Quick F5 PS question

DJNUBZ · 2nd August 2011, 08:00 PM

Would it be ok to use 2W .47ohm resistors as opposed to 3w in the power supply?

vdi_nenna · 2nd August 2011, 08:08 PM

Best to use 3w or better. They get real hot.

DJNUBZ · 2nd August 2011, 08:28 PM

OK thanks.

juma · 2nd August 2011, 08:29 PM

I * I * R = P
1.2 * 1.2 * 0.47 = 0.6768 W

So, 2W resistors are fine here (except if you have 4 Ohm speaker and you drive the amp to full power for long period of time).

DJNUBZ · 2nd August 2011, 08:34 PM

Well I may hook the amps up to a 2 ohm speaker load at some point and I would rather be safe then sorry. I just happened to have 2W available. For 3w or bigger I need to make an order.

Does quality of resistor in this area matter much? Will you notice a difference between a sand-cast or something better? I am guessing not.

juma · 2nd August 2011, 08:50 PM

I don't like the good things to go to waste. You can put 2 x 0R47 in series and parallel them to another two in series. That's equal to one 0R47/8W resistor.
When it comes to quality, aim for low temp. drift and precision, don't waste the money on boutique parts...

DJNUBZ · 2nd August 2011, 08:52 PM

I just found a local source of just what I need (no crazy shipping fees). I am going there tomorrow.

AndrewT · 3rd August 2011, 10:39 AM

five 2r2, 600mW in parallel give an effective 0r44, 3W

2nd August 2011, 08:00 PM	#1
DJNUBZ diyAudio Member Join Date: May 2003 Location: Chicago	Quick F5 PS question Would it be ok to use 2W .47ohm resistors as opposed to 3w in the power supply?

2nd August 2011, 08:08 PM	#2
vdi_nenna diyAudio Member Join Date: Oct 2000 Location: PA, USA Blog Entries: 1	Best to use 3w or better. They get real hot. __________________ I build, therefore I am.

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2nd August 2011, 08:28 PM	#3
DJNUBZ diyAudio Member Join Date: May 2003 Location: Chicago	OK thanks.

2nd August 2011, 08:29 PM	#4
juma diyAudio Member Join Date: Nov 2005 Location: Zemun	I * I * R = P 1.2 * 1.2 * 0.47 = 0.6768 W So, 2W resistors are fine here (except if you have 4 Ohm speaker and you drive the amp to full power for long period of time).

2nd August 2011, 08:34 PM	#5
DJNUBZ diyAudio Member Join Date: May 2003 Location: Chicago	Well I may hook the amps up to a 2 ohm speaker load at some point and I would rather be safe then sorry. I just happened to have 2W available. For 3w or bigger I need to make an order. Does quality of resistor in this area matter much? Will you notice a difference between a sand-cast or something better? I am guessing not.

2nd August 2011, 08:50 PM	#6
juma diyAudio Member Join Date: Nov 2005 Location: Zemun	I don't like the good things to go to waste. You can put 2 x 0R47 in series and parallel them to another two in series. That's equal to one 0R47/8W resistor. When it comes to quality, aim for low temp. drift and precision, don't waste the money on boutique parts...

2nd August 2011, 08:52 PM	#7
DJNUBZ diyAudio Member Join Date: May 2003 Location: Chicago	I just found a local source of just what I need (no crazy shipping fees). I am going there tomorrow.

3rd August 2011, 10:39 AM	#8
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	five 2r2, 600mW in parallel give an effective 0r44, 3W