Newsgroup: it.arti.musica.strumenti.chitarra
Titolo: Lungo trhead su Wah e mod

http://www.ultimate-guitar.com/forum/showthread.php?t=476372
 

WAH WAH - CO- UK
The mods on this page are primarily concerned with the Dunlop Crybaby and 
Vox V847 wahs, but they can be applied to most wahs which have an inductor. 
For an in-depth examination of the Vox wah circuit, vist RG Keen's Geofex 
site and read The Technology of Wah Pedals.
Mods to PCB
These mods are all fairly cheap to do and they're reversible, so it's not 
the end of the world if you don't like the results. Refer to the photos 
below if you're not sure which parts to change.
"Vocal Mod"
Replace the 33K resistor in parallel with the inductor with a 68K. This 
gives a more vocal quality to the wah. Some Vox Clyde McCoy wahs had 100K 
resistors here.
Gain and Bass Response
Replace the 470 ohm resistor (some have 390 or 510) at the emitter of Q1 
with a lower value. This increases gain, which is useful if you've converted 
to true bypass. The bass response is also increased. Too low a value here 
may introduce some distortion and make the wah sound muddy. Try 270 - 330 
ohms to start with.
Midrange
Replace the 1K5 resistor between the base of Q1 and the inductor with a 
larger value. This increases the midrange and helps if your wah sounds dull 
and muted when you rock the pedal back. Try 1K8 to 2K7. Higher values than 
stock also smooth out the bass-treble transition. Most people refer to the 
33K as the "Q" resistor, but this resistor also affects the Q.
Sweep Range
Change the sweep by swapping the 0.01�F cap between the emitter of Q2 and 
the inductor. A smaller value will make the wah sweep more trebly and 
vice-versa. If you're converting to or from a bass wah, this is the one to 
change. Try 0.068�F for a bass wah.
Volume
If you've converted to true bypass, replace the 68K series input resistor 
with a lower value, say 47K. This gives a slight increase in volume. Too low 
a value is likely to result in the pedal picking up radio interference. This 
can be addressed by adding small value (10 - 20pF) capacitors between the 
collector and base of each transistor.
Reference Photos
Vox V847 (US). Dunlop Crybaby Rev. C & D are similar.
http://www.wah-wah.co.uk/effects/v847.jpg
http://www.wah-wah.co.uk/effects/gcb95.jpg
Pots
You can use any old pot, but cheap carbon pots will wear out in no time and 
standard log/lin resistance tapers aren't ideal for use in a wah. Commercial 
wah pots have a kink in the taper, where the resistance suddenly shoots up 
within a small degree of rotation. This kink is the point where the 
bass-treble transition is most noticeable, and which makes the wah so 
expressive.
A standard log (audio) taper pot will produce a sweep which is mostly 
treble, unless you sacrifice the high frequencies to get some low end - a 
pedal with an extra long throw helps. A linear taper pot will sweep more 
quickly from treble to bass, but it's a smooth sweep and not very 
expressive. For a "correct" Vox/Crybaby wah pot, there are a few options, 
but they are relatively expensive. The better ones are modelled on the 
resistance taper of the ICAR pots found in '60s Vox wahs. I recommend the 
Pro Pot.
Colorsounds use a cranked linkage to get a non-linear sweep from a linear 
pot. I recommend Bourns conductive plastic pots for these. Unfortunately, 
they're not available as a dual gang version for wah-swell pedals.
Wah-Volume pedal mod
Lifting the earth connection of the 4.7�F capacitor will cancel the wah 
effect and leave you with a volume pedal. The wah circuit will thin out the 
tone in volume mode - to get around this, the '70s Jen Wah-Volume pedal 
switches in a 4K7 resistor and 0.22�F cap in series across the 0.01�F "sweep 
cap". This isn't a very useful mod in practice; if the pot is set to get a 
good wah sweep, it won't go silent in volume mode, and if it's set up to 
kill the volume, there won't be enough treble in the wah.