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Given:

Two XY-AP50L D-class audio amplifiers (or any other similar boards for that matter).

I want to make them work from a non-stabilized 24 V DC supply (bus alternator + 24 V batteries).

At the moment I'm using a 24 V-12 V DC-DC converter rated at 50 A to feed stabilized 12 V to these amps. This way I can be sure both boards won't get overvoltage, also don't need to push them to the specifitcation limits, so powering by half-voltage seems reasonable. This setup works fine so far.

Now I'm curious is it possible to power these amps by wiring them to to 24 V directly in series like on the picture.

Will they get half of the 24 V (that is, half of 24 V or slightly higher?) What kind of impact on a D-class circuitry such a scheme will make? In general, will this scheme work for two identical 12 V AB-class amplifiers?

enter image description here

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    \$\begingroup\$ DON'T! They won't share voltage equally, one will take more current than the other and that one will see more voltage. \$\endgroup\$
    – winny
    Jul 5 at 15:15
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    \$\begingroup\$ Just because this is a bad idea doesn't mean this is a bad question. +1 \$\endgroup\$
    – JYelton
    Jul 5 at 16:36
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    \$\begingroup\$ you could supply them like this ONLY IF you have an active rail splitter to hold the mid point at 12 V. This device needs to be capable of sourcing or sinking the whole load of one amplifier, in the event that one is drawing essentially no load and the other is working at full power. The complexity of this really means, no, don't put them in series. \$\endgroup\$
    – Neil_UK
    Jul 5 at 18:57

2 Answers 2

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Applying a supply voltage to two series-connected loads doesn't mean that they'll see equal input voltage, because they are dynamic loads.

The input current of a Class-D amp has a pulse waveform, and the two loads will unlikely draw the current in a perfectly synchronised fashion. This means that the modules will act as different impedances (or reactances) at different times.

I don't know if they have some sort of on-board regulator, but if they do, and if one module somehow sees a significantly lower voltage due to the natural dynamic behaviour of the modules then that module will try to draw much higher current to give the same regulated voltage. If they don't have any regulator then you may possible hear unequal/uneven volume from the modules because the peak of the speaker signal is related to supply voltage.

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I agree that you really should not try to connect these amplifiers, or any dynamic and unequal loads, in series on a single supply. However, you might be able to get away with just one 24-12 volt DC converter, which can act as a rail splitter, and it will draw only as much power as needed to provide the voltage balance. Here is a simulation showing how it might be done:

Rail splitter simulation

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