Make a power amp out of op-amp ICs in parallel?

Kolloi · 10th March 2008, 10:58 PM

I was thinking about designing a transistor power amp, when the thought occurred to me that it would easier and cheaper to just buy a load of op-amp ICs such as LM481 and hook them up in parallel. If I put a diode in line with the DC power to each IC, then it should be safe.

Is this feasible or am I overlooking something obvious and important?

Tim__x · 10th March 2008, 11:17 PM

I'm not sure what you think the diode will do, don't use it.
All you need is to make sure the dc offset between channels is low, and to ensure stability, depending on topology current sharing output resistors may also be needed.

I can't remember the name, but I recall a Scandinavian designer on head-fi building such a thing.

Current is limited only by patience and budget, so the max supply safe supply voltage will tend to limit output power.

sawreyrw · 10th March 2008, 11:27 PM

What are the diode used for?

You must use current sharing resistors. The output power will be limited by the supply voltage, not the current capability of the parallel amps.

Tim__x · 10th March 2008, 11:29 PM

I found what I was thinking of, it was Jan Meier posting on Headwize.

Here it is.

Kolloi · 10th March 2008, 11:41 PM

Wow! So it would work.. That's excellent. I'll leave the diode out and just build it, bearing in mind that each op-amp IC has to share the current from the power supply equally. Thanks a lot guys.

Just one more quick question: roughly what level of current in excess of the safe operating limit for an average opamp is required to destroy that opamp? I want to have a rough idea how far I can push it.

jaycee · 10th March 2008, 11:46 PM

If what you want is a power amp which is easy and cheap to construct, why not just build a Gainclone type amplifier ?

You wont get much more than 15V rails out of simple opamps anyway, and not a lot of current.

Kolloi · 11th March 2008, 12:29 AM

Thanks jaycee. I hadn't heard of 'Gainclone', so after you mentioned it I Googled it. It seems that building a Gainclone-type would definitely be the most straightforward solution.

EWorkshop1708 · 11th March 2008, 05:11 AM

Quote:

Originally posted by Tim__x
I found what I was thinking of, it was Jan Meier posting on Headwize.

Here it is.

It uses some pretty badass OP-AMPS to begin with, even before parallelling them.

jcx · 11th March 2008, 06:20 AM

lots faster, higher current competition today, LT1210, LT1795, TPA6120 -and you can effectively heatsink them:

http://www.diyaudio.com/forums/showt...t=#post1392458

jaycee · 11th March 2008, 06:41 AM

Kolloi, on 25v rails an LM3886 IC is easily good for 30W into 8 ohms, the parts count is low and the sound quality is rather good. This sounds like it fits your needs exactly

You can get LM3886 for about £5 each from Farnell, or maybe a bit cheaper on eBay if you can find them.

10th March 2008, 10:58 PM	#1
Kolloi diyAudio Member Join Date: Dec 2007	Make a power amp out of op-amp ICs in parallel? I was thinking about designing a transistor power amp, when the thought occurred to me that it would easier and cheaper to just buy a load of op-amp ICs such as LM481 and hook them up in parallel. If I put a diode in line with the DC power to each IC, then it should be safe. Is this feasible or am I overlooking something obvious and important?

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Parallel Mosfet for Hi Power	Hi Speed	Car Audio	23	30th January 2012 10:24 PM
Power Trans Winding Parallel AC or DC?	sylin	Power Supplies	11	3rd March 2009 09:09 AM
Parallel-ing Switching Power Supplies	JohnT_diy	Power Supplies	11	7th July 2007 04:00 PM
Parallel a dual power supply or two power supplies?	Thunau	Power Supplies	12	16th February 2007 04:21 AM
Parallel power transformers?	paulb	Solid State	12	19th October 2001 09:25 AM

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read


	Please consider donating to help us continue to serve you. Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving

10th March 2008, 11:17 PM	#2
Tim__x diyAudio Member Join Date: Jun 2004 Location: Edmonton area, Alberta	I'm not sure what you think the diode will do, don't use it. All you need is to make sure the dc offset between channels is low, and to ensure stability, depending on topology current sharing output resistors may also be needed. I can't remember the name, but I recall a Scandinavian designer on head-fi building such a thing. Current is limited only by patience and budget, so the max supply safe supply voltage will tend to limit output power.

10th March 2008, 11:27 PM	#3
sawreyrw diyAudio Member Join Date: Apr 2006 Location: Minnesota	What are the diode used for? You must use current sharing resistors. The output power will be limited by the supply voltage, not the current capability of the parallel amps.

10th March 2008, 11:29 PM	#4
Tim__x diyAudio Member Join Date: Jun 2004 Location: Edmonton area, Alberta	I found what I was thinking of, it was Jan Meier posting on Headwize. Here it is.

10th March 2008, 11:41 PM	#5
Kolloi diyAudio Member Join Date: Dec 2007	Wow! So it would work.. That's excellent. I'll leave the diode out and just build it, bearing in mind that each op-amp IC has to share the current from the power supply equally. Thanks a lot guys. Just one more quick question: roughly what level of current in excess of the safe operating limit for an average opamp is required to destroy that opamp? I want to have a rough idea how far I can push it.

10th March 2008, 11:46 PM	#6
jaycee diyAudio Member Join Date: Apr 2004 Location: Norwich, UK	If what you want is a power amp which is easy and cheap to construct, why not just build a Gainclone type amplifier ? You wont get much more than 15V rails out of simple opamps anyway, and not a lot of current.

11th March 2008, 12:29 AM	#7
Kolloi diyAudio Member Join Date: Dec 2007	Thanks jaycee. I hadn't heard of 'Gainclone', so after you mentioned it I Googled it. It seems that building a Gainclone-type would definitely be the most straightforward solution.

11th March 2008, 06:20 AM	#9
jcx diyAudio Member Join Date: Feb 2003 Location: ..	lots faster, higher current competition today, LT1210, LT1795, TPA6120 -and you can effectively heatsink them: http://www.diyaudio.com/forums/showt...t=#post1392458

11th March 2008, 06:41 AM	#10
jaycee diyAudio Member Join Date: Apr 2004 Location: Norwich, UK	Kolloi, on 25v rails an LM3886 IC is easily good for 30W into 8 ohms, the parts count is low and the sound quality is rather good. This sounds like it fits your needs exactly You can get LM3886 for about £5 each from Farnell, or maybe a bit cheaper on eBay if you can find them.

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)