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# stereo plus amp is how many watts? Answered

for instance if my stereo is 20w rms and I put an amp of 45w rms will I have 65w rms?

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No you will have 45 watts output Assuming you mean to drive the amp from your current stereo amp you will get vast amounts of distortion as well.

why would there be vast amounts of distortion and how would I avoid it?

Because the audio amp, unless designed to expect it, will only need a few micro or milli volts to drive it.

Exceeding that level will introduce distortion.

Your existing amp may have an output to the speakers in the range of volts - 1000 times too big.

In the image below (click to see full size) the top example shows the audio input is below the input limits and so is amplified correctly

The lower image shows the effect of exceeding the input limits, the input signal is clipped giving it a square top. For reasons too complex to explain here this introduces noise into the signal - Think good old fashioned guitar Fuzz sound.

Over driving is a common heavy metal technique to produce this type of distortion - Not generally desirable.

Im missing something here. By this logic there would be vast amounts of distortion on every car stereo with an added amp. I just want to boost the output of my stereo to match the speakers I have which are 80w my stereo is probably about 15w give or take, so if I add an amp that is 60 watts would I have 75w or 60w?

The bit you missed was

"Because the audio amp, unless designed to expect it, will only need a few micro or milli volts to drive it."

so im still confused. it seems to me that you are saying every car stereo puts out too much voltage for any amp. but I know people put amps in their cars otherwise why would they even exist. I have a stereo that has output of 2.0v rms and I ordered the soundstream PN4520D 520w amp. what do I need to do to make it work?

Where an audio amp provides a LOT of power then generally it will be preceded by a preamp. This raises the initial output to a high enough level for the main power amp.

HOWEVER these 2 things have been designed to work together.

You need to look at the specification for the power amp you want to use and see what input range it expects and stay within that range if you want to avoid distortion.

By all means try what you have. Be prepared for disappointment and possibly the loss of your speakers.

well it seems this amp has a gain control option but now I have a new obstacle. my Subaru legacy has a fifth speaker in the back window and I don't know how that factors into the wattage distribution since the amp has 4 channels. any idea about that?