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Old 24th January 2007, 10:55 PM   #1
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Default resistor values for lifting ground AND LED

The Aikido saga continues......

Thanks to Sy who suggested a resistor ground lift and Jayel who sent me a layout for one using a cap and bridge, I got the hum down to negligible levels. My wife claims not to be able to hear it.....but I can!!!!

OK, so it is not bothersome at all, but it is there. I used a 10 ohm resistor, 0.1uF cap and 35A 600V bridge to lift the ground loop.

If I replaced the 10 ohm with a 20 ohm, would it likely lower the hum further?

Ordinarily I wouldn't bother too much about it, but I have to order to Vishay resistors to make a pre-attenuator for my stepped attenuator. Mouser will hit me with the same shipping cost even if I buy only $1.50 worth of resistors, so I can easily order a few more high wattage resistors for the ground-loop isolator.

Now for the LED part.

I have a nice tube delay circuit that pre-warms the heaters prior to switching on the B+ The delay is 30 seconds, and I thought that it would be nifty to have a blue LED come on when the B+ gets switched on. I found a circuit that uses 115VAC to power an LED, coupled with a diode to account for the other half of the cycle.

Would this work? Would blue look too much of a cliche (I have one on my main amp and love it)? Are LED's considered passe? Should I not care about other folks opinions of aesthetics?

Thanks,
Charlie
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Old 24th January 2007, 11:46 PM   #2
mach1 is offline mach1  Australia
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I use a yin-yang diode (just wire two diodes in parallel, in opposite directions) ground lift arrangement a la John Camille. You can use diode bridges as well, placing two diodes in series on both the yin and the yang leg.

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