Bench Amplifier

Description: A small 325mW amplifier with a voltage gain of 200 that can be used as a bench amplifier, signal tracer or used to amplify the output from personal radios, etc. Circuit diagram Notes: The circuit is based on the National Semiconductor LM386 amplifier. In the diagram above, the LM386 forms a complete non-inverting amplifier with voltage gain of x200. A datasheet in PDF format can be downloaded from the National Semiconductor website....

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Low impedance microphone amplifier

Description The circuit is a microphone amplifier for use with low impedance (~200 ohm) microphones. It will work with stabilized voltages between 6-30VDC. If you don't build the impedance adapter part with T1, you get a micamp for higher impedance microphones. In this case, you should directly connect the signal to C7. Schematic diagram...

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Amplifier of acoustic frequencies with preamplifier

Technical characteristics:Tendency of catering: 15V Force of expense: 4,2Wrms in the 4W Minimal signal of entry: 94mVp-p with preamplifier, 0,65Vp-p without the preamplifier. Circuit diagram...

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Three-Level Audio Power Indicator

Battery-operated 3 LED display Simply connect it to loudspeaker output Circuit diagram...

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Audio Perimeter Monitor

Circuit diagram Notes: Using a single cable such as speaker wire or doorbell cable, this circuit can be remotely positioned, for example, at the bottom of a garden or garage, and used to detect all sound in that area. The cable can be buried in a hosepipe or duct and is concealed out of sight. The mic is an ordinary dynamic mic insert and should be housed in a waterproof enclosure with the rest of the circuit. The mic output is amplified by the...

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FET Audio Mixer

This simple circuit mixes two or more channels into one channel (eg. stereo into mono). The circuit can mix as many or as few channels as you like and consumes very little power. The mixer is shown with two inputs, but you can add as many as you want by just duplicating the "sections" which are clearly visible on the schematic. Circuit diagram...

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Portable Microphone Preamplifier

circuit diagram...

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Electronic Stethoscope

Stethoscopes are not only useful for doctors, but home mechanics, exterminators, spying and any number of other uses. Standard stethoscopes provide no amplification which limits their use. This circuit uses op-amps to greatly amplify a standard stethoscope, and includes a low pass filter to remove background noise. Circuit diagram Parts: R1 10K 1/4W Resistor R2, R3, R9 2.2K 1/4W Resistor R4 47K 1/4W Resistor R5, R6, R7 33K 1/4W Resistor R8 56K...

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Precision Audio Millivoltmeter

Measures 10mV to 50Volt RMS in eight ranges Simply connect to your Avo-meter set @ 50uA range...

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Electronics Attenuator

circuit diagram Two low voltage, low power zeners are used to control electronically the level of an audio signal. The attenuation range is from 6 to 58dB for an input current from 0.042 to 77 mA corresponding to a control voltage from 2.7 to 7.5V. If control voltage is limited to 5V, the attenuation is around 30dB at a control current of 2mA. This is not an HiFi attenuator but might come useful as a general purpose audio attenuato...

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Stereo Tube Amplifier

The circuit is simple, yet is capable of excellent performance. I designed it specifically for use as an amplifier for the digital sound card in my computer. Audio input can be from any two-channel line level device such as a television, CD player, or VCR. It is of the tube type, using only 5 tubes total with no more than about 45 Watts power consumption from the outlet. It uses 3 types of tube 1 5Y3 GT vacuum rectifier, 2 6SF5 GT high-mu triodes, and 2 6K6 power beam amplifiers. These are all full-size octal type tubes which are commonly available...

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Mini-box 2W Amplifier

Designed for self-powered 8, 4 & 2 Ohm loudspeakers Bass-boost switch Circuit diagram: ...

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Headphone Amplifier

High Quality unit. No need for a preamplifier. circuit diagram...

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Phono Preamplifier

circuit diagram...

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Speaker Box Audio Amp

Design Philosophy I did this design after getting a new computer. After buying the processor, monitor, and printer, I wasn't willing to spring for a set of speakers too. After going "soundless", I decided to add speakers. Of course, this was the perfect excuse warm up the soldering iron to try out a new design. This original design is a variation on a well-known design, examples of which can be found in a great many texts. My variation was to add...

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Amplifier Timer

Turns-off your amplifier when idle for 15 minutes Fed by amplifier tape-output Circuit diagram...

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3 Line Mixer

This project is a 3 or more lines mixer. For more than 3 inputs you can repeat the input parts (P=10K R=22K). It powered with 9Vdc...

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22 Watt Audio Amplifier

The 22 watt amp is easy to build, and very inexpensive. The circuit can be used as a booster in a car audio system, an amp for satellite speakers in a surround sound or home theater system, or as an amp for computer speakers. The circuit is quite compact and uses only about 60 watts. The circuit is not mine, it came from Popular Electronics. Circuit diagram...

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Amplified Ear

circuit diagram...

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Guitar Amplifier

10W Old-Style ultra-compact Combo Two inputs - Overdrive - Treble-enhancement Circuit diagrams:...

