50 Watt power Amplifier

Posted on Dec 28, 2012

This simple audio power amplifier was originally designed for a circuit board workshop, conducted by the OSU IEEE Student Group. At the workshop, 20 participants each constructed this amplifier, by etching and drilling the single sided circuit board, soldering all components, and attaching a pre-built heatsink assembly with the output transistors. Three workshops were held between 1995 to 1996. Though the design is simple, these amplifers have impressive preformance, with a frequency response to approx 40 kHz, very low noise, reasonably fast slew rate, and approx 50 watts (true `RMS` power) with the proper +/- 40 volt unregulated power supply. Someday, I'll do some substantial testing to determine exactly what the power output is, and create some more detailed pages about how to build this amplifier.

50 Watt power Amplifier
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Note: The TIP33C and TIP34C have been discontinued and are generally not available anywhere. A wide range of power transistors will work, but they should be rated for at least 100V, 8A, and 80W power dissipation. Safe area operating curves and good thermal dissipation data are rarely available, so it's a guessing game. The more expensive TO-3 package parts, such as the MJ15003 & MJ15004 will certainly be more than sufficient for replacing the TIP33C & TIP34C. The only really compelling reason to use the TIP33C & TIP34C are because they cost less and come in a TO-218 package, which requires only one mounting hole. If any of these tests fail, the amp is not constructed properly... the easiest and best way to find the problem is visual inspection. Turn variable resistor fully counterclockwise (max resistance) Connect to +/- 24 volt supply with 200mA current limit. No input and no output connected. Monitor current from power supply with a current meter. Apply power... if current is above about 25 mA, shut off immediately! Measure voltage across the 1k resistor connected to the input stage and Vcc. The DC voltage should be about 2 volt, or 2 mA of current through this resistor. Eg, if Vcc is at 24 volts, the side of this resistor connected to the 2N5210 transisor ought to be at about 22 volts. Measure the DC voltage on the output line. It should be appox zero volts. -0.2 volts is probably fine. Turn the variable resistor...

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