amp output voltage calculation
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=98107
Printed Date: April 28, 2024 at 8:23 PM
Topic: amp output voltage calculation
Posted By: Alpine Guy
Subject: amp output voltage calculation
Date Posted: October 19, 2007 at 9:22 AM
What calculation do you use to determine your voltage output on your amplifier when setting the gain? For example, I just repaired my Crossfire VR2000D and want to test it's output voltage, I can either run it with no load 0 ohm of course, or 4 ohm with a load which is supposed to have an rms rating of 1000 wrms.
How is it done for testing, this has never been made clear to me.
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2003 Chevy Avalanche,Eclipse CD7000,Morel Elate 5,Adire Extremis,Alpine PDX-4.150, 15" TC-3000, 2 Alpine PDX-1.1000, 470Amp HO Alt.
Replies:
Posted By: haemphyst
Date Posted: October 19, 2007 at 10:18 AM
Square root of power times resistance.
1000*4=4000
sqrt of 4000=63.245553203367586639977870888654v
(or roughly 63.25V RMS) LOL
And just a small correction, 0 ohms is a dead short. You meant open, which is ~ infinite. You said it right, just used the wrong polynomial.  ------------- It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."
Posted By: DYohn
Date Posted: October 19, 2007 at 10:22 AM
If you are trying to load test the amp, you will need to place a power resister across the output terminals. Typically an 8 or 16 ohm load is used. If you are trying to set the input gain, calculate what the voltage should be for the speaker load you intend to use (use Ohms Law) then apply the max input level you intend to use and adjust the input gain with no speaker connected until your AC volt meter indicates your calculated voltage. ------------- Support the12volt.com
Posted By: Alpine Guy
Date Posted: October 19, 2007 at 1:28 PM
Perfect, thanks.
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2003 Chevy Avalanche,Eclipse CD7000,Morel Elate 5,Adire Extremis,Alpine PDX-4.150, 15" TC-3000, 2 Alpine PDX-1.1000, 470Amp HO Alt.
Posted By: aznboi3644
Date Posted: October 20, 2007 at 1:04 AM
DYohn] wrote:
If you are trying to load test the amp, you will need to place a power resister across the output terminals. Typically an 8 or 16 ohm load is used. If you are trying to set the input gain, calculate what the voltage should be for the speaker load you intend to use (use Ohms Law) then apply the max input level you intend to use and adjust the input gain with no speaker connected until your AC volt meter indicates your calculated voltage.
when doing this i've been told to have the speakers wired up so the amp has a load.
what is the difference of doing this without a load and with a load??
Posted By: stevdart
Date Posted: October 20, 2007 at 11:34 AM
No load = no output.
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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: DYohn
Date Posted: October 20, 2007 at 11:49 AM
Input gain should be set with speakers disconnected. ------------- Support the12volt.com
Posted By: aznboi3644
Date Posted: October 20, 2007 at 11:58 AM
DYohn] wrote:
Input gain should be set with speakers disconnected.
you mean turning up the gain on the amp with no speakers connected??
Posted By: DYohn
Date Posted: October 20, 2007 at 12:20 PM
aznboi3644 wrote:
DYohn] wrote:
Input gain should be set with speakers disconnected.
you mean turning up the gain on the amp with no speakers connected??
Yes. Set your gain without any speakers connected to the amplifier. - Disconnect speakers.
- Turn your gain/input sensitivity all the way down. Turn off any bass boost and bypass crossovers.
- Turn on your head unit. Set the volume control to approx 3/4 of full, or to the point just below where clipping begins. Set all equalization and bass/treble controls to zero. Turn off loudness or BBE processing, etc.
- Connect your AC voltmeter to the amplifier's output channel.
- Insert test tone CD. Select a tone within your amplifier's intended frequency range.
- Adjust the gain until you reach the calculated target voltage for output into your speaker's load.
- Reconnect your speakers and verify proper operation. Set crossovers and adjust levels down if necessary to achieve tonal balance.
------------- Support the12volt.com
Posted By: haemphyst
Date Posted: October 20, 2007 at 10:08 PM
stevdart wrote:
No load = no output.
Ummmm.... No. No load=no POWER. Output voltage will still exist, AND follow the input voltage, but because there is no current (because there is no load) there is no power. ------------- It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."
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