My 10W class AB Amplifier


2011-01-16 4:34 pm
After my last post, Super Simple Class AB, i've decided to try the common approach for build amplifiers because of the inumerous illimitations that it provides. But i've some questions about stability of my amplifier and decided to spent some time over simulations.

I'm trying to find some errors or inconveniences...
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So. Ive used multisim to simulate.
What i've got from this:

10W RMS @ 8 ohm 1Vpp input
THD 0,04% typ @ 100hz(About 0,037%)
THD 0,04% typ @ 1khz
THD 0,06% typ @ 10khz
2,5W dissipation on the power transistor

Other concern is that this amp, when deliver such potency, reachers 1,6A peak, and a stereo theorycally would push 3,2A from the power supply.

I've a transformer 12+12 @ 3A and idk if i can use it to this project because 2 amplifiers overload a little bit the specification. This can be compensated with a good bank of capacitors?

I'm open for suggestions guys!
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2007-10-10 5:21 pm
I've built almost identical amps many moons ago, and run 2 channels from a standard 25.2VCT/2A transformer. No problems overheating, even running it to distortion.

Use the TIP41/42 output pair instead of the 31/32. They'll sound better at 4 ohms load and withstand momentary output shorts. And typically don't cost much more.
It is a pretty good amplifier.
Eventually you will get some DC-offset at the output.
Because you have 22k+2.2k vs. 27k at the other side.
Can be fixed using 22k+2.2k in the feedback instead of 27k.

If you use BC547B and 557B transistors you will increase gain and get a bit lower THD.
Best is if you use BC550C and BC560C transistors.
A = low gain, hfe
B = better gain
C = best gain
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2011-01-16 4:34 pm
Why not make it better? :)

Thanks for all the considerations!

Let's go. For real, i don't know where i was with my head using the BD140 as the VAS current source, that was no need, the current over there is just 10 mA, and i was losing performance with a low gain medium power transistor like this one.

My supplier doesn't have the BC550/560, instead, i've used BC549/559 similar complementary pair

The result is absolutely AMAZING!

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For maximum output 10W RMS & 1,1 Vpp Input

100Hz THD 0,02% typ @ 8Ohm
1KHz THD 0,03% typ @ 8Ohm
10KHz THD 0,05% typ @ 8Ohm

A theorically pretty daam good amplifier. Thanks to everyone who contributed. Now i'm thinking about the method of assembly this baby.
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