Mid control for a Tweed Champ/Princeton

Discussion in 'Shock Brother's DIY Amps' started by Bacha009, Feb 12, 2015.

  1. Bacha009

    Bacha009 TDPRI Member

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    Hey forum !
    Built a couple of fenders here, then did some other amps, but was homesick
    After my Princeton, which sounded so sweet.
    So I built another one. After the other amps I went through, this time
    I did not like the tone control, just too mid, in your face, etc...
    I tried several tone circuits, but they sounded either similar or the insertion loss was too big, until I tried this Mid control from Blencove's book.
    It was used in Framus Cobra amp, but Blencove scaled it up.
    It sounds absolutely amazing with same insertion loss as the Princeton tone circuit!!

    You get blackface like scooped tone fully ccw, then with cw you are adding mids,
    Fully cw it is like tone stack lift!
    Better than my Carmen Ghia mid control with much less insertion loss.
    I 'll try to post some pics

    here is a link - the one way at the bottom:
    http://chasingtone.com/yourguitaramp/guide-to-single-knob-tone-controls/

    The caps are 0.001micF in my case and the resistor is 100K, the pot is 1M
    [​IMG]
     
    Last edited: Feb 12, 2015
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  2. jonrpick

    jonrpick Friend of Leo's

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    Schematic???
     
  3. aabbs20

    aabbs20 Tele-Meister

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    Very cool! Does it act on the highs at all? Is it a pretty bright amp now?
     
  4. joeford

    joeford Friend of Leo's

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    [​IMG]

    he posted a link to it on the original post
     
  5. Bacha009

    Bacha009 TDPRI Member

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    It is bright and scooped even chimey with full CCW pot rotation + negative feedback switched off (that I see as the most useful Tweed Princeton mod)

    It is incredibly simple to make - just remember the Caps are 1nF, the POT is 1M and the Res is 100K
     
  6. jhundt

    jhundt Doctor of Teleocity

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    do you use only this control, in place of the normal tone control? and if so, is it in series between the volume pot and the following preamp stage?
     
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  7. Bacha009

    Bacha009 TDPRI Member

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    It goes like this:
    1st stage 12AX7 plate -> tone control->Volume control ->2nd stage 12AX7 It is grounded through the 100K R independently from the volume pot, so to me it is in parallel.
     
  8. Mr Ridesglide

    Mr Ridesglide Tele-Afflicted Silver Supporter

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    Very nice! Good to see you still working hard at this! Thank you for sharing your results.
     
  9. jonrpick

    jonrpick Friend of Leo's

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    Very cool... The schematic and pic didn't show up when I first viewed the thread.

    And also, thanks for posting this... I'm on tone stack #2 in my MMB. I'll add this one to the list to try.

    Quick question: How much does it interact with the volume pot? I went from the stock stack in my MMB to a Tweed stack. I like the Tweed stack better, but I don't care for how it loses its effectiveness once I have the volume set where I like it.
     
  10. Bacha009

    Bacha009 TDPRI Member

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    Thanks
    Not involved like rest of you, but bit by bit...
     
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  11. FenderLover

    FenderLover Poster Extraordinaire

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    That's the way I use it, so it is actually in series: gain_1>Tone/Vol>gain_2. The Tone/Vol are actually the input of stage 2, so the 100K resistor on the Mid and the Volume ground should actually both be grounded with the 2nd stage cathode resistor. It's an academic point since you mentioned Merlin's book, but I'm sure the way you have it connected works well too.
     
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  12. Bacha009

    Bacha009 TDPRI Member

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    thanks FenderLover, you can tell I am not very versed in this :oops:
    I have a question: I like when I turn the mid tone POT CW to get thicker
    sound for solos.
    Do you think that it could be made switchable with a foot switch ?
    When you lift the tone stack ground from the 100K R, then you get a full bypass,but the volume jump is too big..
    I would not want to bypass it completely just some ..
    actually stand corrected - I just tried it - funny it works by increasing mid and volume, but not as much as if I have the tone pot fully clockwise - which is good :)
     
    Last edited: Feb 15, 2015
  13. FenderLover

    FenderLover Poster Extraordinaire

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    You might try a pot (250K or maybe 500K) in series with the 100K to ground, and the footswitch would short out the pot.

    When the foot switch shorts the pot, you get the standard Mid-scoop circuit operation depending where the Mid pot is set. With the foot switch open, dial the pot for the highest boost you'd want. You get a variable mid-scoop boost depending where the new Boost pot is set. If there is a lot of 'dead space' in the pot rotation, use a smaller pot.

    The pot could stay on the back panel for adjustable boost, or replace it with a resistor once you get a boost setting that you like. This a pretty standard Boost mod that I first read about back in the 70's in Guitar Player magazine.
     
  14. Earth Daddy

    Earth Daddy TDPRI Member

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    I'm trying this setup, but it currently is not pleasing to me. I have used the original call for 10k resistor and .01 cap for my 1M pot, maybe that is the issue. I don't know enough about ee to understand, I just went from the original diagram. I have some questions for you if you don't mid answering please:

    Do I need to switch to 100k and .001 like yours?
    Does tab 1 go into tab 1 and tab 2 into tab 2 on the pots? I have mine switched...
    What is the third wire going into the tone pot?
     
  15. Bendyha

    Bendyha Friend of Leo's Silver Supporter

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    ..............Blencowe, not Blencove. If honouring, or quoting Merlin's great work, lets at least get his name right. Kind of like Jim Kelley, who seems to get spelt (spelled for the US bees) wrong the many times his amps are refered to.
     
  16. robrob

    robrob Poster Extraordinaire Ad Free Member

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    Seems like this would be a good, bypassable mid control. Just use the guitar tone knob to set the highs.
     
  17. jhundt

    jhundt Doctor of Teleocity

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    You HAVE to change the values as suggested, or it won't work right. When it works right, it works very well.
     
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  18. robrob

    robrob Poster Extraordinaire Ad Free Member

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    Here's a layout of the mid control with a built in push-pull raw switch:
    [​IMG]

    Push-Pull 1MA (audio) pot wired as a "Raw Switch." Pulling the knob up breaks the connection between the caps and resistor so the guitar audio is not filtered.
     
  19. anthrotony

    anthrotony Tele-Meister

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    Hi robrob, sorry to revive this, but I'm just about to start a 5E3 build and I wish to add this Framus mod. I wonder whether the 5E3 tone stack would need to feed into it, or be disabled first (I've never played a Tweed so am not sure of the consequences). In any event, I'd considered the possibility of using a footswitch (instead of your idea for a push-pull pot) that would simply switch between the two tone stacks. Would this be easy enough to implement? Cheers!
     
  20. robrob

    robrob Poster Extraordinaire Ad Free Member

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    The Framus mid can work in conjunction with the stock 5E3 tone pot. The Framus could also be called the "Blackface Control" due to the blackface style mid frequency scoop it adds as you turn it down.
     
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