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How to verify amp output?


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poopydavid 
Member - Posts: 6
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Joined: April 04, 2006
Location: United States
Posted: May 31, 2006 at 1:14 PM / IP Logged  

hello 12v, noob to the board here  How to verify amp output? -- posted image.

anyway, I just installed an a/d/s P4100.2 and an a/d/s 12" DVC sub.    The sub should be putting out at least 350 x 2 the way I have it configured but output seems low.

Is there anyway I can use my DMM to verify this amp is fully functional?

Thanks in advance - I will have plenty of more questions in the future.....

poopydavid 
Member - Posts: 6
Member spacespace
Joined: April 04, 2006
Location: United States
Posted: May 31, 2006 at 1:18 PM / IP Logged  

ok, my bad, I did not include the required info!

1993 Camry - completely stock

a/d/s components

a/d/s 12" sub

1 a/d/s P4100.2

1 a/d/s P840

O gauge wiring, no capacitor, stock alternator, normal battery

a/d/s freak
DYohn 
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Joined: April 22, 2003
Location: Arizona, United States
Posted: May 31, 2006 at 1:39 PM / IP Logged  

Good old Ohm's law.  Power = volts squared divided by resistance.

Disconnect your speaker.  Connect your AC volt meter across the speaker terminals.  Turn on the system and play a test tone in the pass band of that amplifier.  Increase HU volume level to your "normal" listening level.  Read the voltage output from your amp.  Square it.  Divide that number by the nominal impedance of your speaker (4-ohms?)  This will give you a rough idea of the nominal power your amp is producing at that volume level.

Why is power level important to you?

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poopydavid 
Member - Posts: 6
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Joined: April 04, 2006
Location: United States
Posted: May 31, 2006 at 3:39 PM / IP Logged  

Thanks for the reply John.  Will try your method tonight..

I wanted to find a way to verify the amp is working ok because it sure doesnt sound like 700watts.

a/d/s freak
torquehead 
Copper - Posts: 144
Copper spacespace
Joined: January 15, 2006
Location: United States
Posted: May 31, 2006 at 6:32 PM / IP Logged  

700W RMS?  Mono 700W Peak more likely?  If so, 700W x 4§Ł = 2800.  Then sq. root of 2800 is 52.92Vp.  52.92V x 0.707=37.41Vrms.  37.41Vrms x 4§Ł= 149.64W RMS (actual power).  This CAN be actually be wrong for the amp you have, but you said you were a noob, just hopefully not to car audio.  Most people still choose to buy an amp with "PEAK" power ratings.  Thats fine and all, but I hope the retail packaging on the amplifier you purchased explained RMS power ratings in the format provided by CEA2006.  If not, I can pretty much explain the WHOLE specification of CEA2006 to anyone, as well as give you a reason to pay full attention to RMS.

Is PoopyDavid aware that most speakers only require 1 watt to hear 90-ish +dB at just 3 feet of distance, which is usually always claimed by all speaker manufacturers?

Mostly, by the way, I hope your amplifier is live and well.....Keep Rockin!!!!!!!!

torquehead 
Copper - Posts: 144
Copper spacespace
Joined: January 15, 2006
Location: United States
Posted: May 31, 2006 at 6:52 PM / IP Logged  

Where did I get 700W????!!!!!!!!!!  Sorry, my mistake right off the bat.  Either way, you can apply that with what you get.  By the way, if you want to conform to CEA2006 a little closer, buy or download some copy of some sound tests.  As long as you get a 1KHz sine wave.  You need an RMS Digital Multimeter.  Get a 4-ohm load, or whatever load the amp is going to be driven with, or at least leave the speaker wired to the amplifier(it will be good enough to figure this out).  Play the CD/media that has the 1KHz sine wave.  During the play, increase volume to....whatever, and touch the amplifier outputs with the meter leads.  Remember THAT AC voltage, while noting the load on that channel.  If your running stereo, make sure both/all channels are loaded, and all RCA inputs are connected with an input signal source.  Take the equation I mumbled above and apply your actual numbers to get your output power...in RMS.

poopydavid 
Member - Posts: 6
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Joined: April 04, 2006
Location: United States
Posted: May 31, 2006 at 7:34 PM / IP Logged  

well, I'll try the formula tonight.    If I read your post correctly and run a 1khz sine wave to a subwoofer, somehow that seems too high a freq. Pls clarify.

I dont think I am a noob to car audio, but havent tried this in particular before.

Yes, poopydavid is quite familiar with sensitivity ratings and what they imply. 

I just read through the CEA2006 standards and I fully agree with the argument they are making.   

Here are the specs of my amp. 

4 x 100W @ 4 ohms (13.8V - 0.01% THD)  (20-20k)

4 x 185W @ 2 ohms (13.8V - 0.01% THD)  (20-20k)
2 x 350W @ 4 ohms bridged (13.8V - 0.01% THD) (20-20k)
Fuse: 2 x 30A
Damping Factor >150

....and if I were getting 14.4 volts it could potentially be more I suppose with enough current

I'd bet good money that a properly working a/d/s amps would definately deliver its stated output rating.    are you familiar with a/d/s? 

Thanks for  both of your input and prompt replies to my post.  How to verify amp output? -- posted image.

a/d/s freak
coppellstereo 
Silver - Posts: 785
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Joined: November 21, 2005
Location: United States
Posted: June 01, 2006 at 9:31 AM / IP Logged  
you could use a 50hz sine wave to test a sub.
I'm assuming you have a 4ohm DVC sub?
poopydavid 
Member - Posts: 6
Member spacespace
Joined: April 04, 2006
Location: United States
Posted: June 01, 2006 at 11:43 AM / IP Logged  

yes, the sub is 4ohm DVC.

BTW, I forgot to mention the sub is brand new.    Perhaps breaking in of the sub is more a culprit than the amp.

a/d/s freak
torquehead 
Copper - Posts: 144
Copper spacespace
Joined: January 15, 2006
Location: United States
Posted: June 01, 2006 at 6:28 PM / IP Logged  

As for the 1kHz, yes, the sub will do it but it is high due to the nature of the sub.  I would use 100Hz actually, because your amp's slope/rolloff, it probably levels out at 35Hz (even though it drops to 20Hz) if we were using a scope or looking at a chart.  So, 100Hz and above is more reasonable.

If the engine was running (from the alternator) 14.4VDC yes, but I realize you know more about car audio than you let on.  So, Im sure you know how the internal regulated power supplies work in amplifiers that determine whether that will make a difference or not.

Ive only installed 13 a/d/s components over the decade.  So, Ill feel more comfortable saying "No" being that I have not had to troubleshoot/repair one.  But, an amplifier is an amplifier.

Got questions.  You have two 4-ohm DVC subs.  An amp with the specifications you show above.  How did you wire them?  Did you wire the subs in series (8-ohms), or in parallel (4-ohms)?  Which ever way you wired the subs voice coils, in what order did you wire them to the amplifier?  Im wondering if you wired them in parallel/4ohm each as to have 2 extra channels that are open, or did you have other speakers not mentioned?  Im wondering, you may have wired them in series/8ohm which would explain theoretically lower sound output, in which you were expecting more....just trying to uncover the specific that you have so far not stated.  Let us know if we could further help.

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