Pot replacement procedure for a Colorsound Wah/Fuzz/Swell

[aquataur]

FYI,

I received a yellow Colorsound Wah/Fuzz/Swell, probably dated ca. 70ies pedal to replace the scratchy pot. The pedal had been in repair for that, but the owner re-installed the original pot again because the pedal did not behave right after the installation of the new pot. This has several reasons (see lateron). Since changing the pot(s) on this pedal presents a problem I would like to share with you how I managed to fixed it. Skip on to the quintessence on the bottom if you do not want to read all.

* The original pot is a stereo (a.k.a. tandem) pot with an additional tap. Not to be found these days anywhere. The pot quality is, compared to a (now no longer produced) Allen Bradley type pot, inferior, mediocre at least.

* The pot is marked "Radiohm" "100k" (linear).

* dual pots for volume pedal usage (which is an abuse for a pot...) are non existant, let alone with a tap. A mechanically liked work-a-like with two single pots is not possible due to the mechanical circumstances in the pedal.

I ordered a 100k dual pot that would be of comparable quality (Piher) less the tap. This did do much on the wah, kind of rumbled round the low quarter. I suspected that the funny mechanical bracket that moves the pot axle does not cover the whole potential mechanical angle and this is true.

Measurements showed that the pot is rather a 220k pot despite its marking and despite the schematic floating around here.
I found a high quality (Ohmite) 220k linear pot (comparable to an Allan Bradley) and this worked for the wah part.

* So the pot is really a 220k linear. A 100k will not do much.

* The tapped portion of it is used on the volume swell which is active only alternatively to the Wah. The tap is shorted to ground, so it measures around 180k. Since a fair portion of its mechanical travel is thus shorted out it will do nothing for a certain region. Careful mechanical trimming will be necessary for the changer arm. (see later...)

* Due to the proprietary mechanical linkage between the pedal and the pot with this funny plastic bracket only something like 150 deg out of the about 300 degrees mechanical travel of the pot are used.

I tried the 100k dual pot I had ordered and the volume kind of worked, although with a funny response. I tried parallel resistors as shown in the "secret life of pots" by R.G. Keen, which improves the situation but changes its input impedance. Theoretically you could order a 220k lin version of the Piher pot and get this going. I suspect that even the original volume swell was not very useful from matters of taper feel, so I did not bother.

Since I was not happy with the quality of the original pot and the replacement I ordered, since a good quality (for volume swells!) dual pot is non existant and since a decent external volume pedal is much easier to be found than a vintage wah, I sacrificed the volume portion and installed the HQ single 220k lin Ohmite pot for the Wah. The two wires that went to the volume pot got soldered together. The bracket appeared to loose for the rather stiff action Ohmite pot and slipped. I fixed this by shrinking a peace of heat-shrink tubing over the pot´s axle which then holds the bracket rock-solid.

The Ohmite pot works a breeze and can be expected to give a much longer lifetime than the original. However, due to the funny mechanical linkage between the pedal and the pot the wah only works well in a region around the center. Below it sounds too bassy, above too trebly. The sweet spot has to be determined by loosening either the bracket and turning the pot shaft, or, more conventional, loosening the pot mount and fixing the pot in a different angle.

[To come back to the beginning, the repairman who had replaced the pot earlier had probably failed to recognize this fact and not done any mechanical tuning. Also, the volume would not work properly for a stock untapped pot...]

Although the entire unit seems to be built very cheaply, the wah sounds really unique I must admit.

In a nutshell: If you are willing to sacrifice the pedal´s volume swell feature, buy a high quality (mil spec) linear 220k pot and wire this to the wah portion. This reqires only a small mechanical adjustment. This way you have sacrificed the volume pedal functionality of doubtful quality but restored a sought-after wah pedal to better-than-original specs.

have fun,

-helmut

[Electric Warrior]

Not sure what the additional tap on yours is, but Omeg makes nice Radiohm replacements: http://omeg.co.uk

The original part probably measueres that high because it's worn out.

[aquataur]

Not sure what the additional tap on yours is

The circuit is shown here:
viewtopic.php?f=19&t=8065

Omeg makes nice Radiohm replacements: http://omeg.co.uk

Thanks for the link, I did not know them. I am pretty sure they don´t have the tapped version. I have never seen such a pot before either.

The original part probably measueres that high because it's worn out.

Nope. The pedal still worked but was scratchy. It wouldn´t if the values were that dramatically out. Support for this claim is that a brand new 100k pot did nearly nothing over its full travel.

greetings,

-helmut

[digi2t]

How about one of these, with resistors to bring it into the range required?

https://www.ebay.com/itm/CENTRALAB-NOS- ... 2ebecc81c4