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Old 4th November 2011, 02:59 AM   #1
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Default Sallen-key active crossover with as few parts as possible

I'm trying to build an amplifier with active crossover for some car speakers out of a TDA8566Q.

See my most recent attempt is just a highpass with 1nF caps, a 604k feedback, and a 31.6k short from the feedback point to ground. The resistor to ground is the internal load resistance of the amplifier (60K). I'm finding the gain of the amplifier, as a whole, far higher than I expect.

I would link to a JavaCircuitSimulator simulation, but the most recent Java update on my work machine killed copy/paste, and I don't want to type out a 2000 character URL. I'll try again from home.
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Old 6th November 2011, 05:43 AM   #2
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The TDA8566 is a BTL amp with an internal gain setting of 26 dB. If that is too much for your application, you need an attenuator.

It is also a single supply amp with an internal virtual ground that cannot be accessed from the outside. An additional external feedback loop will not give meaningful results, because it cannot be referenced to that virtual ground. On such a BTL amp you would need two feedback loops anyhow.

From the above you can derive that the TDA8566 is not a candidate to build a Sallen-Key filter around. The filter needs to be completely before the amp and if a passive filter is not good enough for the purpose, you will need additional op amps.
If you've always done it like that, then it's probably wrong. (Henry Ford)
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