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How to parallel multiple power amps?
How to parallel multiple power amps?
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Old 24th November 2020, 12:39 PM   #1
kokoriantz is offline kokoriantz  Lebanon
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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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Last edited by kokoriantz; 25th November 2020 at 10:23 PM.
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Old 24th November 2020, 09:10 PM   #2
PRR is offline PRR  United States
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How to parallel multiple power amps?
This works only if the amplifiers can be connected at unity-gain. Chip power amplifiers sometimes can't.
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Old 24th November 2020, 11:47 PM   #3
kokoriantz is offline kokoriantz  Lebanon
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On simulator it does work in perfection with a gain of unity.
How to parallel multiple power amps?-current-multiplier-jpg
How to parallel multiple power amps?-lm-jpg
Bellow is the transient for 10khz 10v
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File Type: jpg CURRENT MULTIPLIER.JPG (41.0 KB, 448 views)
File Type: jpg transient.JPG (69.2 KB, 14 views)
File Type: jpg out lm.jpg (70.0 KB, 234 views)

Last edited by kokoriantz; 24th November 2020 at 11:54 PM.
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Old 25th November 2020, 12:23 AM   #4
MAAC0 is offline MAAC0  Portugal
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What's the purpose ? More Watts ?
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Old 25th November 2020, 12:32 AM   #5
kokoriantz is offline kokoriantz  Lebanon
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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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Last edited by kokoriantz; 25th November 2020 at 12:36 AM.
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Old 25th November 2020, 05:16 AM   #6
PRR is offline PRR  United States
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How to parallel multiple power amps?
Quote:
Originally Posted by kokoriantz View Post
On simulator it does work in perfection with a gain of unity. ...
The datasheet says minimum gain is 10.
How to parallel multiple power amps?-lm1875-stab-42-gif
Which suggests your simulation model is incomplete.
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Old 25th November 2020, 05:50 AM   #7
kokoriantz is offline kokoriantz  Lebanon
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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.
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Old 25th November 2020, 06:22 AM   #8
kokoriantz is offline kokoriantz  Lebanon
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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.

How to parallel multiple power amps?-current-multiplier-0load-jpg
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Old 25th November 2020, 06:59 AM   #9
kokoriantz is offline kokoriantz  Lebanon
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How to parallel multiple power amps?-stability-jpg
The stability is perfect but very well damped.
This is modeled with not non inductive resistors worst case and adjusted for perfect stability.How to parallel multiple power amps?-perfect-jpg
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File Type: jpg CURRENT MULTIPLIER (2).JPG (15.2 KB, 7 views)
File Type: jpg stability.JPG (40.7 KB, 221 views)
File Type: jpg CURRENT MULTIPLIER4.JPG (18.8 KB, 8 views)
File Type: jpg perfect.JPG (39.5 KB, 219 views)

Last edited by kokoriantz; 25th November 2020 at 07:10 AM.
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Old 25th November 2020, 07:43 AM   #10
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Hayk,

Is this needed? Rowlands has marketed amps with multiple chips, at high cost, and others had done this with HP amps too.

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