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Old 10th July 2007, 10:42 PM   #1
Don S is offline Don S  United States
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Default PS Audio 200 CX Revisited

I have decided to rebuild my defective PS Audio 200 CX amp. Everything will be updated but the power supply (75 volts per very stiff rail). I can use some help with the front end. The drivers and outputs are just up dates, however the front end is all new (MOSFETS). I have included a schematic of my amp so that someone might help. I have incorporated 2 of Nelson Pass idea’s. Bias feedback (from the A40) and global feedback from the drivers, not the outputs (Stasis e series). Please look it over and let me know what you think.

DonS

P.S. All inputs are appreciated!
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Old 11th July 2007, 12:04 AM   #2
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I don't know what are drawing mistakes and what aren't, but:
- Q6 mosfet is out of polarity
- feedback is 'nearly' global, it is taken from emitter of Q9- this results in high even order crossover distortion
- choice of mosfets is really bad, you need small signal ones, like from IRFDxxx series or IRFx10/IRF9x10 if you stick to IntRect. These you've chosen have too high capacitances.

regards
Adam
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Old 11th July 2007, 02:55 PM   #3
Don S is offline Don S  United States
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Adam, all but the Mosfets are drawing errors. I have fixed the drawing, and changed the devices to 610, 9610's. I thought I might have too large a device there, however I originally designed it with no drivers. I submitted it to Nelson Pass who thought that the VAS would not drive the outputs directly.

The feedback from the emitter resistor is to stabilize bias.

The feedback taken from the driver stage, not the output is global.
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Old 11th July 2007, 09:56 PM   #4
Don S is offline Don S  United States
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Default Original Schematic

The original schematic was sent to me by Paul McGowan. My question is would be does anyone want to see it, and can I post it?
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Old 11th July 2007, 11:25 PM   #5
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Have you done simulations on stability?
You can connect C2 with drain of Q6 for better stability if there are problems.
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Old 11th July 2007, 11:30 PM   #6
Don S is offline Don S  United States
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I have not done any simulations. I am going to build it this weekend. No sim software, but oscill and meters will help.

DonS
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Old 11th July 2007, 11:35 PM   #7
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good luck!
Waiting for your results.
Adam
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Old 11th July 2007, 11:55 PM   #8
Don S is offline Don S  United States
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Thanks, Adam! I will let you know how it goes.

Anyone with more experience than I please join in. That would be about everyone!

There is never a moderator when you need one. Then again no one has ask for the original schematic.

Where are all the guys that normally pop in to help. Am I doing something wrong?
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Old 13th July 2007, 12:30 AM   #9
Don S is offline Don S  United States
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Default Looking for advice!

Can some of the members that are watching this thread help look for smoked semi's before they happen? I thought this might be a good project for a simple high output amp.

I will provide board drawings and test data to all that help!

Has anyone seen or owned a 200C,X?

How about a ham at Christmas? Or any other holiday?

Help, DonS
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Old 13th July 2007, 01:34 AM   #10
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Perhaps someone could loan you some simulation software? Sometimes if you are lucky, folks just key the design in at home and simulate it for you and share the results. Perhaps someone is at home(work) with extra time?

I thought there were some freeware simulators? I have not used one yet but I'd be inclined to do so before such a build.

Looks nice. Good luck!

Shawn.
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