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Tekko 10th October 2007 04:55 PM

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:

Now i built this: 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 11:25 AM

Full schematic:

Lars Clausen 11th October 2007 06:25 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 07:04 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:

fdeck 12th October 2007 01:06 AM


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 02:00 AM

Also, thanks Tekko for the interesting circuit.

Tekko 12th October 2007 08:53 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 05:16 PM

Here are some measurements:

phase_accurate 13th October 2007 07:46 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 ?



Tekko 13th October 2007 10:21 AM

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

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