Simple FM Transmitter

This FM transmitter claimed to be a very good transmitter. This circuit is worked very well since this circuit is actually copied from available electronic kit.

Component part:

R1 100K R2 220K R3 22R R4 1K trimmer R5 1K R6 56K R7 1M R8 1K2 T1 BF244A or BF245A FET T2 2N3819 FET T3 BC307/8/9 or BC557/8/9 PNP

D1 Varicap diode (eg. BB119) D2 1N4148 C1 5pF ceramic C2 6pF ceramic C3 15pF ceramic C4 trimmer cap C5 15pF ceramic C6 1nF ceramic C7 100uF electrolytic C8 4.7uF electrolytic C9 100pF ceramic

Frequency range is 100-108 MHz. The circuit is only mono circuit, and accepts an audio input from either a microphone or other source. The input impedance is 1Mohm. The input sensitivity is 5mV and the max input signal is 10mV. The transmitted signal can be picked up on a FM radio. The circuit can be used for short-range transmission, eg. for wireless microphones.

The power supply to use is 9-14 V DC, one of the little rectangular 9V batteries is fine. Connect this to the + and - points on the PCB. The sound input goes to the points marked "MIKE". The antenna should be connected to the point marked "ANT". The emitter's output impedance is 50 ohms. You can make your own fancy antenna if you like.

Source: http://www.high-voltage-lab.com/77/small-radio-transmitter

50W Power Amplifier circuit based on STK-1050

Here is one of the circuit diagram of a power amplifier with the STK1050 single power chip which is supported by several components that make a better sound output. This amplifier is a single output amplifier, so if you want a stereo amplifier, then you must make a similar circuit.

STK-1050 Features:
STK1050 has some features that make it superior and good for your audio amplifier.

1. Does not require externally connected emitter resistors.
2. Values of emitter resistors have carefully been reviewed to provide superior characteristics.

• Better supply voltage utilization permits designing power supply voltage that are about 0.7V (for RL=4ohms) lower than those required for previous DPP models.
• Maximum allowable power consumption for each resistor is 5W or higher, permitting accomodation for all loads.
• Peak allowable current is 18A or more, providing an ample margin even for peak currents under when short circuited or similar emergencies.
• In particular, maximum output 4 ohms have been enormously improved.

3. Use of emitter resistors facilitates meeting different safety standards and designing PCBs
4. Mutual interferences in the high-frequency range caused by layout of externally connected emitter resistors no longer exist. This facilitates lower distortion factors.
5. Pins are used for emitter resistor output terminals that were not conected in previous DPPs. All other terminals remain uncharged; there is no need for major circuit board changes.

Download STK-1050 datasheet

One Transistor FM Radio

Thi circuit is very simple with only one transistor. No need additional active components, but if you want to hear the sound louder, just build another amplifier circuit... :)

Part designator	Part description
C1a,C1b	10 pf, 50 v, ceramic disc capacitor
C2	22 pf, 50 v, ceramic disc capacitor
C3	RF tuning capacitor
C4	330 pf, 50 v, ceramic disc capacitor
C5,C8	0.001 uf, 50 v, ceramic disc capacitor
C6	0.22 uf, 50 v, film capacitor
C7	0.0047 uf, 50 v, ceramic disc capacitor
C9	22 uf, 16 v, electrolytic capacitor
D1	TL431AIZ voltage control Zener (shunt regulator)
EPH1	High impedance earphone
L2	22 uh RF choke
Q1	2N4416A JFET transistor
R1	470K, 1/4 w, resistor
R2, R3	1K, 1/4 w, resistor
R4	10K, 1/4 w, resistor
R5	1M, 1/4 w, resistor
R6	100 ohm, 1/4 w, resistor
S1	Small SPST switch
screws for C3	screws for mounting C3 (2 needed)
nylon screw	#4 nylon screw used for tuning C3
battery connector	mini battery snap

More instruction how to build this circuit, visit this page

Portable headphone amplifier circuit

This is an easy built portable headphone amplifier circuit. You can use this headphone amplifier to amplify your radio receiver, mp3/mp4 player, computer or dvd/cd player. You may connected the input channel directly to those devices.

R1 _______________ 10K
R2 _______________ 100K
R3 _______________ 68K  (see notes)
R4 _______________ 1K5
R5 _______________ 3K3
R6 _______________ 330R
R7 _______________ 4K7
R8 _______________ 2R2
C1 _______________ 1uF 63V
C2 _______________ 100uF 25V
C3 _______________ 470uF 25V
Q1 _______________ BC239C 25V 100mA NPN High-gain Low-noise Transistor
Q2 _______________ BC337 45V 800mA NPN Transistor
Q3 _______________ BC327 45V 800mA PNP Transistor
J1 _______________ Stereo 3mm. Jack socket
SW1 _______________ SPST Switch
B1 _______________ 3V Battery (2xAAA)

R3 value was calculated for headphone impedance up to 300 Ohms. Using 600 Ohms loads or higher, change R3 value to 100K.
Take a note that above circuit only show single channel.

1.2Watt Mini Audio Amplifier Circuit based KA2214

This mini audio amplifier circuit is based on power IC KA series. This mini amplifier delivers dual audio output (stereo) at 1.2W on each channel.

The KA2214 is a monolithic integrated dual audio power amplifier in a 14-pin plastic dual in line package. It is designed portable audio sets.

Download the KA2214 datasheet for detail features and specifications.

TDA2040 - 20W HI-FI Audio Amplifier

Here the hi-fi power amplifier circuit which will deliver 20W power output. This amplifier circuit use single power IC TDA2040 and a few external components.

Detailed explanation about this 20W Power Amplifier

Simple FM Radio Receiver Circuit with TDA7021T

Here the simple FM radio receiver circuit built based single IC TDA7021T.

Component Parts List:

R1 = 8kΩ2 R2 = 10kΩ R3 = 390Ω C1,C3 = 10nF C2,C6,C9,C16 = 100nF C4 = 33pF C5 = 25pF trimmer (Murata type TZB4Z250AB10R00) C7,C10 = 1nF5 C8 = 820pF

C11 = 1nF C12 = 68pF C13 = 220pF C14 = 47μF 10V (Nichicon UWX1A470MCL1GB 5.5mmL chip type) C15 = 3nF3 L1 = 36nH (4 turns 0.5mm silver-plated wire, inside diameter 4mm; length 7mm) L2 = 1μH, SMD case 0805 (fres > 300 MHz) IC1 = TDA7021T (SMD in SO16 case)

Complete explanation, visit this site

AM Receiver circuit with MK484

This is a AM Receiver with single IC MK484. If your are interested to build this radio circuit, you may buy the kits include the component part list at kitsrus.com.

Part list:

R9, R10_________ 6R8 R6_____________ 100R R3_____________ 1K R1_____________ 4K7 R7_____________ 5K6 R4_____________ 10K R2_____________ 100K R5_____________ 150K R8_____________ 820K Pot_____________ 10K log pot Coil & ferrite bar set

C7______________ 470p ceramic C, C4, C5, C6_____ 470nF monoblock C2______________ 100nF monoblock C3, C8___________ 100uF electrolytic capacitor VariCap__________ 60/160 AM tuning cap D1, D2, D3, D4____ 1N4148 diode Q1, Q3___________ BC548 Q2______________ BC558 IC1_____________ MK484 AM radio IC TO92 Speaker__________ 0.5 or 1W, 8 ohm speaker

Visit this AM Radio Receiver for more explanation.