paralleling amplifiers. - diyAudio
 paralleling amplifiers.
 User Name Stay logged in? Password
 Home Forums Rules Articles diyAudio Store Gallery Wiki Blogs Register Donations FAQ Calendar Search Today's Posts Mark Forums Read Search

 Chip Amps Amplifiers based on integrated circuits

 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
 27th May 2005, 01:23 AM #1 diyAudio Member     Join Date: Dec 2003 Location: Toronto Canada paralleling amplifiers. I was wondering if anyone here knows How to calculate what resistor you need when paralleling amplifiers? it seems like one of those things that could go drastically wrong if the wrong choice is made. I had an idea to make a low watt amp of a bunch of TPA6120s they are current amplifiers so would that make any difference when paralleling them? (or make it impossible)
 27th May 2005, 03:48 AM #2 diyAudio Member     Join Date: Dec 2004 Location: Bukit Mertajam I dont know about any calculation regarding this,but i have seen many using the value of 0.1ohms
 27th May 2005, 05:43 AM #3 diyAudio Member   Join Date: May 2005 Location: BKK BTW, if individual amp has higher DC offset the higher value may be used. I saw some thread long time ago, that the later version of Linn use 0.5 Ohm ballard res.
 27th May 2005, 06:28 AM #4 diyAudio Member   Join Date: Aug 2003 Location: Prague,Czech Republic Minimal load impedance by TPA 6120 is 8 Ohm. So if you use two pieces of this circuit ( four amps ), which will have connected outputs together through this resistor ( each ), you can get output power into 8 Ohm load cca 6 W. Distortion will be in this case very good ( bellow .001 % ), but DF will be low, only four ( 8/2 ), so sound will be similar to single ended tube amp. If you like similar sound, go on.
diyAudio Member

Join Date: Oct 2003
Quote:
 Originally posted by Upupa Epops Minimal load impedance by TPA 6120 is 8 Ohm. So if you use two pieces of this circuit ( four amps ), which will have connected outputs together through this resistor ( each ), you can get output power into 8 Ohm load cca 6 W. Distortion will be in this case very good ( bellow .001 % ), but DF will be low, only four ( 8/2 ), so sound will be similar to single ended tube amp. If you like similar sound, go on.
The load-sharing resistor is not limited by the minimum impedance of the amp. So you could use much lower load sharing resistors than 8 ohms, like the typical 0.1 to 0.5 ohms. Just make sure that the gain of all of the paralleled amps is very closely matched so that current does not flow between the amps via these resistors.

And if you want to keep the Damping Factor high (low output impedance), then you can put the paralleled amplifiers inside the feedback loop of an opamp. This will effectively remove the load sharing resistors from the load - the opamp will adjust the output voltage to remove the effect of the voltage drop across these resistors.

 27th May 2005, 05:25 PM #6 diyAudio Member   Join Date: Aug 2003 Location: Prague,Czech Republic This circuit is very fast, so serial resistor protect output against capacitive load and at datasheet is 8 Ohm recomended as minimal value. Sure, if you all connect into loop, you get lower DF, but circuit will be relatively complicated and PCB will must be designed closely.
 28th May 2005, 03:31 AM #7 diyAudio Member     Join Date: Dec 2003 Location: Toronto Canada Thanks for all the replies! I was actually thinking of using more chips per channel (4 or 5) but 2 is a good place to start. So if i put the load sharing resistors inside the feedback loop, then all of the chips would be getting their feedback from the same node (the final output) ? If they are sharing that node, could they also share the actual feedback resistor, so it is exactly the same value for all the amps?
diyAudio Member

Join Date: Oct 2003
Quote:
 So if i put the load sharing resistors inside the feedback loop, then all of the chips would be getting their feedback from the same node (the final output) ? If they are sharing that node, could they also share the actual feedback resistor, so it is exactly the same value for all the amps?
Ok, I don't quite follow your line of thinking, but basically what I suggested above entails enclosing the parallel amp inside the feedback loop of an opamp. (see attachment). Each individual amp in the parallel amp still has its own output (load-sharing) resistor, and these absolutely must be outside of each chip's feedback loop.

In the attached schematic I have drawn a simplified four-way parallel amp inside the feedback loop of an opamp so that you can get the idea.

Discalimers: This is intended to be representative only and is not a tested design. There are no component values; you will have to choose them appropriately. Most of the National chips are stable at gains of 10 or higher, so set the gains appropriately, and match them very closely. Also note that the overal gain for the input opamp loop must be greater than the gain for the chipamps, even if the opamp is unity-gain stable. As drawn, the circuit probably has some nasty DC offset problems (especially with all the + inputs of the chipamps all tied directly together), and I would personally take extra steps to reduce DC offset.
Attached Images
 parallel-amp.gif (4.6 KB, 730 views)

diyAudio Member

Join Date: May 2005
Location: BKK
Quote:
 Originally posted by macboy Ok, I don't quite follow your line of thinking, but basically what I suggested above entails enclosing the parallel amp inside the feedback loop of an opamp. (see attachment). Each individual amp in the parallel amp still has its own output (load-sharing) resistor, and these absolutely must be outside of each chip's feedback loop. In the attached schematic I have drawn a simplified four-way parallel amp inside the feedback loop of an opamp so that you can get the idea. [/i]

I agreed with macboy. In addition, I would add Cap in the feedback to ensure unity gain of each chip. Also, individual zobel of each chip will be helpful.

Good luck,

Banned

Join Date: Mar 2003
Location: Lisbon, Portugal
Quote:
 Originally posted by methar In addition, I would add Cap in the feedback to ensure unity gain of each chip.
You can't use a cap on the feedback loop of a current-feedback op-amp.

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is OffTrackbacks are Off Pingbacks are Off Refbacks are Off Forum Rules

 Similar Threads Thread Thread Starter Forum Replies Last Post dfdye Chip Amps 10 30th January 2006 05:26 PM bonsai171 Solid State 26 25th February 2004 08:24 PM Corn-Picker Solid State 2 24th January 2004 03:10 AM djdan Solid State 9 17th September 2002 04:40 PM SteveG Pass Labs 14 7th February 2002 09:20 PM

 New To Site? Need Help?

All times are GMT. The time now is 05:58 PM.