2N3055 Power Amplifier

[audioguru]

This project http://www.electronics-lab.com/projects/audio/042/index.html is a nice, simple amplifier that uses bootstrapping to increase its positive-going output swing to maximum.

Its idle current is adjustable with the 500 ohm pot to operate the output transistors in class-AB for reduced crossover distortion. However, the idle current is increased by increased temperature of the output transistors, so I recommend that the BC107 (BC547) be mounted in tight thermal contact with the heatsink (using thermal grease) of the 2N3055 output transistors. ;D 

[MP]

That is pretty standard for this type of amplifier. I am surprised the author did not have more comments like this regarding the build. Looks like a language barrier, reading through the document. Glad you mentioned it. It should be beneficial for someone building the project.

MP

[hti97088]

hi every one
for this project i want to ask if i need more output power can i put more 2N3055 in cascaded mode or there is any other opnion?

[audioguru]

Hi Hti,
With a 60V supply, this amp can deliver about 45W to an 8 ohm speaker or about 80W to a 4 ohm speaker at clipping.

Cascaded transistors are connected in series, which won't accomplish anything.
If you add additional 2N3055 transistors in parallel with the existing ones, using emitter resistors to equalize their different current gains, then the amp won't provide any more power to an existing speaker. Added transistors will provide more current, if you add a speaker in parallel with the existing one. Then the driver transistors will be overloaded.

For an amplifier to provide more power to an existing speaker the voltage swing to the speaker needs to be increased, which automatically increases the current. There are two ways to increase an amp's voltage swing:
1) Use a higher supply voltage, high voltage transistors to match and paralleled transistors to handle the increased current.
2) Bridge two high-current amps so that the speaker is driven at both ends with out of phase signals. The output power is tripled. ;D