Tip & How-To about Car Audio & Video

How to set gain controls on you car audio amplifier

HOW TO SET GAINS

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The ADD version -

1. Play a typically loud music CD in your headunit. Set volume to 75%. Wear ear protection.
2. Starting with the amp gains at their lowest setting, slowly raise one gain at a time until you hear clipping from the corresponding speaker. This will sound like audible distortion.
3. Once you've found the clipping point, back the gain down until you no longer hear the distortion.
4. Repeat for any addt'l gains on the amp/amps.
5. Your new maximum volume setting on the headunit is 75%, never exceed that for happy, healthy speaker life.

(This is the quick & dirty method, it'll get you 80% to proper settings. Read on for the other 20%.)
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How to do things right -

What's gain?
Also known as input sensitivity, gains are the small, typically recessed "volume knobs" on most equipment between the speakers & the headunit. All amps have them, also many EQ's, line output converters, some crossovers.

What's it for?
The idea is to properly match the output from different pieces of gear so that each communicates the cleanest signal to the other, resulting in maximum performance and minimal noise & risk of damage.

Know your enemy - Clipping.
Clipping is the tech term for the distortion that occurs when an amplifier is pushed beyond it's capabilities. In simple terms it sounds like significant distortion of the musical peaks. So for instance a big drum strike will sound muddy or distorted when turned up, but remains clear at a lower volume. That's clipping. What's happening is the amp momentarily runs out of power.

To properly understand this w/o an engineering degree you need to know the difference between constant power (RMS) and peak power. Constant power, very simply, is the amount of juice your amp can produce consistantly. Since there are some standards for measuring this it is one of the few benchmarks we have for amplifiers. But since sound waves are exactly that - waves, with peaks & valleys - understand that an amp's output is never constant, it has to increase & decrease with the music signal.

The amp's "reserve power" is what it uses to deal with the peaks in the music. This is called peak power, or my favorite, headroom. Headroom is typically about twice the RMS power of an amp, but can only be sustained for a few milliseconds before the amp gets totally winded.

So a good way to think of this is a 10 yr old jumping on a bed - that's the music signal. The bed is the amp's RMS power, the ceiling above is the headroom limit. If the kid jumps too high he whacks his head - that's clipping. Do it a couple times & he'll survive. Do it repeatedly & there WILL be permanant damage. This is the single biggest speaker killer out there.

So the object of the game is to adjust the bed height (by using the gains) to the right height so the kid can jump around like a caffeinated monkey without ever whacking into the ceiling. So setting the gains properly allows you to get the amp's maximum output without overtaxing the equipment. With me so far?

A few other basics -
To do this properly you'll need a few things:

Ear protection. Stuff some cotton in your ears if you don't have anything better.

A test CD with a sine wave set to 0db, a 50-80hz stereo tone is ideal. This is important - it's far more accurate than using a music CD. You can purchase these at most any guitar or pro music stores, Amazon, or download a program to make your own. Making your own isn't recommended since there are a lot of variables in computers that can affect the final product.

If you have a crossover, you'll need test tones within the frequency range for each amp. For instance if you have a dedicated sub amp crossed over at 80hz, get a 60hz test tone. For your mains, work with a 120hz tone. If you have a 3-way or more crossover, adjust appropriately, just be sure the test frequency is within the bounds of the speaker range. Test each frequency seperately.

Fader, tone controls, loudness/expansion, etc.
Ideally you'll have the sound from your headunit/EQ completely flat on a normal basis. If so, be sure everything's this way before you test. However, if you KNOW you'll have the bass boost activated, some sort of expansion, or the tone controls preset in some way then go ahead & set them before you test.

Otherwise it's best to have everything flat. If you choose to adjust the tone controls later & leave them that way you can always repeat the process. Regardless, be sure the fader & balance are zeroed out.

Dedicated sub volume controls
A lot of amps have outboard sub volume knobs & headunits frequently have dedicated internal sub volume adjustments. If you plan on using these they should be maxed before setting your gains. If you're not going to use them, best to de-activate them.

Set all amp gains to their lowest point before starting. Usually full counter-clockwise.

Input sensitivity switches
If your amp has a selector switch for different input sensitivities, start by setting it to the highest setting. These are typically expressed in voltages, for example .2-1v, 1-3v, 3-8v. Start with the higher numbers (ex. 3-8v) (lowest sensitivity). If you can't get the amp to clip at those settings, try the next one down until you find the clipping point. You can disregard generally what the markings themselves say since there's no real standard for measuring that stuff. Never trust your system's well-being to those voltage numbers, they're just a guideline best ignored.

Work with one gain at a time.
For example, if you have a L&R gain for your front speakers, you'll be working with each side seperately. If multiple amps, unplug all but the amp you're working with. If a 4+ channel amp, typically you'll have only a single L & R gain, so treat it like a 2 channel. If it has more gains, isolate each & adjust seperately.

Play your test tone thru the headunit. Adjust your headunit volume to 75% of max.
This doesn't need to be precise, just be sure you know where this setting is b/c it's now the HIGHEST you'll ever turn up the volume on the headunit.

(But the amps go to 11...! You're using 75% volume because some CD's will be louder than others. Also b/c there's a small amp in the headunit that will clip if pushed too far. Trust me on this one.)

