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Subject: Re: Cheap 'n' nasty subwoofer amplifier
Date: Thu, 28 Nov 2002 22:22:29 +0000
NNTP-Posting-Date: 28 Nov 2002 22:22:09 GMT
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Al Borowski wrote:
> Hi everyone,
> I'm after a super simple design for a subwoofer amp. Seeing as you
> can't really hear the frequencies in question, sound quality isn't
> much of an issue. What I'd like is a design for an amp putting out
> around 100 watts RMS, with as few parts as possible. It will power a 4
> ohm subwoofer (4 ohm I can get cheaply from the local hoon shop).
> My first idea was to simply use a fast op-amp o make a non-inverting
> amplifier, and put a push pull output stage on it with a few hefty bjt
> transistors. Include a voltage divider in the feedback back loop for
> gain. I have 3 concerns:
> 1)Will the op amp's output be able to supply enough current? The gain
> for the transistors in question would be around 50ish. If I use
> darlingtons distortion will go up.
> 2)Would I need to parallel transistors? Intutition says I should for
> this power output. I just use a small emitter resistor on each bjt,
> 3)I know that there will be distortion introduced by the crossover
> region. If the highest frequency being used is ~300hz, will this be
> 4) I know that I really should bias the output trannies into
> conduction. I have seen this done in the AoE, but I'm not sure how it
> applies to op-amps.
You should also be concerned about voltage, for 100W into 4 Ohms you
need +/- 28 Volts output swing which is quite a lot for an op amp.
The link below shows a circuit which solves three of the problems you
mention, but the power output is way short of your requirements due to
limited output voltage swing on the op amp.
There are some other projects on the same site which may be of more use
To reply to me directly:
Replace the text after the@symbol with: totalise DOT co DOT uk
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