# Mach 1 Overdrive mods?



## frankenteletron

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!


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## Nostradoomus

Try upping the value of R9


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## frankenteletron

I'll try that! Thanks for the info!


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## Mike McLane

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.


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## Nostradoomus

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.


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## phi1

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


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## Nostradoomus

There it is! Thanks


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## Nostradoomus

It’s silly because the last time I did this I upped the resistor 10x haha ?


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## Chuck D. Bones

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.


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## HamishR

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.


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## Chuck D. Bones

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.


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## HamishR

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.


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## frankenteletron

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.


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.


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## Chuck D. Bones

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.


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## frankenteletron

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.



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!


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## music6000

Increase Input Cap C1 - 47nF to 68nf, Confirm with Chuck.


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## Chuck D. Bones

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.


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## Chuck D. Bones

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!



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.


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## frankenteletron

Chuck D. Bones said:


> 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.



My mistake. It was 8.2K. No idea how I got it. Must have been an unused/extra part from something else.


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## Devoureddeth

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.



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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## Chuck D. Bones

For opamps to bias properly, they all need a DC path from their inputs to somewhere.  If an input is left floating, it will cause the input circuit to saturate.  Some dual and quad opamps share internal bias circuitry and if you upset one opamp, you can upset them all.  Also, floating inputs make good antennas and will pick up noise or RF and might spread that around in the circuit.  The LM386 is an exception, it's not really an opamp and it has internal 50K bias resistors to ground.


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## Devoureddeth

Wow well now I know. I don't think I could google an answer that good, thank you.


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## HamishR

So if I want to "fix" my Animal or 45 Caliber pedals where should I connect pin 5?  I understand that it's bad form to leave it disconnected but the pedals sound as good as I could ever want and I have never had any issues with noise or anything other than they sound great!  I'm reluctant to mess with them but if you think that connecting pin 5 to something will help then I can try it.


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## Chuck D. Bones

Best place would be Vref.


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## HamishR

Hey Chuck!  I just built myself another Caliber 45 to put in a box with a Majestic.  I have changed my vero layout so that I can connect pin 5 to Vref and it works perfectly and sounds exactly the same as without, so I guess that's a win.  So the pedal is potentially more stable now?  Whatever, if you recommend I build this way that's good enough for me, especially as it doesn't appear to affect how great this pedal sounds.


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## Chuck D. Bones

It can only help to connect pin 5 to Vref.  When can we see your new creation in Build Reports?


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## HamishR

Well it's all vero but I guess I can post it...


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## phi1

Chuck D. Bones said:


> Best place would be Vref.



The tagboard layouts for blue note and animal have pin5 connected to ground (on the advice of the fsb blue note trace). It’s really handy on vero since you can just leave pin4 and 5 connected. Is vref significantly better than ground? I only ask because I’ve used the same method on a few other circuits where an op amp was unused.


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## Chuck D. Bones

The advantage to using Vref is is doesn't violate the datasheet's common-mode voltage range requirements.  In layman's terms, it means that some opamps go ape-shit if their inputs are driven to the rails.


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## HousTom

Chuck D. Bones said:


> 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.





Chuck D. Bones said:


> You could use an electrolytic cap for C2, but then you would have to observe the correct polarity because there is 4.5VDC across C2.



I deal with this frequently -- for a specific cap (say 220n or 470n) I'll have on hand only electrolytic which is supposed to be polarized but the PCB/schematic expects a ceramic/film/box cap so polarity is unspecified.  I stress out trying to make sure my caps gets installed with the positive lead facing signal/power input and the negative lead facing ground but always wonder what would happen if I get it backwards?  Would the cap explode?  Would the circuit just not work?  Or would everything work fine because even electrolytic caps are somewhat "reversible" as long as we are talking about minimal voltages (i.e. ~ <1v )?  I realize this is a newbie question and also that I ought to just invest in $100 worth of box caps.  Any response from any point of view appreciated.


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## Chuck D. Bones

If you're serious about pedal building, then you really should invest in the right parts. The likelihood of success depends on a good design, good parts and good workmanship.  Compromise any of those and the chances are good you will end up troubleshooting or shit-canning your pedal.

