Hi,
for a volume pedal u can either have
high impedance- it goes right after your guitar and basically acts like your guitar volume pot with a bigger range. This allows you to get good volume swell effects because this changes your amount of drive( when there is a distortion unit after the pedal somewhere in the chain)
examples. boss fv50H, modtone volume pedal
These pedals are meant for volume swell effects and are not effective in controlling general volume levels i.e. doesnt have the effect of turning up or down yr amp volume level
low impedance- this pedal can only be used in your signal chain after a buffer where the impedance is low, this is often placed after the distortion pedals/in effects loop for amp distortion as it allows the user to vary volume levels as if it was turning the volume knob on the amp up. This is useful for a band situation when u feel u are too loud/soft and u can have a volume pedal to allow u to make changes in overall volume levels while playing.
Such pedals must be used after a good buffer as the lower the impedance of the signal source into the pedal the lesser the amount of treble rolloff there is when using the volume pedal to decrease volume. Some even have a built in buffer.
Examples- visual sound volume pedal(built in buffer) , boss fv50l
Buffer
These are basically analog units that converts high impedance inputs into low impedance inputs. Impedance is basically like the concept resistance that accounts for "resistance" brought about by A.C. influnces. By having a low impedance signal, the signal gains the ability to drive through wires better and has lesser treble loss in long wires. Hence it is a good idea to place a buffer at the start of the signal chain
You can either acquire a buffer pedal eg cmatmod buffer or you can purchase pedals which uses buffered bypass switching. Typically all boss, ibanez pedals uses buffered bypass switching
I once used an Ibanez ph-7 phaser which i used at the front of my chain, which caused my signal to become much more crisp and clear. The buffer was more impressive than my pedal LOL
To summarise
If u want a volume pedal that can change volume levels similar to that of turning up/down the amp volume, get a low impedance volume pedal and place it after a buffer pedal after the distortion/drive units
If u want something purely for volume swells get a high impedance volume pedal and use it as your first pedal.
Sidenote:
Low impedance generally uses 25k-50k pots and high impedance generally 250k-500k pots. All are audio tappered. Hence u can easily diy a volume pedal, its really as simple as input jack -> pot -> output jack, with the grounding done properly.
