Archive for the ‘Remote/Rack Wah’ Category

Here’s a variation of the Remote/Rack Wah unit which uses a handwired turret board for the wah circuit.  I was inspired by the Vox V846-HW handwired wah pedal to create this version.  The foot controller is optically isolated as before, and it has a switchable buffer installed on the output.

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Here’s a closeup of the wah circuit:

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I did not copy the Vox layout but instead made my own. However, the principle is very much the same. It’s just like wiring up an amplifier with turret boards. You don’t need a printed circuit board, but it’s more time and labor intensive.

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Here’s the latest version of the Rack/Remote Wah I’ve built:

This version used an Area 51 “Vintage Italian” wah board for the wah circuit.  I like the sound of it a lot.  It’s basically a Vox wah circuit with some mods to make it more vintage-sounding.  According to Area 51 Tube Designs, it’s “The same circuit as the original, early Vox® wahs manufactured by the Jen corporation in Italy”.  They include their own custom inductor.  I also installed the Area 51 output buffer, in case the wah is ever used with a Fuzz Face or similar pedal that can load down the output of a wah circuit.  There is a switch on the back which allows bypass of the buffer.

I put some “retro” embossed labels on it, to make it look more like The Edge’s CAE remote wah:

Here’s a closeup of the auxiliary/breakout board for the remote wah.  The circuit is simple enough that a PCB isn’t really needed.  This is one is wired using an old-fashioned turret board:

Assembling the enclosure and inserting the circuit boards is the easy part.  A few holes are drilled, and some standoffs and washers employed:

The smaller satellite board on the right contains the optocoupler and related circuitry which attaches to the XLR jack.   This isolates the footpedal from the rest of the audio circuit – no audio travels through the expression pedal cable.  The rest of the wiring goes pretty fast, too:

Here is a closeup of the V847 Wah board:

I modded it with a couple of trimpots to control the “Q” factor and the gain on Q1.  I also switched out the inductor for an old Crybaby inductor, as I preferred the sound on it.

The front jacks are normalled to the rear jacks, so if nothing is inserted in the front, the signal will pass through to the rear jacks:

Now we are ready to rock…

Even though the wah circuit is not that large, in this case the goal was to make the unit look like Edge’s, which has a black 1RU rack box enclosing it. I settled on using an off-the-shelf Lansing enclosure Graybox, which comes in many depths and is available in a nice black anodized finish. Based on the photos, I designed a panel with holes for 1/4″ audio, a power indicator LED, and and XLR jack for the expression pedal.

I don’t have an fancy milling or machining tools, so I printed out some full sized patterns from the drawing, and used them to mark the front (and back panels) for drilling with a drill press.

The labels were made using a P-Touch printer.

The basis for this project comes from R.G. Keen’s wonderful article The Technology of Wah Pedals found at his GEOFEX website. It the article he explains how the pedal for a wah circuit can be positioned remotely from the audio using an LED and Light Dependent Resistor:

http://www.geofex.com/article_folders/wahpedl/wah11.gif

So it’s a relatively simple matter to disconnect the pot from the circuit and implement the alternate circuit using a 3 conductor cable (XLR or TRS) and an expression pedal. I use the Boss FV300L since I have one sitting around (and b/c Edge has one too of course…) In place of the LED/LDR pair R.G. describes, I think it’s easier just to use an off-the-shelf NSL-32 optocoupler.

The first step was to build a very rough prototype with some spare jacks and scrap sheet metal parts, to make sure the concept would work. I usually do this for pedal experiments:

Edge’s rack wah is a Vox V847 but I happened to have an old Crybaby board lying around, so I used that instead. The circuits are virtually identical. Next was to attach the FV300L with a mic cable give the wah a test drive. (Note: This also required a cable splitter from TRS to two mono cables) Here I used it for a cover of “The Fly”:

Once I was confident the prototype worked as I hoped, it was time to design a nice box for it…

A fun little custom project, coming soon…The plan here is to copy The Edge’s rack wah.