I'm looking to get a new amp and speakers to replace the Hi-Fi setup that didn't meet expectations. I'm considering at a JL Audio A6450, but the power output vaires by the car's voltage since it doesn't have a power regulator. I know some cars run hotter than 12V. The power output of this amp varies greatly from 12.5V to 14.4V (45 to 70 wpc). Can anyone help out? I would have the power cable run from the battery on the install.

I looked in the 2nd gen forums and couldn't find a related thread that had the info. Thanks in advance.

Jon W.

 

I haven't seen a car produced since 1970 that didn't have a 12 volt electric system. Well, maybe the VW Bug/Beetles of the time... However, generally speaking, the alternator on modern cars usually puts out between 13.8 and 14.8 volts. The amperage varies widely among all cars. Most of the time, the more electrical gadgets a car has such as power windows, seats, convertible top etc, the higher the amperage of the alternator.

 

In an amp with an unregulated power supply, the output power does depend on the alternator voltage, but it's not that big of a difference between 12.5 V and 14.4 V.

If you look at the owner's manual/specs for the A6450, the main reason the power is that much higher at 14.4 V is that they're using a much-higher Total Harmonic Distortion allowance compared to the 12.5 V numbers:

12.5 Volt supply voltage - (45 WRMS * 6) @ 0.08% THD
14.4 Volt supply voltage - (70 WRMS * 6) @ 1.0% THD

Basically, the 70 WRMS isn't coming totally from the fact that the supply voltage is higher. The 12.5 V numbers would have been higher as well if they didn't stop at 0.08% THD during the testing.

 

Scott - Thank you sir! I totally missed that point and it makes total sense. I guess I just keyed in on the voltage difference and was scratching my head.

Jon W.

 

You're welcome - the only reason it jumped out at me is that all else being equal (amplifier efficiency/architecture, etcetera), power increases with the square of the voltage increase.

Going from 12.5 V to 14.4 V should only account for a 33% increase at most, but going from 45 WRMS to 70 WRMS is a 55% increase, so I knew there had to be something different about the way they were measuring the two power ratings (in this case, it's the higher allowed THD).

 

A reasonably healthy lead acid battery in the mini should be on the order of 12.4 to 12.6 volts with the engine off. Engine running, now you're charging, and that should be in the neighborhood 14.1 to 14.4 volts.

I've done a lot of work with switching power supplies. It boggles my mind that someone would market a product with an unregulated switcher in it -- there are so many ways to get tight regulation, and with that tight regulation, much better efficiency.

 

Good point, except the amp he's talking about (the JL A6450) is an older, discontinued Class AB model, so it doesn't have a switching power supply at all. Of course, since it's an AB amp, the efficiency is pretty much in the crapper regardless of whether it's using a regulated power supply or not.

JL Audio's newer "Slash" and "HD" series of amplifiers use "Class D" digital-switching power supplies, so they're a lot more efficient. (They're tightly-regulated, as well - like you said, there's no reason to have an unregulated *switching* power supply.)

(And I know "Class D" isn't technically an amplifier class - that's why I put it in quotes).