50 Watt Amplifier Circuit

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.

Parts List-
R1 - 1 - 200 Ohm 1/4 W Resistor
R2 - 1 - 200K 1/4 W Resistor
R3 - 1 - 30K 1/4 W Resistor
R5 - 1 - 1K 1/4 W Resistor
R6 - 1 - 5K 1/4 W Resistor
R7,R10 - 2 - 1 Meg (5%) 1/2 W Resistor
R8,R9 - 2 - 0.4 Ohm 5 W Resistor
R11 - 1 - 10K Pot
R12,R13 - 2 - 51K 1/4 W Resistor
R14 - 1 - 47K 1/4 W Resistor
C1 - 1 - 100uF 35V Electrolytic Capacitor
C2 - 1 - 0.011uF Capacitor
C3 - 1 - 3750pF Capacitor
C4,C6 - 2 - 1000pF Capacitor
C5,C7,C8 - 3 - 0.001uF Capacitor
C9 - 1 - 50pF Capacitor
C10 - 1 - 0.3uF Capacitor
C11,C12 - 2 - 10,000uF 50V Electrolytic Capacitor
U1,U2 - 2 - 741 Op Amp
U3 - 1 - ICL8063 Audio Amp Transister Driver thingy
Q1 - 1 - 2N3055 NPN Power Transistor
Q2 - 1 - 2N3791 PNP Power Transistor
BR1 - 1 - 250 V 6 Amp Bridge Rectifier
T1 - 1 - 50V Center Tapped 5 Amp Transformer
S1 - 1 - SPST 3 Amp Switch
S2 - 1 - DPDT Switch
F1 - 1 - 2 Amp Fuse
SPKR1 - 1 - 8 Ohm 50W Speaker
MISC - 1 - Case, Knobs, Line Cord, Binding Posts Or Phono Plugs (For Input And Output), Heatsinks For Q1 And Q2

Notes-
1. I know I skipped R4. That is not a problem :-)

2. Distortion is less than 0.1% up to 100HZ and increases to about 1% at 20kHz.

3. I haven't been able to find anyone who sells a suitable T1. You can always use two 24V 5A units in series. If you are building two amps (for stereo), then I would suggest using an old microwave transformer and rewinding it. Follow the instructions in the 12V To 120V Inverter, execpt wind 26 turns, twist a loop (center tap) and wind 26 more turns. That should work out to around 50 volts. You may need to add or remove turns depending on your transformer.

4. Q1 and Q2 will require heatsinks.

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Transformerless Power Supply

Parts List-
C1 - 1 - 0.39uF 250V Capacitor
C2 - 1 - 220uF 25V Electrolytic Capacitor
D1 - 1 - 1N4741 11V Zener Diode (See Notes)
BR1 - 1 - 1 Amp 200V Bridge Rectifier
MISC - 1 - Line Cord, Board, Wire, Case

Notes-
1. The value of C1 can be increased to increase the amount of current the circuit can supply. With the values shown, the circuit can supply up to about 15mA. Remember to increase the size of C2 also.

2. <>A different value can be used for D1 to increase or decrease the voltage as needed.

3. Please note that this circuit is not isolated from 120VAC. Because of this, the circuit must be treated with caution and encosed at all times. Do not work on the circuit (or any other circuits attached to it) when it is plugged in.

4. You may want to add a resisor in series with C1 to limit current if the circuit is plugged in and the mains is at its full voltage.

5. If you are running the circuit from 220VAC, then use a capacitor rated at greater than 400V for C1.

6. If you want isolation from the AC line, you can connect up a small isolation transformer at the inputs of the circuit. Small 600ohm:600ohm audio transformers work nicely.

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Fixed Voltage Power Supply

Parts List-
C1 - 1 - 2200uF 35V Electrolytic Capacitor
C2, C4 - 2 - 0.1uF Ceramic Disc Capacitor
C3 - 1 - 10uF 35V Electrolytic Capacitor
D1, D2 - 2 - 1N4007 Silicon Diode
BR1 - 1 - 2A 30V Bridge Rectifier
U1 - 1 - Regulator (See Notes)
T1 - 1 - Transformer (See Notes)
S1 - 1 - SPST 2 Amp Switch
F1 - 1 - 2A 250V Fuse and Holder
MISC - 1 - Heatsink For U1, Line Cord, Case, Wire

Notes-
1. Since this project operates from 120 (or 220, or 240, etc.) volts AC, it MUST be built inside a case.

2. U1 will reauire a heatsink.

3. You will need to choose T1 and U1 to match the voltage you want. Use the table below as a reference.

Output Voltage

T1U1
5V 6V, 1.5A 7805
6V 6V, 1.5A 7806
9V 12V, 1.5A 7809
12V 12V, 1.5A 7812
15V 24V, 1.5A 7815
18V 24V, 1.5A 7818

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Laser Power Supply

Parts List-
R1 - 1 - 10 Ohm 10W Or Greater Resistor
R2 - 1 - Ballast Resistor, See "Notes"
D1, D2, D3 - 3 - 1N4007 Silicon Diode
C1, C2, C3 - 3 - 0.1 uF 2000V Capacitor
T1 - 1 - 9V 1A Transformer
S1 - 1 - 115V 2A SPST Switch
MISC - 1 - Case, Wire, Binding Posts (for output), Line Cord

Notes-
1. T1 is an ordinary 9V 1A transformer connected backwards for step up.

2. R1 MUST be installed on a LARGE heatsink. A good heatsink is the metal case the supply is built in.

3. R2 Protects the laser tube from excess current. It should be soldered directly to the anode terminal on the tube. To find R2, start with a 500K 10W resistor and work down until the tube lights and remains stable.

4. If you have trouble with the tube not starting easily, use a longer anode lead that is wrapped around the tube.

5. Depending on the transformer you use, the circuit may or may not work. I cannot guarantee the operation of this circuit. Build at your own risk. Some transformers contain very few secondary windings which will quickly saturate the core and basically act like a direct short. The more secondary windings (that is, primary in this circuit) the better.

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