Audio-level-detector
This circuit draws very little power, less than 5 mA with a single 6-V power supply. making it ideal for portable battery-operated equipment. The small size an...
Sound-activated-decoder
The piezo transducer operates as a sound-pickup device as well as a frequency-selective filter. By controlling the gain of the op amps, the oscillator can be t...
Tone-decoder
Adding a pair of one shots to the output of a 567 tone decoder renders it less sensitive to out-of-band signals and noise. Without the one shots, the 56Tis pro...
Second-audio-program-adapter
The baseband-audio input comes from the pole of switch Sl in the stereo decoder, and is coupled to IC1 (a CA3089) via a 78.6 kHz bandpass filter that consists ...
Hi-fi-expander-with-de-emphasis
The expander to complement the compressor is shown. An external op amp is used for high slew rate. Both the compressor and expander have unity gain levels of 0...
Variable-slope-compressor-expander
Compression and expansion ratios other than 2: 1 can be achieved by the circuit shown. Rotation of the dual potentiometer causes the circuit hook-up to change ...
Hi-ficompressor-with-pre-emphasis
The compressor contains a high-frequency, pre-emphasis circuit (C2, R5, and CS, Rl4), which helps solve this problem. Matching de-emphasis on the expander is r...
Tv-audio-amplifier
The amplifier picks up the TV"s audio output signal and amplifies it to drive a set of earphones for private listening. It is built around an LM324 quad op amp...
Mini-stereo
This circuit is built around two chips: the MC1458 dual op amp, configured as a preamplifier, and the LM378 dual4-watt amplifier. The gain of the preamp is giv...
Playback-preamplifier
The preamplifier is configured to provide lowfrequency boost to 50 Hz, flat response to 3 kHz, and high-frequency attenuation above 3 kHz. ...
Riaa-preamplifier
The circuit essentially provides low-frequency boost below 318 Hz and high-frequency attenuation above 3150 Hz. ...
Audio-circuit-bridge
This circuit shows a method which increases the power capability of a drive system for audio speakers. Two HA-2542s are used to operate on half cycles only, whi...
Tone control circuit
A simple single-transistor circuit will give approximately 15 dB boost or cut at 100 Hz and 15 kHz respectively. A low noise audio type transistor is used, and ...
Hi-fi tone control circuit
The 2N5458 JFET provides the function of a high input impedance and low noise characteristics...
High quality tone control
The circuit is based on an inverting op amp using discrete transistors to overcome poor slew rate, fairly high distortion, and high noise problems. The output s...
Three-channel tone control
The iriput signal is fed via SKI to the first active stage built around ICl. Configured as a noninverting amplifier whose gain is set by the ratio of R3 and Rl....
Stereo balance meter
Play any stereo disc or tape and then set the amplifier to mono...
Stereo balancer
This circuit will allow you to set the gain of two stereo channels to the same level. The signal across the two channel-load resistors is sampled by resistors R...
Stereo balance meter
Outputs from each channel are fed to the two inputs of ICl connected as a differential amplifier. IC2 and 3 are driven by the output of ICl. Output of ICl is co...
Sound activated relay
The device remains dormat (in an off condition) until some sound causes it to tum on. The input stage is a 741 operational amplifier connected as a noninverting...