veerman@winston.UUCP (Maarten Veerman) (12/04/86)
I am putting together a new stereo system for my car. I have a head unit with tone controls, balance control, fader control, etc. It has 2 stereo (4 total) outputs, two for front, and two for rear. I plan to use two power amplifiers, one for the bass, and one for the mid & tweeter. The problem is that I'm too cheap (8-) to spend $150 on two electronic crossover units, when I should be able to do the same with a few $ worth of passive components. I would require 2 crossovers in order to make use of the front/rear fader. I need use of the fader because I have no guarantee that with two (differently rated) amps and speakers (of unknown efficiencies) the relative volumes would be correct. Now, I could do it by connecting capacitors in series (bass) and parallel (treble) with the power amps, BUT I would like some kind of network that gives relatively flat response below the cutoff frequency, then attenuates at 12 db/octave (or better) above that, and vice versa for the other amp. Heck, I'm not even sure if that can be done in a passive circuit. I've checked in various circuit manuals in the library, but I'm still unable to come up with a satisfactory solution. It has been suggested to me to use passive crossovers between the amps and the speakers, but I am fairly sure that having each amp working with the full audio spectrum would cause them to be overworked at a time when they need not be, since only part of the output spectrum would be used. OR DOES THE LOAD GET REFLECTED BACK THROUGH THE AMP SO THAT THE AMP DOES NOT WORK WITH THE FULL AUDIO SPECTRUM ?? This question only applies when the crossover on the output blocks the unwanted part of the spectrum, instead of allowing it to bypass the speakers. Da? I'm dealing with 200 mV signals, need a cutoff of about 500 Hz, and have an input impedance of 10 k (Hey, there's no omega on this terminal! 8-) on the high frequency amp , which expects a 200 mV signal. The Bass amp has a 22 k input impedance, but only expects a 75 mV signal. (That's another reason I want use of the F/R fader.) Can anyone suggest a circuit to go between the pre & main amps, or a good reference for passive & active AUDIO circuits ? ---------------------------------------------------------------------------- Maarten Veerman (CONFUSED & FRUSTRATED) New Media Technologies Ltd. Burnaby, British Columbia @ ubc-vision!winston!veerman (604) 291 - 7111