How to best add a volume pot on the output of an Ibanez WH10 V2?

[Josh_bb]

Voltage dividers are present EVERYWHERE (they live among us.. )
It's quite "odd" to get it for an JFET in the meaning of actual resistance (much more easy for BJTs where that resistance appears as equivalent Base-Emitter forward biased diode..)

Signal on Q4 Source, looking back, "sees" a node between Source itself and source load (its eyes are splitted into 2 different paths..)
It considers Source as a Voltage source with its internal resistance(*) in series and source load as whatever Source has to feed(**)..!! 

(*) Due to JFET properties of voltage to current amplification, transconductance (g_m) is the natural parameter for gain - e.g. for a grounded Source CD amp, gain is -g_mR_D)
g_m is the inverse or resistance (in mhOs units - inversed Ω) so 1/g_m "represents" resistance..
That resistance is what signal "sees" inside Source when looking from the node of Source & source load..!!
(the upper part of voltage divider..)

(**) As source load should be considered whatever Source drives..!!
(in our case, R20 in parallel(//) with R21, because we consider OUT as an open circuit - or as a next stage with significally high input impedance..)

Estimating g_m = 3mmhOs, 1/g_m is about 33Ohms (upper part) & R20//R21 = (10k X 100K) / (10k + 100k) = 9.1k (lower part) so voltage dividing effect is 330/9.1k ..

Wow thanks,, I actually mosty understand that and  I now know what I need to read up on to properly understand it!  super useful, many thanks for this .

[antonis]

IMHO, you should start from BJT Common Emitter amp analysis (Ebers-Moll model) with emphasis on "Intrinsic Emitter resistor"  to get you more close to that  @&*^%$ nasty "transconductance".. 
(or go back to tube days..)
Some textbooks may scare you but you can easily omit all complicated formulas, T & Pi models, e.t.c.

[Josh_bb]

IMHO, you should start from BJT Common Emitter amp analysis (Ebers-Moll model) with emphasis on "Intrinsic Emitter resistor"  to get you more close to that  @&*^%$ nasty "transconductance".. 
(or go back to tube days..)
Some textbooks may scare you but you can easily omit all complicated formulas, T & Pi models, e.t.c.

I liked the part about omitting the complicated formulas best. I will get busy on the learning curve thanks.. I will have another pop at this volume control too, I probably did something wrong
It's nice to actually have some idea of why you are doing what you are doing,  Even if you are doing it wrong .

[Josh_bb]

Yay, sorted. it's now true bypass and has an out volume control, so I can use it on a clean channel without silly amounts of boost.
Thanks for the patience, help and lesson. Maybe this will someone else at some point. Now to learn more about transconductance .