Build a Mad Professor Snow-White AutoWah Non-Clone

| January 5, 2011 | 0 Comments

Mad Professor Amplification Ltd. is a Turenki, Finland-based maker of amplifiers and effect pedals owned by Harri Koski. The company’s products use designs by Bjorn Juhl, the “Mad Professor” in this operation. Bjorn is the designer of the BJFE (Bjorn Juhl Forstarker Elektronik) line of pedals. Bjorn began building guitar effects as early as 1981 and he started his BJF Electronics business in 1999 doing amp repairs. In 2000 he was displaying his repair services at a guitar trade show and connected with Harri Koski from Custom Sounds in Stockhold to begin a partnership distributing guitar effects.

BJFE pedals are all handmade by Bjorn. The circuit boards are encased in neoprene rubber to cushion the electronic components inside. The circuit board is also sealed to provide protection, and to preserve trade secrets. His wife Eva paints the lettering and pictures. Each model comes with some unique artwork inside the back pedal cover, which is painted by hand. BJFE pedals typically follow a “color” naming scheme with an adjective to describe the sound.

The Mad Professor line came about when Bjorn was asked by Koski to consider designing amplifiers. Bjorn did not have the time to also build amplifiers so a new company was created where Bjorn designed the effects and amplifiers, but they would be constructed and distributed under the name Mad Professor Amplification. These are pedals and amplifiers designed by Bjorn but not hand-built by him.

A popular pedal in the Mad Professor series is the Snow White AutoWah effect. The inspiration for the sounds of this wah was the old Colorsound Wah-Wah pedal manufactured by Sola Sound in the UK. Let’s start our journey by listening to the Colorsound in action:

By the way, you can build a clone of the Colorsound by visiting the Optochopto page at Beavis Audio Research.

The Snow White AutoWah (SWAW)/Voltage Control Filter effect was designed by Bjorn based on his earlier 1991 Voltage Controlled Filter (VCF) rack mount remote wah circuit. It has the following four controls:

  • Sensitivity – sets the filter trigger level and should be adjusted to fit your guitar/bass output and your playing touch. The sensitivity can also be adjusted from the guitar volume knob while playing.
  • Bias – Controls the filter resonance frequency. When Sensitivity is turned fully off the Bias can be used as a sweepable filter.
  • Resonance – Controls the sharpness or Q-factor of the filter.
  • Decay – Controls how fast the filter frequency falls back to resting point (that is set with the Bias control). This can be set fast (CW) so you get the wah effect on every note or slow for a more traditional auto wah sound.

Here’s a demo of the Snow White AutoWah:

The Snow White AutoWah is a beautiful to hear, and to see, but at $350 its hand made boutique quality is too much for many players to afford. An alternative to consider is the Super White Auto Wah circuit available from GuitarPCB.com. While it is not a clone, and therefore we described it above as a non-clone, it gives a very nice autowah similar to the Mad Professor effect. Click Here to listen to the Super White being played over Stevie Wonder’s Superstition, played by T-Diddy.

The Super White AutoWah isn’t a complete kit, just a printed circuit board (PCB), so you’ll need to buy the PCB from GuitarPCB.com and then purchase the components to create your own kit. The heart of the effect is the LM13700 (Mouser 863-NE5517NG) current-controlled transconductance dual-amplifier chip. Don’t let the term “transconductance” throw you – conductance is the reciprocal of resistance; transconductance is the ratio of the current change at the output port to the voltage change at the input port. A “transconductance amplifier” just means that the amplifier puts out a current proportional to its input voltage. This makes it ideal for a current controlled filter, such as what is needed in a wah circuit.

Here’s a nice demo video of the GuitarPCB.com Super White AutoWah with some very tasty guitar playing:

Visit GuitarPCB.com to purchase the PC Board, see the parts list, and get support for building the kit through their forum.

Category: Pedal & Effects

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