Greer Lightspeed and Southland

[matopotato]

I know I shouldn't be doing this... More modding and pushing things, but I guess it is my nature...
Anyway, I was breadboarding a copy of Greer Southland (PDF Southern Belle)



It was more a case of "if I bread it I will be sure that I do not need it and can move on", but as you might have guessed, it sounds nice. Quite a bite to it and it is probably that OD sound I've been missing.
As I google around I stumbled on the Greer Lightspeed clones (PDF Mach 1)


And it struck me how similar the ciurcuits are. I have assumed PedalPCB made accurate tracing, but if anyone has original schematics for either or both, feel free to share.

Comparing them I notice the following:
(South vs Light)

• BAT41 vs no hard clipping diodes
• Gain A1M vs A500k
• 22k Pin 6&7 vs 4k7
• Opamp TL072 vs OPA2134

So my starts thinking that if I am going to build the one, why not add a switch and get two pedals. (I often end up in that "add a switch..." scenario)
So I try to read up on how it might be possible to switch between two opamps in the same build and found a link http://beavisaudio.com/projects/screamerlab/ Scroll down to "Switching and Stacking".
Looks a bit challenging, but I can see how a 2PDT could do the trick.
I test a bit on the breadboard and for sure the 1. (BAT41) and 3. (22k vs 4k7) seems to have greatest impact.

For 2. is it just a case of getting a wider "swing" of the pot? So that either one might work for both circuits? With the A500k giving less drive to Southland and A1M maybe giving unnecessary much drive to the Lightspeed?
Might be possible to have two pots and one works in the one case.
That might either end up in a 5PDT or a combination of 2+3 or 4+1.

Any thoughts on this?
Are there any smarter shortcuts I could take?

[duck_arse]

volume pots values differ - will load that tone section differently.

[antonis]

Leave ICs alone and use a 3PST switch..

[matopotato]

volume pots values differ - will load that tone section differently.

Sorry, missed that. Yes, that'll make a difference

[matopotato]

Leave ICs alone and use a 3PST switch..

Thanks
Out of the two which would make more sense to use? OPA2134 or the TL072?
Or is the difference so small that I will probably not be able to tell either one?

[matopotato]

Leave ICs alone and use a 3PST switch..

Would a 160k parallel to the Volume pot do the same trick as you did with the gain? And a 4PST...

[antonis]

Sure but I can't see the reason for that..
(10% Tone loading should be considered acceptable..)

P.S.
Bear in mind that resistors across pots alter original taper..

[matopotato]

Sure but I can't see the reason for that..
(10% Tone loading should be considered acceptable..)

P.S.
Bear in mind that resistors across pots alter original taper..

It was based on what duck_arse mentioned about loading the tone section.
But I understand now according to you that it is negligible.

Any thoughts on opamp selection of the two?

EDIT: I guess the BAT41 part (belonging to the Southland) should be closed when the Drive and 5k6 parts are open...

[antonis]

It was based on what duck_arse mentioned about loading the tone section.

Of course, Stephen was correct..
(use any of 100k / 250k value pot for both effects and you shouldn't have problem..)

Any thoughts on opamp selection of the two?

TL072 should work fine..
(in case of "audio high quality" needed, I'd proceed to NE5532..)

I guess the BAT41 part (belonging to the Southland) should be closed when the Drive and 5k6 parts are open...

Right..

[Itchy Scratcherson]

Any thoughts on opamp selection of the two?

Hi guys! Tonight I assembled & auditioned a GPCB Ludicrous Speed and tried first a 2134 op-amp, then after really digging the circuit's response to my noodling, thought it was too trebly. I tweaked all the pots every which way & still thought the tone pot isn't covering all the bases needed for the pristine "natural keep-your-tone" OD I love, so on a whim I thought, "Gee maybe I should build what's in the doc first, then twiddle later". ...what a concept.   So I immediately thought the TL072 was an improvement in tone... basically less trebly (though, I may still try adding some tone options ...and maybe try other/ additional diodes on a switch). I did socket all the 1N914's so there's maybe another rabbit hole to investigate. HTH!

[matopotato]

Thanks!
Great to know what to try and observe. I decided to go with the TL072 but then changed my mind to try the OPA2134. Will test but might stay with the TL072 after all since then it is more Southland.
(I probably won't be able to tell any difference anyway...)

[Itchy Scratcherson]

Looking at the other clones & some discussions, it seems I *might* be in the minority for liking the TL072 better than the OP2134 in this context. I should've also stated I was experimenting with this using my modified G&L Bluesboy tele... going into a (10") Vox AC4TV right at ear level.

[matopotato]

Finally got it all together. I remembered it sounding better during build testing then final assembly. Feels a bit "dirty/scrapy" in the drive, if that makes any sense. Might look into it later.
Anyway this is how it turned out.
Many thanks to all who helped out with this project