Introducing the Passive Pickup Emulator (PPE) June 05, 2013 17:45 6 Comments

Your pedal board and amp collection are a potential playground for manipulating non-guitar signals. Yet, if you've spent some time reamping pre-recorded tracks, patching synths into fuzz pedals, or sending samples through amps, you know that the results are often disappointing compared to the magic of a well-paired guitar and amp. The Passive Pickup Emulator (PPE) is a little, four-component box that attempts to bring that magical guitar/amp interaction to any output device by simulating the sound and behavior of a classic single-coil guitar pickup.PPE Top view

What does it do?

The PPE makes connecting your non-guitar gear to guitar amps and pedals sound "right." Like everything we do here at DIYRE, the PPE draws its magic from the dynamic, interdependent nature of analog electronics. When you connect two pieces of analog gear, they interact. Unlike a digital system in which data is transferred from one stage to the next unaffected, the signal passed between two analog devices is a unique result of the characteristics of both stages. So, one can't substitute one type of device for another and expect the same results.
The PPE makes any output "look like" a passive pickup to the following input, making for a more authentic interaction with guitar amp and pedal inputs.

What's impedance got to do with it?

One of the most important characteristics of analog inputs and outputs is their impedance, often shortened as "Z." Modern gear is typically designed to minimize the sonic effects of impedance. Most guitar gear, on the other hand, takes a vintage approach (if it's not vintage to begin with) and embraces the effects of impedance. Guitar gear expects to see the wildly variable and complex output Z of a passive pickup and tone control. So it's no surprise that your guitar gear may sound a little flat or unnatural when fed a "modern" signal with a low, linear output Z.

How does it work?

The PPE recreates the dynamic, interactive system of a guitar output using only four components. Looking at each of these in turn will provide a fairly complete explanation of how the circuit works.

NOS Inductor L1 - 1 Henry Inductor
In a guitar pickup, the inductor converts the vibration of the strings into an electrical current. There are no vibrating strings in our emulator, but we use an inductor to recreate the pickup's phase and frequency non-linearities. In conjunction with the capacitor and resistors, the inductor creates a resonant low-pass filter.

Carbon Comp ResistorR1 - 15k Ohm Resistor The resistor replicates the impedance of a volume control without the volume attenuation. The resistor's value sets the PPE's output impedance as well as the damping ratio of the resonant filter.
250k Tone Pot250k Ohm Linear Pot
Just like a Fender guitar, we use one leg of a potentiometer as the resistive element of our tone control. The rotation of the pot controls how much of the high frequency signal is thrown away by being shunted to ground.
Ceramic Cap100nF/.1uF Capacitor A capacitor makes up the second half of the tone control circuit. The relatively-large .1uF capacitor sets the initial rolloff frequency around 6kHz; smaller capacitors will yield a brighter tone with a higher rolloff frequency.

How do I build it?

Full kits, including hard-to-source NOS 1H inductors, are available from the Store or you may choose to source your own parts. Either way, you can follow the step-by-step instructions in the PPE Assembly Manual. Estimated build time is 30 minutes to one hour.