op amp selector?

[powder burns]

Hi, new to building pedals as well as this forum. I found this website while trying to find an answer to this question and so far the rabbit hole hasn't been very fruitful for me.

I ordered the diy tube screamer kit from stew mac the other day and I saw they sell a few other op amps that mimic the pro co rat and the klon centaur. I'm looking forward to building my first pedal and trying out the different op amps!

However, I'm the kind of person that likes options and trying things back and forth before I am sure of what I prefer, and opening up the enclosure and pulling out the op amps constantly does not sound very fun at all.

So, I was wondering if it is possible or feasable rather to have a 3 position switch added to the enclosure that could toggle between the 3 op amps I'll end up with. I know its going to be a lot more components required to make that work, and probably an additional board for the extra sockets/solder points. Has anyone done this and could walk me through it or point me in the right direction?

Thanks in advance.

[bamslam69]

My following thoughts come without knowing much about the nitty gritty of the workings of the ICs.

Just looking at the Proco rat schematic
https://www.electrosmash.com/proco-rat
You could possibly get away with adding a 3 way, 3 pole rotary switch, switching the pedal circuit between the 3xICs at terminals 2,3 & 6. Just wire the rest of of the IC terminals as shown...

Here's a rotary switch I found on tayda. Maybe use the 4th pole for LED indication.
https://www.taydaelectronics.com/rotary-switch-4-pole-3-position-alpha-sr2612f.html

Anyway, this is what I'd try. Maybe it'll pop? I dunno.

edit: Klon looks a lot more difficult. CBA helping there.

[DIY Bass]

To switch a dual op amp you would need a 6 pole switch.  Not sure if such a thing exists.  Probably you could find one if you look though.  To switch 3 dual opamps then would take a 3 position 6 pole switch.  You could switch each section of a dual op amp separately - which would then be 2 3 pole 3 position switches.  You are getting into the realm where it might just be easier to use a microcontroller and relays to do the switching. 

To be honest though, I doubt it will make much difference.  I personally suspect there will be little audible difference - especially on a dirt pedal.  If you can hear a difference, then you will make one or two swaps, decide you favourite, and never change it again.  It will be easier in the long run to just do a few swaps and then keep what you like.  Other good option is to build the circuit on a breadboard, swap components around until you get the sound you are looking for and then build those components into the circuit board.

[idy]

Welcome to the forum. This kind of question got a lot of attention around the intertubes... like 10 years ago. Even some great videos where a live audience of golden eared pros were asked to tell the difference.... and could not...

But: there are some basic types that are different.
lm308 is used in the rat because it clips a certain way and lo-fi= smoother distortion
4558 is good in TS because it clips well and was dirt cheap.
I like certain MOSFET/CMOS opamps for the same reason, they clip nicely.
IN reality, the commonly used ones work in the circuits they go in, and if you were going to use a different opamp in a RAT, you would then want to change a few other things to make a new pedal. Combined with the impracticality of switching back and forth...
So socket them and find out for yourself. If you really feel crazy about this, go ahead and build two identical Screamers with sockets... You do realize you need two of every pedal, right? Else why would you be here...

[bamslam69]

One thing I added to my Rat was an 8 pin dipswitch for different clipping diode combinations.
Someday I'll get around to cutting a hole in the enclosure so they're easily switched.

[FiveseveN]

Hi and welcome!

I saw they sell a few other op amps that mimic the pro co rat and the klon centaur.

I detect some confusion! The circuit's topology is what makes a TS or a Rat or a Centaur what it is, not (just) the op amp. Case in point, there are thousands of TS clones out there using a TL072 just like the Centaur but nobody would mistake one for the other.
If you want to satisfy your curiosity use a socket and swap some out (with care). But please buy from an actual electronics supplier, not Stew Mac! A TL072 is supposed to be less than a dollar, not $2.19.

[PandaFeet]

I ordered the diy tube screamer kit from stew mac the other day and I saw they sell a few other op amps that mimic the pro co rat and the klon centaur. I'm looking forward to building my first pedal and trying out the different op amps!

You may find difficulty with switching between an op amp for a Klon and a Rat. The Klon op amp (TL072) is a dual op amp; the op amp for a RAT (LM308 or OP07) is a single op amp. The pin outs are too different, and you'd have to alter the entire circuit to fit one or the other.

Although, I will say that brands like Drunk Beaver do offer the ability to switch between op amps, but they are of the same type (single op amp). So it's feasible to some degree.

[GibsonGM]

Me, I'd try a couple of diff. opamps in a build on the breadboard.  If one stood out, make it permanent.   If you really like 2 or more chips, then pursue the (pretty involved) switching.     Or, build 2, 3 TS's with different opamps if that floats your boat.   

I've personally never experienced much difference beyond the major 'types'...I like a vanilla 4558 in mine, and don't really think about what it would be like with a TL072 - I really don't care much for the FET input type in this application.  YMMV

For Rat etc, I'm more likely to just build another circuit based on it, with a diff. opamp, and change enough of the basic design that it's some frankenstein anyway, and no longer a "Rat"...

