![]() ![]() Hence the final audio output signal is a mix of the input signal and the delayed signal. The output of this op amp is at pin 15, and this is where the final signal is tapped out from. The initial input signal and the delayed signal mix at this point and enter the op-amp at pin 16. It is important to visualise that between pin 15 and 16 there is an internal op amp used to form a low-pass multi-feedback filter. If the wiper is set to the fully minimum position (ground side), then there will be no signal being fed back to the input and the circuit behaves as the basic delay circuit shown in the documentation. The wiper of this potentiometer feeds the signal back to the input stage at pin 16. The length of time from the initial signal to the last echo is usually known as reverb time, hence many designers call this reverb control. The attenuation provided by this potentiometer determines the number of echoes you get, or put in another way, how quickly the echoes fade out. The delayed output of the IC emerges at pin 14 and goes to the 50-kΩ repeats potentiometer. You can get a clearer idea of the filters and signal loops in another diagram showing the The circuit uses a plethora of resistors and capacitors for the low-pass filters, which are usually used to filter out aliasing and quantization noise inherent in analogue and digital conversion processes. This range is consistent for achieving an echo effect however for a subtle guitar reverb significantly smaller delays will be required. Hence according to the table, in the documentation, this limits the delay time range between 342-ms and 151-ms. Hence with the variable resistor to full resistance, the resistance at pin 6 will be 30-Ω, and with the variable resistor to zero ohms the minimum resistance will be 10-kΩ. The documentation suggests R to be 10-kΩ, which limits the range of delay times achievable. As you can see, apart from this one connection, all the rest of the components connect to the analogue ground. ![]() The purpose of keeping the digital ground separate from the analogue ground is to prevent any digital noise entering the analogue circuits. Pin 2 exposes the internal reference voltage of 2.5V for the purposes of connecting a 47-♟ electrolytic capacitor that helps to keep it stable.Īt pin 6 there is a fixed resistor in series with a 20-kΩ variable resistor connecting to the digital ground exposed through pin 4. The designer has also placed 100-♟ and 0.1♟ capacitors across the power planes to ensure a clean power supply. Here we look at some of the features of this circuit and pin functions.Īfter redrawing the basic echo circuit, we can now clearly see that the power is fed through pin 1 and the analogue ground. Furthermore, the level of attenuation in the feedback loop is set by the repeats control potentiometer. The PT2399 basic echo circuit is the one where the delayed output is fed back to the input to produce echoes. ![]()
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