PJK3

from the FAQ:

What are amp gains? How do they work? What do I do if my HU outputs 8 V pre-amp but my amp only accepts 4 V? Aren't they just volume knobs?

The area of gains and inputs are really a very commonly misunderstood subject. Hopefully, this will help clear up some of the misunderstandings people have about amp gains and what they do.
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for a moment, work a rough analogy w/ me... let's think about us being outside in the afternoon (average lighting) and going into a building w/o windows and closing the door behind us. your eyes receive an input from the room's lighting output.

if it's really dark in the room, you're going to be blind in the darkness. the input levels in the room are too low for you to get a good signal. (this is what happens if your gains are set too low. amp is set for a 4 V input and you've got .5 V outputs from the HU)

if it's really bright in the room, you're eyes are going to be overwhelmed when you walk in... you'll be blind, but from visual overload. the input levels are way high for you, and so your visual signal is distorted. (this is what happens if your gains are set too high. amp is set for .5 V and you've got 4 V outputs from the HU OR amp is set for 4 V inputs and you've got 8 or 16 V from the HU.)

if the room is at a similar light level as the outside, when you walk in everything looks just fine and you see great w/o any distortion or problems. your input levels and the output levels of the room match... (this is what happens when your gains are set right. amp set for 4 V and HU outputs 4 V.)

now, of course, your eyes will adjust in time - but your amp's input levels will not.

along the same lines - the signal output by your eyes to your brain didn't increase or decrease based on the lighting of the room... but your perception of the signal did.
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amps generally work in the same way.

sorta.

in an amp's case though, if you set your gains low you can reduce the power output by the amp. BUT setting your amp's gain higher than optimal DOES NOT make more power. this is why you can adjust your gains down slightly and run power slightly above the speaker's rated power. it's because by dialing the gains down, you're actually reducing the amp's output power before the HU starts to clip. (you're losing max volume)


so, in reality can you get away w/ the 8 V preamp outputs on an eclipse head unit w/ an amp that doesn't support them? yes, but you're also distorting the signal before you normally would when the HU's output voltage exceeds the amp's rated input voltage. it doesn't make the amp run cooler or make more power. the best thing to do in that case would be to install some signal attenuators to get your output signal to match up w/ the amp's input range... is it necessary? no...
generally speaking -- amp gains are not volume knobs... (there are exceptions... think Jensen, Kraco, etc.) turning the gain down means you're making the amp less sensitive. turning the gain up means you're making it more sensitive... sensitive to what? the input Voltage.

here's a detailed page all about amplifier gains and setting them: http://www.bcae1.com/gaincon2.htm
please take a few minutes to read this page as it is way enlightening, and not horribly technical. take special note of the shockwave / flash demo at the bottom.

note the first paragraph...

quoting myself from this thread: http://forums.s2ki.com/forums/showthread.p...threadid=203883
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PJK3

From the FAQ:

what's the best way to set the gains on my amp? how do i set the gains on my amp?

the best way to set the gains on your amp is to use an oscilliscope, a spectrum analyzer, and test tones and use the method found here:
http://www.bcae1.com/settinggainswithscope.htm

a much more practical and still very good way to set gains is to do this:
taken and modified from Crutchfield's install advisor at: http://www.crutchfieldadvisor.com/S-m9SNHU...ifiers_faq.html

-Setting the "gain" or input sensitivity control is an important adjustment common to all amplifier installations. Proper gain setting helps reduce noise and distortion and allows for the widest possible dynamic range. Here's how to do it:

1. Turn your amplifier's input level controls all the way down.

2. Choose a CD to tune with and put it the player. You will want to use a very clear musical source, but one that covers a full range of bass, midrange, and treble. Distorted types of music are a very poor selection, as it will confuse your ears. Begin to turn up your receiver's volume control. You'll begin to hear music at faint levels. (Audiophiles and sound competitors may want to use a dedicated test or test tone disc.)

3. Carefully listen for clipping distortion in the music. This distortion will be from the preamp of the Head Unit. Clipping distortion will sound like a blurring of the sound, not a mechanical popping or traditional distortion, and it can be difficult to detect, so listen very carefully. When you start hearing distortion, lower your receiver's volume control until the distortion disappears. This should be at approximately 75% of max volume. (Multiply the max volume number by .75 to confirm this value.) There will be a few exceptions to the 75% rule, where you will have distortion free sound until max volume, but there will be close to 1 in 1,000 odds. Consider this 75% number to be your new 'Max Volume" setting, as turning up the stereo above this level will only gain you distortion, but no further 'volume.'

4. At this point, you have as much signal as possible passing from your receiver into your amp. (This gives you maximum signal-to-noise ratio, so you'll enjoy clean sound and your system will be less prone to engine noise problems).

5. Now begin adjusting your amp's input gain. Turn the input level controls up until the system is as loud as you can stand it or until you begin hearing distortion

p0pe

http://www.bcae1.com/gaincon2.htm

Looking at this page all the adjustment knobs on their amp drawings go from 1v to 4v. Is this MAX gain to MIN gain (MIN volts to MAX volts)?

My amp only has MIN and MAX markings on the gain adjustment knob. Does it go from high volts in the MIN position to low volts in the MAX position? I would think so because the more you turn the knob the louder it gets.

PJK3

confusing as heck isn't it?


seriously tho... i know it is.

if turning the knob to max means it gets louder, then the labeling means it is min sensitivity and max sensitivty. which means the lower voltage matching is at the max setting (.1 V or whatever) and the higher voltage matching is at the min setting (2V or 4V or whatever)



(the actual voltages will depend upon the amp and HU/LOC, so don't strictly stick by those numbers).


looking back, i didn't answer your question. yes, as best i can tell, you have it right.

Rich04

how similar would this be to setting up a sub amp?

PJK3

same.

biggest problem is that hearing the clipping distortion in the smaller frequency range for a sub is a bit harder.