Personal Message Recorder Circuit
The persona] message recorder is built around an ISD1016 CMOS voicc messaging system, which does away with the cumbersome and expensive analog-to-digital and d...
Voice Disguiser Circuit
A complete schematic diagram of the voice disguiser is shown. Microphone MIC1 picks up the voice signal and feeds it to an audio amplifier, consisting of Ql an...
Simple Signal Tracer Circuit
In this circuit, C1/D1/R1 form an envelope detector. C2 couples audio to the base of Ql....
Light-Wave Voice-Communication Receiver Circuit
This light-wave receiver consists of a 741 operated as a preamplifier and an LM386 operated as a power amplifier. Potentiometer R2 is the gain control. Various...
Audio Notch Filter For Shortwave Receivers Circuit
The notch filter can be added to just about any receiver to attenuate a single frequency by more than 30 dB....
Variable Bandpass Audio Filter Circuit
This circuit is a variable audio bandpass filter that has a low cutoff variable from about 25 Hz to 700 Hz and a high cutoff variable from 2.5 kHz to over 20 k...
Variable Q Filter For 400Hz Circuit
A bootstrapped twin notch filter in this circuit can yield an effective Q of up to 10. Rs adjusts the feedback, hence the Q. Values of C1 and C2 can be change...
Electronic Doorbell Circuit
When the doorbell switch is pressed, the two monostable stages are activated in sequence, applying bias to a pair of voltage-controlled resistor stages. These ...
Digital Audio Selector Circuit
This circuit, uses switched emitter followers, rather than the usual analog switch CMOS chips. This yields better reduction of crosstalk between channels....
Agc System For Audio Signals Circuit
This circuit is an AGC system for audio-frequency signals. AGC systems usually consist of three parts: an amplifier, rectifier, and controlled impedance. In th...
Digital Automatic Level Control (Alc) Circuit
This approach to automatic level control (ALC) makes use of digitally switched audio attenuators in the signal path. The output level of the system is sensed, ...
Audio Compressor Circuit
This compressor will compress a 25-mV p-p to 20-V p-p audio output to input levels remaining between 1.5 V p-p to 3.5 V p-p, and has a frequency response of 7 ...
Audio Line Driver Circuit
This line driver can drive low-impedance lines with up to 70 V p-p max. IC1 is a low-noise op amp suitable for 15-V operation. T1 and T2 are regulators for the...
Wireless Microphone
Ql amplifies the output from an electret microphone MIC1. Audio is fed into oscillator Q2, which modulates the signal. ...
Signal Conditioner
This circuit takes audio from a receiver that might have a weak CW or tone signal and uses a PLL (Ul) to recover the wea...
Scanner Voice Squelch
This circuit detects the presence of audio (voice) on the output of a scanner. If the scanner stops on a "dead carrie...
Simple Audio-Frequency Vco
A VOX is a voice-operated switch that is often used as a substitute for the press-to-talk switch on" a microphon...
Tremolo Circuit
This circuit adds a VLF AM component to an audio signal. This effect is widely used in musical instruments. U1C, a phase-sh...
Baxandall Tone-Control Audio Amplifier
This circuit exploits the high slew rate, high input impedance, and high output-voltage capability o...
Telephone Amplifier
This amplifier can be used in telephone work or where a simple speech amplifier is required. The frequency response can...