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 delay time control uses a resistor-potentiometer network connected to Pin 6, varying voltage to adjust delay length. Princeton’s datasheet specifies minimum 1kΩ total resistance preventing chip latch-up—critical safety requirement. A 20kΩ pot with 1kΩ series resistor provides good delay range while maintaining safe operation.
Input and output coupling capacitors (typically 0.1µF to 1µF input, 10µF or larger output) block DC while passing audio frequencies. These AC coupling components prevent DC offsets from corrupting audio signals or loading subsequent stages improperly. The 5V power supply requirement necessitates voltage regulation from typical 9V pedal supplies using 7805 or equivalent regulators.
Power Supply Considerations
Proper power filtering proves essential for clean PT2399 operation. The chip’s internal clock generates high-frequency digital noise that couples into audio paths without adequate decoupling. Use 100nF ceramic capacitors plus 10µF electrolytics at all three VDD pins (2, 3, 4). The VREF pin (Pin 10) requires particularly heavy filtering—47µF or larger electrolytic plus 100nF ceramic prevents noise injection into the critical voltage reference biasing all internal analog circuitry.
Getting Started
Build this circuit first before attempting more complex PT2399 projects. Understanding the basic echo application provides foundation for modifications, multi-chip designs, and modulation effects. Component substitutions work fine for experimentation—exact capacitor values aren’t critical, though staying reasonably close to specified values ensures proper frequency response.
For comprehensive PT2399 technical information, see our complete PT2399 guide, pinout and power supply reference, and troubleshooting guide. Advanced applications appear in our multi-chip reverb designs and modulation effects guide.