Wiring to select between 3 stacked op amps

[mordechai]

I am going to try to do something like the legendary Beavis Screamer Lab, and I'd like to be able to choose between three op-amps.  Like Dano did in his project, I am going to stack them together and leave pins 1/7 on each op amp free and connected to their own wires.  What I'd like to do is wire them to a single toggle switch to select between them.  Dano mentioned on the Beavis site that he used a 4pdt switch to accomplish this, but in looking at the wiring diagram on the site, I'm not very clear on how to actually wire the terminals on the switch to make this work.  Wondering if anybody can help.

[mth5044]

Looks like Beavis audio is down, so it's hard to help without seeing what you're talking about. In any case, it will be hard to switch between three opamps when you only have a two position switch. Perhaps it could be done with an on-on-on, but I'm not sure if I've ever seen a 4PDT on-on-on switch. Perhaps a 4P3T rotary switch would be of use to you here.

[mordechai]

I'd be happy to use a rotary 4P3T rotary switch, but I'm still unclear on how to wire pins 1/7 of each op amp to that switch.  Never used one before!

[mth5044]

Do you have a saved picture of how the ICs are set up?

[mordechai]

Sure, you can see it here.  It's a saved picture of the Screamer Lab wiring, but I'm not clear on how the op amps would connect to a single switch -- it looks like they're on different switches, which I'd like to avoid...
http://s1130.photobucket.com/user/mordechaibenzev/media/ScreamerWiring_zps15p2tp5y.gif.html?sort=3&o=0

[pinkjimiphoton]

i'll send dano a message about his site.

[armdnrdy]

You may want to look through this thread and watch some of the videos to see if this is really what you want to do.

http://www.diystompboxes.com/smfforum/index.php?topic=99414.0

In my opinion, switching op amps is very subtle. There are other switchable mods that will give the user more "mileage"....especially in a live band situation.

[Keppy]

If you want to use just one switch, you need the rotary. Get a 2P3T rotary (usually what's available is a 2P6T that you can set for only 3 throws). Connect pins 1 & 7 of the PCB to the switch poles. Connect pins 1 & 7 of the opamps to the throws.

Note that using separate switches as in Dano's diagram allows you to connect multiple opamps at the same time, while the rotary does not.

I haven't compared opamps in a TS, but in every drive pedal I have tried the opamp has made a significant (to me) difference. However, there's always been just one I liked best for each circuit. I'll join the others here in suggesting you test differences on a breadboard to make sure this is what you really want to do. Have you auditioned different chips yet?

[mth5044]

With the 2P6T rotary that Keppy is talking about, you could do combinations of opamps. With six throws, you could do 1, 2, 3, 12, 13, 23. Wouldn't be able to fit in 123, but ya know.

[bool]

IMHO on-the-fly opamp switching has no real practical useful value.

It's much more valid to select an opamp that feels/sounds best to you and then optimize the rest of the circuit to that particular opamp.

ymmv

[mordechai]

Thanks everyone.  Keppy, your instructions are very helpful and I appreciate that.

As for op-amps -- the ones I've selected really DO make a difference, especially with the clipping diode options I've experimented with.

Basically, I found three tones that I like:

OP-AMP          DIODES          DESCRIPTRION
RC4558P        1S1588 (x 2)  Sounds a lot like the original TS-808 in terms of harmonics and compression (not as compressed as 1N914's)
OPA2134        Red LED (x 2) The setup in the Clay Jones Overdrive circuit, which really works nicely with certain amp setups
TLC2262         BA282 (x 4)    A big surprise in terms of how good this sounds; very different, "softer", but strong and tight

It is precisely because each sounds so different that I don't want to have the option to combine them.  I've actually tried that with a test rig and the qualities of one op-am/diode combo didn't come through as nicely, so I am opting to not have dual or triple op amps working at the same time.  One at a time, with the diodes I've selected, will do what I'm looking for. 

Of the combinations above, the TLC2262 really stands out at higher gain settings. I stumbled upon the combination by sheer accident but the sound was immediately very sweet and warm, but still plenty ballsy. 

[bool]

... so you discovered the allures of the "sansamp" opamp ...

[mordechai]

Yep.  I did discover later that they use it because it sounds good when it clips on its own, but it interacts very nicely with clipping diodes too even at lower gain settings.