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j s machine 
Member - Posts: 12
Member spacespace
Joined: October 25, 2008
Location: Alabama, United States
Posted: May 27, 2010 at 9:26 AM / IP Logged  
Lets say I have two drivers, both 4 ohm DVC. If I wire the voice coils in a series and the speakers in parallel, that should produce a 4 ohm load to the amp.
Let's say the amplifier is an A/B class and only stable down to 4 ohms.
I have an overheating issue, where the amp is turning off. When I measure the resistance coming from the drivers I get 3.2 ohms. I know that the accuracy can vary with many factors, but it is measuring 3.2 ohms. Is the drop of .8 ohms - down from 4 to 3.2 enough to make the amplifier run hot, or do I possibly have another issue such as a poor ground or too small of a power wire?
KPierson 
Platinum - Posts: 3,527
Platinum spaceThis member consistently provides reliable informationspace
Joined: April 14, 2005
Location: Ohio, United States
Posted: May 27, 2010 at 4:51 PM / IP Logged  
Your load sounds fine. How is your gain set? Do you have a reason so suspect that your ground wire isn't grounded sufficiently?
Kevin Pierson
blanx218 
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Joined: September 23, 2008
Location: Pennsylvania, United States
Posted: May 27, 2010 at 9:32 PM / IP Logged  

just a tip. i always advise my customers to get an amp that will supply enough power at a higher ohm load so they arent pushing their amp to the limit. especially if they do the install on their own.

example close to your situation would be to get 2 SVC 4ohm subs to go with your amp and connect them in stereo. if going with or already have 2 4ohm DVCs then I would suggest to get a 2ohm stable amp. either situation is a somewhat standard way to setup your system but wont push the amp to overheating

roadshop570 
Copper - Posts: 128
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Joined: August 25, 2009
Location: South Carolina, United States
Posted: May 28, 2010 at 12:43 AM / IP Logged  

Right on with blanx218, try it in stereo and if you have the same issue check your ground and power, is it the correct size?, then it could be a defective amp.

Chadillac
forbidden 
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Posted: May 29, 2010 at 12:11 AM / IP Logged  

I don't agree in part. You have a class AB amp that under ideal conditions is going to be perhaps 60% efficient when cold. As it heats up it is going to drop like a rock. The longer you play it at a sustained level, the more the heat is going to build up. As this amp is driving subs and not much smaller speakers, the current output is also going to be far higher. You have a couple of things going against you here.

1) you want to play the system long and loud, this makes a class ab amp the wrong choice of amplifier for the application. While it works and you have it wired properly, for what you are asking it to do, especially in the summer season, it is not the right type of amp for you.

2) your gain may be set incorrectly resulting in the amp going thermal prematurely.

3) if you have a bad ground on the amp, resistance is going to build up and this creates a breeding ground for heat.

4) is the amplifier mounted in a area that it cannot cool properly? Is it mounted on it's side on the back of a sub box and up against a seat for example. This will also keep an amp from cooling properly.

5) too small a power wire is going to be the same as me wrapping my hands around your throat and having you try to breathe. An amp needs to have a good solid source of power.

6) the amp is just too small for the application and you are overworking it.

This should give you some things to start looking at. While we have had class AB amps for the 22 years I have been installing, this problem has been there every single year. It is solved by proper wiring methods, proper setting of the amplifer, proper installation and cooling of the amplifier, proper use of the amplifier and knowing it's capabilities and limitations.

Top Secret, I can tell you but then my wife will kill me.

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