[Rodgre]

I admit that I am commenting basically just to hear myself talk here, but if anyone gets anything beneficial from this, then that's gravy!

Anyway....

I was confused by the OP as well, since a TS, Klon and Rat are completely different circuits so no simple op-amp swap will do anything to make one behave like another.

I'm similar to the OP in that I like the idea of options, but like DIYBassm, once I find the tone I like, at least for myself (I also work as a producer recording other artists) I set it and forget it. I have never felt the need to experiment with different op-amps or any other active component once I found a tone that I liked. If I didn't like a circuit in general, I'm pretty sure I just don't like that circuit. Any difference in op-amp/transistor, etc, will be basically a different flavor of the same circuit that I don't love.

That's just me.

I feel like the desire that one might have to have a DIY analog drive pedal that can switch between modes that simulate a TS or a Rat or what have you..... It's not lost on me the irony that I feel like we've come full circle from the days when I started and had an overdrive pedal that did overdrive, a Phase 90 that did the Phase 90 thing and a Small Stone that did the Small Stone thing, etc. Then came digital multi-effect units, which have gotten better and better over the decades. They gave you so many options built into each algorithm, which you could tailor to your wishes and control in real-time. It sort of spoiled us into thinking that these infinite options are what we want, ultimately. Now we have come full circle and want one analog box that will give us the options to be any pedal that we want it to be.

It's important to note that I don't mean to sound dismissive at all. By all means, if someone wants to build a single pedal with complex digitally-controlled switching (which I think is the only efficient/affordable way to do what we're talking about here - swapping out op-amps or many sub-circuits in a pedal), by all means do it! Do it and share your results and inspire other people with your ideas!

I think this is the concept of the JHS Pack Rat, in that in order to have all the switchable options to mimic various versions of the Rat, there needed to be complex digital switching circuitry to handle the changes between versions. Didn't the Fender Cyber Twin do this as well? I seem to recall that it had analog circuitry that would be reconfigured by digitally controlled switches/relays, in order to get the tones of different kinds of amps, before IR Profiling made that sort of unnecessary.

If you're set on analog drive pedals on the floor though (I am. Call me a luddite. LOL), you might end up where I am eventually: You have a Klon and a Rat and a Blues Breaker and an ODR-1 and a DS-1 (etc....) and when you want THAT tone, you click the footswitch on THAT pedal and BAM!  See, I love options too, but no THAT many. Hahaha! I want all those pedals at my disposal, but I don't personally want one pedal that does all of that. If having something like that was more important to me than I had pedalboard space to accommodate, I would buy something digital.

Roger

[powder burns]

I suspected the minor differences in the op amps would only result in subtle changes to the tone. You've all convinced me its not worth the effort to incorporate multiple op amps into the circuit. Doing so would also have been pretty ambitious for a first build as well. I'll try out the op amps I got and just stick with the one I like best. Once I finish this ts808 clone, I'll either have scratched that itch or I'll go after building a rat clone next. Do you guys have a supplier for enclosures or build them from scratch? I have access to metal fab equipment but its easier to just buy something pre-made.

[GibsonGM]

I'll give you your FIRST "like" for that, powder.   DO mess around w/different opamps on the breadboard, though!!  You never know...

For enclosures (USA), I use Small Bear electronics, great reputation and has served the DIY community for decades - new ownership now, but ppl report they are still highly reliable.   There are other sources, Ebay etc.  But I haven't needed them to-date.

https://smallbear-electronics.mybigcommerce.com/enclosures-1/

[bamslam69]

I just get mine from Tayda.
Painted and ready to go.

[Matthew Sanford]

Piggybacking a question related to this, and a desire to switch between a StompFLO and one shot (constant/on demand madness), is it possible to have multiple flip flops tied to one momentary switch? To control switching all the corresponding pins at once?

[idy]

Yes. As soon as you start using logic chips or physical relays (or opto cells/isolators) you can have as many poles as you wish. Sky's the limit. Flip a switch and add a different IC, different clipping diodes, (and a resistor to keep the volume similar) have a different gain knob, turn some lights on, turn the coffee machine on....

[Matthew Sanford]

Thanks Idy, I figured the switch is just a path for caps to drain (ok originally I'd thought flip flops flipping other flip flops...but that's just the madness). Of course for me it's turn the tea kettle on, then the hot water pump to fill the French press....mmmm...French presses dark roast...mmmmm

[powder burns]

update: got the kit a few hours ago and I was shorted the 4558 op amp. Soldered everything up and popped the TL072 in and everything works as it should. Managed to grab the barrel of my iron for a moment so I won't be playing with the pedal much today. Got a tic tac size blister on my middle finger. I think the itch to build my own pedal has been scratched. Might do another one in the future, discontinued pedals at cost of materials are what comes to mind versus paying collector prices. Anyway thanks everyone for their input, I really appreciated it.