Switching diodes

[comfortably_numb]

I know that electrons take the path of least resistance, so is it safe to say I could add a switch to connect to the signal before and after clipping diodes to take them out o the path?  I know there is an easier way if starting from scratch, but i am modifying an existing circuit similar to a distortion plus.

thanks

[GibsonGM]

Try this, numb, should work just fine on a Dist+ type circuit. No need to be fancy    There are other ways to do this, using more complex switches to change out different diodes, etc...this is the basic way using the basic SPDT.
Note that this would go to the RIGHT of the volume pot (think it's the 10K), and will take the diodes out completely, so no through-put from that leg of the ckt.

[GibsonGM]

"Out" in this case would be where the cap goes, disregard the label for your use, lol.

[comfortably_numb]

Yes, I'm familiar with this type of switching.  Issue is that I'm modifying an existing circuit which would make this a pain in rear.  The way the diodes are already connected on the board makes this unreasonable.  Thus, the suggested alternative.

Thanks

[TheBigMan]

I know that electrons take the path of least resistance, so is it safe to say I could add a switch to connect to the signal before and after clipping diodes to take them out o the path?  I know there is an easier way if starting from scratch, but i am modifying an existing circuit similar to a distortion plus.

thanks

No, not in this application.  Adding a switch to bypass the diodes like that would shunt the output signal straight to ground, effectively muting it.  Before and after but in-line to the signal won't work either.  The simplest way is to break either of the traces connecting to the diodes and use an SPST toggle switch to make or break the connection.

[GibsonGM]

That'll work fine, BigMan, I know what you're thinking based on that diagram...check out the schematic of the Distortion+....where I have it labeled "IN" is a pot to ground, output comes off the wiper.  The diodes are actually in parallel with it.  This will just remove it from the chain.    "OUT" on the image is just a cap to ground for that schem.

Another way would be to parallel the diodes with the switch, so when it's "on", it shorts them out..."off" is like the switch is not even there. 
The following image is CLOSE to the MXR, not exact, note the output off the wiper of the pot. Values are also not correct, but the switching is.   Good luck!   

[PaulC]

That way would have the output of the op shorted to ground by the 1UF cap.  You'd kill the signal.  Can you not just lift one end of the diode pair up from the board (or cut a trace) and reconnect them with a switch?

PaulC

[billings]

Take a look at that diagram again!   A bypass in that situation doesn't really work - it's bypassing a bypass.

Replacing either the diodes' connection to the line or to ground with an SPST as TheBigMan and PaulC suggested will work.  Adding conductivity to the circuit won't work, some connection will have to be snipped/lifted.

[GibsonGM]

Sorry boys, I see the error in my ways, LOLOL!  The ground connection with the diodes foils my idea. Otherwise it would work.  I just DO this stuff, not schem it out, ha ha.  How 'bout this? Interrupting the ground connection:

[PaulC]

You still have the issue with the 1uf hanging on the output of the opamp. This will shunt your signal to ground.   I think what you want to do is put it in series with the pot if you're using it to decouple the pot from the DC.  Also you'd move the diodes to the pot side of the cap. 

PaulC

[GibsonGM]

Sigh...  I don't do things like this often...when I do, I just experiment until it works.
I don't think that cap will do a lot without the diodes.  In reality, it's .001 uf.  The signal won't short to gnd, for sure, since that cap's always in the chain anyway as a low pass filter with the 10K resistor, and it belongs there I presume, even if you take out the diodes.  Additionally, in the Dist+ there is a 1uf blocking cap between the OA and that pot.  I'm just giving some ideas here.  I think my last schem would work just fine!  The other option is a SPDT to the left of the diodes as in my 1st drawing - which I mislabeled as OUTPUT -  (probly have to break a trace coming off the 741), and just leave it open, omitting diodes but messing with that low pass filter since the 10K resistor is behind it.

I build Dist+'s, not modify them, lol. In the end, you'll still get an overdrive, because the 741 the ckt is built around naturally will distort...and I doubt it will sound very good.   But play with it, and you shall discover what works!  Good discussion )