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Old 7th February 2008, 04:19 PM   #11
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This may be troublesome, but you can try to replace 6N137 with transformer (PulseEng gate driver or something else), to know for sure if it is the optocoupler that is making the noise.
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Old 7th February 2008, 04:43 PM   #12
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I'm already ordered HCPL2611 and HCPL0611 (smd version of 2611) used in PowerSoft and Crown comercial PA. But i have to wait a couple of days before i will try to change my 6N137 optocouplers. In the meantime i will try to figure out what other else is the source of the white noise...
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Old 7th February 2008, 04:43 PM   #13
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If you got a soundcard and FFT program, you can iterate the noise problem. If it is audible, then it should show up in fft below 20khz. Try to change something, then look at the fft whether it becomes louder or fainter, or if it is shifting frequency. Then you can try to approximate what is causing the problem.
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Old 7th February 2008, 05:05 PM   #14
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Thanks lumanauw for your valuable advice!
I will try this maybe tommorow, when i repaired my final stage (i'm abusing a little: +/-130v at 2 ohm, only a few minute, then...)
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Old 7th February 2008, 05:26 PM   #15
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What happen if you replace your 2 floating supply with 9V battery? Be sur to completly diconect floating PSU to avoid coupling inside transformer...If it solve your probleme, try using 2 small separate transformer...Even if you adjust flaoting power supply to same frequency of your amplifier, this do not syncronize them!
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Old 8th February 2008, 12:17 PM   #16
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Some photos of my prototype (incomplete, only power stage without floating smps...)
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Old 8th February 2008, 12:19 PM   #17
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and top:
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Old 8th February 2008, 02:05 PM   #18
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Some measurement. +/-90v, 4 ohm, 10mhz oscilloscope

TC429 out, 2v/div, 0.5uS
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Old 8th February 2008, 02:06 PM   #19
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-vcc to gnd
1v/div, 1us
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Old 8th February 2008, 02:08 PM   #20
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+vcc to gnd
1v/div, 1us
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