Mach 1 Overdrive mods?

F

frankenteletron

Member
Hello. Wondering if anyone might be familiar enough with the Mach 1 circuit to suggest mod possibilities for this particular pcb?

I have an original Greer Lightspeed and I've heard that Greer's Southland pedal picks up where the Lightspeed leaves off so to speak.

Basically, if there was a component swap that would increase the gain to allow the Mach 1 a bit more dirt and nastiness... I'd be super interested.

If not, no worries!

Thanks!
 
Nostra . . . got a suggestion for the proper value? I absolutely LOVE this pedal and would like to get it up to the "dirt" level of the Pauper (OD mode). Might have to build a second one. . . one low gain the other higher . . . we could put it in one enclosusre and call it the "Mach of Tone" or some such nonsense.
 
I’d try 22k to start, maybe socket it and experiment. I can’t tell you how or why it works exactly (paging Chuck? :) ), but I’ve upped the feedback loop resistors on several builds and it usually works out.
 
One way would be to just use a 1M gain pot.

Gain is defined (in part) by the total resistance between pin 1 and 2 of the op amp, so R9 plus the gain pot setting. So upping R9 to 22k only increases you max possible resistance from 505.6k to 522k (not very significant). You could use a much higher value for R9, like 220k, but then you couldn’t access lower gains. So R9 sets the minimum gain, and the pot value sets how much range you have above that.

another option is to change the clipping diode arrangement. The light speed arrangement (3 one direction, 2 the other), clips the signal lightly (high clipping threshold). Using 1 diode each direction, or 1 one direction and 2 the other, will clip the signal harder (without needing to change the pot value), but will sound more compressed
 
Increasing the DRIVE pot to A1M will give 6dB more gain, which is not a lot. If you really want to goose it, then reduce R11 & R12, increase C5 & C6. I'd try 680R, 2.4K, 2.2uF and 220nF, respectively for a 14dB boost (with 500K DRIVE pot). You can use film or electrolytic for C5. The DC voltage across C5 is close to zero, so polarity won't matter if you use electrolytic.
 
If you like this pedal you may also like the Timmy/Tommy - the Lightspeed is just a Timmy with the bass and treble pots removed and a simple treble roll-off added as a tone pot. You might also like the Mammal. It's a bit further away from the Timmy schematic but I actually prefer it and it has a lot of gain.
 
The Mammal is a simple, straightforward overdrive design. The only silly part is using a dual opamp and then abandoning half of it. BTW, leaving pin 5 floating is an absolute no-no in good circuit design.
 
Yeah I wondered about that. The Caliber 45 leaves pins 5-6-7 completely unattached to anything as well but damn it sounds good.

In the end (and you know I don't know half as much as you do) I feel that as long as it works... And I haven't heard any overdrive I like more than the 45 with my Gibsons. As long as it doesn't blow up I'm ok with it. :oops:
 
Chuck D. Bones said:
Increasing the DRIVE pot to A1M will give 6dB more gain, which is not a lot. If you really want to goose it, then reduce R11 & R12, increase C5 & C6. I'd try 680R, 2.4K, 2.2uF and 220nF, respectively for a 14dB boost (with 500K DRIVE pot). You can use film or electrolytic for C5. The DC voltage across C5 is close to zero, so polarity won't matter if you use electrolytic.
Click to expand...
Great info! Thanks! Would 3.3uf for C5 (instead of 2.2uf) and 560R for R11 (instead of 680R) be OK? A huge difference? More or less gain? It's all I've got on hand at the moment. Next time I source parts I'll order those exact ones if needed. What I'm going for, since I already have another Lightspeed, is to push both the gain/"dirt" and the mid frequencies a few smidges if possible.
 
Those values will work, but if you're looking for only a "few smidges" more gain then shoot for these values instead:
R11 - 1.5K
R12 - 5.6K
C5 - 1uF
C6 - 100nF

Just get as close as you can. Making those resistors smaller and capacitors bigger increases gain proportionately. As long as you increase caps & decrease resistors by the same ratios, the freq response will stay the same.

C6 influences the midrange. For fatter mids, increase C6 further. Try 220nF.
 
Chuck D. Bones said:
Those values will work, but if you're looking for only a "few smidges" more gain then shoot for these values instead:
R11 - 1.5K
R12 - 5.6K
C5 - 1uF
C6 - 100nF

Just get as close as you can. Making those resistors smaller and capacitors bigger increases gain proportionately. As long as you increase caps & decrease resistors by the same ratios, the freq response will stay the same.

C6 influences the midrange. For fatter mids, increase C6 further. Try 220nF.
Click to expand...

I got as close as I could.
R11-1K
R12-8.4K
C5-1uF
C6-220nF

Love it! More dirt and definitely more mids. Killer!
The only *slight* drawback is it sounds to my ear like I'm losing a tad of the bass.
If I could get some of those back it would be absolutely perfect!

I think I can manage though. Sounds glorious!

I really appreciate the help tweaking this circuit!
 
Last edited:
Where did you find an 8.4K resistor? Not a standard value.

No advantage to increasing C1. The C1*R2 cutoff freq is <8Hz, already below the range of human hearing.
 
frankenteletron said:
I got as close as I could.
R11-1K
R12-8.4K
C5-1uF
C6-220nF

Love it! More dirt and definitely more mids. Killer!
The only *slight* drawback is it sounds to my ear like I'm losing a tad of the bass.
If I could get some of those back it would be absolutely perfect!

I think I can manage though. Sounds glorious!

I really appreciate the help tweaking this circuit!
Click to expand...

If you want more bass, make R12 smaller. Maybe temp install a 10K pot and dial in what you want, then replace the pot with a fixed resistor of the correct value. Saves the board from repeated soldering and desoldering.
 
Chuck D. Bones said:
The Mammal is a simple, straightforward overdrive design. The only silly part is using a dual opamp and then abandoning half of it. BTW, leaving pin 5 floating is an absolute no-no in good circuit design.
Click to expand...

I have always heard this so I don't do it when I breadboard but I don't have a clue as to specifically why.
 
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