The PT2399 is one of the most rewarding chips a DIYer can experiment with. A stock circuit from the datasheet can nearly complete a guitar pedal project, and there are load of other applications for projects that require an analog-sounding digital delay (more on this later). For you circuit tweakers out there, I will include a Mods section to get you going in the right direction.
The PT2399 is a CMOS echo/delay processor developed by Princeton Technology Corp. This digital chip includes an ADC (Analog to Digital converter), 44Kb of RAM to store the samples and a DAC (Digital to Analog converter). Although this chip was created as a simple solution to add delay/reverb/echo to karaokes and set-up entertainment systems, it became very popular in the guitar pedal community due to its ability to emulate BBD-based delay circuits, good price, through-hole package, 5V power supply and tolerance to modifications.
This integrated circuit has also demonstrated that with a careful design and good tuning, could be a fantastic sounding solution. Many well-known effects like Belton/Accu-Tronics reverb module, Danelectro FAB-Echo, and the Rebote Delay use this chip as the core of the circuit.
With a minimum delay of 30ms and a maximum of 340ms (that could be extended up to 1 second at the expense of sound quality) makes it perfect for delay, echo and reverb effects.
The official Princeton Technology PT2399 datasheet is vague and many of the internal functions of the IC are not explained either, giving the foundations for mods and think-out-of-the-box solutions. In this article, we are trying to give more insights and information about how this chip works.
PT2399 is an echo audio processor IC utilizing CMOS Technology which is equipped with ADC and
DAC, high sampling frequency and an internal memory of 44K Digital processing is used to generate
the delay time, it also features an internal VCO circuit in the system clock, thereby, making the frequency easily adjustable. PT2399 boast of very low distortion (THD<0.5%) and very low noise
(No<-90dBV), thus producing high quality audio output. The pin assignments and application circuit
are optimized for easy PCB layout and cost saving advantage.
r CMOS Technology
r Least External Components
r Auto Reset Function
r Low Noise, No<-90dBV Typical
r Low Distortion, THD<0.5% Typical
r External Adjustable VCO
r Available in 16 pins, DIP or SO package