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Class D Switching Power Amplifiers and Power D/A conversion

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Old 12th May 2006, 03:51 PM   #31
bck2diy is offline bck2diy  United States
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Sorry for the confusion :-) I calculated for a scenario of about 60V DC between one of the rails and GND:

1. Using a 10k resistor to bleed, say, 2x10,000uF capacitors would require the resistor to be rated atleast 1/2W (double that to 1W) and it would take about 35 minutes

2. Using a 1k resistor for the same would require the resistor to be atleast 4W (double - 8W) but the time taken would drop to about 4 minutes

I am going for a longer discharge time so my final choice would be closer to option 1 (use a 2W or higher rated resistor as you suggested).

-bck2diy
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Old 12th May 2006, 05:26 PM   #32
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I would just use a small power resistor across the terminals and de-rate it, i.e. use a 1W resistor but choose the resistance such that it only dissipates 0.5W.

You don't need to it discharge quicker than a good few minutes.
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Old 12th May 2006, 07:45 PM   #33
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Default Discharging caps

Quote:
Originally posted by bck2diy
Sorry for the confusion :-) I calculated for a scenario of about 60V DC between one of the rails and GND:

1. Using a 10k resistor to bleed, say, 2x10,000uF capacitors would require the resistor to be rated atleast 1/2W (double that to 1W) and it would take about 35 minutes

2. Using a 1k resistor for the same would require the resistor to be atleast 4W (double - 8W) but the time taken would drop to about 4 minutes

I am going for a longer discharge time so my final choice would be closer to option 1 (use a 2W or higher rated resistor as you suggested).

-bck2diy

Discharging to safe levels and not to zero is what you are after. The times you stated are much longer than to a safe level. Even 6 time constants should be conservative and would give a time value 1/2 what you called out. This exercise does give one a good feel of just how much energy is stored in these caps. Certainly not something you want to dump across your test probe!
Roger
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Old 13th May 2006, 11:53 PM   #34
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Default synchronicity

strangely, i am in the exact same boat.

i have a circuit quite similiar to your last one, although
i am using some 42000uF 90V caps i have lying around.
for what it is worth, i am slowly grinding my way through
making a small PC board for everything other than the big
caps (standard "use anything from the Mouser catalog" project).

although i am unsure when they would be ready
(i intend to use a commercial pc fab), i'd be happy
to share them with you.

andrew
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Old 21st May 2006, 10:28 AM   #35
Bgt is offline Bgt  Netherlands
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Quote:
Originally posted by bck2diy
so a single transformer does provide good channel separation (soundstaging) if the bridge circuit is done correctly? Do I correctly understand what you're saying?
Just to show you the wiring layout of a 1 transformer stereo amp. with superb soundstage. I use this for the UCD amps. and the Coldamps.



http://www.grotel.nl/photo/wiring%20...d%20stereo.jpg
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Old 21st May 2006, 11:37 AM   #36
Bgt is offline Bgt  Netherlands
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This grounding scheme did not work for me, was to much humm and a lot of crosstalk. Touching the input cable changed my soundstage completely.(UCD400's had increased gain)


http://www.grotel.nl/photo/wiring%20...%20stereo2.jpg

Just waiting for Coldamps new SMPS(model30) when finished and to try them.
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