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DIY Low Power Class A (or AB) amplifier suggestions
DIY Low Power Class A (or AB) amplifier suggestions
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Old 16th June 2009, 03:25 PM   #1
gareth is offline gareth  Wales
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Default DIY Low Power Class A (or AB) amplifier suggestions

Hi guys (and girls),

I would like to build myself my first Class A (maybe AB) amplifier. I have some NPN and PNP BJT's.

I have 22 of each 2N5551 and complimentary 2N5401 BJT's and would like to use these in parallel if possible. The reason for this is that i had read somewhere, sometime ago, that utilising smaller powered devices in parallel helps 'iron-out' any differences between the devices.

At most I am looking for about 30watts per channel in stereo and I have a +-35v centre tapped (secondary side) transformer with a 10.5v output (non centre-tapped). I salvaged this from a Technics Class AA amp and it has PC-OFC windings and a nice copper strip covering the windings to keep stry electromagnetics under 'control', or at least that is whatI thought it was for. The Technics amp it came from was capable of 50w/ch into 4ohm so I think it will be ok.

Thanks in advance

P.S I have other complimentary BJT's at my disposal and I would really like to try out these as my first amp, also i would really like to go down the class-a route even though they are not energy efficient. This is my firat amp and i am very anxious and excited at the same time. Thanks again
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Old 16th June 2009, 03:39 PM   #2
destroyer X is offline destroyer X  Brazil
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Default Base to emitter capacitances may be a problem

As i have never tried....do not know the result....will be watching your results.

Dx unbeatable amplifiers; https://www.youtube.com/watch?v=u4tGBiqMnzQ
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Old 16th June 2009, 03:46 PM   #3
wg_ski is offline wg_ski  United States
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Couple of things.... Class A at that power (voltage) level will overload the transformer. Unless you do some sort of advanced sliding bias like the original amp did. I doubt that trafo would be up to the task of a hotter than blazes Pass type amp. High-bias class AB maybe. But forget about paralleling a bunch of TO-92 transistors to get higher power. You would need too many of them and it's more trouble than it's worth when you consider layout and heat sinking. Paralleled TO-126 or TO-220 pairs are more practical, because you can bolt them all down to a common heat sink easily.
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