Childish impatience gets the best of me....

[KD6VXI]

What to do,  what to do.

Amidon order not going to be here until mid week.   Build PDM modulator,  tested into 10 ohm load,  all looks good. No way I'm going to put it to an amp without the low pass filter though.

Check USPS website,  Wednesday at the earliest.

So out comes the number 12 wire and PVC coil forms.

Will this make the solid state PDM modulator qualify as at least SEMI buzzardly?  Homebrew coils?

--Shane
KD6VXI

(everyone else talking about their projects made me think I should maybe do the same....) 

[KB2WIG]

"  SEMI buzzardly  "

Maybe you can find some of the knob and tube cloth covered wire. Wind your coils. Then you'll be buzzardly fer sure.


klc

[KD6VXI]

I did wind my coils :-)

The other dupe thread showed them.

Just finished testing,  and I'm getting a odd ringing on the waveform.   I'm going to upload some pics,  maybe someone can tell me what's up.   I have a feeling that it's just driving the audio input too hard,  but not positive.

[KD6VXI]

The pic with the coils standing up,  they are on my bench.   The horizontal ones,  the coils are mounted above a sheet of plywood.  In the spirit of Rich Measures 'Plywood Box'  8170, I decided to do the prototype of my pdm on plywood.

Here are some waveforms.   My scope and probe are both tektronix,  but the probe isn't compensated.   I noticed squarewaves are funky!

At very high levels of audio input,  I get a ringing,  as evidenced on the last pic.   Is this normal for audio overdrive,  or is there something else I should look at?

In true class E /PDM form,  I am using clip leads.   

Thanks!

Shane
KD6VXI

[N2DTS]

I am not interested in pdm rigs but love looking at peoples projects.

[Steve - K4HX]

I hear peach baskets make good coil forms.

[steve_qix]

Those are rather large coils !  What are the filter values you're using?

The air-wound PWM filter inductors are better than using cores.  Their inductance will not vary with load, unlike an inductor wound on a core.  I use air wound for most of my rigs at least somewhere in the filter, and for some of them, every inductor is air would just like yours.

Looks pretty good !!!

Regards,  Steve

[KD6VXI]

88 and 33 uhy.   With 4 and 2 uf of capacitance.   Filter values from a website.

Last night while running a triangle wave at 14 kHz,  my 4 uF cap started making great noise.   I'm guessing I'll need to parallel a few.   This setup is just a test.

The ringing was due to overdrive on the audio input.   

Pdm is pretty amazing.   Using a 28 volt HT supply,  I'm able to go from a 2 volt carrier to almost 28 volts on the scope.   The rms meter shows just shy of 8 volts.   

Can't wait to hook up an amplifier.   

--Shane
KD6VXI