Now, about determining the correct polarity for a cap when the build docs don't tell you (through no fault of their own).  The easiest and most reliable way to determine the correct polarity is to measure it in-circuit.  Build you board, minus the unpolarized caps that you're subbing with polarized electrolytics.  Power it up and measure the DC voltage from one capacitor pad to the other.  There's your answer.  Don't be surprised if the DC voltage is close to zero.  In that case polarity doesn't matter.  In some rare cases, the polarity can go either direction depending on signal level.  In those situations, I refer you back to the notion of using the right parts.

Polarized capacitors will leak current if enough reverse voltage is present.  That voltage is somewhere between 1V and 5V, depending on the cap.  If enough current is available, the capacitor will overheat and either explode or catch fire.  This is usually not a problem in guitar pedals because the currents are so small.  The circuit might not work right with a backwards cap, but there is no safety hazard. The only cap that is likely to explode if installed backwards is the one between +9V and ground. I have seen some pedal schematics where a polarized caps is backwards.  Because the DC voltage on the cap is low enough to not upset the circuit, the designer never caught the mistake.


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## Markus Kersius

I have both original pedals, LS & SL and degooped them both.
The SL is literally build on the LS pcb.

Differences are:

LS: 
a100 vol, a10k tone, a500k gain pots, 5 1n914 diodes and a opa2134 ic

SL:
a 250k vol, a10k tone, a1meg gain, 5 1n914 plus 2 extra Bat41's diodes in the loop and a tl072 ic.

Resistor and cap values are the same in both pedals


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## music6000

Markus Kersius said:


> I have both original pedals, LS & SL and degooped them both.
> The SL is literally build on the LS pcb.
> 
> Differences are:
> 
> LS:
> a100 vol, a10k tone, a500k gain pots, 5 1n914 diodes and a opa2134 ic
> 
> SL:
> a 250k vol, a10k tone, a1meg gain, 5 1n914 plus 2 extra Bat41's diodes in the loop and a tl072 ic.
> 
> Resistor and cap values are the same in both pedals


Where are the 2 BAT 41's in the Diagram :


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## Markus Kersius

music6000 said:


> Where are the 2 BAT 41's in the Diagram :
> View attachment 6673


Haven't traced it yet, just visual identifying on my part.
But it seems to be a pair of asymmetric bat41's in the 430k, 3.9k resitor and 220nf cap loop.
If that makes any sense..


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## music6000

Does R4 - 4K7 still remain or has it been replaced by the Bat 41's.
Continuity test would tell you if you are in the Ballpark.


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## Robert

Markus Kersius said:


> But it seems to be a pair of asymmetric bat41's in the 430k, 3.9k resitor and 220nf cap loop.



Those are all in different parts of the circuit going to Vref, so it _sounds_ like the BAT41s might be hard clipping to Vref, possibly after R10?

Could you post a pic of the board?


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## Markus Kersius

All resistors remain as in the lightspeed, i have some pics of both pedals though only component side.
Never thought of taking pictures of the back.. doh..
A piece of doublesided grey tape is on the bottom to protect from shorting and fix the pcb to the pots.
The southland is a "first batch" november 2014 with the 1st rev lightspeed pcb "v3.0" on it, i replaced the poly caps with wima cause i like them better.
The degooped lighspeed is 2019 model 2nd rev.
I also have an unmolested Lightspeed from 2017 but both Lightspeeds share the same pcb.


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## Markus Kersius




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## Markus Kersius

And the Lightspeed:











You see the 2 extra spots for the bat41 on the lightspeed pcb.
I put sockets in just for experimenting with diodes types and configuration.


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## Robert

Very cool, thank you!

Which cap is this?   10n?





I suspect you'll have continuity between pin 5 and the two BAT41 diodes, like this:


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## Markus Kersius

Correct.
The cap you circled red is the 10nf.


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## Robert

Markus Kersius said:


> Correct.



Excellent, thank you!

