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Analog Line Level Preamplifiers , Passive Pre-amps, Crossovers, etc.

Questions on xover and preamps.
Questions on xover and preamps.
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Old 31st March 2011, 10:13 AM   #1
jdraughn is offline jdraughn  United States
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Default Questions on xover and preamps.

I have been into home and car audio for 15 years, and more recently electronics and microcontrollers. I have a 1990 Corvette that I want to install a very high quality sound system, but I would like to design and build most of the electronics myself (xovers, amps, ect..).

I would like to build a preamp to take my signal and boost it so I don't have to turn the gains on my amplifiers up all the way.

Also, while the design is not nailed down yet, I think I want a 4-way system with a subwoofer in the rear, and tweeters, mid ranges and mid woofers in the front.

My questions are:
1. Is it feasible for me to build an active crossover with very low distortion? Circuits on the web show it basically just requires an op amp and about 4 resistors and two capacitors for a low or high pass filter.

2. Should I preamp the signal before splitting frequencies, split the signal first and then boost each one, or both?

3. More questions to come as these are answered and I learn more about this stuff.
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Old 31st March 2011, 12:22 PM   #2
Mooly is offline Mooly  United Kingdom
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Questions on xover and preamps.
It's thought of as bad practice to amplify a signal and then have to attenuate it, mainly because of the very very small noise penalty.

1. Depends on your construction abilities... and yes, basically an opamp and a few passives. Getting the values of the filter correct and realising there are many different types of filter response is a whole different thing. Look up Butterworth, Linkwitz-Riley and Chebyshev filters.

2. It's good practice as a general rule to buffer the signal... so the input characteristics of the design are known. The signal that is split and fed off to different filters should be buffered too because filters need to be fed from as low an impedance source as possible. If they are not then the source impedance driving the filter affects the actual response of the filter and causes it to deviate from the ideal.

Noise from extra opamps is a non issue in practice, just keep the impedances at sensible values.
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