Archive for the ‘Audio’ Category
- Simple LDR Light Alarm
This is a light alarm circuit. This circuit uses Light dependent resistor (LDR). When there is no light fall on the LDR, the transistor driving the speaker is not turned on, because its resistance is high. When the LDR receives light, its resistance decreases and the collector of the second transistor falls. The first transistor …[Read More]
- Discrete 9-12V Microphone Pre-Amplifier
This is a microphone pre-amplifier circuit that use discrete components. The gain of this circuit is 100 and should be enough for most microphones. It is set by the ratio of the 10k resistor to the 100R. As common-emitter amplifiers, This circuit uses two directly coupled transistors. Here is the schematic diagram of circuit: Please …[Read More]
- Intercom
Below is a 2-station intercom using common 8R mini speakers. The “press-to-talk” switches should have a spring-return so the intercom can never be left ON. Power the speaker from a separate power supply is the secret to preventing instability (motor-boating) with a high gain circuit like this. An extra station (or two extra stations …
Passive Baxandall Tone Control (2 Band Equalizer)
Variation of the famous Baxandall circuit is shown in the passive circuit in figure 1. Smoothly increasing +- 6 dB/octave slope of boost or cut is the feature of this circuit. Although the “shelves” are outside the audible range with these component values, the bass and treble filters have a shelving response. The threshold and …[Read More]
Single Cell 1.5V Hearing Aid
This is a hearing aid circuit with 1.5v supply. This circuit is used to detect very faint sounds, then deliver the sounds to an 8 ohm earpiece. This circuit requires 1.5v input voltage, need only a single cell battery. Here is the schematic diagram of the circuit: This circuit can be assembled in a small …[Read More]
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