Determining Amplifier Input Power

Thread Starter

ARK Tech

Joined Jul 3, 2022
2
Hi All,

I am trying to setup my Sony N500 Xplod Car Amplifier in home environment. I have presently a 20A fuse placed in a 25A socket of the Amplifier. Its input is 12V. So I believe a SMPS of 25A 12V will suffice its working. I am intending to change the 20A fuse to 25A as well to support this. Previously I used a 15A 12V SMPS and it stopped working, I do not know the reason but I believe it was because the current drawn was high and SMPS stopped working. I even had wire caught fire once. I want to do everything perfectly this time. So your suggestions are welcome.
Can I use my 25A SMPS with 20A amplifier fuse? Is it better to buy 20A SMPS? such questions arise. Please comment.
 

MrChips

Joined Oct 2, 2009
26,480
Welcome to AAC!

The wattage of the PSU and the fuse in the amplifier are two separate issues. The fuse is to prevent burning down your house.

15A @ 12V input power is 180W. It is unlikely that your amplifier was using that much power. I suspect something is wrong with your SMPS.
 

Thread Starter

ARK Tech

Joined Jul 3, 2022
2
Thank you for the reply.
Can you please comment on?

Can I use my 25A SMPS with 20A amplifier fuse? Is it good to buy 20A SMPS? or 25A SMPS is better?
 

BobTPH

Joined Jun 5, 2013
5,227
Power supplies run cooler and last longer when they are oversized for the job, so yes, using a 25A supply with something that uses close to 20A is a good idea.
 

BobTPH

Joined Jun 5, 2013
5,227
Expounding on Ian’s post. You would have to have 2 channels driving 2 Ohms at full blast to get anywhere near 15A at 12V.
 

MrChips

Joined Oct 2, 2009
26,480
Expounding on Ian’s post. You would have to have 2 channels driving 2 Ohms at full blast to get anywhere near 15A at 12V.
Automotive audio amplifiers operate on the system’s 12V supply.
Internally, the supply voltage is increased to a higher voltage, e.g. ±40V in order to drive 8Ω speakers.

With more recent Class-D amplifiers, that is a different story.

Ignoring efficiency losses for now, 180W of acoustic power is still ear deafening.
 

Ian0

Joined Aug 7, 2020
5,504
Automotive audio amplifiers operate on the system’s 12V supply.
Internally, the supply voltage is increased to a higher voltage, e.g. ±40V in order to drive 8Ω speakers.

With more recent Class-D amplifiers, that is a different story.

Ignoring efficiency losses for now, 180W of acoustic power is still ear deafening.
It's not much of a different story - it's still boosted to the same higher voltage, because it needs the same peak voltage for the same output. The only difference is the output stage is rather more efficient.

Apologies in advance for the pedantry - but whilst 180W of acoustic power is deafening; what you actually get from a 180W loudspeaker (of the automotive subwoofer variety) is 179.9W of thermal power and 0.1W of acoustic power. They are notoriously inefficient, less so than a Newcomen engine.
 

MisterBill2

Joined Jan 23, 2018
12,399
I am not familiar with the Sony N500 amplifier, but if it is rated at 500 watts output, then the amplifier must draw at least 500 watts power in at max output. (assuming 100% efficiency, which it is always less than that)
If the specified fuse is 25 amps then the amplifier probably draws less than 25 amps. But for that sort of application the supply should be rated for at least 25 amps.
And MrChips is right about the voltage boosting. Even a class "D" amplifier will need a higher voltage to force the power through the speakers, that is basic Ohms Law.
A more efficient scheme is to use an external power supply as a substitute for the internal higher voltage inverter supply. That does require digging into the amplifier but it will reduce the heat load quite a bit.
 

Audioguru again

Joined Oct 21, 2019
4,793
Most Sony Xplod amplifiers are sold on ebay and other Chinese places. They say PMPO which is fake power at very high distortion. 90W of real distorted power or 72W real low distortion total power for all 4 channels. 72/4= 15W per channel into 4 ohm speakers.

A car amplifier output power is usually rated when the battery is charging at 14.4V. 15W into 4 ohms is produced by a bridged amplifier producing 22Vp-p. A voltage boost circuit is not needed.

If the amplifier output is 72W then its heating might be 86W for a total of 158W. 158W/14.4V= 11A then a 15A fuse is used..
 

MisterBill2

Joined Jan 23, 2018
12,399
We are still left with the question of supply input power. That might even be found in some published literature, but certainly not on an amazon sales listing.
 
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