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Old 24th January 2012, 11:07 PM   #1521
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Usually, 0.1 -0.2R is recommended. If you play at normal levels. 0.47 should work too.
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Old 25th January 2012, 06:14 PM   #1522
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I got the wiring of my power umbilical wrong and sent reversed voltage to the chips. They smoked in about 2 seconds. I installed 2 new chips fix the umbilical and it powered up fine.

I have .106 dc on both channels. It's a bit higher than the last amp i built. only difference between the two is I'm using an input resistor on the new one.

I'm wondering if the capacitors could have been damaged by having reverse polarity for a couple seconds. If so, could that cause the dc offset to be higher?
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Old 25th January 2012, 07:06 PM   #1523
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cure for mistakes like that.
fit a 1n400x diode across one of the main electrolytic decoupling caps mounted on the PCB and fit another to the other half of the dual supply.

You can also fit a 1n400x from each power rail to the output.

These 4 diodes save a lot of damage if the PSU is ever swapped around and can help with IV protected amplifiers driving dynamic (VC) speakers.
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Old 26th January 2012, 01:20 PM   #1524
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Just finished my Audio Sector kit last night and it's working wonderfully. It's a dual mono arrangement with the Twisted Pear USB receiver/DAC as the input device. I use it with my computer. I put so much capacitance in the power supply that I can flip off the power and it still plays for a while!
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Old 26th January 2012, 04:08 PM   #1525
ss007 is offline ss007  United States
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Thanks Andrew! Great tip.

I'm still curious about the reverse voltages damaging capacitors. Is that a possibility after 2-3 seconds?
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Old 26th January 2012, 06:29 PM   #1526
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Damage is very possible.
Remove at least one leg of each and reform them, noting how the reforming current varies over 24hrs.
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Old 26th January 2012, 06:38 PM   #1527
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A couple of seconds won't probably create any damage, just use them. If the cap is rounded at the top, then you should react.
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Last edited by peranders; 26th January 2012 at 06:40 PM.
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Old 26th January 2012, 07:30 PM   #1528
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Quote:
Originally Posted by peranders View Post
A couple of seconds won't probably create any damage, just use them. If the cap is rounded at the top, then you should react.
They look fine. Didn't get hot or do anything weird.
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Old 26th January 2012, 11:33 PM   #1529
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Quote:
Originally Posted by ss007 View Post
I got the wiring of my power umbilical wrong and sent reversed voltage to the chips. They smoked in about 2 seconds. I installed 2 new chips fix the umbilical and it powered up fine.

I have .106 dc on both channels. It's a bit higher than the last amp i built. only difference between the two is I'm using an input resistor on the new one.

I'm wondering if the capacitors could have been damaged by having reverse polarity for a couple seconds. If so, could that cause the dc offset to be higher?
As it was explained here: Commercial Gainclone kit- building instructions the actual offset will depend on a particular chip, and varies sometimes significantly, from sample to sample.

The caps are fine.
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Old 26th January 2012, 11:44 PM   #1530
ss007 is offline ss007  United States
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Thanks Peter
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