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Old 15th January 2014, 04:00 PM   #21
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I am not going to argue either way as I don't have the experience but this is how I was putting it together in my head. I was summing the quiescent current of each output device. So IF I could idle the outputs at .75amp I would have 3A across the 80V peak to peak or 3*.707 = 2.12A rms
2.12*2.12*8= 35.9Wrms at 8ohms?
Is this accurate?
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Old 15th January 2014, 04:08 PM   #22
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yes. that is correct.
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Old 16th January 2014, 01:42 AM   #23
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Good. Just bought a bigger fan and more heat transfer compound. I would imagine if I ran analog amp meters on the outputs I should see 3 amps at idle and during class. If the meters start to dance I will know that we are leaving class a. Too simple?
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Old 16th January 2014, 02:08 AM   #24
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no. you will only see 1.5A at idle. 3A is peak class a current.
and that is enough for 2 output pairs 0.75A*40V=30W dissipation pr output device. and a total dissipation of 120W pr ch at idle.

Last edited by AudioSan; 16th January 2014 at 02:12 AM.
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Old 16th January 2014, 10:08 AM   #25
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You would need to put meters in each rail not in the output.
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Old 16th January 2014, 12:30 PM   #26
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Thanks for your help guys. If I put the ammeters before the outputs in line with the common rail ground I think I should see the sum of all the current draw, or 3 amps at .75a per output device times 4 devices per channel.
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Old 16th January 2014, 12:51 PM   #27
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you will never see 3A at idle. 3A are peak current. with 0.75A pr device you will see 1.5A at idle. N ch devices are -40V at 1.5A. P ch devices are +40V at 1.5A.
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Old 16th January 2014, 02:16 PM   #28
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Idle current does not flow into ground, it flows from +ve rail to -ve rail. A meter in the +ve rail will show idle and jump up on +ve swings above idle, but would be idle on -ve swings above idle.
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Old 16th January 2014, 05:41 PM   #29
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Then that's what I'll do I cleaned, re-greased, and reset the transistors. Mounted a 5 inch 12v DC fan and running it at 5v. Idling at .165v a at .22 ohm emitter resistor so .75A per device.
All is barely warm to the touch with the transistors not being too hot to keep you finger on.
Pulling 4 amps per channel off the secondary winding or the toroidal and 2.3 A at 155V out of the wall.
Not sure if i need a soft start as there did not seem to be too much effort in the cold charge when firing it up. (90,000 uf).
Next, put in ammeters for fun and connect a source and speakers.
I am sharing a power supply for both channels so i will run the gauges at + and - total for both channels.
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Old 16th January 2014, 05:45 PM   #30
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Sorry, pulling 4 amps of each coil of the secondary windings.
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