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3 Channel Spectrum Analyzer

This 3 channel 15 LED spectrum analyzer is the perfect addition to any audio amp project. It produces fantastic displays on three LED bars that can be individually adjusted for any particular frequency range. The circuit will take line level output from most any audio source, and operates on 12V DC. This means that it can even be run in a ca...

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Motorola Hi-Fi power amplifier

This is a very simple, low cost, Hi-Fi quality power amplifier. You can build it 5 ways, like it’s shown in the table (from 20 W to 80 W RMS). Some comments: - The first thing that you must do, is to measure the end transistors (T3 and T4) amplifying coefficient, the hfe or β. If their disagreement is bigger than 30 %, the amplifier would not give a clear sound. I used MJ3001 and MJ2501 transistors, and this disagreement was around 5%. - Before the first “turning on” you must short circuit the inputs of the amp, and put a mA-meter on...

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Digital Volume Control

circuit diagram Circuit of a digital volume control using six discrete ICs, including a 5V regulator, is presented. IC1 (555) is configured to function as astable flip-flop. Its frequency or period may be adjusted by proper choice of resistors R44, R45 and capacitor C6 combination. Here it is for 0.3 second period. IC2 is a presetable up/down counter. In this circuit up-mode is used for increasing and down-mode is used for decreasing the volume....

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Bass-treble tone control circuit

Circuit diagram The LM1036 is a DC controlled tone (bass/treble), volume and balance circuit for stereo applications in car radio, TV and audio systems. An additional control input allows loudness compensation to be simply effected. Four control inputs provide control of the bass, treble, balance and volume functions through application of DC voltages from a remote control system or, alternatively, from four potentiometers which may be biased from...

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Amplifier 2x30W with STK465

A amplifier of acoustic frequencies can be manufactured with discernible materials, despite is known so much the difficulties of finding of materials, what the problem of regulations. These difficulties are overcome relatively easily if we find amplifier in form completed. Completed STK465 is an amplifier of acoustic frequencies that offers qualitative output, using minimal exterior elements. Substantially he is one of big completed force. Has...

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Simple Digital Volume Control

This digital volume control has no pot to wear out and introduces almost no noise in the circuit. Instead, the volume is controlled by pressing UP and DOWN buttons. This simple circuit would be a great touch to any home audio project. Schematic: Parts: C1 0.1uf Ceramic Disc Capacitor U1 DS1669 Digital Pot IC (See Notes) S1, S2 Momentary Push Button Switch MISC Board, Wire, Socket For U1 Notes: 1. U1 is available from Dallas Semiconductor. 2. S1...

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Stereo Preamplifier with Bass-boost

circuit diagram: Comments: This preamplifier was designed to cope with CD players, tuners, tape recorders etc., providing a gain of 4, in order to drive less sensitive power amplifiers. As modern Hi-Fi home equipment is frequently fitted with small loudspeaker cabinets, the bass frequency range is rather sacrificed. This circuit features also a bass-boost, in order to overcome this problem. You can use a variable resistor to set the bass-boost...

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Portable Mixer

High-quality modular design. 9V Battery powered - Very low current drawing. Design description: The target of this project was the design of a small portable mixer supplied by a 9V PP3 battery, keeping high quality performance. The mixer is formed assembling three main modules that can be varied in number and/or disposition to suit everyone needs. The three main modules are: Input Amplifier Module: a low noise circuit equipped with a variable...

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25W Mosfet audio amplifier

High Quality simple unit No need for a preamplifier circuit diagram Parts: R1,R4 = 47K 1/4W Resistors R2 = 4K7 1/4W Resistors R3 = 1K5 1/4W Resistors R5 = 390R 1/4W Resistors R6 = 470R 1/4W Resistors R7 = 33K 1/4W Resistors R8 = 150K 1/4W Resistors R9 = 15K 1/4W Resistors R10 = 27R 1/4W Resistors R11 = 500R 1/2W Trimmer Cermet R12,R13,R16 = 10R 1/4W Resistors R14,R15 = 220R 1/4W Resistors R17 = 8R2 2W Resistor R18 = R22 4W Resistor (wirewound) C1...

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Sound Level Meter

This nifty sound level meter is a perfect one chip replacement for the standard analog meters. It is completely solid state and will never wear out. The whole circuit is based on the LM3915 audio level IC and uses only a few external components. Circuit diagram Original Schematic Parts C1 2.2uF 25V Electrolytic Capacitor R1 1K 1/4W Resistor D1 1N4002 Silicon Diode LED1-LED10 Standard LED or LED Array U1 LM3915 Audio Level IC MISC Board, Wire,...

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50 Watt Amplifier

This is a handy, easy to build general purpose 50 watt amp. The amp has an input for a radio, TV, stereo or other line level device. It also has a phono input for a record player, guitar, microphone or other un-amplified source. With the addition of a low pass filter at the input, it makes a great amp for a small subwoofer. circuit diagram parts R1 200 Ohm 1/4 W Resistor R2 200K 1/4 W Resistor R3 30K 1/4 W Resistor R5 1K 1/4 W Resistor R6 5K 1/4...

