Category «Audio»

LM3900 Audio Mixer

This audio mixer circuit doesn’t use a low impedance input to mix no ideal  sources, but use many amplifiers to provide  ideal sources before mixed through simple resistors. Ideal source means a sources with low impedances, make the interaction between signals in the output doesn’t affect the input.   Please note that this mixer circuit has …

Discrete Sliding Tone (Frequency Ramp) Doorbell

This doorbell circuit produces a low tone that will slide up to higher frequency. The equivalent total resistance connected between the base of Q1 and ground (Rbg) , and coupling capacitor  C1  determines the AF oscillator’s frequency. The resistance (Rbg) is equal to (R2+R1)R3.  Here is the schematic diagram of the circuit: The R2 is …

53 dB Stereo Preamp for Tape or Phonographs

With the circuit shown in the following schematic diagram, both channels of this stereo preamp is constructed using  RCA CA3052 quad AC amplifier.  this pre-amplifier circuit is featured with tone control (bass – treble). Make a similar circuit to complete the other channel, since the circuit for left and right channel are similar. To be …

Simple 9V Wireless Microphone FM Transmitter

This FM transmitter circuit can be used as a wireless microphone,  can be received by an ordinary 88- to 108-MHz FM broadcast receiver. For the power supply, this transmitter circuit is powered by a 9 V battery. To comply with the radiation limit of FCC rules, keep the antenna length under 12 inches. L1 is …

LM380, Simple 2 Watts Audio Amplifier

Small audio amplifier is useful for audio troubleshooting or simple audio projects. It should be a low cost and easy to build. Using integrated circuit for this purpose is the right choice. With LM380  audio amplifier integrated circuit, 2 Watts power can be delivered. For better thermal endurance, a large copper track can be printed …

Simple Theremin with Inverter Gates

This simple but complete Theremin circuit is constructed using only two inverter chip plus one regulator IC. This Theremin circuit consist of five functional blocks: power supply regulator, hand controlled oscillator, null oscillator, mixer, and filter. Here is the complete schematic diagram:     Voltage Regulator and Circuit Protector The power supply regulator consist of …