later...

    [​IMG]
     
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  16. Guitar-Rocker

    Guitar-Rocker Well-Known Member

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    Great deal that it worked out so well, kudos.
     
  17. johnfv

    johnfv Well-Known Member

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    I finally got the amp put back together today - I had ordered a Classictone choke and it took some time for Triode to ship to me. Overall I'm very happy with the results. I tried a number of different mods and now the gain and tone of the amp is much more useful to me. Before it really was a humbucker only amp and had a lot of distortion/gain. Now it is much more Fender friendly and I have a more headroom available. In addition to the Cut on the back panel, I tweaked a few resistor and capacitor values; I also added the choke. I played around with choke location to see if it made a noise difference (it didn't) so I put it where it was easiest. Here are a couple of pics, my mods are pretty obvious - I did them piggyback style where possible (and the mediocre solder skills show :) ). I tweaked the bias a bit and now it really sounds great!

    TW_Express_clone_guts_mods.JPG TW_Express_clone_back_panel_Cut.JPG
     
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  18. johnfv

    johnfv Well-Known Member

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    oops double post, mods please delete
     
    Last edited: Feb 12, 2019
  19. Guitar-Rocker

    Guitar-Rocker Well-Known Member

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    Just out of curiosity, what brand of EL34's are you using in it?
     
  20. johnfv

    johnfv Well-Known Member

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    It has the Mullard RI tubes in there, they're pretty good. I think the TADs are still my favorite for EL34. EH is not bad either.
     

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