ROG Mockman 2.0 - Gain control?

[Elijah-Baley]

Hello.
I'm searching for a long time a tiny distortion circuit to build on veroboard, or in case on perfboard.
I found the Mockman 2.0 by ROG, maybe not so famous, but I could like it.
http://www.runoffgroove.com/mm2.html

Schematic:



I didn't build it, yet.
I just want to make it more versatile adding a gain control. I'm simulating it with the a software I have.
I see a suggestion about it, using a 100k linear pot in line after the input cap, but I'm afraid it doesn't good, I'm not sure, of course. (But I'll try it, anyway).

How we can see it use two inverting input stages, and I know I can decrease the gain with less resistance in the two feedback opamp.
Initially I thought about the first stage, because I guess it work a bit better as gain stage than the second stage. I could add a fixed small resistor to get at minimum setting a clean or slitghly overdrive sound and not cut completely the volume, and to use in series a 1M pot.
It could even work like this, but I know in the first stage the 10k input resistor and the 1M resistor in the feedback set the impedance. I don't know if I'll mess up the impedance with this mod. Or maybe yes, but that's ok. I really don't know.

I'd like get some clarity, please.

Thanks!

[Elijah-Baley]

[...]
Double post. Oops.

[drachir81]

Resurrecting an old thread but I recently built one of these and did add a gain control and it works really well.

I put it after the first 10k resistor, I can't remember what value of pot I used but it might have been a 500k, which means the circuit is still a bit dirty with the gain as low as possible.

It's a very harsh sounding circuit, and cuts a lot of bass, I'm thinking of adjusting the input capacitor too (the 10nF one) to let more low end through and also adding a high cut tone control somewhere sensible if that doesn't resolve things.

I added an LPB-1 circuit in front of the whole thing to give a full-range input boost and this is really excellent!  It takes the Mockman V2 circuit into high-gain territory, especially into a slightly dirty amp.

Stripboard layout: https://tagboardeffects.blogspot.com/2013/01/electro-harmonix-lpb1-with-trimmer.html

[antonis]

Hi & Welcome..

As for the gain control, it should be better to replace BOTH 10k resistors with a 100k dual gang pot..
(actually, place each gang in series with each 10k resistor)
You see, whatever the 1^st stage gain is, the 2^nd stage has a fixed gain of 40dB (x100) so you can't go lower unless you make 1^st stage gain less than unity..
(1M feedback resistor smaller than 10k+whatever series/gain one..)

As for low-end gain, it needs BOTH 10nF caps to be changed..
(each 10nF/10k pair forms a 1^st order HPF (-6dB/oct) resulting into a 2^nd order cascaded HPF (-12dB/oct)..)
By adjusting only the first 10nF cap you effectively alter the slope of the second HPF and not its corner frequency..
(it still cuts the "same" bass but in a less abrubt rate)..

Of course, any gain change via 10k resistors would result into HPFs corner frequency alteration..
(i.e. High gain -> Less Bass and vice-versa..)
For fixed Bass cut frequency of your liking, let those 10k resistors in place and implement gain control via a dual gang pot in place of those 1M feedback resistors.
(in the cost of Treble cut, of course..)

[Elijah-Baley]

I totally forget this thread.
I worked on this circuit a lot of time ago, of course. In the end I replace the 1M resistor with a 1M pot in the first stage, using a small resistor as minimum setting. But even a 500k pot in front of the circuit, and a small cap as treble bleed, avoiding too much cut of treble at lower setting.
Left off the switch and fixed the Modern mode, and added just one silicon diode across the ground as a hard clipping (I know, just one diodes never used, but with one I got that extra grit in the sound and not too much cut in the volume) before the Volume pot. But even a pair of diodes isn't a bad idea.
And I rised up the coupling cap to have a bit more of bass.

I wanted a distortion pedal using a stripboard, or in this case a protoboard, into a 1590A size box, so none switches or dual gang pot to save more space.

And this is my pedal:



And this is a demo: https://soundcloud.com/elijah-baley-pedali-artigianali/mockman-30-all
My version sounds from sparkle clean to dynamic drive, smooth crunch and distortion. But this circuit is very "moddable".