Epoch Bias Out Now!

Vox Cry Baby

It’s no secret that wah is one of my favorite effects types, and the Cabinet is not short on them. I’ve regaled you all about the Cry Baby, but what I haven’t talked much about is the technology behind it, what more you can do with it besides play the “Shaft” theme, and what modifications can be done to them to more tailor them to your rig.

For those of you not hip to the history of the wah, let me give you a quick refresher: in 1966, Bradley Plunkett was working as a technician for Thomas Organ Co., who was owned by the larger Warwick Electronics. Prior to the wah’s invention, Warwick had entered into a deal with JMI, parent company of Vox amps, to manufacture and distribute Vox gear in the States. JMI had asked Warwick to manufacture a lower-cost solid-state line of Vox amps, and the task fell to Thomas. An engineer there tasked Plunkett with replacing one of the most expensive circuit components—the Jennings Mid Range Boost (MRB) three-position circuit with a solid-state version controlled by a potentiometer. 

To make a very long story short, the original was marketed towards saxophonists because it allegedly sounded like an electric mute, and the result was the Clyde McCoy wah-wah, which eventually became the Cry Baby. The big takeaways here is that the original was housed in an organ footpedal, which Thomas conveniently had on hand, and Thomas failed to trademark the Cry Baby name which caused them to be made by just about every musical manufacturer of the day, including many in Italy, which made hay with the name while same-but-different versions were being sold in the States, both of Vox and Thomas lineage. The genealogy is murky and the variants many, but that’s the story with almost all pieces of highly influential gear.

So, what is a wah doing exactly? Glad you asked! While the circuit was originally a three-position model, it comprised a circuit called an LC bandpass filter. A bandpass filter only allows a certain *ahem* band of frequencies to pass through, attenuating ones above and below it. The L and C parts stand for inductance and capacitance (“L” for Heinrich Lenz, a VIP in the world of electromagnetics). Much like a wah pedal contains an inductor, (a copper-wrapped component with a ferrite core, a rather expensive piece), the MRB circuit contains two, hence Thomas’s need for simplification.

You may have heard the term “Q” in reference to wah pedals. This simply is referring to “quality factor” or in terms that are more comfortable for us, “bandwidth.” Moving the foot pedal up and down rotates the potentiometer, which shifts the band left to right. At toe down, the band is centered at 1.6KHz, and at heel down, the band is centered at 450Hz. At center position the filter is centered at 750Hz, which is right in the sweet spot for guitarists and where the sound most “feels” like a wah. These frequencies are boosted at somewhere around 18dB while everything above and below is rolled off in a bell curve. However, wahs with Q adjustment let you widen or narrow the band that is allowed to pass through. You can simulate this on any graphic EQ with 18dB of boost per band, by making a physical bell shape with the sliders. The more sliders, the more easily you are able to simulate the filter width Fun!

Knowing this simple fact can transform the way you think about the wah. If you might use an EQ pedal to dial in a killer “Money For Nothing,” you can do the same thing with a wah, and it gets much easier when the Q is adjustable. Don’t have a wah with a Q control? Can you solder? No problem! There’s a 33K resistor on most standard models that runs parallel to the inductor. This value dictates the Q of the wah. Change the resistor to something higher for a more “vocal” quality since you’re narrowing the band and increasing the sharpness of the filter. The original Clyde McCoy model had 100K in this position, which makes for a much different sounding beast than most folks have been privy to. 

Perhaps my favorite simple mod to the classic wah circuit is switching out the Q1 emitter resistor for a lower value. This increases the voltage gain and when this resistor is essentially jumpered to ground it creates a very unique and pleasing gritty distortion. The stock value is typically around 470 ohms, I prefer something lower, 240 ohms is a somewhat standard value that’s readily available. A 1K potentiometer is best, since noon is essentially stock, it gives a nice range of control. 

There are plenty more mods to the wah circuit that change the sweep range and add slight mids enhancements, but those are perhaps for another time. Maybe someday I’ll even get to tell you about my friend Andy Martin’s favorite wah mod! I leave you with this sparkling example of an early Vox Cry Baby, one of the cleanest examples I’ve seen in a minute and real joy to play.