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PRRI "Raw" Control mod?

Discussion in 'Amp Tech Center' started by ruger9, Oct 21, 2013.

  1. ruger9

    ruger9 Poster Extraordinaire Ad Free Member

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    I love the sound of Allen's Raw control on his amps... I see where people have done this to their PR/PRRIs.... having a hard time finding details of it, but did find this...

    mid/raw-pot (replaced the 6.8k resistor going to ground from the bass pot with a 25k pot) - I found that my amp sounds best (again, with clean tones!) when that pot is set right at about 6 to 8k, so that wasn't so useful...


    Is that it? The whole mod? Just replace the mids resistor with a 25K pot?

    I assume the 25K pot is also going to ground?

    Which resistor in a PRRI is the mids resistor?
     
  2. waparker4

    waparker4 Doctor of Teleocity Ad Free Member

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    The mid resistor is like the stopper in the sink. Bigger resistor and less signal goes 'down the drain'

    Here is a tone stack calculator simulation of the Fender tone stack, Bass/Treb 5/5, with bottom to top, 6.8k, 25k, 50k, and 100k mids resistor.

    [​IMG]

    On Fender's Princeton 65 schematic, the mids resistor is R52 on the front PCB
    http://support.fender.com/schematics/guitar_amplifiers/65_Princeton_Reverb_schematic.pdf

    You would want to wire the pot lugs 2 and 3 together, connected to one hole of the R52 location on the pcb, the remaining lug on the other hole of R52. Like the mids pot is depicted in this pic. ymmv
     
  3. ruger9

    ruger9 Poster Extraordinaire Ad Free Member

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    So, to ground... because one side of R52 is going to ground, right?
     
  4. waparker4

    waparker4 Doctor of Teleocity Ad Free Member

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    I'd just keep use the two holes from R 52 for two leads. Different ground locations may introduce noise
     
  5. Matty D

    Matty D TDPRI Member

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    Is this control definitely in the tone stack or is it a variable nfb control?
     
  6. ruger9

    ruger9 Poster Extraordinaire Ad Free Member

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    It's not a NFB. I'm still trying to figure out if it's a "mid pot", or if it's a pot that actually shunts the tone stack to ground, which is what I THINK Allen's Raw control is?
     
  7. printer2

    printer2 Poster Extraordinaire

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    Or both.
     
  8. ruger9

    ruger9 Poster Extraordinaire Ad Free Member

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    Well, I've seen discussions whether the "mid pot" is better than the "raw control"... while they might sonically amount to the same thing, they are not implemented in the same way, apparently...

    The raw control seems to be about a 50/50 love/hate thing, while the mid control is about 80% like it alot.
     
  9. printer2

    printer2 Poster Extraordinaire

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    Have yet to see a different way of implementing it.
     
  10. ruger9

    ruger9 Poster Extraordinaire Ad Free Member

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    I've seen people who have REPLACED the fixed mid resistor with a pot, and people who have ADDED a pot the the fixed mid resistor... I'm guessing the former is the "raw" control and the latter is the "mid" control?
     
  11. Mart the Hat

    Mart the Hat Tele-Holic

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    The only difference between those two approaches is that the first method (replacing the resistor) would enable you to cut mids below the stock value when the pot is turned down, while the second method runs from the stock value upwards.
     
  12. MikeMurray

    MikeMurray Tele-Holic

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    Off on a tangent, Waparker, how do you make the snapshots in TSC different colours? Mine are all just plain old green
     
  13. ruger9

    ruger9 Poster Extraordinaire Ad Free Member

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    So, if you wanted "0" on the mid control to = stock PRRI mid scoop, you would run the pot in series with the stock resistor?

    And what value pot might you suggest to add mids? I realize this is personal taste, but I have to start somewhere... I've seen 3 or 4 different values people have used...
     
  14. printer2

    printer2 Poster Extraordinaire

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    Basically you are changing the resistance of R4 in the TSC. How you go about it is just a detail.
     
  15. ruger9

    ruger9 Poster Extraordinaire Ad Free Member

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    ok, by searching for "PRRI mid control" instead of "PRRI raw control", I found this, right here at TDPRI.... this looks to be the ticket, at 0 gives you the stock mids tone, then you add mids as you increase the control...

    Raw Control - I mentioned this back in March:

    "The midrange on a Princeton Reverb is like a Deluxe Reverb or Vibrolux Reverb...it's set by a 6.8K resister going to ground located on the Bass pot. What you do is move that resister to the middle lug of a 25K pot with the other end grounded to the casing. Stick the 25K pot in the extra output jack hole (you'll have to move the output jack wires over to the primary jack) and run a wire from where the 6.8K resister was located on the Bass pot over to the "left" lug of the 25K pot (if looking at the pot casing with the lugs pointed up).

    Note: You can also put control pot this in place of the ground switch, which should be useless since you should already have a grounded cord installed in your amp right?

    This mod gives you an adjustable midrange control which on zero is the same as the stock 6.8K value...anything above that adds midrange crunch. It's reversable, but I doubt you'll take it out. The folks at The ToneQuest Report called this a "raw control." It's works great and gives you more flexibility like you would find in the larger BF amps. I put these controls in all my Fender amps."

    Use an audio taper pot.
     
  16. FenderLover

    FenderLover Poster Extraordinaire

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    It's a Variable 'Lift' control. If it isn't obvious, the higher the resistance is, the less effect the Bass and Treble controls have (in terms of the amount of control).

    Another circuit is attached. This one shunts around the Tone stack for the same effect.
     

    Attached Files:

  17. ruger9

    ruger9 Poster Extraordinaire Ad Free Member

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    Does it matter which side goes to ground? If so, how do I know which hole of R52 goes to ground?
     
  18. ruger9

    ruger9 Poster Extraordinaire Ad Free Member

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    Well, I did it. 25K pot, with the 6.8k resistor in series, so at full CCW it's the stock tone stack. Interesting. Not sure that it's "worth it", almost would rather just change the mid resistor to something I prefer.

    Like how I have left the mod in the "still testing, easily reversible" stage? :lol:

    [​IMG]
     
  19. waparker4

    waparker4 Doctor of Teleocity Ad Free Member

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    Well surely you thought of this already. But you can set the thing by ear then measure the pot setting, add 6.8k, and solder that resistor in
     
  20. ruger9

    ruger9 Poster Extraordinaire Ad Free Member

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    yeah of course. Just trying to find out where that is, to my ear... I think I definitely like a little more mids/makes the circuit a tad hotter and more sensitive, but even with only a 25k pot, at full up it's just too much.

    This experiment has shown me that a "mid pot" or "raw control" doesn't REALLY "brownface" or "tweed" a blackface. It pushes you in that direction, but it's not really the same thing.


    NEXT UP: SLOWING THE TREMOLO DOOOOWWWNNNN.......
     
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