It appears like the 12K resistor in the Lightspeed is 22K in the Southland.

BTW let me know if you want a PCB for this when they're available.


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## Chuck D. Bones

I can see the trace connecting one end of the BAT41's to Vref.  Didn't Michael Fuller claim doing that in his Plimsoul patent? ?


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## Robert

Chuck D. Bones said:


> I can see the trace connecting one end of the BAT41's to Vref.  Didn't Michael Fuller claim doing that in his Plimsoul patent? ?



He also recently invented a new circuit that allows his positive ground "Ranger" pedal to be powered from a standard center negative 9V supply with no daisy-chain grounding issues.

Groundbreaking..... wait... wouldn't that actually be _not_ ground breaking?   I can't decide.

If only he had gooped it with hot glue like Martha Stewart with something to hide, we might not be having this conversation right now.....
(Markus knows exactly what I mean)


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## Robert

Markus Kersius said:


> Correct.



What is this circled in the pic?   Is that the top end of a resistor?


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## music6000

As PedalPCB noted above, Is that a hidden 4K7 resistor in the Pic above.


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## music6000

Confirm Hidden Resistor Value pictured above ^^^^^^^^^^^^^.

Can you confirm Continuity between matching Circles highlited? :


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## Markus Kersius

The "hidden" resistor is the 12k.
The one right next to the bat41's is a 22k... that might be the alternative for the one missing 4.7k!


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## Markus Kersius

music6000 said:


> Can you confirm Continuity between matching Circles highlited?
> View attachment 6691



Almost, measuring gives me the following:


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## Robert

Markus Kersius said:


> The "hidden" resistor is the 12k.
> The one right next to the bat41's is a 22k... that might be the alternative for the one missing 4.7k!



That makes sense.   Probably increasing the gain of the second stage to make up for the added hard clipping.


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## Markus Kersius

Robert said:


> BTW let me know if you want a PCB for this when they're available.



That would be excellent!


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## Robert

One last measurement (if you don't mind).... 

Can you confirm that the 22K is connected to pins 6 and 7 of the TL072?

Then I think we'll be good to.


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## Markus Kersius




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## Dali

Robert said:


> One last measurement (if you don't mind)....
> 
> Can you confirm that the 22K is connected to pins 6 and 7 of the TL072?
> 
> Then I think we'll be good to.



I thought you didn't trace by photo...

 

I'm just trolling.


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## Markus Kersius

Robert said:


> One last measurement (if you don't mind)....
> 
> Can you confirm that the 22K is connected to pins 6 and 7 of the TL072?
> 
> Then I think we'll be good to.



Yes!
That's correct ??


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## Robert

Dali said:


> I thought you didn't trace by photo...
> 
> 
> 
> I'm just trolling.



Well, when they're good photos like _that_ there's no harm. ?



Markus Kersius said:


> Yes!
> That's correct ??



Perfect, couldn't ask for a better pic than that.


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## music6000

Markus Kersius said:


> View attachment 6696
> View attachment 6697


Thanks @Markus Kersius, We really needed to see the Back of the Board!
All I can say now is looking forward to building it on a Quality PedalPCB Board!!!
Bring it On!!!

Cheers music6000


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## Flying

I’m assuming the silver mica cap is the 100pf in the feedback, but why use a silver mica cap?


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## music6000

They are regarded as being Smoother, Beefier than Ceramic.
Some say it's the Placebo effect, It cost more & has to be Better!


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## Chuck D. Bones

SM is more reliable & not microphonic.  And they are prettier.


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## Flying

Great, thanks.

The only time I used one was in the tone stack of my valve amp and that was because of the voltage rating.

 But to be faithful, I'll get some in stock


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## NickDanger

These mods for goosing the gain up a bit are great! Love the slight mid girth the 220n cap got. One thing: what should I try if I want some more brightness? The tone knob maxed is a PERFECT sound, but there may be instances I’d need a little more high end on tap. A resistor/cap or maybe even just a different tone pot value?


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## NickDanger

Lowered C9 to 4n7 and it sounds great! Nice tonal palette.


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