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Old 23rd June 2005, 08:21 PM   #1
ChevS-10 is offline ChevS-10  United States
diyAudio Member
Join Date: May 2005
Location: Appleton
Question Active Filter Questions

Here's the deal, I'm trying to filter at about 250 hz. for my 4x6 fronts. The fronts are 2-way Pioneer. I realize that the passive filters are more common but I was going through and can't find the capcitance on the 2-way highpass filter. I was wondering if the opamp would serve as a buffer between the two RC circuits? Meaning the RC circuit in the speaker and the RC circuit out in front of the opamp. Or would the combination of the internal circuits of the opamp+Rc circuit out in front+the capcitor in the speaker throw the phase of the signal into chaos?
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Old 24th June 2005, 04:13 PM   #2
ChevS-10 is offline ChevS-10  United States
diyAudio Member
Join Date: May 2005
Location: Appleton
Hope I didn't stump anyone, the thing I have a hard time believing is that with all the semi-conductors in an opamp that the one cap could possibly overcome that. One other question, that hopefully will get answered. If I want a gain of one on the Opamp do I need to apply the positive/negative DC to VCC & VEE.
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Old 26th June 2005, 06:37 PM   #3
John Sheerin is offline John Sheerin  United States
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Join Date: Nov 2003
Location: California
Use an opamp as a buffer between filter sections before the amplifier, not after. Opamps are typically not high current devices. They work better into high impedance loads (like the input of an amp, maybe 20kohms or so) as opposed to the low impedance load of a speaker (8 ohms, 4 ohms, etc.).

If you want to add on passive crossover components after the amplifier outputs, your best bet is to measure the frequency response and impedance of the two drivers you're trying to design a crossover for and then simulate the response with added components. That will let you see what adding additional components does to the repsonse.

If you want to use an active crossover (with opamps), put it before the amplifier driving the 4x6's.

To set the gain of an opamp, you need to use the correct resistors in the feedback loop. The exact details depend on whether you're using the opamp with an inverting or non-inverting input. Read the data sheet for the opamp for more details.
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