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20v DC from the amp speaker outputs?


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sin0cide 
Copper - Posts: 49
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Posted: November 23, 2006 at 1:59 PM / IP Logged  
It was my understanding that you should not see any DC voltage from the speaker outputs. I talk to this guy at my work who is a Electrical Engineer and he said that is common but I was told that if you see dc expectialy alot of it coming out of the speaker outputs its clipping or something even worse. The amp under question was not functioning but was hooked up and had the light on. It was an older amp so it had no status lights just the power light. Any idea's and has anyone ever tested for DC voltage on known good amp? This has been racking my brain
DYohn 
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Joined: April 22, 2003
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Posted: November 23, 2006 at 2:10 PM / IP Logged  

An amp should not have DC at the speaker outputs.  In fact it should not have significant voltage on the speaker outputs at all if there is no input.  Your amp is bad.

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i am an idiot 
Platinum - Posts: 13,666
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Posted: November 23, 2006 at 6:00 PM / IP Logged  

     It really depends on what kind of amp it is.   There are some class D amps that have DC voltage on the speaker wires.   Of course the amps have the same DC voltage on the positive and negative wire.  If you check from positive to negative you get no voltage  but if you check from ground to either speaker wire it will read 40 volts. 

       I need to know where you are getting your voltage from   speaker positive to ground  or  speaker positive to speaker negative.

aznboi3644 
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Posted: November 23, 2006 at 6:02 PM / IP Logged  
If an amp is clipping really really badly it'll put out a dc signal from the power supply...correct me if I'm wrong
sparkie 
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Posted: November 23, 2006 at 7:03 PM / IP Logged  
If you measure on a DC voltage scale, from a good ground to either one of the speaker output wires, you should get a reading of 1/2 the power input voltage. In most vehicles the operating voltage is 12 to 14 volts. Therefore you should expect to see roughly 6 volts DC when measuring one or the other speaker output wire. If you measure across the speaker outputs (negative to positive) your meter should be set to an AC voltage scale. It will vary depending on the volume setting and from other factors.
sparky
sin0cide 
Copper - Posts: 49
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Posted: November 23, 2006 at 9:17 PM / IP Logged  
I was reading the left channel + and - and did have a input signal.
i am an idiot 
Platinum - Posts: 13,666
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Posted: November 23, 2006 at 9:21 PM / IP Logged  

        Your amp has shorted output transistors    We are still trying to find out what kind of amp it is.

sin0cide 
Copper - Posts: 49
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Posted: November 23, 2006 at 9:32 PM / IP Logged  
I think it was a crap emerson
master5 
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Posted: November 24, 2006 at 5:06 PM / IP Logged  

If your amp is operating properly it should only send out a low voltage AC signal that will increase with volume. If you are reading DC directly from a set of speaker outputs there is a major problem with the amp, or your meter is bad or being used wrong.

Does the amp actually work? Because if it is sending 20volt dc to a speaker you will not have sound and the speaker cone will move in or out depending on the polarity and just stay there until it cooks, you will not get music.

master5 
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Posted: November 24, 2006 at 5:11 PM / IP Logged  
Nevermind, you posted the amp does not operate. But yes, I have seen defective amplifiers "dc" before so it is absolutly possible, but it is NOT something that is supposed to happen per say. I couldn't imagine a speaker handling DC for any length of time.
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