Years later, i finally acquired a stunning Parker Fly Classic, and it did not disappoint. Well, except for the fact i found that i wanted to be able to move between the magnetic and piezo sounds while playing, and with two hands already occupied with picking and fretting, that seemed like an ideal task for one of my feet.

Read on…

I was surprised to learn that nobody had made a true “blend” pedal that worked the same way the magnetic/piezo balance pot worked on the Fly. At one end of the knob’s travel, it was full magnetic. At the other end, it was full piezo. In the middle, it was 100% of both, with any blend available between the two extremes.

Stereo volume pedals tracked two inputs and two outputs in parallel. Pan pedals usually swept one input between two outputs. And the occasional “blend” pedal i found either allowed the player to add the piezo sound to a fixed magnetic sound (like the Fishman PowerBlend pedal) or didn’t allow 100% of both signals in the middle position.

So i took it upon myself to design and build the pedal i envisioned.

My design criteria were that the pedal had to work exactly as i wanted and be a 100% passive design, so i wouldn’t have to mess around with preamps, buffers, batteries, impedance matching and so on. I wanted it to be universally workable for anyone with a magnetic/piezo equipped guitar like a Parker, a Music Man, or any guitar equipped with an aftermarket bridge and preamp from Fishman, L.R. Baggs or GraphTech.

I had to make a few assumptions, the first of which was that the guitar’s magnetic signal would be buffered by the piezo’s preamp. I know that GraphTech’s AcoustiPhonic preamp does. The advantage of this is that a 25 kOhm pot can be used because both circuits are active. If the magnetic signal is not buffered, then a 250 k, 500 k or 1 Meg pot would have to be used.

I found empty wah pedal shells available at Small Bear Electronics, bought blend pots through StewMac, found various jacks locally, and set to work creating the first prototype.

In my R&D process, i discovered that the automatic stereo/mono switching used in some preamp circuits (such as the AcoustiPhonic and newer Parkers) presented a problem. From my testing, it appeared that a tiny amount of voltage is sent down the piezo (ring) signal wire, and when that voltage is detected on the ground circuit (which would happen when a mono TS plug is inserted in a stereo TRS jack… the ring would be shorted to ground), the preamp switches into mono mode, sending both magnetic and piezo signals down the “tip” of the connector. It’s my understanding that newer Parkers that lack the red mono/stereo button next to the output jack also work in this way.

Wiring the pot backwards succesfully isolated the voltage from the guitar’s onboard preamp, but resulted in a faint “zipper-like” sound as the pot was moved through its range.

I worked around it by putting an effects insert in the piezo circuit, where i placed a Tech21 Acoustic DI. This active preamp effectively isolated the voltage from heading back up the ground wire to trip the preamp into mono mode. But it didn’t meet my “100% passive” rule, so i knew i wasn’t done.

I left it alone for a while, because in my pedalboard at the time, it worked. But as my rig evolved and changed over time, i knew i’d have to revisit it. Further research into balanced and unbalanced circuits gave me an idea to try a “pseudo ground lift” whereby a resistor and a capacitor in line with the ground, which filters any voltage from travelling back up the ground wire. Eureka!

And here i present to you the schematic diagram for the pedal:

Click here to download it in PDF form.

I don’t believe in keeping what seems like a common-sense solution a “secret”, or trying to apply for a patent for what is essentially a blend pot stuffed into a wah pedal casing. (Chances are, a patent would not be granted for such an obvious solution.) So i’ve published the schematic here for anyone who wants to DIY their own pedal together, or improve upon my design.

On customer request, i will be including one of these pedals with each Decibel guitar that’s equipped with a GraphTech AcoustiPhonic piezo system. In my opinion, it’s the simplest, most elegant way to handle the switching or blending between magnetic and piezo sounds in a hybrid guitar.

Currently, i’m using a Dunlop-style wah pedal shell from Small Bear, but i would love to be able to retrofit this into an Ernie Ball VP or VP Jr. pedal. Unfortunately, the Ernie Ball pedals use a long-shaft pot, and i have not been successful in sourcing a long-shaft blend pot that would make this retrofit possible. If anyone can point me in the right direction, that would be great!

I have an interesting electronics/surplus store nearby, and while rummaging through the bins there, i came across these:

Prototype 2 is already the first recipient of one of the dome type buttons, and we have a few more on hand for future builds. Sadly, they only seem to be available in a chrome (or nickel) finish.

In these early stages of building, i’ve opted to go for a bolt-on design, for a few reasons. First, the bolt-on design gives maximum versatility. I’m building guitars with very different body and neck woods. They’ll all have the same scale length, bolt pattern and neck pocket, so they’ll be easily interchangeable, so i can experiment with how different neck woods and body woods interact. Second, if anything goes catastrophically wrong at any point in the build, i’ve only lost a body or a neck. With a set-neck or neck-thru, i’d have to trash the whole instrument. I’d rather not do that.

But i won’t be using just any old bolt-on design. The classic Fender “bolt-on” is actually mis-named. The necks are actually screwed on. Bolts are usually threaded to receive a nut. Most “bolt-on” necks just use big wood screws and a metal plate (or recessed metal grommets). Not a bad design, but its strength is limited by thin threads biting into wood. Repeated neck removals weaken the joint every single time.

Here’s how we’re building our bolt-on necks: