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Class D Switching Power Amplifiers and Power D/A conversion

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Old 10th October 2007, 04:55 PM   #1
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Default Another classd from Tekko Audio Labs

Im once again working on a class d, iŽd revisiting the sigma delta class d that at first try failed.

This is the one i tried building but failed: http://ece.wpi.edu/analog/mqps/ClassD_MQP_Final.pdf

Now i built this: http://diymania.hv4all.com/sigma%20d...amodulator.PNG and it works nicely, apart from a slight beep, which i blame on a crappy layout on a breadboard with no bypass caps what so ever on the rails.

It runs off a TL074, a 74HC74 with a 8MHz clock and uses a TC4422 as output device. The output filter is yet a dc choke, gonna wind a proper choke later on.

What do you think, worth to continue to work on ? It does sound very good for what it is.
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Old 11th October 2007, 11:25 AM   #2
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Full schematic:
Click the image to open in full size.
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Old 11th October 2007, 06:25 PM   #3
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Tekko: Drop the 1 bit quantiziser, it will only increase quantization noise. Simply short it out, then you are in better shape.
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Old 11th October 2007, 07:04 PM   #4
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Now i have improved this thing quite a bit.

Only background nice that is hearable now is a faint hum that i dunno where it comes from since this thing runs off a smps.

Sound is very good for beeing a quick lashup on a breadboard

It looks like this: http://diymania.hv4all.com/sigma%20d...ator/sdamp.wmv
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Old 12th October 2007, 01:06 AM   #5
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Quote:
Originally posted by Lars Clausen
Tekko: Drop the 1 bit quantiziser, it will only increase quantization noise. Simply short it out, then you are in better shape.
I did as you suggested, modeling it with LTSpice. In fact I left out the quantizer and the power driver. Sure enough, it works. Is that all there is to a self-oscillating Class-D?

What determines the modulation frequency?
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Old 12th October 2007, 02:00 AM   #6
fdeck is offline fdeck  United States
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Also, thanks Tekko for the interesting circuit.
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Old 12th October 2007, 08:53 AM   #7
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This amp is now stereo and sounding good, but since its a breadboard, the channels interfer with each other = hissing.

Nope i dident drop the quantizer. Removing it would make this a standard self oscillating pwm amp, not delta sigma as it is now.

Im ny case the TL074 limits freq to 2MHz, should be 4MHz, clock is 8MHz as stated before.
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Old 12th October 2007, 05:16 PM   #8
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Here are some measurements:

http://diymania.hv4all.com/sigma%20d...mp%20measures/
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Old 13th October 2007, 07:46 AM   #9
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These results are quite good for a first-order loop. Are you going to increase the loop order ? Do you intend to add dither ? Have you somehow determined the average switching frequency when driven by an input signal ?

Regards

Charles
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Old 13th October 2007, 10:21 AM   #10
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I have thought of adding more stages, dithering i dunno what that is really.
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