Wednesday 12 February 2014

Fender Eric Clapton 25db Mid Boost

Fender's take on trying to get EC's strat to sound like a Gibson. Some people seem to like it a lot, while others.. Not so much. But as i stumbled on a schematic, i thought this could work well as a pedal. With four transistors and not-so-simple design, there's little chance of fitting this onboard any guitar.. There are some non-standard values for the resistors, but as always, you should be fine with the closest ones you have. The layout doesn't have the magical TBX Tone control in it, but i've added another image that shows how to wire it up.






Posted by at 08:25
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37 comments:

  1. Unknown12 February 2014 at 11:52

    If adding the TBX, any idea where you would connect the guitar input to the pot?

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    1. mirosol12 February 2014 at 13:06

      Input from the guitar to both, board and the TBX pot...
      +m

      Delete
  2. Geezer12 February 2014 at 12:20

    John, looks like it is wired just like a simple tone control....parallel (to ground) with the input.

    http://www.strat-talk.com/forum/353673-post4.html

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  3. Geiri12 February 2014 at 23:01

    I have a 1987 Fender Strat Plus with TBX tone control and it's pretty cool. I personally don't use tone controls ever but those who do should like it.

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  4. Bear26 February 2014 at 14:46

    How hard is it to change this to the lower-gain boost from the Elite Strats and Teles? (This is supposed to be the evolution of the Elite preamp, which was a James Demeter design.)

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    1. Anonymous20 September 2015 at 18:50

      To reduce the gain to 12dB you must add a pair of resistors in the MDX pot.

      Delete
    2. Sage13 August 2019 at 23:19

      It's much more than just a pair of resistors. The circuit is slightly different and the values of many of the components are different as well. I've made my own layout of the original MDX circuit here:

      https://flic.kr/p/2gWyjju

      I put this together by referencing the schematic and parts list from the original Elite Strat, found here:

      http://eledar.net/Music/walnelite/index.htm

      Delete
  5. Unknown16 June 2014 at 14:07

    Hi mirosol,
    First thing first: thanks for the layout. You and IvIark are doing an outstanding job, here. :)
    Now, I have searched for a schematic, for this, and all the ones I have found include a 330K or 332K resistor to ground, at the base of Q1, which your layout does not include.
    I have no idea, though, what this resistor is present for, so I'll let you advise whether it's important or not. :)
    The schematics I am referring to are the following ones:
    http://guitarwork.ru/electronic/Fender/Eric_Clapton_Strat_25dB_midbooster-preamp/
    http://www.blueguitar.org/new/schem/_gtr/ec_schem_fact.jpg
    http://i197.photobucket.com/albums/aa211/bajaman002/FenderEricClaptonActiveElectronics.jpg
    I'd love to give this one a go, and hopefully make it verified. :)
    Thanks
    Fred

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    1. MJG25 November 2014 at 02:13

      Just FYI, when I tried to surf to the guitarwork.ru site my virus detection lit up like a Christmas tree.

      Just sayin'...

      Delete
  6. coi20013 July 2014 at 11:42

    Mirosol, I have built this and it works. I had to use a 100K volume pot because the circuit oscillated with the 250K pot at the mid point of the rotation range. Works with all kind of transistors including germaniums.
    Thank you for another great layout
    Coi2001

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    Replies
    1. mirosol3 July 2014 at 12:51

      Strange thing with the pot value.. I'll tag it anyway. Cheers!
      +m

      Delete
    2. mirosol25 November 2014 at 15:15

      I think Frederic was correct about that missing resistor, so i added it to the layout. Updated now...
      +m

      Delete
    3. FabGTO11 February 2015 at 15:12

      Hi, I made one too with Frederic's correction and as coi2001 I have a resonance and an oscillation when the volume pot is at 12 and when the mid pot is at max.
      The volume pot works as a master up to 12 and after it change the frequency response and the mid pot just increase the boost.
      I don't know how it supposed to work, but it's fun.

