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Class D Switching Power Amplifiers and Power D/A conversion

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Old 18th March 2005, 03:18 PM   #1
spudspud is offline spudspud  United Kingdom
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Red face class d with atch

Iím building a class D amplifier using the LM4651 and LM4652 chip set I intend to provide two full range and a subwoofer/ low pass channel. Power will be provided by three separate toroidal transformers to avoid crosstalk and something like 30 and 18 odd thousand uF on the board which I hope will stabilise it without regs. Any comments on this are welcome.
Iíve simulated a filter system which seems to work quite well which hopefully I can post here somewhere, but how does this affect the input resistance the main amplifier is required to see or match with the values of R1, R2 (not their ratio) and RLP, CLP should they be removed with such an active filter?
Is this a good way to take a low pass from a stereo signal?
Anyway has anybody please got any ideas on how to implement a volume control?

Cheers from spud
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Old 11th April 2005, 10:23 PM   #2
jmateus is offline jmateus  United States
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Just curious, what did you do for PCB?
Or, on the other hand are you using perf board?
JLH 2005, Cyrus and so on...
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Old 13th April 2005, 08:43 PM   #3
SpittinLLama is offline SpittinLLama  United States
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If you are using an active filter then check out the full range schematic in the LM4651/52 datasheet. The Gerbers for it are also on the National site. On this board is a pre-amp with a gain of 10V/V and a 2nd order active low pass filter. The low pass filter is set up around 22kHz, I think. I think this might answer most of your questions.

As for your other circuits have you ever seen the AN-31 App. Note from National? Lots of Op. Amp circuits in there. If you want to sum the left and right signals you could probably use the summing circuit then low pass filter them. The order of filtering and summing probably doesn't matter.
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Old 14th April 2005, 10:07 AM   #4
rfasic is offline rfasic  France
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I got rather good results with the stereo digital volume control chip from Crystal (Cirrus Logic) CS3310.

The only extra thing you need is a little Ķc (pic, 8051 etc) with
very little code inside (16 bits data on SPI bus) to control the
output level.

Some high end audio amps are using this chip too.

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Old 19th April 2005, 07:01 PM   #5
spudspud is offline spudspud  United Kingdom
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hi folks, not been here for a while, but the project is coming along fine, I've finished the power supply, we etched the boards at college as national sems data sheet shown and Ive been drilling the 273 holes per board at home for the last couple of days, I'm getting more proficient . I'm online to order some parts so best crack on, see ya later. Cheers for filter info.
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Old 19th April 2005, 07:05 PM   #6
spudspud is offline spudspud  United Kingdom
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To Rfasic was that with this amp (been to your city a few times)
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