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Subject Topic: How to Set Your Gains

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boulderguy
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Posted: November 11, 2006 at 2:42 PM - IP Logged
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HOW TO SET GAINS

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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%.)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


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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1lowgalant
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Posted: November 15, 2006 at 8:21 PM - IP Logged
Link to Post  Post Reply Quote 1lowgalant

pretty nice write up, exect for the "kids jumping on the bed" analogy. i think haemphyst debunked that analogy in the clipping sticky.

and i highly disagree with your ears being more accurate than an o-scope. sure, the average enthusiest probably don't have a scope nor know how to use it, but your ears are far from accurate, just accurate for your listening preferances.


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soultinter
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Posted: November 29, 2006 at 7:12 PM - IP Logged
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how do you do it w a DMM ?
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master5
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Posted: November 30, 2006 at 1:33 AM - IP Logged
Link to Post  Post Reply Quote master5

Unless you have a DMM that can read and display a sine wave..it can't be done. However, I do believe you can properly set gains by ear but you have to be on the conservative side..especially with subs because there could be clipping that can lead to overpowering the subs that you might not notice..but a scope will. This is even more critical with a bandpass enclosure since alot may be going on inside that your ear won't pick up.
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boulderguy
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Posted: December 02, 2006 at 1:35 PM - IP Logged
Link to Post  Post Reply Quote boulderguy

Of course an O-scope is the most accurate method, but if you have one & know how to use it - why are you reading this?

Using a DMM is a different story. You need to be really adept with it. Lots of ppl have differing philosophies on using a DMM, I've never seen ay definitive methods that are foolproof w/o being overly complex tho.

As for the "kids jumping on the bed" analogy - nothing wrong with that metaphor if it's used correctly. Which it is. Remember the idea is to explain a relatively complex theory in simple terms, so take it with a grain of salt.
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spaceman74
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Posted: December 05, 2006 at 10:05 AM - IP Logged
Link to Post  Post Reply Quote spaceman74

Yes! The amp runs out of power but the speaker is begging for more. The VC's resistance goes way up as the voltage is going way down. The speaker then becomes "NON LINEAR" and pushes back on the amp causing it to clip. And at the same time, the VC is getting damaged due to the high risistance (heat). "UNDERPOWER".It is not a myth! And not to mention that its aggravated when the spekers are in a wrong size undamped box. I laugh at the guys that say " I have 1000 watts! (on a 12volt charging system)
They crank it up all the time and wonder why their subs keep blowing.
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DYohn
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Posted: December 06, 2006 at 1:36 PM - IP Logged
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spaceman74 wrote:
Yes! The amp runs out of power but the speaker is begging for more. The VC's resistance goes way up as the voltage is going way down. The speaker then becomes "NON LINEAR" and pushes back on the amp causing it to clip. And at the same time, the VC is getting damaged due to the high risistance (heat). "UNDERPOWER".It is not a myth! And not to mention that its aggravated when the spekers are in a wrong size undamped box. I laugh at the guys that say " I have 1000 watts! (on a 12volt charging system)
They crank it up all the time and wonder why their subs keep blowing.

Speakers do not cause amplifiers to clip because they become "non-linear" or because their VC resistance has gone up.  This is complete nonsense.


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garagexti
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Posted: December 10, 2006 at 9:57 PM - IP Logged
Link to Post  Post Reply Quote garagexti

I see it mentions to have subwoofer level controls in a head unit maxxed out before setting the gains on the sub channel...

I was curious if you still use the same setting procedure after the level control is maxxed to set the sub channel? Do you still use the same wave output (50-80)? Is it still easy to hear audible distortion with only the subs playing?


regards,
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boulderguy
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Posted: December 11, 2006 at 12:19 PM - IP Logged
Link to Post  Post Reply Quote boulderguy

triple-yes.
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master5
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Posted: January 13, 2007 at 1:32 PM - IP Logged
Link to Post  Post Reply Quote master5

As far as "sub" level control you really want that set to full while adjusting the gains. Note that the sub control is NOT a boost....in other words it is not designed to give more power to the sub. It is used to compensate for the listeners preference or for different type music or recoring levels. However, if you allow any "headroom" on the sub control it will increase the chance of blowing subs..especially with "typical" listeners.

Many think the sub control is designed to increase the power, but think about it....if you didn't have the control (or if you unplugged a remote bass controller) the bass would not decrease...it would remain at the setting of the gain and equal to the MAX setting of the bass control. However I do agree with EQ settings to be flat during gain adjustment especially if any are on the amp. IMO an amp should not "shape" the sound...only add power, which is what an amp is for.

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