      Great layout !
      Fab

      Delete
  7. ab6 December 2014 at 17:31

    hi...is there a wiring diagram on how to connect the circuit to the guitar

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  8. zzzzzz7 December 2014 at 18:17

    hello. I'm trying to put this circuit together, and i have a couple of questions (i'm a beginner but i'm learning...)
    Can this circuit be used with both active and passive pickups?
    I assume that the wires 'Volume 1, Volume 2 and Volume 3' go to the connectors of the volume potentiometer. Same thing with the tone pot. But are you counting the pot connectors from the bottom or the top side?
    Thanks
    z.z.

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  9. Unknown21 June 2015 at 05:16

    Hi

    Initially, it was a dual preamp stage, the second one being an op amp.
    Both have a little tone correction.

    I am a French engineer and I have designed exactly the same preamp with a simpler design.
    It gives exactly the same result but is way simpler to achieve.

    Would you like me to post it?

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    Replies
    1. Dellamorte1 July 2015 at 10:30

      Yes please do share :)

      Delete
    2. Dellamorte1 July 2015 at 10:38

      This comment has been removed by the author.

      Delete
    3. Unknown4 January 2016 at 07:57

      Hi,Dominique! I'm ukrainian engineer and I'm interested at your discrette opamp schematic! Please send me a message to boxcustompedalsdoggmail.com

      Delete
  10. Unknown2 July 2015 at 17:08

    I'd love to share. But how do I upload the schematics?
    Dominique

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  11. Dellamorte11 July 2015 at 08:35

    upload to imgur ,then share the link?

    ReplyDelete
  12. honzikd3 October 2015 at 10:58

    Thanks for the circuit! I've just built it, and I have to unfortunately confirm it oscillates with 250K volume pot. Would there be any tip how to get rid of that - other than lowering the resistance of the pot? Many thanks!

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    1. honzikd3 October 2015 at 11:33

      ... Just because I currently don't have a 100K pot handy... :)

      Delete
  13. honzikd5 October 2015 at 09:50

    OK, I've found out why the circuit might oscilate - all the "original" Fender schematics use only 50K(!) pot for the volume. I'll replace my 250K with 50K in my guitar during the week and will post the results here. Cheers!

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  14. Jürgen Schöpf20 December 2015 at 21:25

    I had the same problem - self-oscillation! - and it's true: after changing the volume pot to a 50k and putting the 250k to the mid boost knob everything works as expected! areyouexperienced.net also makes a note on this fact easily overlooked.

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  15. Andrew Wasson15 December 2016 at 17:33

    Great layout! I found the schematic on the web and was drafting it out in DIYLC when I found the layout here. This saved me a ton of time.

    The resulting circuit is super clean. Even inline between my guitar and amp unboxed or shielded it is quiet without inducing hum or noise. The mid boost adds a nice amount of gain as you roll it on and it really fattens up the tone as it pushes the front of the amp.

    I'm using PN2222A transistors for my NPN transistors and the 2N5087 for the PNP. The only part I didn't have in my bin was a trustworthy PNP transistor so the total cost for this build in new parts was a 55 cent transistor from Digikey.

    I'm using Log potentiometers 50K for volume 250K for mid-boost, as per the original schematic. I haven't tried a 250K for the volume yet but I will be experimenting with different values. They use this circuit in the Fender Custom Shop Andy Summers Tribute Telecaster guitar and it uses a fairly standard telecaster volume control and tone stack so it should be possible to use it with a 250K volume but maybe not quite as it is wired in this layout. I'll post back once I'm done.

    Pictures of the build can be found here: http://www.tdpri.com/media/albums/fender-eric-clapton-25db-mid-boost.1873/

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  16. Andrew Wasson24 December 2016 at 00:28

    Just a quick update regarding some experimenting with the volume control value. 50K seems to be optimum for a clean volume control. Anything higher starts to distort the signal at the top of the volume regardless of where the mid boost potentiometer is positioned.

