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Old 13th February 2009, 03:13 AM   #931
sasmit is offline sasmit  India
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drop some voltage but where ? because of track length ? if u were talking about dirty soldering tat's because of the flux once it gets cleaned it'll be shiny.
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Old 13th February 2009, 04:46 AM   #932
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LED will not drop the voltage down, but it is a noisy device, so is not preferred.
It is discussed in one thread. U will have to search for it.

Gajanan Phadte
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Old 13th February 2009, 08:23 PM   #933
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So, how would a few nV/SQR(Hz) noise of a LED affect a power supply?
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Old 13th February 2009, 08:39 PM   #934
Dr_EM is online now Dr_EM  United Kingdom
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I am sure it can be considered negligible, especially with chipamps which typically have a high PSRR
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Old 13th February 2009, 11:43 PM   #935
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Default LED connection

Another method I've seen for connecting an LED as a power on indicator is to wrap about 25 turns of small gauge wire around the power transformer. Check the voltage and adjust the turns as needed to get below the LED Vforward rating. Connect this directly to the LED and you're done. I haven't tried this, but it sounds quite easy with an open torroid.

My LED is connected to the positive rail, and doesn't inject any noise that I can hear...
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Old 14th February 2009, 01:04 AM   #936
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" ... Check the voltage and adjust the turns as needed to get below the LED Vforward rating. Connect this directly to the LED and you're done. ..."

This could be quite thrilling if you don't have a voltmeter = checking the AC volts first of course ... a small value cap can protect the LED from the power up surge, a larger cap will make a nice 'fade away" light effect on power off. A daisy chain of diodes, in series, across the fashioned coil with the LED paralleling the last two in the chain will insure proper illumination without the need of regulation ... and to prevent the coil from heating to greatly, the length & number of the diode chain may be increased ...
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Old 14th February 2009, 03:21 AM   #937
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Quote:
[i]a small value cap can protect the LED from the power up surge, a larger cap will make a nice 'fade away" light effect on power off[/B]

Very true, I've noticed that my LED takes over a minute to go dark. A gentle reminder that bleeder resistors aren't a bad idea, burnt screwdriver tips and exploding caps being the not so gentle reminder... (I built my amp with a traditional power supply)
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Old 15th February 2009, 08:55 AM   #938
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Default Here's mine

I wanted to build a rugged, small, 30 to 50 watt amp for testing speakers and casual use. Beftus (post 860) and Matjans (post 32) povided the ideas. The schematic is Rod Elliott's
http://sound.westhost.com/project19.htm
and Mick Feuerbacher’s methodology & layout was used to build the circuits http://www.dogbreath.de/Chipamps/Gai...nCardCopy.html

This is a dual channel amp, completely contained in one case about 3" tall, 5 3/4" wide, and 8" long.

I consider myself unbelievably lucky, this amp makes zero noise. No hum, no thumps, ticks, or hiss. I have no sophisticated test gear, just an old used scope and a cheap signal generator, however, the amp's output changes less that a trace's thickness from 20 Hz to about 100 kHz. I'm really pleased with it
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Old 15th February 2009, 08:55 AM   #939
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Default Here's mine (2)

Nothing on the back but power entry with fuse and switch.
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Old 15th February 2009, 08:55 AM   #940
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Default Here's mine (3)

The power supply is a traditional filter bank (although necessarily small). It consists of four 4700 µF caps, 100 v, 35 bridge rectifier & an Antek 200 VA, 22-0-22 transformer. The white rectangles at top of the pic, to the right of the transformer are the loop breaker (Elliott's design) with another 1000V-35A bridge, 10Ů/5W resistor & 0.22 µF 275V MKT cap.
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