Marshall Supa Fuzz/Tone Bender 2 - layout questions

[tracer03]

I'm looking to build the Marshall Supa Fuzz, but I want to build it with the onboard inverter as on the Tonebender Mk II with Negative Ground - since they're pretty much the same, except for some component values, could I use the 'Bender MK 2 layout with inverter?

2nd question: I want mod it per the comments, especially to make the suggested mod of using a 25K pot for external bias - to do that, would I remove the 8k2 resistor and run wires to lugs 1 and 2 of the pot? Or what is the correct way?

I tried to tweak the layout so I didn't have wires running out of the center of the board, but it started to become a mess, so if anyone wants to tackle that, I could drop a request in the correct forum.

Thanks in advance!

[Travis]

Yes you can use the MKII and change the values to match the Marshall. I find batteries to be more reliable than charge pumps for this type of thing personally

For the bias mod you would ideally have a resistor in series with the pot to set the minimum level but yes you can do that.

On my first MKII build years ago I did the Q3 bias mod and it really didn’t offer anything exciting after all. I since found that altering the bias of Q2 is more important in that circuit. The value for the Q2 collector resistor ranges from 47K to 100K in MKII type circuits. So you could swap that resistor with something like a 100K pot with a series resistor to set the minimum level and it would be much more effective overall

My personal preference is simplicity and I try to just get the best sound I can with the stock circuit, but if you like the bias mod I recommend Q2 instead of Q3 :)

[tracer03]

Travis wrote

Yes you can use the MKII and change the values to match the Marshall. I find batteries to be more reliable than charge pumps for this type of thing personally

I'm trying to avoid batteries altogether: I know on many of the older circuits the draw is low enough that batteries last a long time, but no one I know uses them in pedals anymore, so...

Travis wrote

For the bias mod you would ideally have a resistor in series with the pot to set the minimum level but yes you can do that.

On my first MKII build years ago I did the Q3 bias mod and it really didn’t offer anything exciting after all. I since found that altering the bias of Q2 is more important in that circuit. The value for the Q2 collector resistor ranges from 47K to 100K in MKII type circuits. So you could swap that resistor with something like a 100K pot with a series resistor to set the minimum level and it would be much more effective overall

My personal preference is simplicity and I try to just get the best sound I can with the stock circuit, but if you like the bias mod I recommend Q2 instead of Q3 :)

So...that would mean wiring in a 100k pot & 20k ohm resistor (or something like that) in series in place of the 100k that's just above the 8k2 - connecting lug 1 and 2 (3 would be unconnected) correct?

I've build a couple of 'Benders with external bias pots, and I've always liked the ability to tweak the bias to make it splatty or lo-fi sounding.

[Travis]

Pretty much!