How to set input sensitivity on amp?

02tjsport · Mar 30, 2006

I have a kenwood HU that has (3) 5V preamp outputs. My sub amp's input sensitivity goes from .25V - 4.5V What should i set it at. I've read somewhere that you are supposed to match it. And i have blown a few subs when setting it lower than the preamp voltage. But it hits alot harder at lower volumes.

Currently i have a JL 10w6, so i really dont want to blow it. I'm thinking that if i keep the two sides the same it will reduce the chances of blowing the sub.

Just wondering if someone can explain exactly what it does or how it works so i better understand and set it up properly.

Thanks all

Giviner · Mar 30, 2006

Basically, you need a multimeter to set them. The formula is:

Square root (Expected amp output power X wired impedance) = voltage

My setup for example: 375W total output, wired into 2 ohms

= sqrt(375x2) = 27.4V

So I used my multimeter and adjusted my gain until the reading was 27.4V.....pretty simple huh?

From this point you can adjust the gain down as required to match but don't raise it above this point.

SirGcal has a good calculator built into his website. www.sirgcal.com just follow the link "SirGcal's Audio Setup Tips" and "Adjusting Gain Controls Correctly"

02tjsport · Mar 30, 2006

Well thanks for that tip, but that is not what i am talking about. However that does help me understand how to tune it.

The input sensitivity on my amp is seperate from my gain (i think):
The input sensitivity dial has the readings of ".25V (highest)", .".50" "1.0" 2.0" "2.5" "3" "4" and "4.5V (lowest)"

With my sony head unit i had 3v preouts, so i set it at 3v. Now i have a kenwood with 5v preouts and so i set it at 4-4.5. Is that right, and does that make any sense?

02tjsport · Mar 30, 2006

Just found my amp user manual
it says "Adjust this control according to the pre-out of your center unit connected to this amplifier. I was wrong the min is 5v, max is .2

Is all of this the same as gain?

Giviner · Mar 30, 2006

They are interrelated actually,

Your amp basically acts as a voltage multiplier. It will take the input voltage, multiply it, and output it to drive your speaker(s). The factor by which it multiplies is the gain. If you divide the amp's maximum output voltage by its maximum gain, you get input sensitivity.

So if your amp outputs 80V just shy of clipping, and your "gain" is set at 40x, then your input sensitivity would be 2V.

A higher input sensitivity means a lower gain setting (they are inversely related).......which is indicated on your dial, hence the reason the 5v is at the low end, and .25 is at the high end.

I would check the voltage with a multimeter just to make sure that you're not exceeding your max voltage (and as a result causing clipping).

:thumbsup:

02tjsport · Mar 31, 2006

Alright i understand but i dont. How would you have an amp that would output 80V...on my amp specs it says it is 14.4V (11-16 Allowable)

Do you mean 80W instead...im guess im kinda confused

ImRaptor · Mar 31, 2006

output voltage =/= input voltage

Namely the voltage range that you can output to the speakers is different than whats being brought in.

02tjsport · Mar 31, 2006

Namely the voltage ranger that you can output to the speakers (output from HU or from amp)?????

Giviner · Mar 31, 2006

the 14.4V is simply the voltage required to run the amp, that is how much travels through the power wire and has nothing to do with the amplified signal.

The signal that is amplified is the signal from the head unit. In your case, the output voltage from your head unit is 5V, therefore, when you set your input sensitivity to that value, your amp will take the 5 volts, increase it by a multiplier (your gain) and arrive at your maximum output voltage (for example 80V).

Now, in your case, if the lowest you can set your input sensitivity is at 4.5V you may have an issue exceeding your maximum voltage, since you can't turn the amp down any lower, but like I said, use the formula above to figure out what your maximum output voltage "should" be, and then hook up your amp and test it using a multimeter to see if it is acceptabl (i.e. equal to or lower than the # you calculated)

02tjsport · Mar 31, 2006

OH, somewhere along the lines i missed that formula being mentioned....WOW...and i was wrong about the amp the min is 5v, not 4.5

got it...34.641v for me....300w@4ohms or should i do the MAX amp output which is 1600 @ 4ohms (then it would be 80v)?

Giviner · Apr 2, 2006

no what you did is correct..............max power rating is basically useless something that the manufacturers use to sell their merchandise.

So, now that you calculated that, just set your amp to 5v input sensitivity, and measure the voltage across the channel.