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Sound Level Indicator

This project uses an LM3915 bar-graph IC driving two sets of ten LEDs for a 30dB range. The circuit is unique because it has an additional range of 20dB provided by an automatic gain control to allow it to be very sensitive to low sound levels but it increases its range 20dB for loud sounds. The LEDs are operating at 26mA each with the brightness control at maximum, which is very bright. The circuit has a switch to select the modes of operation:...

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10W Mini Audio Amplifier

finished device Componets Layout PCB Componets List R1 : 6 Ohm R2 : 220 Ohm R3 : nothing R4 : 10 KOhm pontesiometer C1 : 2200 uF / 25V C2 : 470 uF / 16V C3 : 470 nF / 63V C4 : 100 nF C5 : nothing C6 : nothing IC1 : TDA 20...

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Speaker Microphone Circuit

Description: This circuit takes an ordinary loudspeaker and allows it to be used in reverse, as a microphone. Circuit diagram Notes: This circuits allows you to use a cheap loudspeaker as a microphone.Sound waves reaching the speaker cone cause fluctuations in the voice coil. The voice coil moving in the speakers magnetic field will produce a small electrical signal . The circuit is designed to be used with an operating voltage between 6 and 12...

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Automatic Loudness Control

circuit diagram: Parts: P1 10K Linear Potentiometer (Dual-gang for stereo) R1,R6,R8 100K 1/4W Resistors R2 27K 1/4W Resistor R3,R5 1K 1/4W Resistors R4 1M 1/4W Resistor R7 20K 1/2W Trimmer Cermet C1 100nF 63V Polyester Capacitor C2 47nF 63V Polyester Capacitor C3 470nF 63V Polyester Capacitor C4 15nF 63V Polyester Capacitor C5,C9 1µF 63V Electrolytic or Polyester Capacitors C6,C8 47µF 63V Electrolytic Capacitors C7 100pF 63V Ceramic Capacitor IC1...

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18W Audio Amplifier

circuit diagram Amplifier parts: P1 = 22K Log.Potentiometer (Dual-gang for stereo) R1 = 1K 1/4W Resistor R2 = 4K7 1/4W Resistor R3 = 100R 1/4W Resistor R4 = 4K7 1/4W Resistor R5 = 82K 1/4W Resistor R6 = 10R 1/2W Resistor R7 = R22 4W Resistor (wire wound) R8 = 1K 1/2W Trimmer Cermet (optional) C1 = 470nF 63V Polyester Capacitor C2,C5 = 100uF 3V Tantalum bead Capacitors C3,C4 = 470uF 25V Electrolytic Capacitors C6 = 100nF 63V Polyester Capacitor D1...

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60W Bass Amplifier

Low-cut and Bass controls Output power: 40W on 8 Ohm and 60W on 4 Ohm loads Amplifier circuit diagram: Amplifier parts: R1 6K8 1W Resistor R2,R4 470R 1/4W Resistors R3 2K 1/2W Trimmer Cermet R5,R6 4K7 1/2W Resistors R7 220R 1/2W Resistor R8 2K2 1/2W Resistor R9 50K 1/2W Trimmer Cermet R10 68K 1/4W Resistor R11,R12 R47 4W Wirewound Resistors C1,C2,C4,C5 47µF 63V Electrolytic Capacitors C3 100µF 25V Electrolytic Capacitor C6 33pF 63V Ceramic Capacitor C7...

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Ultrasonic Dog Whistle

It's well known that many animals are particularly sensitive to high-frequency sounds that humans can't hear. Many commercial pest repellers based on this principle are available, most of them operating in the range of 30 to 50 kHz. My aim was, however, to design a slightly different and somewhat more powerful audio frequency/ultrasonic sound generator that could be used to train dogs. Just imagine the possibilities - you could make your pet think...

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10W Audio Amplifier with Bass-boost

circuit diagram Parts: P1 22K Log.Potentiometer (Dual-gang for stereo) P2 100K Log.Potentiometer (Dual-gang for stereo) R1 820R 1/4W Resistor R2,R4,R8 4K7 1/4W Resistors R3 500R 1/2W Trimmer Cermet R5 82K 1/4W Resistor R6,R7 47K 1/4W Resistors R9 10R 1/2W Resistor R10 R22 4W Resistor (wirewound) C1,C8 470nF 63V Polyester Capacitor C2,C5 100uF 25V Electrolytic Capacitors C3,C4 470uF 25V Electrolytic Capacitors C6 47pF 63V Ceramic or Polystyrene...

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High Quality Intercom

Description: A very high quality intercom, which may also be used for room monitoring. Circuit diagram Notes: This circuit consists of two identical intercom units. Each unit contains a power supply, microphone preamplifier, audio amplifier and a Push To Talk (PTT) relay circuit. Only 2 wires are required to connect the units together. Due to the low output impedance of the mic preamp, screened cable is not necessary and ordinary 2 core speaker...

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