MXR - Badass Modified Overdrive

Ice-9 · Post by **Ice-9** » 30 Jul 2012, 10:57

I just bought a MXR Badass Modified Distortion to trace, so here are some PCB pictures and a schematic.
I have traced the full effect but as usual I don't bother with the fet bypass and led indicating lights.

first the PCB pics. There are two PCB's one has the main circuit and the second has the control pots and is connected to the main PCB with a ribbon cable.

PCB top with the pots

PCB bottom with the pots

MAIN PCB bottom

Main PCB top

Main PCB top with hardware removed for easier tracing

Ice-9 · Post by **Ice-9** » 30 Jul 2012, 11:17

Here is the schematic I have traced and component value list, I have just hand drawn it but it should be readable.

MXR Badass Modified Overdrive circuit description.

Ok so here it is, Not a lot different to the zakk Wilde ZW44, it starts with the same input buffer based around Q2 then into an opamp clipping section with assymetrical clipping diodes in the feedback loop. The next opamp section is a tone control with the addition of R6 which is switched to 1/2V (bump switch).

The only real difference is in the next opamp section which is a 100hz boost/cut build around a gyrator circuit.

Schematic

Ice-9 · Post by **Ice-9** » 30 Jul 2012, 11:25

And the component values.

StefSamy · Post by **StefSamy** » 01 Aug 2012, 10:15

Very good job for this nice overdrive, man

StefSamy · Post by **StefSamy** » 01 Aug 2012, 10:30

Sorry but what is U2?

Is it a 33178 and in fact U1 and U3 are "duals" 33178?

StefSamy · Post by **StefSamy** » 01 Aug 2012, 11:04

Sorry again, for multi posting, but I don't find how to edit my posts....

- is the part with Q1,3,4,5,6 and R18,22,23,25 a buffer part?

If so, if we build the stompbox in truebypass mode, we don't need them, but do we need C13 that is listed in your LoC?

Ice-9 · Post by **Ice-9** » 01 Aug 2012, 11:26

StefSamy wrote:Sorry but what is U2?

Is it a 33178 and in fact U1 and U3 are "duals" 33178?

U2 is i the power rails and is just there for polarity protection, so to build a clone just use standard power and polarity.
Yes U1 and U3 are both 33178 dual opamps.

Ice-9 · Post by **Ice-9** » 01 Aug 2012, 11:30

StefSamy wrote:Sorry again, for multi posting, but I don't find how to edit my posts....

- is the part with Q1,3,4,5,6 and R18,22,23,25 a buffer part?

If so, if we build the stompbox in truebypass mode, we don't need them, but do we need C13 that is listed in your LoC?

None of the above parts are needed as you say, they are all just part of the bypass switching and led indicators. If you build this with true bypass switching.

also C13 is not needed. ( It's only in the LOC because I wrote it down before realizing and wasn't goin to right the lit out again

)

StefSamy · Post by **StefSamy** » 01 Aug 2012, 12:19

Ice-9 wrote:
StefSamy wrote:Sorry but what is U2?

Is it a 33178 and in fact U1 and U3 are "duals" 33178?
U2 is i the power rails and is just there for polarity protection, so to build a clone just use standard power and polarity.
Yes U1 and U3 are both 33178 dual opamps.

OK, that's clear with your other reply too, thanks for all

Ice-9 wrote:
StefSamy wrote:Sorry again, for multi posting, but I don't find how to edit my posts....

- is the part with Q1,3,4,5,6 and R18,22,23,25 a buffer part?

If so, if we build the stompbox in truebypass mode, we don't need them, but do we need C13 that is listed in your LoC?
None of the above parts are needed as you say, they are all just part of the bypass switching and led indicators. If you build this with true bypass switching.

also C13 is not needed. ( It's only in the LOC because I wrote it down before realizing and wasn't goin to right the lit out again )

I was wrong with my post, it was R24 and not R22 that is not needed (i write this for other readers

)

Ice-9 · Post by **Ice-9** » 01 Aug 2012, 12:24

If i can get round to it I will try and do a layout for through hole components for this. Just a bit pushed for time at the moment.

StefSamy · Post by **StefSamy** » 09 Sep 2013, 09:58

A VERO, YES, nice job

mirosol · Post by **mirosol** » 09 Sep 2013, 10:49

I misread R13 and R17, so the input resistor should in fact be 10K and not 240K. Someone is currently building this, so i'll update the layout once i hear back from him.

mirosol · Post by **mirosol** » 09 Sep 2013, 17:46

The edit time of the posts close up so fast :)

One of our blog's trusted readers just notified us that the layout is now verified. And the wrong resistor value is also fixed...

Bill_Mountain · Post by **Bill_Mountain** » 25 Sep 2013, 18:59

Those 2 separate eq stages seem redundant. Couldn't the tone and 100Hz control be combined in the same network like a graphic eq (with a peaking low and shelving high)?

LightandLIfe · Post by **LightandLIfe** » 09 Dec 2013, 22:52

Been searching far and wide and you guys seems like you guys can help. My Custom OD only works with the Bump switch engaged. When dis engaged, no sound comes out? Can anyone point me in the right direction?

bunyaman · Post by **bunyaman** » 19 Jan 2014, 22:21

Hi! What is VS1 and VS2 on a schematics?

bunyaman · Post by **bunyaman** » 21 Jan 2014, 22:30

My PCB. Layout was edited after making PCB

theroan · Post by **theroan** » 15 Jul 2014, 18:54

Thanks for this!

p88wright · Post by **p88wright** » 04 May 2015, 03:24

Hi ICE-9,

I just wanted to check if the values for the Capacitors were measured in-circuit or did these parts get removed and measured? Reason I ask is that some of the values seem a little out when I did a couple of quick calcs for the tone and 100 Hz filter networks

Thanks,

Phil.

Ice-9 · Post by **Ice-9** » 08 May 2015, 10:30

p88wright wrote:Hi ICE-9,

I just wanted to check if the values for the Capacitors were measured in-circuit or did these parts get removed and measured? Reason I ask is that some of the values seem a little out when I did a couple of quick calcs for the tone and 100 Hz filter networks

Thanks,

Phil.

Yeah, they were measured in circuit which can account for odd readings.

MXR - Badass Modified Overdrive [schematic]