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formula for setting gain?


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jeffchilcott 
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Posted: March 26, 2005 at 2:04 PM / IP Logged  
I know jl has a chart for thier amps. that will tell you the voltage output on certian amps.    btu is there a formula that you can plug in say, you are using a amp that is actually running at 200x2@1/2 ohm and you want to set the gains.     is there a formula to use to figure this out?
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DYohn 
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Joined: April 22, 2003
Location: Arizona, United States
Posted: March 26, 2005 at 2:26 PM / IP Logged  
Ohm's Law will get you pretty darn close.
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Lizardking 
Copper - Posts: 184
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Joined: August 23, 2004
Posted: March 26, 2005 at 8:20 PM / IP Logged  

This is what I use when setting mine!! Not perfect but it will get you darn close.

So many people have their amp gains set wrong, and to be honest setting them by ear is quite a crapshoot. Doing it properly with a multimeter is actually quite simple.

Here's how you do it:
Set head unit volume to 3/4 of maximum. Turn off all eqs/presets in the head unit.
DISCONNECT SPEAKERS
P = Power in watts
I = Current in amperes
R = Resistance in ohms (effectively the nominal impedance)
V = Potential in volts (Voltage)
Knowns:
Resistance (nominal impedance of your speakers)
Power (desired wattage)
Unknowns:
Voltage (we'll measure this)
Current
Formulas:
P = I*V (formula for power)
V = I*R (Ohm's law)
So after a little substitution to get Voltage in terms of simply power and resistance we get
V = square_root(P*R)
So, for example, say you have a 4 ohm load presented to a 150 watt amp.
V = square_root(150*4) = 24.5 volts
This means you should increase the gain until you read 24.5 volts AC on the speaker outputs of your amplifier.
As a source, use a sine wave recorded at 0db at a frequency within the range you intend to amplify. You can generate tones in cool edit or use a program such as NCH tone generator. (credit for NCH to imtfox, IIRC)
Additionally, you could use a scope to actually check if the signal is clipping, but I'm not going to get into that here as I doubt very few people have access to that type of equipment.
UPDATE:
After playing around with the following programs:
Cool Edit 200
Test Tone Generator
NCH Tone generator

Eclipse "Approaching Perfection"
DYohn 
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Joined: April 22, 2003
Location: Arizona, United States
Posted: March 26, 2005 at 8:40 PM / IP Logged  
Like I said, Ohm's Law.
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jeffchilcott 
Platinum - Posts: 2,483
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Location: United States
Posted: March 30, 2005 at 5:06 PM / IP Logged  
kinda the way I tried to explain to someone, but they didnt want to listen I just wanted to get a little more info and print it off. thanks guys
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2006 USACI Finals 2nd Place

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