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From: email@example.com (N. Thornton)
Subject: Re: 40W bridge audio amp + signal-level crossover
Date: 9 Sep 2002 03:54:25 -0700
NNTP-Posting-Date: 9 Sep 2002 10:54:26 GMT
Paul Evans wrote in message news:<firstname.lastname@example.org>...
> 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..?
The all in one amp chips would be waaay easier. The catalogs usually
include at least one circuit for them too. They seem to vary a fair
bit in quality, some are very good.
Take care to get your PSU voltages right. Too high a V will drop your
amp's Power output considerably by increasing the amp's dissipation,
too low a V will reduce Pout too. Calculate correctly, and allow 2v
per rail for output tr drops for a discrete amp, or just follow the
instructions for an IC amp. Dont forget to take supply regulation into
acount when calculating PSU Vs too.
If this is beyond you I could probably spin some numbers and explain
> 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, 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?
Yep perfectly. Bear in mind your typical power ratio is in the order
of tweeter 20% and woofer 80% for a typ 2 way speaker. So 40w woofer
and 25w tweeter I would not choose myself. 10w tweeter more like.
> 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
It depends on the type of amplifier. Your filter will remove lower
rfequencies, so you dont need a cap for that. The question is the
amp's dc offset. Some amps are good enough to run with no capacitor,
many aren't and will need a cap to keep dc out of the tweeter.
Also a cap keeps dc off the tweeter when amps go faulty. And a
respectabe cap will not be a problem distortion wise, despite what
audiophools will tell you. Genuinely knowledgeable audiophiles know
that the signal goes through many far more distorting things than an
output cpacitor in any amp.
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