Circuit Schematic learn

Some lovers of High Fidelity headphone listening prefer the use of battery powered headphone amplifiers, not only for portable units but also for home "table" applications. This design is intended to fulfill their needs. An improved output driving capability is gained by making this a push-pull Class-B arrangement. Output power can reach 100mW RMS into a 16 Ohm load at 6V supply with low standing and mean current consumption, allowing long battery duration.

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Circuit diagram:

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Parts:Resistors:
P1 = 22K Potentiometer
R1 = 15K Resistor
R2 = 100K Resistor
R3 = 100K Resistor
R4 = 47K Resistor
R5 = 470R Resistor
R6 = 500R Resistor
R7 = 1K Resistor
R8 = 18K Resistor
R9 = 18K Resistor
R10 = 2.2R Resistor
R11 = 2.2R Resistor
R12 = 33R Resistor
R13 = 4.7K ResistorCapacitors:
C1 = 10uF-25V Capacitors
C2 = 10uF-25V Capacitors
C3 = 100nF-63V (PF)
C4 = 220uF-25V Capacitors
C5 = 100nF-63V (PF)
C6 = 220uF-25V CapacitorsSemiconductors:
Q1 = BC560C PNP Transistor
Q2 = BC560C PNP Transistor
Q3 = BC550C NPN Transistor
Q4 = BC550C NPN Transistor
Q5 = BC560C PNP Transistor
Q6 = BC327 PNP Transistor
Q7 = BC337 NPN TransistorMiscellaneous:
J1 = RCA Audio Input Socket
J2 = 3mm Stereo Jack Socket
B1 = 6V Battery Rechargeable
SW1=SPST Slide or Toggle Switch

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Notes:

• For a Stereo version of this circuit, all parts must be doubled except P1, SW1, J2 and B1.
• Before setting quiescent current rotate the volume control P1 to the minimum, Trimmer R6 to maximum resistance and Trimmer R3 to about the middle of its travel.
• Connect a suitable headphone set or, better, a 33 Ohm 1/2W resistor to the amplifier output.
• Switch on the supply and measure the battery voltage with a Multimeter set to about 10Vdc fsd.
• Connect the Multimeter across the positive end of C4 and the negative ground.
• Rotate R3 in order to read on the Multimeter display exactly half of the battery voltage previously measured.
• Switch off the supply, disconnect the Multimeter and reconnect it, set to measure about 10mA fsd, in series to the positive supply of the amplifier.
• Switch on the supply and rotate R6 slowly until a reading of about 3mA is displayed.
• Check again the voltage at the positive end of C4 and readjust R3 if necessary.
• Wait about 15 minutes, watch if the current is varying and readjust if necessary.
• Those lucky enough to reach an oscilloscope and a 1 KHz sine wave generator can drive the amplifier to the maximum output power and adjust R3 in order to obtain a symmetrical clipping of the sine wave displayed.

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Technical data:Output power (1 KHz sine wave):

• 16 Ohm: 100mW RMS
• 32 Ohm: 60mW RMS
• 64 Ohm: 35mW RMS
• 100 Ohm: 22.5mW RMS
• 300 Ohm: 8.5mW RMS

Sensitivity:

• 160mV input for 1V RMS output into 32 Ohm load (31mW)
• 200mV input for 1.27V RMS output into 32 Ohm load (50mW)

Frequency response @ 1V RMS:

• Flat from 45Hz to 20 KHz, -1dB @ 35Hz, -2dB @ 24Hz

Total harmonic distortion into 16 Ohm load @ 1 KHz:

• 1V RMS (62mW) 0.015% 1.27V RMS (onset of clipping, 100mW) 0.04%

Total harmonic distortion into 16 Ohm load @ 10 KHz:

• 1V RMS (62mW) 0.05% 1.27V RMS (onset of clipping, 100mW) 0.1%
• Unconditionally stable on capacitive loads
  

• Wide supply voltage range, 9V to 16V
• Large volume control range, 75 dB typical
• Tone control, ±15 dB typical
• Channel separation, 75 dB typical
• Low distortion, 0.06% typical for an input level of 0.3 Vrms
• High signal to noise, 80 dB typical for an input level of 0.3 Vrms
• Few external components required

Note:
Vcc can be anything between 9V to 16V and the output capacitors are
10uF/25V electrolytic.

If you are looking for a new hobby, here is a project which is exciting and yet so easy to construct. Imagine inviting your guests to watch the next foot ball world championship on your home theater from a small TV.

The thing which can make this possible is a lens called frensel lens.


Construction of the projector unit

The projector can be made from almost any material, cardboard being the easiest to work with. It is advisable to l make the first construction with cardboard and, after gain- ing confidence, the final case may be made of wood or decorative boards. The projector is built as shown in Fig. 1. The inside measurements A and B correspond to width and height respectively of the TV screen, the depth, is 48.25 cm and is the same for all sizes of TV sets. The rear of the case remains open. The front has a square opening where the-objective unit will slide in. The case can be made more stable by using good adhesive and masking tape around the corners and angles. Stability of the case is very important. The square opening D x D should be 30.5 cm x 30.5 cm for all TV sets above and up to 33 cm screen size.


