LM567 Infrared Transmitter Circuit

This infrared transmitter use PWM (pulse width modulation).
The transmitter is equiped with LM567, tone decoder circuit. Audio signal ( at least 50mVvv ) is amplified with T1 and then it is used to modulate IC1. Infrared transmitter frequency is adjusted with P2 between 25 and 40KHz.

LM567 Infrared Transmitter Circuit

Basic Low Power AM transmitter

Basic Low Power AM transmitter

This transmitter is basic but allows transmission of audio to an AM radio. It consists of an RF oscillator operating in the AM broadcast band, together with a modulator stage, which mixes the incoming audio and the RF. A signal appears on the output, which has an AM component that can be picked up on a nearby AM radio receiver.

Basic Low Power AM transmitter

The transmitter consists of oscillator stage Q1 and modulator/buffer stage Q2. Q1 is biased via R1, R2, and R3. L1, C3, and C4 form the tank circuit with feedback network C3-C4 providing feedback to the emitter of Q1. RF voltage at the junction of C3 and L1 drives buffer/modulator stage Q2. Q2 is biased by base current produced by RF rectification in the base emitter junction of Q2. C6 is an RF and AF bypass capacitor. C9, C10, and L2 form the tank circuit for the collector of Q2. RF is taken from the junction of C9 and C10 and fed to a short-wire antenna. Audio is fed to modulator Q2 via C8 and isolation resistor R5 and mixes with the RF signal in the collector circuit of Q2, producing a signal that has sum and difference frequencies if the RF carrier and AF input  along with the carrier signal.

An AM signal appears at the collector of Q2. Audio with an RMS voltage equal to about 0.7 times the collector voltage of Q2 is needed for full modulation of the output. Because of the high level of audio needed, the modulation obtained from this circuit is somewhat limited with conventional audio sources because several volts of audio into a few hundred ohms is needed. The circuit demonstrates the principle of an AM transmitter, however, and with a suitable audio drive level, produces a well modulated AM signal.

Classic Tone Control Circuit with Low Noise Transistor

Tone control is a type of equalization used to make specific pitches or “frequencies” in an audio signal softer or louder. A tone control circuit is an electronic circuit that consists of a network of filters which modify the signal before it is fed to speakers, headphones or recording devices by way of an amplifier.Tone control allows listeners to adjust sound to their liking. It also enables them to compensate for recording deficiencies, hearing impairments, room acoustics or shortcomings with playback equipment. For example, older people with hearing problems may want to increase the loudness of high pitch sounds they have difficulty hearing.

Classic Tone Control Circuit with Low Noise Transistor

Tone control is also used to adjust an audio signal during recording. For instance, if the acoustics of the recording site cause it to absorb some frequencies more than others, tone control can be used to amplify or “boost” the frequencies the room dampens. This classic tone control circuit uses a low noise transistor model which is interesting. The transistor makes the adjustment more suitable for the person to hear. The variable resistor also plays an important role in controlling the output. In the simulation it was transformed into a voltage divider theory having 50% resistance each. Notice the blue color waveform is the control output while the black is the input. For further simulation please see Project Link.

TPA3122D2 Class D Audio Amplifier

TPA3122D2 Class D Audio Amplifier

TPA3122D2 IC is used as a class D audio amplifier and can deliver up to 15W of power at 10% distortions. The real advantage of using a class D amp, especially TPA3122 is the fact that this IC doesn’t need a heatsink because it has a high efficiency. Another great thing about it is that you can buy a $20 built-it-yourself kit or even cheaper from ebay but you need to be careful not to buy a fake one.

TPA3122D2 Class D Audio Amplifier

I discovered this IC while searching for an audio amplifier circuit that I need for the 2 x 10W/4Ω speakers received from my brother-in-law. I think that TPA3122 can provide enough power for what I need even though it can output only 8W with 1% distortions on a 4Ω speaker (something that some of you might find too low). The main reason I would choose this instead of a class A or B IC is the fact it doesn’t need a heatsink, so the whole amplifier will be lighter in weight and cheaper.

Equalized-preamp-for-magnetic-phonograph-cartridges

 Equalized-preamp-for-magnetic-phonograph-cartridges.

 Equalized-preamp-for-magnetic-phonograph-cartridges  

Audio Preamplifier with balance loudness controls

 Audio Preamplifier with balance loudness controls

 Audio Preamplifier with balance loudness controls

Pulse-Frequency Modulated Receiver

This receiver uses an IR-sensitive phototransistor (Clairex, HP, etc.) mounted in a light-tight enclosur

e with an aperture for the incoming IR beam. An optical system can be used with this receiver for increased range. A 741 amplifies the pulsed IR signal and a 565 PLL FM demodulator recovers the audio, which drives an LM386 audio amplifier and speaker.

