From: email@example.com (Bob Wilson)
Subject: Re: 40W bridge audio amp + signal-level crossover
Date: Thu, 12 Sep 2002 03:04:17 -0000
Organization: Your Organization
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In article <firstname.lastname@example.org>, email@example.com
>On Mon, 09 Sep 2002 06:15:44 -0000
>firstname.lastname@example.org (Bob Wilson) wrote:
>> Mosfet or bipolar, it is irrelivant. The voltage needed are essentially
>> related to your load impedance and your desired power level only. Your
>> rail voltage needs to be theoretically 50 Volts (plus a little headroom
>> for the transistors to work) for a non-bridged topology. So, say 60
>> Volts, or +/- 30V for a split rail.
>I do believe I said bridge mode :) Can I safely say halve this? 0 to 60
>non-bridged is the same as -30 to 30 bridged, no?
No, of course not. In both cases, the amplifier has 60 volts across its
rails. "Bridging" is NOT splitting the power supplies (i.e. changing a 0-60
suply to a pair of rails that are -30 and +30. To the amplifier, these are
the same thing). Bridging is the process of driving 2 identical amps
anti-phase, and connecting a speaker BETWEEN their outputs. A pair of
bridged amps is theoretically capable of outputting 4x as much power as one
amp operating from the same supply voltage (the speaker sees double the
drive voltage, and power output is V^2/R). In practice, it is a lot less
>> Sure it is workable. This is what bi-amping is all about. Even 25 W to a
>> tweeter is a hell of a lot of power. Probably far too high.
>Really? I only say that because the driver is rated at that. Do you think
>I should run it below that; say 15W?
You don't have any choice at what power you "run it". This is determined by
the high frequency content of your music, and the volume level you play it
at. My point is that normal music at an overall power output of only 40
Watts, most certainly does not contain more than a few watts of high
frequency content. Most of the output power is in the sub 2KHz range
(actually, below a few hundred Hz).
>> A blocking cap is simply a poor man's high pass crossover for a tweeter.
>> If you are bi-amping the tweeter, the crossover is already taken care
>> of, and a blocking cap will be useless (there will be nothing to
>Not even a small DC offset due to bad amp design? Or to guard against a
You aren't concerned about this when connecting a woofer, so why are you so
concerned about the effects of an amp failure on the tweeter? Both are
simply 8 Ohm pieces of wire. If you have a "bad" amp design or a failure,
any directly connected speaker can be toast.