Setting gain on amp

Printed From: the12volt.com
Forum Name: Car Audio
Forum Discription: Car Stereos, Amplifiers, Crossovers, Processors, Speakers, Subwoofers, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=31505
Printed Date: June 11, 2024 at 7:25 AM

Topic: Setting gain on amp

Posted By: GSRrR
Subject: Setting gain on amp
Date Posted: May 03, 2004 at 2:34 AM

I would like to set the gain on my amp but I am confused. I would be using a multimeter and will be using the E=(P*R)^.5 BUT I am confused which number goes where because I will be bridging the amp. In JL's tutorial, it says that I have to half the load and then double the voltage at the end.

i have a Rockford Fosgate 500a2 and 2-HE2 10" subs wired for 4 ohms. The amp is rated at 125 W X 2 @ 4 Ohms RMS,250 W X 2 @ 2 Ohms RMS, and 500 W X 1 @ 4 Ohms Bridged RMS

If I use P=500 and R=2 (half of 4) I get 31.62 which doubled is 63.34 Volts. Seems kind of high? Thanks.

Replies:

Posted By: DYohn
Date Posted: May 03, 2004 at 9:04 AM

Assuming the load you are placing on the amp is 4-ohms TOTAL, your correct target is 31.62. The JL tutorial is refering to using their charts which do not include the bridged power rating of the amp. Since you know yours is 500 watts @ 4 ohms, 500 X 2 = 1000, sq. rt. of 1000 = 31.62 volts. Remember to use a test tone of about 50Hz and to be sure your head unit is set below it's clipping threshold.

Your amp cannot handle anything lower than 4-ohms in bridged mode.

-------------
Support the12volt.com

Posted By: GSRrR
Date Posted: May 03, 2004 at 9:23 AM

since it 4 ohms total, should it be 500 X 4 = 2000, sq rt that which is 44.72? where can i get/borrow posted_image

test tones? thanks for your help.

Posted By: DYohn
Date Posted: May 03, 2004 at 9:34 AM

No, since it is 4-ohms total each amplifier channel will see 2-ohms of load. Buy a setup CD like this one.

-------------
Support the12volt.com

Posted By: GSRrR
Date Posted: May 03, 2004 at 9:36 AM

i see, thanks!

Posted By: GSRrR
Date Posted: May 03, 2004 at 7:36 PM

sorry to bring this back up. but, i think I have finally got it and want to double check. the 31.62 reading, i should be doing that to each channel correct? if i were to check it in mono, it will rear twice that whic h is 63.34

someone else tells me to do it this way:

"V = square_root(500*4)

V = 44.72"

Posted By: stevdart
Date Posted: May 03, 2004 at 8:07 PM

Look again at the specs you listed in original post: "The amp is rated at 125 W X 2 @ 4 Ohms RMS..."

125 X 2 = 250

The amp is rated at 250 Watts at 4 ohms.

Arithmetic.

-------------
Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.

Posted By: GSRrR
Date Posted: May 04, 2004 at 2:53 AM

i bridged it therefore its 500 W X 1 @ 4 ohms.

Posted By: Ketel22
Date Posted: May 04, 2004 at 3:45 AM

GSRrR] wrote:

p>sorry to bring this back up. but, i think I have finally got it and want to double check. the 31.62 reading, i should be doing that to each channel correct? if i were to check it in mono, it will rear twice that whic h is 63.34

i do believe your 63.34 reading would be correct for the amp in the bridged mode....31.62 per channel i do believe.

-------------
Quad L Handyman services