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Class D Switching Power Amplifiers and Power D/A conversion

Class D Questions
Class D Questions
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Old 6th August 2019, 12:52 AM   #11
Telnet100 is offline Telnet100  New Zealand
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Question Class D problems

Hello, and thanks --
Good Idea -- I had previously only looked at the supply voltages of Plus and Minus 75 Volts, which looked very stable; but did not check them under load, as the ESR of all the electros looked to be good.
Strange thing though, is that when separated into two amps, each one sounded quite powerful and clean. Only seems to be when You put them back into bridge mode that the problem exists.
There is something in the Bridge Output Waveform that I don't quite understand --
This was taken with an 80 Hz input, (where it seems the filtering is centred at) via the onboard preamp.
I have attached a shot of the scope view; the second shot is the RF signal as viewed at the Output Terminals -- Doesn't look that good
Thanks for all --
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File Type: jpg DSC00867.JPG (330.4 KB, 140 views)
File Type: jpg DSC00870.JPG (337.6 KB, 140 views)
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Old 6th August 2019, 07:39 AM   #12
NMOS is offline NMOS  Germany
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Quote:
Originally Posted by Telnet100 View Post
Hello
Thanks for all.
In this particular case the clocks are set to exactly the same frequency, eg; 480Khz, and as I explained, there is no way that These 2 clocks can 'Lock' to each other, as they are each only part of an Opamp and are not connected to each other in any way.
Maybe if Mackie had used a Phase Locked Loop, this problem might not exist. The existing Circuit is very simple. I have attached the circuit to help --Thanks for any help --
can you provide full schematic ?
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Old 6th August 2019, 08:07 AM   #13
Telnet100 is offline Telnet100  New Zealand
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Hello
Here is the Full Schematic -- Supply Rails are Plus and Minus 75 volts.
The Power Supply is of course Switch Mode -- Would You also like to see the Schematic of that?
Thanks for all --
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File Type: pdf Mackie 3.pdf (797.8 KB, 24 views)
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Old 6th August 2019, 07:15 PM   #14
NMOS is offline NMOS  Germany
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Quote:
Originally Posted by Telnet100 View Post
Hello
Here is the Full Schematic -- Supply Rails are Plus and Minus 75 volts.
The Power Supply is of course Switch Mode -- Would You also like to see the Schematic of that?
Thanks for all --
Yes please I like to see Schematic Power Supply too, please provide
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Old 6th August 2019, 11:19 PM   #15
Telnet100 is offline Telnet100  New Zealand
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Hello
There are 2 Switch Mode Power Supplies. Main and Auxiliary --
Attached are both --
Thanks, and Best Regards
Telnet100
Attached Files
File Type: pdf Mackie 4.pdf (495.2 KB, 15 views)
File Type: pdf Mackie 5.pdf (517.6 KB, 13 views)
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Old 7th August 2019, 06:45 PM   #16
NMOS is offline NMOS  Germany
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Quote:
Originally Posted by Telnet100 View Post
Hello
There are 2 Switch Mode Power Supplies. Main and Auxiliary --
Attached are both --
Thanks, and Best Regards
Telnet100
thanks

Problem fixed, Bridge mode working ?
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Old 7th August 2019, 10:41 PM   #17
Telnet100 is offline Telnet100  New Zealand
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Hello
The Bridge Mode is working, but only with limited Power Output and Distorted Sound.
I was waiting from some more advice on it. There are two pages of stuff about it here.
Class D is something that I do not know much about; only the principle of operation --
This is because up until now, I have only been involved with the repair of analogue amps and so forth. This current repair belongs to a Band Member who relies on His gear to make a living, and so I need to get this thing sorted.
Thanks for any help, and best regards --
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Old 11th August 2019, 08:57 AM   #18
Telnet100 is offline Telnet100  New Zealand
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Hello Again --
I decided to Drive the Output into my Fan cooled 8 Ohm Resistor Stack, and here are the results. I am Unable to drive it into clipping, but I suspect that is due to the fact that there is a Soft Limiting Stage in the front end.
The Output Waveform at 80 Hz does look clean, but with quite a bit of residual RF component. The Last Two were taken with a 100Hz input, but at a lower Power Level.
What is the artifact that you are able to see on the signal? -- Do these results appear to show a well functioning Class Bridge Amplifier?
The Measured Output on the 'scope is 90 Volts P-P, which, divided by 2 to get peak, and then Multiplied by 0.707 to get RMS, is 31.8 Volts. Divide that by the 8 Ohm Load Resistor Value, and You get 3.97 Amps RMS. Multiply 3.97A x 31.8 Volts and the result becomes 126 Watts RMS Undistorted. Where on Earth can Mackie get an Output Claim of 1000 Watts? - or am I missing something here?
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File Type: jpg DSC00857.JPG (332.9 KB, 62 views)
File Type: jpg DSC00860.JPG (321.9 KB, 60 views)
File Type: jpg DSC00862.JPG (330.1 KB, 58 views)
File Type: jpg DSC00863.JPG (321.4 KB, 12 views)
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Old 11th August 2019, 11:00 PM   #19
Turbowatch2 is offline Turbowatch2  Germany
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can you drive the load just with the +/- power supply and measure V and A at 8 ohms? so you can proof the PS is OK and the fault is at the amp section? If that is OK, IŽd go to next idea:
Seems like there is a problem when going over zero in the negative half wave. This might sound OK in SE but will distort bridged for sure. So one half of your two amps has a problem.
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Old 12th August 2019, 02:05 AM   #20
Telnet100 is offline Telnet100  New Zealand
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Hello
Thanks for that --
So what You mean: is to place an 8 Ohm resistor across each of the Plus and Minus Power Supply Rails and measure the V and I? I have some pretty big Fan Cooled Resistors that can cope with this -- It Runs Plus and Minus 75 Volts, so I guess that I'll be looking for at least 9.37 Amps Output -- Agreed? Attached is a shot of what I mean by big resistors --
Awaiting your helpful comments --
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