Circuits

Over the years, I have greatly benefited from the generous work of the open source community. Whether it’s a reverse-engineered schematic of a early 70’s drum machine to source code for the Arduino, there is a lot of unpaid work that I have used for my hobbies and my work. As a token of my appreciation, I am making the official DIY Audio Circuits Eagle CAD Parts Library and Schematics available to the general public. Many of these custom-built parts and circuits have been manufactured and tested, while others were for demonstration purposes only. Please feel free to download these files and use them for whatever purpose you see fit. ...

Just found an awesome MIDI schematic used in a production model MIDI multiple-output buffer. In the works is a tutorial on how to make you own MIDI buffer! I’ll even have Eagle files! Woohoo!

Use a NAND Gate to get a square wave oscillator. Typically, the 4093 is used due to it being a Schmitt Trigger and there being 4 of them in the IC package. The potentiometer allows for user-adjustable frequency control. Lots of uses for this circuit building block.

Use this circuit with your circuits to output a staircase-style CV. The 4516 Binary UP/DOWN Counter is controlled by a two 4093 CMOS NAND Gate oscillators; one controls the clock speed, the other controls the direction of the binary count. A R-2R resistor ladder converts the binary output into a scalable voltage, which is then limited by a potentiometer and buffered for use with synthesizers that can accept a Control Voltage.

The 555 timer can be configured with external components to output a single pulse for a fixed duration. When the switch is toggled to “ON”, the output will go high/1/ON for a brief moment of time, then go back to its stable state. You may find that some switches will need to be debounced, which is a pain in the ass reality of dealing with physical components.

A simple 2 Transformer, 4 Germanium Diode Ring Modulator with a true bypass switching scheme. Includes input for Carrier Wave modulation. Power is only required for the status LED.

A simple switching circuit that allows you to route a signal to two different paths. LEDs help indicate which signal path is active, although this circuit can also be used without battery/DC Jack power.

Originally made by Coron, the DS-8 Drum Synth circuit is a fairly complex circuit that generates some awesome analog synth tones.

The PT2399 Echo Application Circuit comes straight from the Princeton datasheet, providing the simplest functional delay circuit possible with this impressive chip. This minimalist design demonstrates the PT2399’s core capabilities using approximately 15-20 components—perfect for breadboarding and learning how digital delay chips operate. Circuit Overview This basic echo circuit includes input coupling, the PT2399 chip itself, delay time control via Pin 6 potentiometer, feedback regeneration control, and output coupling. The elegant simplicity makes it ideal for first-time PT2399 experiments. You can breadboard this circuit in under an hour and immediately hear functional echo effects. ...

The PT2399 Surround/Delay Application Circuit represents Princeton’s second datasheet example circuit, designed for creating ambient “surround” effects that approach reverb-like characteristics. While single PT2399 chips inherently produce echo rather than true reverberation, this circuit demonstrates techniques pointing toward more complex reverb implementations. Understanding “Surround” Effects Princeton’s “surround” terminology suggests spatial effects beyond simple echo. This circuit configuration uses specific feedback and filtering strategies creating denser echo patterns than the basic echo application. While not achieving authentic reverb—which requires multiple delay taps with varied timing—this design moves beyond discrete echoes toward more continuous decay characteristics. ...