Greer of Tone: Possible to make Southern Belle switchable to Mach 1 specs?

Grubb

Well-known member
I have a Greer of Tone (Mach1 & Southern Belle dual pedal) project in mind. I'd like there to be order switching, but I'd also like to add an additional switch function. Ideally, the switch would modify the Southern Belle to be more like a second Mach 1, because the Greer LS sounds amazing when stacked with another LS. I think this should be possible because of the high degree of similarity between the circuits, but I don't know where to start.

In the Mach 1 Mods thread (click here) - one of the most interesting threads I've seen on this forum - we find out that a real Greer Southland is actually built on a Lightspeed PCB, with very slight modifications:

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.

R4 also has a value of 4K7 in the Mach 1 and 12K in the Southern Belle. Otherwise, both circuits are identical.

What drives the gain difference between both pedals? Is it pot values, the IC or the additional diodes? It seems like it would be easy to make the diodes switchable in and out, would this have a noticeable effect? Would it be possible to have even 3 diode options such as OFF, BAT41, and a 3rd option?

Thanks for any suggestions you might have for this project.
 

Grubb

Well-known member
Playing around with the schematic in DipTrace so that I can understand how it might work. Would using a DPDT toggle like this work? Diode switching.png
 

cooder

Well-known member
You can do that with a SPDT and if you use an on/off/on you have the lightspeed in middle position, the southern Belle on one side and have another side to choose another clipping configuration again. Like here:
yWQsPzt.jpg
 

Grubb

Well-known member
@cooder that is amazing mate, perfect thanks. Is this a mod you tried or you just whipped that up? Either way, thanks
 

cooder

Well-known member
I tried it on the very board, works great. Experiment with alternative diodes, maybe use 4148s there.
 

cooder

Well-known member
There is some volume drop but not too much, similar to other circuits that use this principal. I tried three LEDs as an option, but that was not much difference to middle/no diodes, might experiment a bit more.
 

Grubb

Well-known member
Have you tried a red and a green for asymmetrical clipping? Just an idea I read on a thread here somewhere. Or do you already get that from 1 vs 2?

Edit: I found a helpful thread on here and answered my own question - it's already asymmetrical =)
 
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Feral Feline

Well-known member
Something I like to do is use a 4PDT stomper for...

2 poles to swap two pots,
1 pole switches whatever SPDT on-on function is needed
1 pole for LED indication of which mode/channel is active.

If it's a 4PDT Toggle, you can ditch the LED indication for another function;
things can get really fun with a 4PDT on-off-on toggle.
 
I was wondering, is there a good way to make the Mach 1 into a Southern Belle? I am still very much a beginner with all of this, but am I right in assuming I could add two BAT41s in between C9 and pin 5 of IC1? Also, if I want it switchable, would it be better to use the pot values, IC, and 12k resistor in R4 from the Southern Belle or keep the Lightspeed values? Any help/advice is much appreciated, thanks!
 

Grubb

Well-known member
I was wondering, is there a good way to make the Mach 1 into a Southern Belle? I am still very much a beginner with all of this, but am I right in assuming I could add two BAT41s in between C9 and pin 5 of IC1? Also, if I want it switchable, would it be better to use the pot values, IC, and 12k resistor in R4 from the Southern Belle or keep the Lightspeed values? Any help/advice is much appreciated, thanks!
Hi Stephen, I recently brewed my own PCB that has both circuits on it as a dual overdrive:

Southern Lights Dual OD

I made my Southland channel so that you can alternate and drop out the hard clipping diodes with an on-off-on SPDT switch. This cleans it up a bit but it's still grittier than the Lightspeed side. I would start with Southern Belle specs, put the BAT41 diodes you mentioned on a switch, and then keep the drive control low to get an approximate sound to the Mach 1. It's not exact though, so temper your expectations 😁
 
Hi Stephen, I recently brewed my own PCB that has both circuits on it as a dual overdrive:

Southern Lights Dual OD

I made my Southland channel so that you can alternate and drop out the hard clipping diodes with an on-off-on SPDT switch. This cleans it up a bit but it's still grittier than the Lightspeed side. I would start with Southern Belle specs, put the BAT41 diodes you mentioned on a switch, and then keep the drive control low to get an approximate sound to the Mach 1. It's not exact though, so temper your expectations 😁
Sorry for not responding quicker, I didn't get a notification that anyone had replied. Thanks for the advice. I may just stick with the lightspeed and then build a Southland later with the diode switching. I really want to play the lightspeed, but thought I might be able to get the best of both worlds with the mod. Your advice is really helpful. Your Southern Lights looks absolute class, well done!
 

Grubb

Well-known member
Thanks for the kind words @Stephenthegun

I think you will really enjoy the Lightspeed/Mach 1. It's the pedal I most frequently "get in the zone" with for periods of time. Just makes everything sound better.
 
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