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Old 3rd March 2010, 03:33 AM   #31
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It's been awhile since I last posted, but I got distracted with a sub crossover I had to finish. Needed more bass.

Anyway, I got this thing working! But, not without some excitement. When I first hooked up everything, after doing the modifications, it still had problems. And upon inspection I found the MOSFETs (same ones I used last time) were IRF9510 P-Channels, not the IRF510. Fortunately, the JFETs survived. And I pulled them out and put in the IRF510s. Crazy!

Click the image to open in full size.

1kHz triangle, open loop -

Click the image to open in full size.

1kHz square, open loop -
Click the image to open in full size.

Got some ringing, and remembered I forgot to increase the gate stopper resistance like Nelson recommended.
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File Type: jpg 1kHz_Triangle.jpg (65.3 KB, 239 views)
File Type: jpg Cascode_BOZ_Fixed.jpg (140.2 KB, 238 views)
File Type: jpg IkHz_square_openloop.jpg (65.0 KB, 239 views)
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Old 3rd March 2010, 03:50 AM   #32
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I increased the gate stopper R1 to 240 ohms, which took care of the ringing. Thanks Nelson!

Click the image to open in full size.

Then I applied feedback -

Click the image to open in full size.

Works! So, now got to find a box to put it in. I'll probably just hook it up to the output of a passive preamp I have for now instead of going all out. Makes it easier to experiment with different circuits and evaluate.

I'll given listening impressions when I get that far.
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File Type: jpg 10kHz_square_OL_Fixed.jpg (62.8 KB, 242 views)
File Type: jpg 10kHz_square_CL_fixed.jpg (43.0 KB, 241 views)
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Old 3rd March 2010, 10:13 PM   #33
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Any ideas on where I can get some inexpensive project boxes? They need to be 3.5 inches high. Right now I'm thinking Hammond but welcome other suggestions.

And I neglected to mention that the second square wave responses are the open loop and closed loop at 10kHz, not 1kHz. For 1kHz those responses wouldn't be so good, I think. Here's what 10kHz open loop looked like before increasing the value of R1.

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Old 24th January 2011, 06:48 PM   #34
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It's been awhile, but I finally put this in a test box to see how it sounds. Only problem is I found it's noisy. Even though the power supply is real quiet, on the other side of the drain resistor is noise (MOSFET drain) it is noisy. It's at -81dBV.

I bread boarded a shunt regulator to make it even quieter ( -122 dBV ) right at the limit of what I can measure.

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