Marshall Bluesbreaker mods

Marshall Bluesbreaker KOT 1
Here’s a Marshall Bluesbreaker. The goal will be to modify it to get closer to the legendary King Of Tone (KOT) of AnalogMan …

I like the original BB Marshall. It sounds a little harsh but not too much let’s say bright … one of the flaws : the overdrive starts from 3 hours (before, there is not much, and the overall level of output remains fairly low), the pots spit (that’s marshall) and even treated with KF Contact (or equivalent), this is far from perfection and, finally, as for the Guv’nor, the plastic jack welded directly on the circuit board are quite weak (cracked, do not take out the guitar jack etc..).

The quality of electronic circuit is not very suitable for mods (but it’s OK anyway, huh …) : the components have their legs bent copper side, and to desolder it’s much less convenient than the Japanese (Boss, Ibanez).

Stop criticizing and here are the schematics : the original, then that inspired the Analogman KOT.

Marshall Bluesbreaker first version blackbox

Marshall Bluesbreaker schematic

KOT marshall bluesbreaker

Analogman KOT schematic

Marshall Bluesbreaker KOT 4

Marshall Bluesbreaker KOT 5Audio printed circuit board

Marshall Bluesbreaker KOT 6“Power supply” PCB and jacks (in/out)

I begin by replacing the resistor R8 with a carbon resistor 1M  (instead of 2.2M for the stock pedal). I also solder a 100uF electrolytic capacitor of the terminals of R6, R7, and a small MKT 0.1uF Wima of the terminals C6 (Vr = 4.5V approx).

Then I replaced C3 by a Styroflex 100pF, and R1 by a 27k and R2 with a 33k :

Marshall Bluesbreaker KOT 7

I must then add the 10k resistor in series with the gain pot. Tweak ! I desolder one leg of the pot and I place there the 10k resistor :

Marshall Bluesbreaker KOT 8

My stock Marshall Bluesbreaker pedal chip is a JRC072BD :

Marshall Bluesbreaker KOT 9
From what I’ve read here and there, this chip is pretty good. Nevertheless, it could be nice to try other ICs so I put a support instead :

Marshall Bluesbreaker KOT 10
I replace the original chip … I’ll try with a Burr Brown OPA 2134 and other ICs ; I replace R3 (1k) by a carbon resistor (I would have replaced C4 and C7 of the Panasonic DMC-V film and R10 and R11 by carbon resistors, but I do not have the ingredients on hand …)
Marshall Bluesbreaker KOT11
Now let’s face the big tweak of death : in soft clipping, we replace the 4 by 4 diodes original MA856 (that are just wonderful in my TS9DX modded) and in hard clipping (not provided in the original Bluesbreaker) 2 diodes placed 1S1588. The transition from one to another will be made with a DPDT switch.
Marshall Bluesbreaker KOT12

The 4 MA856 diodes and the switch …

For the addition of diodes 1S1588 hard clipping, I connected directly to the pots,  Vr is on the volume knob :
Marshall Bluesbreaker KOT13
Then I mounted a 50k potentiometer (as a variable resistor) between C8 and volume pot (I moved C8 to solder it directly on the knob of presence) :


To finish the job, I replace C10 by a 1uF panasonic ECQ-V :

Marshall Bluesbreaker KOT15OK, that’s it !

Marshall Bluesbreaker KOT16
Firsts tests on my nice little clone of tweed field (I definitely prefer soft to hard clipping clipping, more harsh to my ears, already found on TS9DX modded). The guitar is a Squier Classic Vibe Telecaster Custom w/ Lollar Special-T pickups : Marshall bluesbreaker modded analogman KOT sample

Here are 2 samples with my Gibson Les Paul Custom on a AC30 CCH, cabinet Orange PPC 1×12 V30 :
Les Paul Gibson 2PUs Marshall Bluesbreaker KOT Modded
Les Paul Gibson PU Bridge Marshall Bluesbreaker KOT Modded

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17 Responses to Marshall Bluesbreaker mods

  1. Mike says:

    Have you seen the Jhs Morning Glory OD?
    It’s based on a bluesbreaker circuit and sounds amazing!
    eventually I’m going to try and replicate it

  2. t-geek says:

    Never tried this Morning Glory. A lot of buzz anyway : it seems to sound very nice !
    Have you eared my HonkScreamer (specially samples #4 and 8) ? Not a BB but I like very much the sound it makes !

  3. BoX says:

    Hi, t-geek! At the same time you connect hard clipping – you disconnect 4 diodes in the feedback of the opamp, wright?

  4. t-geek says:

    Yes sir !

  5. Brit says:


    I was wondering if the person who added these custom modification can add these to my stock Marshall BB pedal. Any contact information?

  6. Greg Charles says:

    Hi, looks like your pretty deep into your BB, do you have any sound clips? i have enjoyed mine off and on over the years for its modest gain.

    I have a cracked input jack, do you a wiring tip for replacement with a switchcraft? i cant seem to get it right because it looks like the circuit is in parallel but i must be missing something.

  7. Mallory Penland says:

    I have been using BB1′s forever! I have 3-4 now with 2 out of commission. The
    problem is input and output jacks cracking. I did replace the output jack with a
    switchcraft with little problem. I am not sure how to replace the input jack as there are more connections, I assume having to do with the battery etc. How do I fix it?
    Or, do you know where I can get original replacements?

    I also have one down because the footswitch broke. What do I replace it with?

    Mallory Penland

    • t-geek says:

      Yes, I like the blue and black BB !
      I never succeed to find original replacements jacks (I was looking for my Guv’Nor ‘cause input jack was broken, finally took the « loop jack » to replace the input jack …)
      For the footswitch, you should look after a 2PDT (DPDT) PCB mount, hoping it fits with the BB1 PCB …

  8. Adam says:

    Hi all,

    Does any one know were to buy the MA856 diodes?


  9. Miguel says:

    Nice one man, this is brilliant!
    I was expecting you to change the IC for the JRC 4580D ahah.
    I think the bluesbreaker was one of the most underrated pedals (except for Mike Piera).
    I found out the possibility of changing between softclipping and hardclipping with one switch brilliant, never though about that. I’m gonna make to one mine one for hard clipping and one for soft clipping so you can have all the variety, no diodes, soft, hard or both!
    How does he do with the 3 way switch in the Prince of the Tone?
    Thanks for this man

  10. Lucian says:

    i’d like to know if you have the PCB layout in pdf to share with us!!

    See you <3

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