Now turn up the gain you're working with until you hear the tone quality change - it'll be a distinct change in the tone, there will be distortion. This is where your amp clips. Now turn the gain back down to just below where that distortion occurs. That gain's now set. Repeat for all other gains. Repeat for all other amps.


Final tweaking -
Have an EQ? Want to use the "loudness" button? Want to adjust the bass/mid/treble controls? If you're making minor tweaks (+/-1) there's no real need to worry about gains. If you're talking about bigger changes (+4/-3, etc) you may want to run the tones again to be sure you're still set right.

Also now that the gains are properly set you can adjust them DOWN to balance your system. Need more front volume but don't have a fader? Turn down the rear gains. Sub underpowered? Turn down the mains. The important thing is to never turn them UP from where they are, just down.


A few other notes -

Can't I just use an O-scope or DMM to set gains?
Sure, IF you know the exact output (rarely the rated output) of your amp and you're a freakin' genius with your toys. Generally more accurate & far easier to use your ears.

What about the gains on the EQ/X-over/line-output converter?
Ooh, good question. The general idea here is to follow the same process but use the gains that are the furthest UPSTREAM (I.E. closest to the headunit) and set all the others to their lowest setting. This will send the hottest signal possible thru all the components. Just remember that anywhere the signal splits you'll have to set them there also. For example, if you have a LOC & an outboard crossover you'll need to set gains on both, starting with the LOC. This can get tricky. Let your ears guide you.

What if my headunit says "9v output" and the amp only says "5v input?"
Eh, doesn't really matter. Again, there isn't really any set standard for measuring this stuff & it's usually just marketing. Also remember that music is a wave, not a line, so that rated output is usually a max, not a constant. Just set everything according to the above process, nothing changes.

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Follow the instructions on this site for accurate tuning....
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Manual For Download:
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There is so much bad information and VOODOO going around the internet about how to set car audio amplifier gain controls that I thought I better write this. Gain controls on an amplifier are basically just small potentiometers (variable resistors) or volume controls if you will, that allow you to adjust the incoming signal to the amplifier so the amplifier works well with your headunit of choice or to match the level of other amplifiers in your system.
Its not rocket science to set the gains. Gains are like little volume controls, (I don't know why so many installers are taught that gains are NOT volume controls, when in fact that is EXACTLY what they are!) its super simple to just set them where the level sounds good to you.
With one amplifier its desirable to have a nice swing on your headunits volume control. Let me try to clarify this a little.
If we hook up a head unit with a 8volt (or more) output to an amplifier, then the volume will get loud very fast when we start to turn it up...In other words if our digital volume control goes from 1-30, then a HIGH VOLT output to an amplifier might make the amplifier reach full power at 5 on the volume scale... That kinda sucks cause it would be nice if you had a little more swing in your 1-30 range!
And by the same token a headunit with a LOW VOLT output might have to be turned up all the way to 30 and might still not quite drive the amplifier to full power... That sucks too!
A gain control in this case will allow you to adjust the amplifier so it allows the volume of a headunit to control the amplifier so it will get loud at a desirable point in the 1-30 swing... Usually about 3/4 the way up. We don't want it to get loud too fast as we wont have a good control as music levels differ. And we don't want it to have to be turned up all the way to get loud either, because since different music may be recorded at different levels if we set the gains for max output with one music source it might not get loud with a music source recorded at a lesser level.
So, by setting the gains so 3/4 turn of the headunits volume knob gets it LOUD gives you plenty of control and some extra above the 3/4 mark in case you get some music that's recorded at a lesser level...
To do this its easiest to do it by ear. No need to drag out the TEST TONES and OSCILLOSCOPES! They will do you absolutely no good.
One MYTH is how the gain controls will help to prevent amplifier distortion and amplifier clipping... That's simply not true, UNLESS you set the gains at a level where the headunit cannot possibly drive the amplifier to full power.. And even if you were to find this magic spot for your gain controls then (A) you would have to turn that volume control FULL SWING to get your system loud and (B) since many music sources (or disks) are not all recorded at the same level, its likely that if you have a disk recorded lower then you cant get it loud at all! and if you have a disk recorded louder then you can still surpass your magic spot... So in reality searching for this magic spot is fruitless! Dont waste your time...
In the early 80s when high fidelity car amplifiers were just starting to make the scene I worked with a pretty crazy installer that was kind of legendary around these parts... I wont mention his name but he was pretty highly respected at the time.. Well anyway, this crazy installer had heard that the amplifier gain control was to prevent amplifier clipping.. (still widely heard today).. Well this crazy installer set up EVERY CAR WE DID to the point where the gain control was so LOW that if you turned the head unit all the way up the amplifier WOULD NOT DISTORT.. And of course if you did turn the headunit all the way up the system would just be getting loud...
Customers would find that some cassettes would be recorded at a lower level and the music just wouldn't get loud enough... The Crazy installer would FLIP OUT and tell the customer that a REAL AUDIOPHILE doesn't want his music to distort or be that loud! The customers were NOT HAPPY and came to me to say "Gee Eddie, I don't want to make the other guy mad but can you adjust my system so it sounds good and please dont tell the other guy? Of course I said yes, and some of those customers from back in the early 80s are still my customers and they are sending sending their children to me for work as well.
SO, you see the only way the gains can be used to eliminate clipping or distortion will also limit your top end volume! And for most of us it is NOT DESIRABLE to do so.
As long as this is not done, it is just as possible to turn your system up to FULL power and beyond to clipping no matter where the gains are set....

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