When paralleling opa549

bigmike216 · 14th May 2005, 05:49 AM

what power rating does the .01 ohm resistor in series with the outputs need to be?

JhonDoe · 14th May 2005, 05:56 AM

3 or 5 watts

macboy · 16th May 2005, 02:39 PM

I'd very strongly suggest using something much larger than 0.01 ohm. Like to 0.1 ohm to 0.5 ohm.

With 0.01 ohm, even a difference of 10 mV will cause 1 amp of current to flow between the amplifiers. Think about it... if at any instant, one amp is outputting say 25.490 V and the other is 25.480 V (only a 0.04 % difference!) then you get a significant current of 1 A flowing between the two amps. This is completely wasted power creating heat rather than music. If the gain of the two amps is matched even more poorly, say to 1% (which is actually quite closely matched), then you could get some major problems with 0.01 ohm. With one amp outputting 25.000 V and the other merely 1% higher at 25.250 V, you would get 25 A of current trying to flow between the amps. Of course, either the current limitting of the amp will kick in long before that (causing distortion and greatly reduced power output), or if you've chosen not to use the current limitting, the chips will go up in smoke. And everyone knows that once the magic smoke gets out, you can't put it back in.

bigmike216 · 16th May 2005, 06:48 PM

That was a typo on my part, I meant to type 0.1 ohm. I've ordered them now, and will use two 0.22 ohm 5 watt in parallel.

pinkmouse · 16th May 2005, 06:58 PM

Just use a single R22 for each chip. The power loss is insignificant, and current sharing will be much better.

bigmike216 · 16th May 2005, 08:07 PM

Cool, even easier

14th May 2005, 05:49 AM	#1
bigmike216 diyAudio Member Join Date: Jul 2004 Location: BC, Canada	When paralleling opa549 what power rating does the .01 ohm resistor in series with the outputs need to be?

16th May 2005, 06:58 PM	#5
pinkmouse diyAudio Moderator Join Date: Apr 2002 Location: Chatham, England	Just use a single R22 for each chip. The power loss is insignificant, and current sharing will be much better. __________________ Al I conceive of nothing, in religion, science or philosophy, that is more than the proper thing to wear, for a while. Charles Fort

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14th May 2005, 05:56 AM	#2
JhonDoe diyAudio Member Join Date: Jan 2004 Location: ac	3 or 5 watts

16th May 2005, 02:39 PM	#3
macboy diyAudio Member Join Date: Oct 2003 Location: Ottawa, Canada	I'd very strongly suggest using something much larger than 0.01 ohm. Like to 0.1 ohm to 0.5 ohm. With 0.01 ohm, even a difference of 10 mV will cause 1 amp of current to flow between the amplifiers. Think about it... if at any instant, one amp is outputting say 25.490 V and the other is 25.480 V (only a 0.04 % difference!) then you get a significant current of 1 A flowing between the two amps. This is completely wasted power creating heat rather than music. If the gain of the two amps is matched even more poorly, say to 1% (which is actually quite closely matched), then you could get some major problems with 0.01 ohm. With one amp outputting 25.000 V and the other merely 1% higher at 25.250 V, you would get 25 A of current trying to flow between the amps. Of course, either the current limitting of the amp will kick in long before that (causing distortion and greatly reduced power output), or if you've chosen not to use the current limitting, the chips will go up in smoke. And everyone knows that once the magic smoke gets out, you can't put it back in.

16th May 2005, 06:48 PM	#4
bigmike216 diyAudio Member Join Date: Jul 2004 Location: BC, Canada	That was a typo on my part, I meant to type 0.1 ohm. I've ordered them now, and will use two 0.22 ohm 5 watt in parallel.

16th May 2005, 08:07 PM	#6
bigmike216 diyAudio Member Join Date: Jul 2004 Location: BC, Canada	Cool, even easier