Reverberator with TDA1022
The first reverberator we present is based on TDA1022, the most used BBD.
Reverberator adjustements for proper functionality:
Before we connect the power supply, extract IC2 and IC3 from its base and adjust the potentiometers to middle position. On one of IC2 or IC3 entries connect a frequency-meter and/or oscilloscope. On oscilloscope monitor will be visualized the rectangular pulses with point to point amplitude equal to power supply voltage and a space factor of 1:1. The frequency of this pulses is adjusted with P3 between 3 and 18kHz. Check that voltage value on IC2 pin 5 is 7.5V dc.
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Low noise microphone preamplifier
The microphone preamplifier circuit design presented in this schematic use SSM2015 produced by Precision Monolithics Inc. (PMI) which offers a high amplification and low noise ( 1.3nV/√f).
Has been designed to work with differential input signals and can deliver 10 to 2000x amplification and it is term of R4 value. For R5 = R6 the amplification is A = (20000/R4)+3.5
The values from the schematic correspond to 1000x amplification. Noise signal ratio is 95dB.
Distorsions were 0.006% at 1kHz and 0dBV and lower than 0.01% at 10kHz. Bandwidth is 180kHz at 3V and 1kΩ impendance.
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Audio duplex communication link schematic
You need two of this circuits to create a duplex communication.
Duplex circuit adjustment: connect those 2 circuits thru a cable and inject a sinusoidal signal at 1KHz and 5Vef voltage into one circuit, the others circuit input must be shortcircuited. Adjust P1 for a minimum value at K2, then increase signal frequency to 10kHz and adjust C5 for a minimum value on K2. Repeat this operation for the other circuit.
The duplex audio communication schematic:
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