Objective unit

This is made of same material as the projector unit. Here the front is open while the rear carries the lens. The wall thickness of the projector unit should be such that one should be able to slide this objective unit easily and horizontally, yet not so loose that it gets tilted in the square opening of the projector unit. The length E of the objective unit is 22.9 cm. The lens carrying sheet has a 14.6cm diameter hole in the center ( Fig. 1). Tape the special fresnel lens over this hole. Make sure you tape the edge of the lens only and not on the grooves as this will affect the clarity of the picture. The grooves on the lens, should always face towards the objective unit. When pushed into the projector, the grooved side should face the TV screen.  


Mirror

 Though the lens will magnify the TV picture, it will be inverted. lf the picture is vertically inverted, placing the TV set upside down can be avoided in the following manner:

I. Turn the deflection coil at the neck of the picture tube by 180 degree.

2. Alternatively, invert the terminals of the vertical and horizontal deflection coils through a slide switch as per the connection plan in Fig. 2; This will allow you to see the picture projected on giant screen or, by removing the projector unit, normally on TV by simply sliding the switch either way·as desired. If you have a 33cm transistorised portable set, ideal for  projection sharpness, you can turn the set upside down as this will not damage the set anyway. lf the picture is inverted side wise it can be remedied by inverting the vertical deflection coils. As an alternate method a mirror can be used. The mirror of 30.5 cm x 30.5 cm in size should be fixed on the projector mounting plate with the help of a mirror holder. The mirror  holder is easily made by using two wooden planks of l .27 cm x 5 cm x 30.5 cm each and fixing them at the mirror edge by contact adhesive. Now the mirror can stand vertically. The mirror should stand vertically making 450 angle to the lens. The light path through the TV projector is shown in Fig. 3. Final fixing of the mirror holder and the projector unit on a board should be done only after the final adjustments fora good. picture have been made.


Final construction

 After adjusting the TV set to obtain an upright picture,  bring the projector unit exactly in front of the TV screen. Use a supporting board of proper size and height for resting} the projector unit. Slide in the objective unit with the lens turned inside towards the TV screen and the grooved side of the lens facing the TV screen. Thereafter, place the big projector screen about 1.4m  away from, the projector, shutting off the room lights or external lights completely. Picture will be very bright only when the room is fully dark as in a cinema. Adjust the objective unit by sliding until a very sharp picture is projected on the screen. Now the screen can be moved back and forth and the objective unit adjusted again until the desired size and sharpness are obtained.

 very important point may be mentioned here. The brightness of the picture will depend on the reflective power, of the projector screen. The screen should be straight without any curve anywhere on its surface. Its bright white surface should be light reflecting type, not light-absorbing. For this reason Kodak’s Ektalit screen has been found to give picture so bright that it could be viewed even in a half-dark room.

In case of non-availability of this material similar results can be achieved by trying out small size (about 30.5 cm x 30.5 cm) smooth surfaces of different materials and painting them with different types of bright white paints. The one that gives the brightest picture can then be selected. Fix everything after the final adjustment. To give it a professional look, a black stripe can be painted on the screen to border the picture size. Allow little time to let your eyes get used to the darkness and enjoy your home cinema. To make it a realistic home cinema, an extra loudspeaker box can be placed behind the projector screen. The outside loudspeaker box and the TV loudspeaker can be easily connected in `either-or’ manner by means of a three pole jack or a slide switch. All these new switches can be fitted together on a small case or even built into the TV case. The inside walls of both objective and projector cases should be painted matt black to arrest diffused light and thereby obtain extra sharpness for the projected picture

Sensitivity and selectivity are the major concerns of a short wave enthusiast when he looks up for a receiver. Commercial communications models with superhet circuitry surely satisfy his requirements, but these are expensive. He would rather go for a homebrewed radio, being a regenerative receiver an affordable choice.

Im also a short wave listener and for some time I used my familys MW and SW tube radio, Philips brand. Then I switched to a Sony ICF-7600 with ceramic filters in the IF stages. High selectivity was attained with this radio receiver.

A Short Wave Regenerative Receiver Circuit Diagram

 I then discovered how much fun it was to build radios in my spare time, having tested a variety of designs available in books and on the web. Finally, I managed to make my own designs. One of them is shown in Fig. 1. It is a nice performer and will tune from the 22 meter international broadcasting band down to the 11 meter band.

It is best that the 100 pF variable capacitor be a vernier type. Tuning will be easier this way.

Q1 is the amplifier-detector and along with its associated circuitry forms a common collector Colpitts oscillator that not actually oscillates: it operates as a regenerative amplifier, with R9 as the reaction control. In achieving this result, the transistors input capacitance plays an important role. The oscillating mode is employed when copying CW or SSB. Otherwise, the stage should be left very near the threshold of oscillation for maximum sensitivity and selectivity.

Q2 and Q3 form a high gain audio amplifier and ample volume should be expected at the output. This is why a volume control has been included in the circuit. A high impedance crystal earphone should be used at the output.

Pictures of My Prototype:

Below a sheet of metal used as a ground system: