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Disclaimer: Saying I have very little knowledge of electrical engineering theory is an understatement. I very much appreciate your help and patience. I'm not finding any questions similar to mine, but this could very well be due to me being completely off base in my understanding of the problem.

Since I have so little knowledge on the principles at work in this problem, I will try to detail everything I'm doing. That way there is no assumptions made in terms of what I know and don't know.

The general scenario: When I connect a multimeter to the output of a ac to dc power adapter and then to the input of an amplifier board it is reading very low amperage, even when the volume is set to maximum on the computer which is creating the input. Below is a very rudimentary, and probably comical, drawing of the setup.

enter image description here

Specific components used

Amplifier Board:
The class d amplifier board that I'm using is the wondom 2x25watt audio amplifier board using the TDA7492. the Sku is AA-AB32165 and can be found here http://store.sure-electronics.com/product/AA-AB32165. The specifications on store page require a 14V-19V power supply.

Power Supply:
I am using an old Toshiba laptop power ac/dc adapter which states its input as 100-240V~1.2A 50-60Hz and its output at 19V 2.37A.

Speakers:
I am using two 16 ohm, 25watt speakers.

Input generation (not sure what the term for this is)
I'm using a RCA to 3.5mm Aux cable from my computer to the board.

My question: The multimeter on the DC amps setting is reading only 0.05A. It is my understanding that Power = voltage x current. If this applies here that means the board is only being supplied 0.95watts. Wouldn't that mean this board is not capable of supplying a total of 25 watts to each speaker if not even that much power is inputted into the board. If these assumptions on my part are right and I'm measuring the amperage correctly, why is the amperage so low and how can I increase the current draw?

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    \$\begingroup\$ The amplifier will only draw the current it needs at any given instant. Check the current at full volume. \$\endgroup\$
    – user105652
    Mar 22, 2019 at 1:20
  • \$\begingroup\$ The current stayed around 0.04 to 0.05 while the computer it was connected to was at full volume. I noticed that the amplifier board itself does not have a speaker volume control does that have something to do with it. Is the amplifier board not at full volume. If it isn't, how would it be adjusted to be higher volume. \$\endgroup\$
    – Walrath21
    Mar 22, 2019 at 2:04
  • \$\begingroup\$ 0.04 to 0.05 A* \$\endgroup\$
    – Walrath21
    Mar 22, 2019 at 2:31
  • \$\begingroup\$ class D if very efficient, it's basically an audio speed buck converter. If you are delivering a low voltage to your speakers (maybe through not having enough gain), and as they are high impedance (16ohm), and with a high supply voltage you might be measuring the correct current draw. 2x25 watts would be very loud indeed, are they? Are you measuring the current on the correct meter range? Measure that of a resistor \$\endgroup\$
    – Neil_UK
    Mar 22, 2019 at 6:28
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    \$\begingroup\$ Music (As opposed to tone) has a very high peak to average ratio, and the peaks are often short. With a 19V rail into 16 ohm speakers (say 16V peak across the speakers because it makes the maths easy), your amp can push 1A peak into the speaker, so 16W peak per speaker, but 16W peak is 8W average, and audio types design for music having a 1/8th peak to average ratio, so you are seeing at most 2W or so per channel average with music program (Which is just fine, that is actually sufficient for most living room situations). Loudness is only loosely coupled to power consumption for real programs. \$\endgroup\$
    – Dan Mills
    Mar 22, 2019 at 15:45

1 Answer 1

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class D if very efficient, it's basically an audio speed buck converter. If you are delivering a low voltage to your speakers (maybe through not having enough gain), and as they are high impedance (16ohm), and with a high supply voltage you might be measuring the correct current draw. 2x25 watts would be very loud indeed, are they? Are you measuring the current on the correct meter range? Measure that of a resistor – Neil_UK 11 hours ago

Neil was right. The voltage delivered to the speakers was apparently pretty low without the gain turned up quite a bit.

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    \$\begingroup\$ A relatively average normal speaker produces audio of about 80-90 dB when fed with 1 Watt of power and measured at 1m distance (3 feet). That's approximately as loud as a lawnmower, I expect normal listening levels are less than that. And the D-class amp is very efficient so very little power is wasted in the amp. So yes, consumption below 1 Watt sounds reasonable with low volume levels. \$\endgroup\$
    – Justme
    Mar 22, 2019 at 19:05

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