Oh yeah, i forgot to mention this but to test the voltage, you will need to burn a cd of a "test tone". For subs you will need a 0 khz frequency recorded at 0db, for mids, 1 khz is good. SirG has some tones on his site that are ideal for this. You need to play the tone while you are testing the voltage. Set your bass, treble, faders, balance, bass boost, sub channel all to 0, and have your volume at what you feel is the max you would ever set it to while listening to music.

Sorry that's a bit confusing, but i cut up my finger pretty bad so i'm typing real slow,,,,,

Let me know if you need any more clarification

02tjsport · Apr 2, 2006

No, not confusing at all...i was thinking i would need a constant sound, or else the volt meter would be all crazy...i also saw the tones on SirGCal's website, so i will download those

However, i cant find the gain on my amp. I will have to scan a pic from the manual to show you that from what i think, there is no gain, but i cant do that until later tonight.

Giviner · Apr 3, 2006

Your dial witth your input sensitivities on it IS your gain. They are interrelated and all that gauge is showing is the resulting input sensitivity that you get from a certain gain adjustment. Here is a quick drawing of what I'm talking about:

SirGCal · Apr 3, 2006

In this example, input sensativity and gain are the same thing. Input sensativity is actually a more correct term for what the function is in car audio amps.

Using the printed scale is ok (and better than just cranking it up like so many people do) but using the DMM meter method is a very accurate way to do it.

Giviner · Apr 3, 2006

I was under the impression that "gain" was the multiplier by which the voltage gets increased by. Is this not correct?

I'm guessing the numbers on the dial are for more of a "ballpark" adjustment, using the multimeter is the only way to know if you are getting the desired voltage.

SirGCal · Apr 3, 2006

Jeepguy81 said:
I was under the impression that "gain" was the multiplier by which the voltage gets increased by. Is this not correct?

Yea, that is the term for gain. Adjusting the magnitude between input and output ratio. In car audio equipment, the amp section is fixed and the expected input voltage is what you are adjusting. Input sensativity is just a better term in my opinion for what this function does but it is still in effect a gain adjustment when viewed to a fixed input source.

Jeepguy81 said:
I'm guessing the numbers on the dial are for more of a "ballpark" adjustment, using the multimeter is the only way to know if you are getting the desired voltage.

Yup. Well, not the only way, but the only affordable way. An O-scope is the preferred way but that's an expensive piece of equipment.

Giviner · Apr 3, 2006

SirGCal said:
Yea, that is the term for gain. Adjusting the magnitude between input and output ratio. In car audio equipment, the amp section is fixed and the expected input voltage is what you are adjusting. Input sensativity is just a better term in my opinion for what this function does but it is still in effect a gain adjustment when viewed to a fixed input source.

Gotcha...........thanks for the clarification.

SirGCal said:
Yup. Well, not the only way, but the only affordable way. An O-scope is the preferred way but that's an expensive piece of equipment.

Yeah, but an o-scope measures sound waves, not voltage......to check the desired voltage he would need a DMM. I'm a picky bastard eh? hahaha :thumbsup:

but yeah...............if you can get your hands on one an o-scope is the way to go.

SirGCal · Apr 3, 2006

Jeepguy81 said:
Yeah, but an o-scope measures sound waves, not voltage......to check the desired voltage he would need a DMM. I'm a picky bastard eh? hahaha :thumbsup:

Well, yea, to check voltage a DMM is easiest. But with an o-scope, what you are doing is checking the sound wave itself and you can accurately set the source to just before max no clipping and then also set the amplifier to the same and you get the max potential out of the equipment with no assumptions. (even the DMM method still assumes potential power and clipping point)

Giviner · Apr 3, 2006

SirGCal said:
Well, yea, to check voltage a DMM is easiest. But with an o-scope, what you are doing is checking the sound wave itself and you can accurately set the source to just before max no clipping and then also set the amplifier to the same and you get the max potential out of the equipment with no assumptions. (even the DMM method still assumes potential power and clipping point)

hahaha...... yeah, know, just felt like being a nitpicking nerdy engineer for a second there. I'm fine now....................really...............stop staring at me!

02tjsport · Apr 3, 2006

Alright thanks guys for all your help! So i just have to adjust the input sensitivity to whatever it was i came up with before (34.64 V or something)
That really helps out alot.

How to set input sensitivity on amp?

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