    I'm using a stacked set of 250K Log pots so to bring it down, I've paralleled a pair of 70K resistors with the legs of my volume potentiometer. This gives approximates the 50K value necessary and it doesn't seem to skew the rate of control badly.

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  17. Andrew Wasson25 December 2016 at 00:49

    One more update based on my testing and observations.

    If you want to experiment with any of the wiring combinations Fender has produced, you'll need to know the pinout and colour code they use. According to my finding, the pinout for the Fender preamp module used in the Clapton guitar is as follows:
    1) Red - Power
    2) Black - Ground
    3) Yellow - Input
    4) N/C
    5) Green - Volume 3
    6) Violet - Mid 3
    7) Brown - Volume 2, Mid 1

    In the design above generously posted by Mirosol, the volume control tends to present a problem because it should be a 50K potentiometer but is marked 250K. It's not a huge deal and as I noted above, you can either use a 50K potentiometer or parallel resistors across the larger value potentiometer to tailor the resistance to 50K.

    Another option, especially if the preamp is going to be mounted onboard your guitar is to remove the volume control from the preamp circuit and use the one in the guitar. I've modded mine for this and for my use, it makes for a much more useful unit. To achieve this omit the volume control pot from the layout, tie the leads from Volume 3 and Volume 2 together; ignore the lead for Volume 1, it's just a ground wire. Input, output and the mid control stay the same. This is how it will be installed in my Andy Summers inspired Telecaster and it will rock!

    Merry Christmas all!

    Andrew

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    1. Unknown17 March 2017 at 02:06

      I hope I'm not chiming in too late but all the information here is very good. Unlike Fender's circuit where the mid boost is always in the circuit, does the modification above bypass the boost when it is off?

      Delete
    2. Gutbucket5 September 2017 at 21:14

      Hey dude put it in pedal casing then u can use on any guitar

      Delete
  18. Renegadrian16 June 2017 at 00:29

    This comment has been removed by the author.

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  19. Renegadrian16 June 2017 at 11:18

    mmm Built it using this layout. mid control works like a reversed volume so no sound when fully ccw so I can say the mid boost part is not working...where have I gone wrong!? Used 5088s and 3906 as the pnp - wiring and soldering seems ok.
    Renegadrian

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  20. Unknown14 July 2017 at 20:49

    I'm I correct that when you add the TBX pot in total there a 3 pots: TBX, MID and Volume?. What is the downside if you don't add the TBX pot? (soundwise?)

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  21. Gutbucket5 September 2017 at 21:09

    You dont need the tbx dude, you got tone pot on guitar anyway, no downside

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  22. StefC29 July 2019 at 14:24

    Could somebody please share a diagram of the complete wiring (pickups, 5-way-switch and output jack, values of potentiometers included) with this board and also where to install the TBX control? Thank you

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  23. Sage13 August 2019 at 21:46

    This is a great layout but there are a few errors that should be corrected:
    1. The leftmost 10uF capacitor is redundant -- it connects the same points as the one directly to the right of it. This extra cap is not part of the schematic and should be omitted.
    2. The 232K resistor directly to the left of Q2 should actually be 332K.
    3. The volume pot should be 50K Audio taper.
    4. The mid pot should be 250K Audio, not Linear.
    5. Q1-Q3 are specified as 2n6429, but Fender specifies the BC550 as a suitable replacement. As the 2n6429 is no longer in production, I would recommend the BC550 over the 2n5088.
    6. It seems you've rounded off the values of many of the resistors, but Fender specifies a 1% tolerance, which is a much narrower variance than many of the substitutions you've made here. Just a thought.

    Also worth mentioning to readers that D1 does not exist in the original schematic and can be replaced with a direct link if you want to sacrifice polarity protection for authenticity. It probably doesn't hurt though.

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  24. Gutbucket25 December 2021 at 18:09

    Can thsi have true bypass switch

    ReplyDelete

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