From: John Woodgate
Subject: Re: 40W bridge audio amp + signal-level crossover
Date: Mon, 9 Sep 2002 08:24:32 +0100
Organization: JMWA Electronics Consultancy
Reply-To: John Woodgate
NNTP-Posting-Date: Mon, 9 Sep 2002 20:09:00 +0000 (UTC)
X-Newsreader: Turnpike (32) Version 4.01 <5Z8C9wtxbnpWyFnyfFzqmVF739>
I read in sci.electronics.design that Paul Evans wrote
(in <firstname.lastname@example.org>) about '40W bridge audio
amp + signal-level crossover', on Sun, 8 Sep 2002:
>I require a circuit diagram / ideas to drive 40W(rms) into 8ohms. Ideally
>a bridge amp to reduce power supply requirements, but as I'm building the
>power supply as well, I can do split-rail to moderate (30v?) voltages.
>Perhaps MOSFET..? Or maybe one of those all-in-one amplifier chips..?
There are hundreds of such designs around, a few of them good. I suggest
you look at Douglas Self's designs in 'Electronics World' a few years
>Also, I'm looking to bi-amp this with a 25W tweeter... (yes, I know
>bi-amping is really for the several-hundred watt range,
No, where did you get that idea?
> but so what..?) I
>thought of making a small signal-level crossover, then feeding the HF/LF
>outputs into the two separate amps (the above, plus a 25W version). Is
>this a workable idea?
Yes, this is a very good technique. You can make much more complex and
accurate crossover filters at low level and you don't have to cope with
the filters being terminated in the fluctuating impedances of the
I've just done a tri-amp preamplifier and crossover with 4th order
Linkwitz-Riley filters. My friend who is not deaf says it sounds very
>Finally, would the tweeter in this case need a blocking capacitor, or
>would it be fine without one (for audio quality I suppose without would be
No, that crossover filter eliminates the low frequencies already, of
Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk
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