PT2399: The Next-Gen Digital Delay and Echo Audio Processor IC

Ⅰ. What is PT2399?

Ⅱ. Structure and working principle of PT2399

Ⅲ. Total harmonic distortion and noise of PT2399

Ⅳ. Which one is better, PT2399 or PT2399?

Ⅴ. Who is the manufacturer of PT2399?

Ⅵ. How to adjust the reverberation and eliminate howling in PT2399?

Ⅶ. How to solve the fault of PT2399?

The PT2399 is an echo processor IC commonly used in audio circuits to generate digital delays. This article focuses on its basic concepts, structure and working principle to help you better understand the features of this chip. It also provides information about the manufacturer and troubleshooting in case you need it. Let's take a detailed look at this powerful chip!

The PT2399 is a CMOS single-chip echo or delay processor. It accepts a pattern audio input signal, converts the analog signal to a binary bitstream, and stores it in internal 44Kbit RAM. This bitstream is then processed and demodulated for output via a DAC and low-pass filter. The chip is mainly used in a variety of audio devices such as stereos, TVs, and karaoke reverberators.

The PT2399 has a built-in operational amplifier, voltage controlled oscillator(VCO), analog-to-digital and digital-to-analog converters, SRAM, and a delay time control circuit. It is unique in that the built-in VCO simplifies the external application circuitry and makes it easy to control the oscillation frequency, which enables fine-tuning of the delay time. In addition, the PT2399 has only 16 pins and requires a minimal number of external components, which helps simplify PCB layout and can further reduce costs.

Replacements and equivalents:

• ASB1020

• BU9253

• CD4046

• MN3005

• MN3101

• XR2206

PT2399 integrated circuit mainly consists of a power supply regulator circuit, clock oscillator circuit, microphone signal processing circuit, the reference supply voltage circuit, sampling signal processing circuit, digital reverb preamplifier circuit, reverb contrast processing circuit, reverb delay circuit and other ancillary functions of the circuit and other common components. These circuits collaborate with each other to make the PT2399 IC excel in audio processing.

The PT2399 converts analog audio signals to digital signals via a high sampling rate ADC, which is stored in the internal 44Kbit RAM. Next, it processes the digital signal through internal processing circuitry, such as adding effects like reverb and echo. Finally, after demodulation by a DAC and a low-pass filter, it outputs the processed analog audio signal.

According to the datasheet, the total harmonic distortion (THD) is specified as typically less than 0.5% at 0.5Vrms, with 0.13% THD at a delay of 31.3ms and 1% THD at a delay of 342ms. When measured, the results are as follows:

The graph illustrates that at a minimum delay of 30ms, the measured total harmonic distortion (THD) is 0.28%, and the noise level is approximately -90dBF, as specified in the datasheet. As the delay time is extended, the THD rises to 3 % or higher. As long as the delay time remains under 350ms (with a 25K resistor), the THD stays at a satisfactory level of around 0.5%.

In summary, optimal sound quality is achieved when the delay is set below 350ms, as per the datasheet. While an increase in delay may introduce distortion, some users find that this can produce a warm and musically appealing effect, particularly at around 450ms.

Both the PT2399 and M65831 can be used in microphone processing circuits, but there are some differences between them. PT2399 fine-tunes the oscillation frequency of the oscillator to adjust the delay time by adjusting the external resistor value of the oscillator. In addition to using the simple parallel control mode and adjusting the delay time by changing the DC level combination of the delay control pin, the M65831 also supports the use of the serial control mode, making its interface with the CPU more convenient. Hence, a direct comparison of the advantages and disadvantages is not feasible, given their distinct attributes. The selection of the appropriate chip should be determined by the specific needs of the application and the configuration of the device.

PTC is a CMOS echo or delay processor developed by Princeton Technology Corp. The company was founded in 1985 and revolutionized digital 3D design in 1986. In 1998, they were the first to launch Internet-based PLM software to the market. As the most representative software company in the field of CAID/CADICAE/CAM/PDM, the solutions they provide have helped enterprises successfully integrate the physical and digital worlds and create business value. PTC's independent industrial software products include Creo, Windchill, ThingWorx and Vuforia, etc.

The following figure shows the PT2399 reverb circuit. If the MIC signal is not loud enough when it enters PT2399 directly, then you can add a level of amplification before entering PT2399. To eliminate whistling, we need to connect 103 capacitors in parallel with the amplification feedback resistor R40.

The following picture shows the reverb part of the circuit. To eliminate interference from the reverb circuit to the radio and other circuits, we use a single point grounding method. Resistor R31 is connected to pin 6 of the circuit to adjust the reverb time. If we need to increase the reverberation time, we can increase the resistance value of R31; conversely, if we need to reduce the reverberation time, we can reduce the resistance value of R31. Connected to the circuit capacitor C37, C36 is mainly used to adjust the reverberation effect, the general selection of 683 to 104 specifications of the capacitor can be, without too many changes. At the same time, the capacity of the two capacitors should be kept as consistent as possible.

The capacitors C38 and C26 connected in the circuit are also used to adjust the reverberation effect, and generally use 681 to 102 specification capacitors. If you need to adjust the capacity of these two capacitors, should be consistent. The 14th foot connected to the R44 and C40 RC circuit, the reverb of the whistling to play a regulatory role. Proper adjustment of R44 and C40 can effectively suppress whistling.

C29 and C28 are the coupling capacitors of the reverb circuit, which can regulate the clarity and fullness of the reverb sound. Reducing the capacity of these two capacitors can reduce the low frequency sound of the reverb sound and make the sound clearer at the same time. However, it should be noted that if the capacity is reduced too much, the reverb may become thin and not loud enough. If the shouting sound is too low, we can reduce the input capacitor C20 and the output capacitor C31.

First, we check the power supply of the MIC circuit. We first confirm whether the power supply of RSM2399 is normal. Normal power supply RSM2399 PIN1 pin to ground voltage of 4.7V to 5V, no signal input is 5V. similarly, we also need to confirm that the microphone IC1 dual-amplifier power supply is normal. Next, we check the MIC signal path. We input the MIC signal (inserted into the microphone for audition, while testing), and use an oscilloscope to observe whether C15 has a coupled signal output. If there is no signal output from C15, this may indicate that the fault is in the amplifier circuit of IC1. At this time, we need to focus on detecting whether the power supply of IC1 is normal, as well as whether the coupling electrolytic is open circuit, whether the volume potentiometer is soldered, as well as whether the signal is short-circuited and other possible problems. Through these troubleshooting, we can troubleshoot step by step. If there is a signal output from C15, it means that the RSM2399 input signal is normal. However, if the RSM2399 has no output, we should first detect whether the signal coupled by 2C11 is shorted to ground due to a bad microphone socket. If this is not the problem, then we may need to test the peripheral circuit of RSM2399 and RSM2399 itself.

Frequently Asked Questions

1. What is PT2399?

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).

2. What is the frequency response of PT2399?

So the frequency response at the input to the PT2399 delay chip is limited to about 2 kHz, and higher frequencies are rolled off at 12 dB per octave. This may sound extreme, but this filter performance is typical for analog delays.

3. What is the delay range of PT2399?

With 44Kb internal RAM, the time is set using an external resistor which makes it perfect to simplify the circuit. It has a minimum delay of 30ms and a maximum of 340ms.

4. Is PT2399 being discontinued?

The complete (pedal) version of this product has been discontinued, but the PCB/kit is still available. We replaced the pedal with the Cosmic ECHO for guitar or synth. It has all the mods and is a much simpler build.