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amp output voltage calculation


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Alpine Guy 
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Posted: October 19, 2007 at 9:22 AM / IP Logged  
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.
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.
haemphyst 
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Posted: October 19, 2007 at 10:18 AM / IP Logged  
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. amp output voltage calculation -- posted image.
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."
DYohn 
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Joined: April 22, 2003
Location: Arizona, United States
Posted: October 19, 2007 at 10:22 AM / IP Logged  
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.
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Alpine Guy 
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Posted: October 19, 2007 at 1:28 PM / IP Logged  
Perfect, thanks.
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.
aznboi3644 
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Posted: October 20, 2007 at 1:04 AM / IP Logged  
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??
stevdart 
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Posted: October 20, 2007 at 11:34 AM / IP Logged  
No load = no output. 
Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.
DYohn 
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Joined: April 22, 2003
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Posted: October 20, 2007 at 11:49 AM / IP Logged  
Input gain should be set with speakers disconnected.
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aznboi3644 
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Posted: October 20, 2007 at 11:58 AM / IP Logged  
DYohn wrote:
Input gain should be set with speakers disconnected.
you mean turning up the gain on the amp with no speakers connected??
DYohn 
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Joined: April 22, 2003
Location: Arizona, United States
Posted: October 20, 2007 at 12:20 PM / IP Logged  

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.

  1. Disconnect speakers.
  2. Turn your gain/input sensitivity all the way down. Turn off any bass boost and bypass crossovers.
  3. 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.
  4. Connect your AC voltmeter to the amplifier's output channel.
  5. Insert test tone CD. Select a tone within your amplifier's intended frequency range.
  6. Adjust the gain until you reach the calculated target voltage for output into your speaker's load.
  7. Reconnect your speakers and verify proper operation. Set crossovers and adjust levels down if necessary to achieve tonal balance.
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haemphyst 
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Posted: October 20, 2007 at 10:08 PM / IP Logged  
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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