The Ultimate List of PT2399 Delays and Circuits (2025 Update)

Designed by Taiwan-based semiconductor company Princeton Technology and discovered by the DIY audio hardware and synth-builder community in the early 2000s, the PT2399 is a self-contained digital delay chip: it has a built-in ADC, DAC, RAM delay line, and a variable internal clock. In plain terms, that means it can create digital delay effects with just a handful of external components. It was cheap, compact, and did the job—perfect for adding slapback echo to karaoke machines and other low-cost audio gear.

But musicians, pedal builders, and synth DIYers quickly realized this chip had a lot more to offer.

At short delay times, it’s clean and analog-ish. Push the timing longer, and it starts to wobble and degrade in gloriously unpredictable ways—adding hiss, aliasing, and crunchy digital smear. Feed it back into itself, and it can self-oscillate, glitch, or dissolve into reverb-like ambience. Builders started putting it in guitar pedals, then in Eurorack modules, then in 5U systems, desktop boxes, even toy rewires. It eventually became the core of the Accutronics/Belton “Brick” reverb modules—each of which actually chains together three PT2399s under the hood.

Two decades later, the PT2399 is still going strong, showing up in everything from professional-grade delay units to chaotic noise machines. It’s been modded, stacked, voltage-controlled, clock-divided, and circuit-bent in ways that Princeton probably never imagined. The charm lies not just in its sound, but in its flexibility. The PT2399 can be a clean delay line, a lo-fi reverb core, or an unstable glitch generator—depending on how you build around it.

One thing you won’t see very often is full sync capability. The chip was never designed with external synchronization in mind, and coaxing it into time-locking with other gear is tricky. Some builders attempt this with external clocks or microcontroller control, but most designs either settle for manual timing or expose the chip’s internal clock as a pulse output—which can be used to sync other effects to the delay time, rather than the other way around. It’s a clever workaround, and one of many design choices we’ve tried to capture in this list.

What follows is the most complete roundup we could assemble of PT2399-based hardware: guitar pedals, Eurorack and 5U modules, desktop effects, and DIY kits. You'll find simple single-chip delays, stereo and cascading builds, hybrid reverb designs that pair a Belton Brick with external modulation, and even oddball instruments that use the PT2399 in unexpected ways. Each entry includes details on whether it's in production, DIY-friendly, voltage-controllable, sync-capable, and—crucially—how many PT2399 chips are under the hood (not counting the ones inside a Belton Brick).

We’ve included links wherever possible: to schematics, build guides, shop pages, and documentation, so you can dive deeper or start building yourself.

Whether you're searching for a warm delay for your pedalboard, a voltage-controlled echo for your modular system, or just exploring how far this humble karaoke chip can be pushed, this list is for you.

Let’s get into it.