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Hi there, welcome to my blog - La Revolution Deux. It's an odd name - but I like it! Here you will find all the info on my various DIY Guitar effects builds, amplifiers and guitars. Everything from a humble Ibanez tubescreamer to the holiest KLON Overdrive.

You may also find a few effects builds that I am looking to move on - usually in exchange for other effects/gear/cash. You can always check my ebay account to see what I've got up for grabs.

Have fun, enjoy the blog - Fred Briggs :-)


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Thursday, 5 June 2008

Xotic RC/AC Booster Overdrive

The Xotic AC Booster a well loved booster/overdrive pedal, this demo shows why -

And here's a scheme for you:

You can clearly see it is a traditional style opamp based clipper. With one interesting addtion, it has an active tone stack present after the clipping section! Here's some more info, available on the Xotic site: http://www.xotic.us/effects/ac_booster/

Kusi of the freestompboxes.org forum contributed these mods to change the xotic AC booster into the xotic RC Booster:
C1 = 47nF
C2 = 1uF / NP
R8 = remove and bridge
C4 = remove
R5 = 22k
R7 = 250k
Clipping-Diodes = 3x 1N4148 each side


  1. Thank you for the information. About the RC booster mod, what do you call 3 on each side?


  2. Me again,

    I am not able to find the 4557. It is probably obvious for you which opamp should be used, but I am a complete starter in this field. Could you then please give the complete name of the opamp and/or a potential replacement for it?


  3. "3 4148 diodes" would be 3 diodes in the feedback loop of the opamp positively biased and 3 diodes negatively biased, parallel to one another. Basically something like this:

    v----| Gain Pot
    |-->->->--| Diodes

    The opamp you should be able to find at all the major retailers such as mouser e.t.c I would recommend trying other dual opamps too - the LF353 is a good 'un for example, or the clasic JRC4558, the choice is yours.

  4. Hi, any news for the PCB?
    Have someone tried to figure out a layout?
    Thanks a lot!

  5. so waiting for a pcb or layout for this baby...


  6. Any body test these schem??. What are the results, sound great?.

    Ghosteaser I think that the JRC4558, 4559 are equivalent of 4557.


  7. i found your site when i search scheme use IC LF353 (gift from my bro). well i don't promise too build that :-). good site...Deux.

  8. Has anybody ever seen a 4557? I haven´t... ;-)))

  9. The new spec RC which is the same as the Scott Henderson has a 1uf cap as C1. Thats the only difference according to Xotic. Im assuming they use a metal film cap.

  10. R8 on the schematic should be 1K resistor not a 10K as shown.

    Find NEC 4557 op amp at


  11. this is version 1,version 2 has 4 diodes,gain 1meg lin,vol 100k lin,r8 1k,led is powered via a mosfet circuit.

  12. Great info Alex, Cheers for that...

  13. any idea about the AC-Comp Booster? does it have additional circuitry to achieve the compression or just a siwtch that selects differently valued components for something already in the circuit above to achieve a more compressed sound?

  14. Anyone done a vero layout for this yet?

  15. @alexandroid @Briggs I just built this using a PCB from Madbean for the Quasar. I've used a 1uf for C1 and .1uf for C2, 4 diodes, B1M gain, B100K vol.
    What I'm wondering about is that it seems that the values specified on jan 31-2012 are mixed for the RC and AC Booster?

    Does the RC Booster still use the 250K volume pot? I like what I have now but I need to leave the Gain low for more clean boosting.

    So question is: what resistor, cap and pot values are for RC and for AC?



    1. hello
      the values i was referring to were obviously for the AC booster,having a 1M gain pot means a lot of gain,an RC has a 250k for gain and 100kB for volume.
      anyway,an Ac with the gain at zero is slightly fatter than the RC but similar

  16. This comment has been removed by the author.

  17. Any idea how this differs from the Bass RC booster? I'm guessing maybe just a larger input cap since the tone control is already an active eq.

  18. Any idea how this differs from the Bass RC booster? I'm guessing maybe just a larger input cap since the tone control is already an active eq.

  19. Any idea how this differs from the Bass RC booster? I'm guessing maybe just a larger input cap since the tone control is already an active eq.


Comments are welcome on Revolution Deux. However, please do not spam links to unrelated sites - these comments will be removed! Thanks - Briggs.