Headphone Amplifier

R1-4= 1.2Kohm R12= 4.7 ohm C8-10= 470uF 25V
R2-3= 3.9Kohm RV1= 10Kohm  Log. pot. C9-11= 100nF 100V ceramic
R5-10= 10Kohm TR1= 10Kohm Trimmer Q1-3= BC184
R6=100Kohm C1= 4.7uF 63V MKT Q2-4= BC214
R7-9= 2.2Kohm C2-7= 100uF 25V Q5= BD136 or BD538
R8= 150 ohm C3-5= 100nF 100V  MKT Q6= BD135 or BD537
R11-13= 6R8 ohm C4-6= 100uF 16V All resistors is 1/4W 1%

Balanced Microphone Preamp

Car Voltage Gauge

The Car Voltage Gauge is based on 3 parts. The input circuit is an Analog to Digital Converter (IC2 CA3162E). The purpose of this chip is to sample an analog voltage and convert it to a decimal value which is read by a Display/Decoder Driver (IC1 CA3161E). This chip will turn each seven segment display on through the driver transistor Q1 - Q3. The power is derived from the car and is converted to 5 volts by the 5 volt regulator. The circuit works as follows: The 10uf capacitor is charged up by the cars voltage. Its value is then read by IC2 and a decimal value of that voltage is provided to IC1 which multiplexes the three display units. Each display is turned on sequentially with its appropriate value displayed. The transistors Q1 through Q3 control the drive to each seven segment display. By monitoring the cars voltage with an accurate multimeter you can adjust the "Zero Adj." pot and the "Gain Adj." pot for accurate readings. LED 1 and 2 are optional. They can be used to indicate power on or can light up a cut out display that says "Volts". This can be made by a plastic module that has a thin plastic cover on it with the word "Volts" cut into it. The LED's would be mounted inside the module.

R/C Car(27 MHz)

L1, L4=9 turns, .15mm wire on 4.5mm diameter tunable ferrite coil former
L2=15 turns, .5mm wire, 5mm diameter
L3=3.5 turns, .5mm wire, 5mm diameter

Step-Up Converter (MC34063A)

This solidstate DC switch can be assembled using just three transistors and some passive components. It can be used to switch on one gadget while switching off the second gadget with momentary operation of switch. To reverse the operation, you just have to momentarily
depress another switch.


The circuit operates over 6V-15V DC supply voltage. It uses positive feedback from transistor T2 to transistor T1 to keep this transistor pair in latched state (on/off), while the state of the third transistor stage is the complement of transistor T2’s conduction state.


Initially when switch S3 is closed, both transistors T1 and T2 are off, as no forward bias is available to these, while the base of transistor T3 is effectively grounded via resistors R8 and R6 (shunted by the load of the first gadget). As a result, transistor T3 is forward biased and gadget 2 gets the supply. This is indicated by glowing of LED2.


When switch S1 is momentarily depressed, T1 gets the base drive and it grounds the base of transistor T2 via resistor R4.


Hence transistor T2 (pnp) also conducts. The positive voltage available at the collector of transistor T2 is fed back to the base of transistor T1 via resistor R3. Hence a latch is formed and transistor T2 (as also transistor T1) continues to conduct, which activates gadget 1 and LED1 glows.


Conduction of transistor T2 causes its collector to be pulled towards positive rail. Since the collector of T2 is connected to the base of pnp transistor T3, it causes transistor T3 to cut off, switching off the supply to gadget 2) as well as extinguishing LED2. This status is maintained until switch S2 is momentarily pressed. Depression of switch S2 effectively grounds the base of transistor T1, which cuts off and thus virtually opens the base-emitter circuit of transistor T2 and thus cutting it off. This is the same condition as was obtained initially. This condition can be reversed by momentarily pressing switch S1 as explained earlier.


EFY lab note. During testing, it was noticed that for proper operation of the circuit, gadget 1 must draw a current of more than 100 mA (i.e. the resistance of gadget 1 must be less than 220 ohms) to sustain the latched ‘on’ state. But this stipulation is not applicable for gadget 2. A maximum current of 275 mA could be drawn by any gadget.

credit : PRAVEEN SHANKER

Stereo 1W audio amplifier with DC volume control

The TDA7053A is an integrated stereo audio power amplifier with DC volume control in a 16-pin dual-in-line plastic package. It is designed for use in TVs and monitors but is also suitable for battery-operated equipment.

The circuit used is straight out of the data book. PCB dimensions are a tiny 43mm x 40mm (1.7” x 1.6”).


TDA7053A SPECIFICATIONS

• 4.5 - 18V supply voltage range
• 1.5A max non-repetitive peak output current
• 1.25A max repetitive peak output current
• 1.1W output power using 6V supply into 8 load
• (THD = 10%)
• 20k internal input impedance
• 210uV noise output voltage
• 20Hz to 300kHz bandwidth (typical) at –1 dB

The kit is constructed on single-sided printed circuit board. Protel Autotrax & Schematic were used.

CONSTRUCTION

Start with the two resistors followed by the small monobloc capacitor. Next comes the IC socket with the electrolytic and polyester capacitors last. Be careful to get the electrolytic capacitors in the right way around. The positive lead is marked on the overlay. The negative lead is marked on the body of the capacitor.

Solder the power and audio cables (supplied by you) directly to the pads provided on the PCB.

CIRCUIT DESCRIPTION

All the work is done internally in the IC. The internal circuit consists of a differential input stage with integrated DC volume control, two class AB output stages and a stabiliser circuit.

Resistors R1 and R2 provide a DC input impedance to ground. The input signal is AC coupled into the amplifier via capacitors C3 and C4. The output stages are a BTL (Bridge Tied Load) configuration, resulting in increased output power at low supply voltages.

The gain of each amplifier channel is controlled by the DC voltage level on pins 2 and 8. This voltage is derived from the DC supply using a simple voltage divider network of resistor R3 and potentiometer VR1. Capacitor C5 across the potentiometer provides power supply decoupling of the volume control inputs. If the DC volume control voltage falls below 0.4V the chip will switch to mute mode.

The maximum voltage gain of the amplifier is internally fixed at 40.5dB. The DC volume control has a logarithmic characteristic. The total gain can be controlled from +40.5 to –33 dB.

Due to the BTL output configuration the outputs are floating with respect to ground. Therefore the outputs of the amplifier should never be connected to ground.

Capacitors C1 and C2 provide power supply decoupling.

IF IT DOES NOT WORK

Poor soldering (“dry joints”) is the most common reason that the circuit does not work. Check all soldered joints carefully under a good light. Re-solder any that look

suspicious. Check that all components are in their correct position on the PCB. Are the electrolytic capacitors the right way round?

PARTS LIST – K107A

Resistors (0.25W carbon)

4K7 yellow violet red .........R1,2 .............................. 2

27K red violet orange .........R3 ................................. 1

Capacitors

100nF monobloc 104 ..........C1 ................................. 1

470nF polyester 474 ...........C3,4 .............................. 2

1uF 16V electrolytic ...........C5 ................................. 1

220uF 25V electrolytic .......C2 ................................. 1

Semiconductors

TDA7053A......................... IC1 ................................ 1

Stereo Audio Amplifier IC with DC volume control

Miscellaneous

Potentiometer, 10K.............VR1 .............................. 1

Single gang, PCB mounting

IC socket, 16 pin, for mounting IC1 .......................... 1

PCB, K139................................................................. 1

credit : kitsrus.com