STK4221 Audio Amplifier 2x80w

STK4221 general description:

The STK4221II IC from SANYO is a dual high power amplifier chip, preferably suited for compact high power audio applications, for example in cars and luxury transport vehicle audio systems. The chip provides a hassle free stereo output through a single package and a hand full of few external components, making the construction of this circuit rather easy and straightforward. However since the idea presented here does not include a CD or a memory card driver circuit, the input may be derived from readymade audio sources like an ipod, CD walkman, cellphone etc. The circuit discussed here is intended specifically for car audio applications and provides a simple alternative for 

making a 100 watt car stereo amplifier circuit. The diagram may be understood with the following points: An RC network formed by R5, R6 and C3, C4 together helps to reduce and filter stray frequency interferences and is therefore included at the input of the amplifiers. Capacitors C5 and C6 are the coupling capacitors used for blocking DC. The values of these capacitors are chosen such that it does not introduce high reactance levels at low frequencies. This particularly helps to reduce the influence of the input interference noises over the signal source resistance. The value of these capacitors may also be optimized for reducing the “pop” noise when power is switched ON.

STK4221 features:

• Quiescent current ICCO VCC = ±54V 20 40 100 mA
• Output power POTHD = 0.4%, f = 20Hz to 20kHz 80 W
• Total harmonic distortion THD PO = 1.0W, f = 1kHz 0.3 %
• Frequency response fL, fH PO = 1.0W, dB 20 to 50k Hz
• Input impedance ri PO = 1.0W, f = 1kHz 55 kΩ
• Output noise voltage VNO VCC = ±54V, Rg = 10kΩ 1.2 mVrms
• Neutral voltage VN VCC = ±54V -70 0 +70 mV
• Muting voltage VM -2 -5 -10 V

STK4221 circuit diagram: 

STK4221 Audio Amplifier 2x80w

STK4221 pcb layout:

STK4221 Audio Amplifier 2x80w

TDA1015 Audio Amplifier 1x4W

TDA1015 general description:

The TDA1015 is a monolithic integrated audio amplifier circuit in a 9-lead single in-line (SIL) plastic package. The device is especially designed for portable radio and recorder applications and delivers up to 4 W in a 4Ω load impedance. The very low applicable supply voltage of 3,6 V permits 6 V spplications.

TDA1015 features:

• single in-line (SIL) construction for easy mounting
• separated preamplifier and power amplifier
• high output power
• thermal protection
• high input impedance
• low current drain
• limited noise behaviour at radio frequencies

TDA1015 reference data:

• Supply voltage range VP 3,6 to 18 V
• Peak output current IOM max. 2,5 A
• Output power at dtot= 10%
• VP = 12 V; RL = 4 Ω Po typ. 4,2 W
• VP = 9 V; RL = 4 Ω Po typ. 2,3 W
• VP = 6 V; RL = 4 Ω Po typ. 1,0 W
• Total harmonic distortion at Po = 1 W; RL = 4 Ω dtot typ. 0,3 %
• Input impedance preamplifier (pin 8) |Zi | > 100 kΩ power amplifier (pin 6) |Zi| typ. 20 kΩ
• Total quiescent current Itot typ. 14 mA
• Operating ambient temperature Tamb −25 to + 150 °C
• Storage temperature Tstg −55 to + 150 °C

TDA1015 circuit diagram:

Circuit diagram TDA1015 Audio Amplifier 1x4W

TDA7490 Audio Amplifier 2 x 25W / 1 x 50W

TDA7490 general description:

The TDA7490 is a dual audio class D amplifier assembled in Flexiwatt 25 package; it is specially designed for high efficiency application mainly for TV and Home Stereo sets.  TDA7490 Audio Amplifier 2 x 25W / 1 x 50W

TDA7490 features:

• 25W + 25W OUTPUT POWER:
• RL = 8Ω/4Ω; THD = 10%
• HIGH EFFICIENCY
• WIDE SUPPLY VOLTAGE RANGE (FROM
• ±10 TO ±25V)
• SPLIT SUPPLY
• TURN OFF/ON POP FREE
• ST-BY AND MUTE FEATURES
• SHORT CIRCUIT PROTECTION ACROSS
• THE LOAD
• THERMAL OVERLOAD PROTECTION
• EXTERNALLY SINCHRONIZABLE
• BRIDGE CONFIGURATION

TDA7490 sterio circuit diagram:

TDA7490 Audio Amplifier 2 x 25W / 1 x 50W circuit diagram

TDA7490 mono circuit diagram:

TDA7490 Audio Amplifier 2 x 25W / 1 x 50W mono circuit diagram

TDA7490 sterio circuit pcb:

TDA 7490 pcb layout