Foxx Tone Machine Diode Lift Mod

[scott_v]

According to the schematic found on this site using Mark Hammer's initial suggestion to lift the the diode using a dpdt switch:
http://user.eduhi.at/aquataur/aquataur/musicstuff/foxxtone.html

schematic: http://user.eduhi.at/aquataur/aquataur/musicstuff/FTM+S_diode_sw_details.PDF

I'm looking to do this on my FTM clone, I plan on using an SPDT/SPST switch and not worried about the volume boost (which I'm kind of looking for too) and just want to do the diode lift part, the part I don't understand is the way 100k resistor is connected across the switch.  Wouldn't doing it as shown in the schematic always keep the diodes connected to ground? even when the switch is lifting them, the 100k resistor is always in contact between the diodes and ground?
This schematic looks wrong to me... 

[Mark Hammer]

The 100k resistor may simply be there to minimize or avoid audible popping when switching.   The need to do that would, in turn, depend on whether one plans to make the switch a toggle or a stompswitch to use while playing.

There are plenty of things that pop like crazy, but you're not going to use in real time.  For example, I'm a big fan of the "phase-filter" mod for OTA-based phasers.  Switching between phase-flter and normal phaser mode pops like crazy, but it is the sort of thing you do when the effect is not on.  So I ask the zen question: if a pedal gets switched when it's not engaged or on, does it really pop?

I've made FTMs that have a diode-lift switch, and they work just fine by simply disabling the conenction between the diodes and ground.  But the switch I implemented was not intended to be used in real time, so that eliminated the need to figure out how to prevent any audible pop and maintain constant volume despite switching back and forth.

[scott_v]

Thanks Mark... since my plan is to use a toggle, i'll first forgo the 100K resisitor to stop dc shift (the "pops") and see what happens.

Now that we are on the subject of such things as toggles and "pops".... I noticed that on my clone that when switching from fuzz to octave setting, there is a very brief lapse in sound.  Its not a "pop" but like a very quick "mute", and pending on how quickly i toggle the octave switch will affect this muting.  I also have a danelectro french toast and it does the same thing, so i'm assuming this is something that is part of the circuit design.  I was thinking about switching this toggle to a footswitch, but i find this muted effect or signal dropout while switching to be annoying enough to not want to make this change.

Is there a way to prevent this?  Is it related to the original circuit leaving the diode in place for the non-octave setting, introducing a kind of crossover distortion by requiring the collector signal to be at or above the forward voltage of the diode before allowing it to pass.  So now I'm also thinking of replacing the spst octave switch with a 3 position center off spdt switch the 3rd position shunting the diode.  I know it will help the fuzz tone too...  this was also one of your recommended mods from awhile back.

[Mark Hammer]

Wish I could confirm, but I sold off the FTM clone that had the 3-position switch to a fellow over a year ago, and the 2 that I presently have use a 2-position octave switch, so I can't easily compare whether the diode bridging results in a different degree of lag/mute during mode-switchover (octave<->fuzz) than non-diode-bridging.

Maybe someone else can confirm.

My gut says it likely has something to do with the charging up of the 10uf cap just before the Drive control, via the 100k resistor tied to +9v.