class d with atch

spudspud · 18th March 2005, 02:18 PM

I’m 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.
I’ve 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

jmateus · 11th April 2005, 09:23 PM

Just curious, what did you do for PCB?
Or, on the other hand are you using perf board?

SpittinLLama · 13th April 2005, 07:43 PM

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.

rfasic · 14th April 2005, 09:07 AM

Spudspud,

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 µc (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.

Regards

spudspud · 19th April 2005, 06:01 PM

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.

spudspud · 19th April 2005, 06:05 PM

To Rfasic was that with this amp (been to your city a few times)

11th April 2005, 09:23 PM	#2
jmateus diyAudio Member Join Date: Mar 2003 Location: US, New Jersey	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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13th April 2005, 07:43 PM	#3
SpittinLLama diyAudio Member Join Date: Apr 2005 Location: In the Wild, Wild West	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.

14th April 2005, 09:07 AM	#4
rfasic diyAudio Member Join Date: Jan 2005 Location: PARIS	Spudspud, 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 µc (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. Regards

19th April 2005, 06:01 PM	#5
spudspud diyAudio Member Join Date: Mar 2005 Location: somerset	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.

19th April 2005, 06:05 PM	#6
spudspud diyAudio Member Join Date: Mar 2005 Location: somerset	To Rfasic was that with this amp (been to your city a few times)