Setting my gains correctly...

[ps2cho 10+ year member]

So I have a 12" JBL GT5 sub running on a dual xpa2500 @ 150W RMS bridged. Yeh amp is cheap, but it does what I want for the price.

I would like to set the gains correctly although from what I have read I am very unlikely to damage the sub because it is rated for 275W RMS and I am running it at 150W RMS.

So let me get this straight...

150W RMS x 2ohms impedance on sub = 300

Sqrt 300 = ~ 17.3v

Now I turn off all bass boost and put normal listening volume on deck then read the + - with DMM on amplifier /w sub NOT attached and keep adjusting dials until I get 17.3v?

Do I need to bring my bass + sub bass on HU to zero? when do I adjust the HU settings?

Thanks

Click to read more...

 

[Supergumby5000 5,000+ posts]

you can have the settings on the headunit be whatever you want them to, just make sure you dont set the sub at a bass level of 0, than after its tuned, crank the bass level up to +15 (because then you wont be set at 17.3 volts, and you are at risk of clipping/damaging equipment)

setting everything at 0 is just a rough rule of thumb, because then you can fine tune your gain settings to perform at maximum with music styles you listen to (you can turn the bass up or down lsightly from the headunit after your gains are roughly set)

 

[bubbagumper6 5,000+ posts]

If you normally leave your bass boost at 0 then set your gain with it at 0, if you normally have it at 5, then set your gains with it at 5.

Basically you want to leave all your boost settings where you normally have them, and turn the volume up to what you want to be the max, then set your gain. After you've set the gain do not turn up the bass boost and do not turn the volume up past the number you chose, otherwise you'll clip the amp.

And it doesn't matter what the sub is rated for, a clipped signal will kill it.

 

[ps2cho 10+ year member]

Okay I used a 50Hz test tone and the highest it would read was 16.1v...so I'm all good right?

 

[bubbagumper6 5,000+ posts]

you mean you turned the gain to max and the most you could get was 16.1v?

 

[ps2cho 10+ year member]

you mean you turned the gain to max and the most you could get was 16.1v?

Yeh...

Oh you know what...Does the car have to be started or just ignition ok? I remember reading that somewhere...

 

[SicAudio 5,000+ posts]

start the car //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

are you running 1 4 ohm sub or 2?

the amp bridged at 4 ohm is 150 rms right? that means you need 24.5 volts.

 

[ps2cho 10+ year member]

This is my stuff:

http://www.crutchfield.com/p_10951202BR/JBL-GT5-1202BR.html?search=JBL+VENDORID109&ssi=0&searchdisplay=JBL

+

http://www.crutchfield.com/p_070XPA2500/Dual-XPA2500.html?search=xpa2500&ssi=0&tp=115

Running bridged.

 

[T3mpest 10+ year member]

If you normally leave your bass boost at 0 then set your gain with it at 0, if you normally have it at 5, then set your gains with it at 5.
Basically you want to leave all your boost settings where you normally have them, and turn the volume up to what you want to be the max, then set your gain. After you've set the gain do not turn up the bass boost and do not turn the volume up past the number you chose, otherwise you'll clip the amp.

And it doesn't matter what the sub is rated for, a clipped signal will kill it.

Clipped signals are only dangerous because they produce more power than the amp is rated for and often more power the speaker is rated for. 150 watt amp under heavy clipping might put out 300 watts, but depending on his box I' still put money the amp overheats and dies before the coils go.