Switch

DJ Exprice · 14th June 2006, 09:47 PM

I have made a Bleeder Resistor Switch. It only bleeds the ± Rails when you turn it off. This cuts down on LOTS of heat.

Tell me what you think!

Cheers,

DJ EXPRiCE

DJ Exprice · 15th June 2006, 03:19 PM

Anyone like it?

Wynand · 15th June 2006, 03:25 PM

After a quick look, it looks good to me.

I'll remember the idea.

raromachine · 16th June 2006, 02:13 AM

Can you explain a little more about the situation in which you'd use this?

In most cases I would have thought that in most cases the amp/speakers/led would have dissipated any energy left in any capacitors?

Or is the idea that we don't want that to happen?

rpapps · 16th June 2006, 02:44 AM

I think 10 Ohms is a bit small. Think about what happens when you throw the switch. Let's assume the power rails are +/- 40 volts (could be much higher). Suddenly you've got 80 volts across 10 Ohms. Instantaneous current is 8 Amps and power is
640 Watts. You would want a substantial switch and resistor to stand up to that for any length of time.
You don't need to bleed off the charge that quickly, 100 Ohms would be OK.
Cheers
Rob

I_Forgot · 16th June 2006, 02:59 AM

Or even a 10K resistor without the switch.

The point of a bleeder resistor is to make the circuit safe for someone servicing the device. The bleeder resistor ensures that the charge has been bled off the caps by the time a service tech opens the box up. Back when vacuum tubes were more common and power supplies had 500V caps, and the tubes had essentially infinite resistance shortly after the circuit was shut off, bleeder resistors were a real necessity.
Caps could hold a charge for a long time and then knock some unsuspecting weekend-tech on their butt.

With the low voltages on solid state amps, and the behaviour of transistor circuits, they are pretty much optional these days. The circuit will pull the cap voltage down pretty quickly after the power is shut off, unless a fuse on the DC rail blows, in which case it IS a good idea to have a bleeder.

If you don't have fuses downstream of the power supply filter caps, a bleeder isn't a real necessity in a solid state amp.

I_F

lndm · 16th June 2006, 03:16 AM

Ah! but there's nothing like an unexpected short from a low voltage on a massive cap, to make a novice fall off their chair with a dumb look on their face

DJ Exprice · 25th June 2006, 09:13 PM

Quote:

Originally posted by rpapps
I think 10 Ohms is a bit small. Think about what happens when you throw the switch. Let's assume the power rails are +/- 40 volts (could be much higher). Suddenly you've got 80 volts across 10 Ohms. Instantaneous current is 8 Amps and power is
640 Watts. You would want a substantial switch and resistor to stand up to that for any length of time.
You don't need to bleed off the charge that quickly, 100 Ohms would be OK.
Cheers
Rob

Sounds good too. I've tested some things with a 1 watt 10 ohm resistor and it didn't even get that warm when I threw the switch off. I will however advise that the ohm-age is between 10 and 100 ohms and at LEAST 1 watt. I have some 10w 10 ohm and some 10w 100 ohm resistors (ceramic type from radioshack). I think that they are perfect for me

.

DJ Exprice · 25th June 2006, 09:19 PM

EDIT: BOTH of the upper right pins on the switch can touch if you want to drain even faster if there are lager caps on the amp circuit itself! You may want to use a 100 ohm resistor for this though.

cliffhiker · 28th June 2006, 10:49 PM

I've used this a number of times and I think posted it here sometime back..
As far as I know the best explanation and probably original source of this idea is here...

http://www.edn.com/contents/images/70501di.pdf

14th June 2006, 09:47 PM	#1
DJ Exprice diyAudio Member Join Date: Mar 2006 Location: San Francisco, California	Switch I have made a Bleeder Resistor Switch. It only bleeds the ± Rails when you turn it off. This cuts down on LOTS of heat. Tell me what you think! Cheers, DJ EXPRiCE

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15th June 2006, 03:19 PM	#2
DJ Exprice diyAudio Member Join Date: Mar 2006 Location: San Francisco, California	Anyone like it?

15th June 2006, 03:25 PM	#3
Wynand diyAudio Member Join Date: Mar 2005 Location: Cape Town	After a quick look, it looks good to me. I'll remember the idea.

16th June 2006, 02:13 AM	#4
raromachine Account disabled at member's request Join Date: Jun 2006	Can you explain a little more about the situation in which you'd use this? In most cases I would have thought that in most cases the amp/speakers/led would have dissipated any energy left in any capacitors? Or is the idea that we don't want that to happen?

16th June 2006, 02:44 AM	#5
rpapps diyAudio Member Join Date: Jul 2004 Location: nowhere of interest	I think 10 Ohms is a bit small. Think about what happens when you throw the switch. Let's assume the power rails are +/- 40 volts (could be much higher). Suddenly you've got 80 volts across 10 Ohms. Instantaneous current is 8 Amps and power is 640 Watts. You would want a substantial switch and resistor to stand up to that for any length of time. You don't need to bleed off the charge that quickly, 100 Ohms would be OK. Cheers Rob

16th June 2006, 02:59 AM	#6
I_Forgot diyAudio Member Join Date: Jan 2005 Location: Phoenix, Az.	Or even a 10K resistor without the switch. The point of a bleeder resistor is to make the circuit safe for someone servicing the device. The bleeder resistor ensures that the charge has been bled off the caps by the time a service tech opens the box up. Back when vacuum tubes were more common and power supplies had 500V caps, and the tubes had essentially infinite resistance shortly after the circuit was shut off, bleeder resistors were a real necessity. Caps could hold a charge for a long time and then knock some unsuspecting weekend-tech on their butt. With the low voltages on solid state amps, and the behaviour of transistor circuits, they are pretty much optional these days. The circuit will pull the cap voltage down pretty quickly after the power is shut off, unless a fuse on the DC rail blows, in which case it IS a good idea to have a bleeder. If you don't have fuses downstream of the power supply filter caps, a bleeder isn't a real necessity in a solid state amp. I_F

16th June 2006, 03:16 AM	#7
lndm diyAudio Member Join Date: Mar 2006 Location: nsw	Ah! but there's nothing like an unexpected short from a low voltage on a massive cap, to make a novice fall off their chair with a dumb look on their face

25th June 2006, 09:19 PM	#9
DJ Exprice diyAudio Member Join Date: Mar 2006 Location: San Francisco, California	EDIT: BOTH of the upper right pins on the switch can touch if you want to drain even faster if there are lager caps on the amp circuit itself! You may want to use a 100 ohm resistor for this though.

28th June 2006, 10:49 PM	#10
cliffhiker diyAudio Member Join Date: Mar 2004 Location: Virginia	I've used this a number of times and I think posted it here sometime back.. As far as I know the best explanation and probably original source of this idea is here... http://www.edn.com/contents/images/70501di.pdf

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