How to parallel multiple power amps?
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kokoriantz
diyAudio Member

Join Date: Dec 2015
Location: south east asia
How to parallel multiple power amps?

Each paralleled amp equates the voltage of its resistor to be equal to the master's resistor. By this the output current is multiplied here by four. the main amp sees the load as Rload×4. The load sees the impedance of the main amp as Z/4.
Hayk
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 parallel amps.JPG (21.5 KB, 517 views)

Last edited by kokoriantz; 25th November 2020 at 10:23 PM.

 24th November 2020, 09:10 PM #2 PRR   diyAudio Member     Join Date: Jun 2003 Location: Maine USA This works only if the amplifiers can be connected at unity-gain. Chip power amplifiers sometimes can't.
kokoriantz
diyAudio Member

Join Date: Dec 2015
Location: south east asia
On simulator it does work in perfection with a gain of unity.

Bellow is the transient for 10khz 10v
Attached Images
 CURRENT MULTIPLIER.JPG (41.0 KB, 450 views) transient.JPG (69.2 KB, 14 views) out lm.jpg (70.0 KB, 235 views)

Last edited by kokoriantz; 24th November 2020 at 11:54 PM.

 25th November 2020, 12:23 AM #4 MAAC0   diyAudio Member   Join Date: May 2010 What's the purpose ? More Watts ?
kokoriantz
diyAudio Member

Join Date: Dec 2015
Location: south east asia
Parallel bridge configuration is widely used to get high power amplifiers by using small chips. The LM1875 gives its best with 8 ohms 15 watts only.
Bellow is the impedance that sees the main driving amplifier. To note that the simulating model doesn't have inductive component of the output impedance, it is fixed for simplicity to 0.1 ohms. This why the high frequency impedance falling to 0.5 ohm is wrong.
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 reflected.jpg (64.9 KB, 11 views)

Last edited by kokoriantz; 25th November 2020 at 12:36 AM.

PRR
diyAudio Member

Join Date: Jun 2003
Location: Maine USA
Quote:
 Originally Posted by kokoriantz On simulator it does work in perfection with a gain of unity. ...
The datasheet says minimum gain is 10.

Which suggests your simulation model is incomplete.
Attached Images
 LM1875-stab-42.gif (3.5 KB, 217 views)

 25th November 2020, 05:50 AM #7 kokoriantz   diyAudio Member   Join Date: Dec 2015 Location: south east asia I appreciate your attention about the subject. The datasheet also precise that it is loaded 2k. The open loop gain depends greatly with the load. The datasheet also precise that with one ohms in series, it is stable with any capacitive load. In other words, the OLG with one ohm gets considerably reduced to remain stable. How about loading 0.22 ohms! The OLG decreases by far by 10 fold to be stable at unity gain. If an amplifier still oscillate, to feedback by 1k resistor and shunt the inputs by 100 ohms. The gain decreases by ten fold. See applied by Mooly The LM1875 for best After testing on simulator, it is the positive feedback is the reason of stability. Last edited by kokoriantz; 25th November 2020 at 06:09 AM.
kokoriantz
diyAudio Member

Join Date: Dec 2015
Location: south east asia
This is response as unity follower with 0.22 ohm. Is stable but this is not reason of stability. The load if not zero is receiving feedback, I don't know yet how.

Attached Images
 CURRENT MULTIPLIER 0load.JPG (117.9 KB, 218 views)

kokoriantz
diyAudio Member

Join Date: Dec 2015
Location: south east asia

The stability is perfect but very well damped.
This is modeled with not non inductive resistors worst case and adjusted for perfect stability.
Attached Images
 CURRENT MULTIPLIER (2).JPG (15.2 KB, 7 views) stability.JPG (40.7 KB, 222 views) CURRENT MULTIPLIER4.JPG (18.8 KB, 8 views) perfect.JPG (39.5 KB, 220 views)

Last edited by kokoriantz; 25th November 2020 at 07:10 AM.

 25th November 2020, 07:43 AM #10 AKSA   diyAudio Member   Join Date: Sep 2001 Location: Melbourne, Australia Hayk, Is this needed? Rowlands has marketed amps with multiple chips, at high cost, and others had done this with HP amps too. HD __________________ Aspen Amplifiers P/L (Australia) www.aksaonline.com

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