Another classd from Tekko Audio Labs

Tekko · 10th October 2007, 05:55 PM

Im once again working on a class d, i´d 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.

Tekko · 11th October 2007, 12:25 PM

Full schematic:

Lars Clausen · 11th October 2007, 07:25 PM

Tekko: Drop the 1 bit quantiziser, it will only increase quantization noise. Simply short it out, then you are in better shape.

Tekko · 11th October 2007, 08:04 PM

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

fdeck · 12th October 2007, 02:06 AM

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?

fdeck · 12th October 2007, 03:00 AM

Also, thanks Tekko for the interesting circuit.

Tekko · 12th October 2007, 09:53 AM

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.

Tekko · 12th October 2007, 06:16 PM

Here are some measurements:

http://diymania.hv4all.com/sigma%20d...mp%20measures/

phase_accurate · 13th October 2007, 08:46 AM

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

Tekko · 13th October 2007, 11:21 AM

I have thought of adding more stages, dithering i dunno what that is really.

10th October 2007, 05:55 PM	#1
Tekko diyAudio Member Join Date: Jan 2005	Another classd from Tekko Audio Labs Im once again working on a class d, i´d 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.

11th October 2007, 07:25 PM	#3
Lars Clausen diyAudio Member Join Date: Oct 2003 Location: The Lab	Tekko: Drop the 1 bit quantiziser, it will only increase quantization noise. Simply short it out, then you are in better shape. __________________ www.newclassd.com

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11th October 2007, 12:25 PM	#2
Tekko diyAudio Member Join Date: Jan 2005	Full schematic:

11th October 2007, 08:04 PM	#4
Tekko diyAudio Member Join Date: Jan 2005	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

12th October 2007, 03:00 AM	#6
fdeck diyAudio Member Join Date: Feb 2006 Location: Wisconsin	Also, thanks Tekko for the interesting circuit.

12th October 2007, 09:53 AM	#7
Tekko diyAudio Member Join Date: Jan 2005	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.

12th October 2007, 06:16 PM	#8
Tekko diyAudio Member Join Date: Jan 2005	Here are some measurements: http://diymania.hv4all.com/sigma%20d...mp%20measures/

13th October 2007, 08:46 AM	#9
phase_accurate diyAudio Member Join Date: May 2002 Location: Switzerland	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

13th October 2007, 11:21 AM	#10
Tekko diyAudio Member Join Date: Jan 2005	I have thought of adding more stages, dithering i dunno what that is really.

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