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PT2399 based Delay

2017-12-21 14:35  
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PT2399 based Delay

Introduction

This circuit is take on a delay unit based on the PT2399 chip.

The PT2399  is a single chip echo processor IC utilizing CMOS technology. Which accept analog audio input signal, a high sample rate ADC transfer the analog signal into a bit stream then storage to internal 44Kbit RAM, after processing the bit stream will de-modulate by DAC and lowpass filter. Overall delay time is determined by internal VCO clock frequency, and user can easy to change the VCO frequency by changing the external resistance. The PT2399 performs low distortion (THD<0.5%@0.5Vrms) and low noise (No<-90dBV) characteristic for audio purpose, and pin arrangement and application circuit are optimized foreasy PCB layout and cost saving advantage.

PT2399

The circuit

There are only some minor tweaks to the schematic from the datasheet, first of all I lowered the 100nF capacitors in the Delta Encoders and Decoders, this gives the unit a higer bandwidth. So I also had to change the filters to accomodate for that. At longer delay settings the circuit might therefore have somewhat more noise, while at shorter settings it has more bandwidth. Since I didn't like the clipping of the chip, and to make the response more like an analog (tape) delay I added a softclipper before the digital delay core. So the delay allows going softly into selfregeneration, with feedback even stronger than 1. The pots permit setting the amount of regeneration and the relative amplitudes of the dry and delayed signal.