Opamps - floating ins and outs?

[DWBH]

So I have this pedal in which I'm currently using an opamp only (the chip is a 4558).
I want to switch the 2nd opamp in and out of the circuit.
So I want to have two 'settings':
a) Opamp 1 -> tonestack
b) opamp 1 -> opamp 2 -> tonestack

Well, this is very simple to do. The problem is that I don't have DPDT, and therefore can't switch both the opamp's input and output at the same time.
I do however, have SPDTs. This means I can only switch the opamp's input or output, which leads me to the conclusion that either the input or the output of the opamps has to be connected to the circuit at all times.
If I switch the opamps input, (http://andrebispo.googlepages.com/hybriddirt2.gif/hybriddirt2-full;init:.gif), I'll leave the opamps output connected at all times, and switch the input in and out of the circuit (it 'floats' when it's out of the circuit).
On the other hand, if I switch the opamps output, the input will be connected to the circuit at all times (http://andrebispo.googlepages.com/hybriddirt.gif/hybriddirt-full;init:.gif)

I'd like to know where any of these schematics is doable, or do I really have to use a DPDT?

Btw, how would a OCD sound with a rat filter?

[Thomeeque]

I'd like to know where any of these schematics is doable, or do I really have to use a DPDT?

IMO second is doable (first not, because 2nd opamp output would act like a ground for the signal), at least you can try it (it's possible that second opamp will generate some audible noise via power wires - it would be safer to ground it's input when it's not used, but maybe it will be OK even without it).

Btw. you can remove C16, you don't need it there - C18 will do the job.

[Thomeeque]

Btw. you can switch function of second opamp by switching off 39k+100n branch (it will act as unity gain buffer without this branch, so it should not alter the tone /theoretically/*).

* If the C13 influences the tone in unity gain mode, this can be switched off together with 39k+100n by one switch.

EDIT: To make myself clear:

[DWBH]

So if I switch on and off the connection between pin 6 and C13 or the connection between pin 7 and C13, there should be no problem (theoretically)?

EDIT: I think I can't do this ^^
But I can connect pin 6 directly to pin 7.

[Thomeeque]

Btw. you can switch function of second opamp by switching off 39k+100n branch (it will act as unity gain buffer without this branch, so it should not alter the tone /theoretically/*).

* If the C13 influences the tone in unity gain mode, this can be switched off together with 39k+100n by one switch.

EDIT: To make myself clear:

EDIT2: redesigned

OK, now I have pressed QUOTE instead of MODIFY button, but I'll leave it as it is before I made even bigger mess 

[DWBH]

oh, ok. What if the inverting input (pin2) is directly connected to the output (r1 = 0 ohm)?

[Thomeeque]

oh, ok. What if the inverting input (pin2) is directly connected to the output (r1 = 0 ohm)?

That's classic opamp buffer setup



Theoretically, when I think about it now, you don't even have to disconnect R2+C2 (39k+100n) branch, just bypassing of R1||C1 to 0 ohm should make it (R2+C2 branch would become only very weak load applied to opamp output). You can try it..

[Ben N]

+1 on Tomas's suggestion to lower the second stage gain to unity. This is, more or less, how the "bypass" works on the Crowther Hotcake and the DOD FX10 Bifet boost, and it works well.

[DWBH]

This:

Thanks guys, I'll try to give it a shot later this night.