Burning Amplifier BA-2 - Page 48

Backbones · 18th November 2010, 03:12 PM

Quote:

Originally Posted by Tea-Bag

I beleive he means using a 3-10W 2-2.2K resistor across positive to ground and from negative to ground across a set of caps in the power supply. When powered off, they will bleed down the voltage and discharge.

Doesn't Nelson already have a 2.2K, 3W resistor across the terminals as you describe, just after the rectifier? Would these not bleed down the voltage?
Regards,
Chris

Chad · 03:37 PM

Yes that is the bleed down resistor in Nelsons Power supply schematic. It can go any where in the DC voltage rails just needs to connect the DC voltage rails to the audio/ power ground. A capacitor will hold its charge for long time without them if no load is present, making for a bad day if you stick a hand in thinking everything is off. When I was in Air Force we would slightly charge a small capacitor then throw it to someone when they walked in shop door, your natural reaction was to catch it which was always good for a laugh. Another fun one was take the protection resistor out of a ground wrist/ankle strap, then when the person was wearing it we'ed take a Megger and connect it to the building ground system and send them a nice wake up shock. It would always take them a while to figure out why they where getting shocked.

Andrew described very clearly what I tried to say in my post. Both chassis have a direct earth ground and the Cl-60 connects the earth to power/audio ground in my power chassis.

Chad

bobodioulasso · 18th November 2010, 04:05 PM

Who has ever been shocked when touching 24v outlets?

AndrewT · 18th November 2010, 04:30 PM

Is that a serious question?

I read decades ago before the internet was even thought about, that with the wrong conditions a 12V car/automobile battery can kill people.

No, I don't mean throwing it from a great height!

bobodioulasso · 18th November 2010, 04:55 PM

I am sceptical.

BobEllis · 18th November 2010, 05:05 PM

Either way, the charge in the cap bank can do some damage to a circuit that you attach to it or anything conductive that finds its way across the terminals. I arced the tip off a screwdriver discharging a big cap the wrong way years ago.

bobodioulasso · 18th November 2010, 06:14 PM

Except if faulty, a class A amp discharges the caps very quickly.
I wonder if there is there an other reason to use bleeders?

BobEllis · 18th November 2010, 06:17 PM

Such as here where the PSU and amp are in different enclosures and may become disconnected.

AndrewT · 19th November 2010, 08:50 AM

or the fuse/s have blown

Chad · 21st November 2010, 01:10 AM

Hopefully some one here can help me. I want to figure out how many amps of bias current I'm drawing. Does anyone know the formula for this? Papa states in his manual that the six deep pairs using 1 ohm resistors equals 1.5 amps when biased to 250mv across the resistor. I'm running three deep pairs using .47 ohm resistors at 350mv. I'm trying to get a better understanding how this all works. My heatsinks are running cooler than Papa's 55C max but I don't want to crank the bias any more till I know what I'm doing.

Did I mention how detailed this amp sounds. Can't wait to finish the BA-1 to compare the two. I also ordered some Axon caps to compare to the Elna silks.

Chad

18th November 2010, 03:33 PM	#472
Chad diyAudio Member Join Date: Aug 2001 Location: Florida, USA	Yes that is the bleed down resistor in Nelsons Power supply schematic. It can go any where in the DC voltage rails just needs to connect the DC voltage rails to the audio/ power ground. A capacitor will hold its charge for long time without them if no load is present, making for a bad day if you stick a hand in thinking everything is off. When I was in Air Force we would slightly charge a small capacitor then throw it to someone when they walked in shop door, your natural reaction was to catch it which was always good for a laugh. Another fun one was take the protection resistor out of a ground wrist/ankle strap, then when the person was wearing it we'ed take a Megger and connect it to the building ground system and send them a nice wake up shock. It would always take them a while to figure out why they where getting shocked. Andrew described very clearly what I tried to say in my post. Both chassis have a direct earth ground and the Cl-60 connects the earth to power/audio ground in my power chassis. Chad Last edited by Chad; 18th November 2010 at 03:37 PM.

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18th November 2010, 04:05 PM	#473
bobodioulasso diyAudio Member Join Date: May 2008	Who has ever been shocked when touching 24v outlets?

18th November 2010, 04:30 PM	#474
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	Is that a serious question? I read decades ago before the internet was even thought about, that with the wrong conditions a 12V car/automobile battery can kill people. No, I don't mean throwing it from a great height!

18th November 2010, 04:55 PM	#475
bobodioulasso diyAudio Member Join Date: May 2008	I am sceptical.

18th November 2010, 05:05 PM	#476
BobEllis diyAudio Member Join Date: Sep 2003 Location: Upstate NY	Either way, the charge in the cap bank can do some damage to a circuit that you attach to it or anything conductive that finds its way across the terminals. I arced the tip off a screwdriver discharging a big cap the wrong way years ago.

18th November 2010, 06:14 PM	#477
bobodioulasso diyAudio Member Join Date: May 2008	Except if faulty, a class A amp discharges the caps very quickly. I wonder if there is there an other reason to use bleeders?

18th November 2010, 06:17 PM	#478
BobEllis diyAudio Member Join Date: Sep 2003 Location: Upstate NY	Such as here where the PSU and amp are in different enclosures and may become disconnected.

19th November 2010, 08:50 AM	#479
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	or the fuse/s have blown

21st November 2010, 01:10 AM	#480
Chad diyAudio Member Join Date: Aug 2001 Location: Florida, USA	Hopefully some one here can help me. I want to figure out how many amps of bias current I'm drawing. Does anyone know the formula for this? Papa states in his manual that the six deep pairs using 1 ohm resistors equals 1.5 amps when biased to 250mv across the resistor. I'm running three deep pairs using .47 ohm resistors at 350mv. I'm trying to get a better understanding how this all works. My heatsinks are running cooler than Papa's 55C max but I don't want to crank the bias any more till I know what I'm doing. Did I mention how detailed this amp sounds. Can't wait to finish the BA-1 to compare the two. I also ordered some Axon caps to compare to the Elna silks. Chad