Why two fuses in one amplifier?

**thebigthn** · 06-26-2009, 03:44 AM

I'm shopping around for a cheap 4 channel amplifier just to run my stock speaker. I know that peak power means nothing and to look at the fuse that the amp comes with to get a general idea of how much power the amp is really putting out.

I've run into some amps where they come with two fuses installed. For example, 25A x 2. Now I'm thinking that if one fuse blows, the amp turns off right? So that means that the amp is rated at only 25A, not 50A? Maybe the other fuse is just for protection in case the first one doesn't blow? Or maybe there's two separate parts inside the amp, each rated at 25A?

**Crinos** · 06-26-2009, 03:56 AM

Two fuses is not THAT bad.. It do reduce the current abit, and with that, allso the quality of the audio.

The idea behind two fuses at in this case 25A, instead of one fuse at 50A. Is that it's easier to buy a 25A fuse at a gass station, than a 50A.

Well, a 50A fuse is not so hard to get at a gass station. But higher fuses is seldom, becaus they sell to little of them.

There is some that say that two fuses in series is better than one big fuse when it comes to stopping dangerous peak voltages.

Having two fuses at 25A equals a 50A fuse.
So the amp will do about 50A * 13.8V = 690W @ 100%
About 650W on a class-d and about 520W on a class-b amp

**mroverkill** · 07-04-2009, 04:33 PM

also,

Some amps have one fuse per channel. not many are dual mono as such except for some of the higher end amps.

Internally its easier to deal with. you can make a wide circuit area with lots of contact to two fuse clips rather then try and go from a thin flat PCB trace to a large thick fuse clip.

**thebigthn** · 07-06-2009, 12:11 AM

Originally Posted by mroverkill

also,

Some amps have one fuse per channel. not many are dual mono as such except for some of the higher end amps.

Internally its easier to deal with. you can make a wide circuit area with lots of contact to two fuse clips rather then try and go from a thin flat PCB trace to a large thick fuse clip.

Ahh, okay. That makes more sense. But does that mean that 25A + 25A fuses equal a 50A fuse? Or does that mean that each separate channel is rated at 25A?

I mean, would it take 25A on the line to blow one or both fuses? Or is it still waiting until 50A to blow?

**mroverkill** · 07-06-2009, 12:16 AM

If the fuses are internally paralleled and the fuses are 25 amps each, then it would take 50+ amps before they blew and they both would go.

**thebigthn** · 07-06-2009, 04:07 AM

Ah okay, I get it now. Thanks!

**bbfoto** · 07-06-2009, 04:37 AM

Most 2-Channel Amplifiers will have just One Fuse because there is typically just One Power Supply feeding the 2 Channels (Left & Right, or "Stereo").

If you are looking at a 4-Channel Amp and see just a Single Fuse, this indicates that there is probably only One Power Supply for all 4 Channels!

A typical, well-designed 4-Channel amplifier will have Two Power Supplies with a separate Fuse for Each Power Supply. Each power supply will provide current to a Stereo "Pair" of channels, typically Left & Right.

Generally, it's best to have an Individual Power Supply for each PAIR of Channels in the amplifier. Among other things, this allows individual or independent Gain (Amplitude) control for the Front and Rear Channel Pairs.

For example: Channels 1&2, and Channels 3&4 can be set at different levels to accomodate the balance of volume between small tweeters that don't need as much power, and larger Mid-woofers that might need more power to achieve the same volume level as the tweeters.)

Most modern amplifiers also have Variable Crossovers built in to the amp. Crossovers divide or filter the frequencies above or below a certain "cut-off" frequency and output or "Pass" only those frequencies to the speaker.

They are typically called "High-Pass" and "Low-Pass" crossovers. You would set the Low-Pass Crossover for a Subwoofer to say 80Hz, and the Crossover will only let the Sound or Frequencies lower than 80Hz "Pass Through" to the speaker outputs connected to the Subwoofer.

You would typically use a "High-Pass" Crossover to allow only the higher frequencies to be sent to a tweeter or midrange speaker. This protects the tweeter or midrange speaker from dangerous low-frequencies that could damage or overload the voice coil in the smaller speaker.

What I'm getting at regarding the Crossovers is...

It's much easier to implement Separate and/or Variable Low- & High-Pass Crossovers in a 4- or more channel amplifier when each set of stereo channels is driven by a separate power supply!

Low frequencies demand much more power than high frequencies do to achieve a set output or volume level, so you can set the 2 Individual power supply or amplifier Gain knobs separately this way.

Because of this, separate Power supplies let the amplifier run much more efficiently, with less wasted power and with less stress on the amplifier and on the electrical system of the vehicle as a whole.

/end of rant. lol