Switching between two gain settings on a single pedal

[sjaltenb]

Ok guys, let me know if you tink this would work

Can you use a switch to select between two gain pots on a pedal so you can use that pedal for clean and dirty tones??

Gilmour uses two tube drivers, one for a clean tone boost and one as an overdrive ...but i dont want to spend that much money.

I dont see why it wouldnt work...

[aron]

You can, but you don't even need to do that. Put the two pots in series and then short one of them in/out for different drive amounts.

[demonstar]

Can you not just switch a extra resistor in somewhere. Eg in a opamp based circuit there are two resistor that set the gain. Well if you switched a parallel resistor in alongside one already there you can reduce the resistance to alter the gain. This would be easier than putting a second pot in as most pots have a resistor in series with them anyhow ready to switch a resistor alongside in parallel.

I don't feel I've explained that very well. If you post or direct me to the schematic you've got in mind I may be able to help and explain a little clearer.

is it the tubescreamer your thinking of doing this to?

[Gilles C]

You could also add a booster before the pedal and bypass it when you want less gain.

A very simple FET buffer would be easy and not very costly to build, and could be used with any other pedal or even all by itself.

Gilles

[GibsonGM]

+1 on the 2 pots idea, I do that all the time...a DPDT switch shorts one. See the schematic for the Fulldrive 2, it is done on there!   

[Mark Hammer]

I've done this on one of my modded tube-sound fuzz pedals.  A simple switch can adjust the gain of an early stage and the amount of attenuation on the output at the same time.  Essentially what the switch does is get lotsa push plus more output attenuation, OR less push with less attenuation on the output; essentialy a simultaneous gain+master adjustment.

Howzitwork?  Imagine you had a Tube Screamer.  Here, courtesy of RG, is the clipping section:

The gain/drive is set by the pot, but also depends on the 4k7 resistor to ground.  Increase it, and the drive amount is reduced.  Hold that thought.  Below is the output level section, again, courtesy of RG:

The level is set by the 100k pot, but the 1k series resistor also plays a role.  Increase that resistance, and the level is automatically dropped.  The explanation is in my post near the bottom here:  http://www.diystompboxes.com/smfforum/index.php?topic=60530.0

Let's say we had a switch that could place a second resistor in parallel with the 4k7 unit and the 1k resistor at the same time. It would adjust both the drive and the volume.  Remove those parallel resistors, and everything reverts back.

Okay, now if a smaller resistance in the first picture (we'll call that Ra) increases drive, and a larger resistor in the second illustration (we'll call that Rb) reduces output, then having a switch that goes from slightly scuffed to dirty without changing level would increase Ra at the same time as is reduces Rb, while in position 1, and decrease Ra while it increases Rb in position 2.

Okay.  Let's replace Ra with a 10k resistor, and replace Rb with a 22k or thereabouts resistor.  Normal gain will be restored if we stick a 9k1 resistor in parallel with the 10k, and normal attenuation/volume level will be restored if we stick a 1k in parallel with the 22k.  What we need our switch to do is place resistor Rb2 in parallel when resistor Ra2 is out of circuit, and place resistor Ra1 in parallel when resistor Rb2 is out of circuit.  Voila.  Instant hair/no hair with no discernible level change.

[Dragonfly]

This is in my folder...

will work for gain controls as well as volume...

[R.G.]

You can go as simple as a footswitch, or as complicated as a multi-volume selector setup, each of which has a loop for different effects.

http://geofex.com/Article_Folders/multivol/multivol.htm