Opamp stacking / switching pins 1 & 7, tone loss?

[Jurbo]

Hi!

Sorry, if I'm asking an old question here, but after searching this forum (and the internet) for quite a while, I couldn't find a definitive answer on the (possible) tone loss matter.

I have an MXR Distortion III that has been a testbed for some modding. I have put in a 4558P opamp, as it sounds the best to me out of 4558D, 4558P, TL072CP, TL072CN, OPA2134, MC33178PG.

Today I tried opamp stacking for the first time. With two stacked 4558P's, the pedal sounded really great. But, I also like the single 4558P.
Now, I'd like to have a switch for these two sounds (1 opamp / 2 stacked opamps). I know the easy way is to use a DPDT for pins 1 and 7 of the other chip. But, when using just one opamp, does the other chip cause tone loss as it has its pins 2,3,4,5,6,8 connected? I think there is a small, but definite tone loss. Could someone give a scientific angle to this? Any easy way to prevent the loss?

[stringsthings]

Today I tried opamp stacking for the first time.

what is "op-amp stacking"?

[Jurbo]

It means adding an opamp on top of another with all pins connected in parallel. Gives a different sound that some like, some don't.
Stacked / piggybacked / etc. There are a couple of different names for the same thing.

[maarten]

The types you are referring to, are duals opamps. That means you are stacking 2 opamps (sitting in one casing) at the same time.
Switching pins 1 and 7 means that you are only connecting/disconnecting both outputs of the stacked IC. Whether the stacked iC is switched in or out, the signal going into it is always connected; maybe this is what you perceive to hear as a tone loss. You should add a second switch to disconnect the relevant inputs to the stacked IC also. These could be on either pin 2 or 3 of one opamp (to go with pin 1) and on either pin 5 or 6 (corresponding to the output of the second opamp on pin 7). Whether it is pin 2 or 3, and pin 5 or 6, depends upon how the opamp in question is configured (inverting or non inverting) - you will have to determine this from the schematic; or use just trial and error - remember though that one could be inverting and the other not, or both could be inverting, etc.

And alternative maybe would be to connect all pins, and just switch pin  8 (positive supply) on or off, but I am not sure whether this would work 100%.

You also could further investigate the tone loss you mentioned: maybe changing values of capacitors, resistors. If you go this route and need further help, be sure to post the relevant part of the schematic and give a good definition of what you mean by "tone loss", maybe someone can help you fix that....

Regards, Maarten