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Using Amp or Head Unit to power speakers

Old 06-03-2016, 03:33 AM
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Default Using Amp or Head Unit to power speakers

I am getting ready to take the plunge and install an amp on my boat. I've always just used the head unit to power them. What I want to do is use the amp when I am running, and turn it off when I am stationary to save battery power. I have a friend who's boat is wired like this.

Is there some kind of device that is wired between the speakers and amp/head unit to prevent the amp from backfeeding to the head unit? Or are there just diodes to prevent this.

Thanks
Old 06-03-2016, 04:22 AM
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You will need to put a switch on the blue remote turn on wire from the head unit to the amplifier. Ideally this signal is also connected to the coil of a changeover relay. The changeover relay has the speakers connected to the common terminal and switches them to either the head units amplifier when the amp remote is off, or to the power amplifier when on. The relay is multipole depending on number of speakers with contact rating to match the amplifier RMS power output.
Old 06-03-2016, 06:42 AM
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You cannot wire the output of a HU amplifier and the output of an external amplifier to the same speaker by any means. So you have to use a switch(s) with a ton of poles, or relays with a ton of poles. If using four channels you have to switch eight poles from both the HU and amplifier. Keep in mind that the HU likely uses a bridged 4-channel chip so there is no common ground.
An external amplifier is only going to pull a couple of amps at idle. An external amplifier will have a switching power supply that is about 95% efficient. If using a Class D external amplifier the audio portion is likely more efficient than the HU. So in the big picture, at the exact same power level (determined by the HU limitations), the current draw between the HU and amplifier will not be substantially different. Yes, the amplifier will pull just slightly more current while the HU power is dormant . The easy method would be....when at rest, simply turn the system down to a level equal to what the HU would have been. You have a numeric indicator on the HU to go by when the day gets long and your hearing becomes fatigued.
Old 06-03-2016, 06:47 AM
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Originally Posted by Duramax3 View Post
I am getting ready to take the plunge and install an amp on my boat. I've always just used the head unit to power them. What I want to do is use the amp when I am running, and turn it off when I am stationary to save battery power. I have a friend who's boat is wired like this.

Is there some kind of device that is wired between the speakers and amp/head unit to prevent the amp from backfeeding to the head unit? Or are there just diodes to prevent this.

Thanks
I gather you want to use the HU internal amp when just sitting vs using the amp.
The ways to do this can get quite complex and some routes will end up giving you the know how to wire a nuclear sub.
Keeping it simple since your set up seems pretty easy...

You could always do this a little more by the book. Buy a class d amp. They are close to 90% efficient. What they pull from batt they put out in power. Older a/b amps took 1000watts of batt power to put out 500. So batts go bye bye fast. Wire amp directly to house batt or separate batt and put on its own perko. Get to fishing spot and seperate batt from rest and listen to your hearts desire. Recharge when running. Or simply leave as you have now and simply lower the volume as the amp will greatly exceed anything your head unit puts out.

Last edited by Dockholiday74; 06-03-2016 at 08:28 AM.
Old 06-03-2016, 07:43 AM
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Quote..."Keeping it simple since your set up seems pretty easy...
1. Put the external amps remote on/off in a toggle switch. Don't use the one from the radio. Hook up all the speakers to both the HU and amp. When you don't want to use the amp just turn it off via the toggle switch. This might not work on all head units."

Dock,
You just can't do the above (hook up all speakers to both the HU and amp) for any number of reasons.
Old 06-03-2016, 08:02 AM
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In answer to your request for a device to be wired between speakers and HU and Amp...use .one of these for each speaker...

NC connected to Head unit out speaker wires.
NO connected to AMP out speaker wires
COM connected to speaker
All high impedance coils wired in parallel to REM.
Simple.
Although you never asked for advice on how to use your equipment, anything that reduces the operating hours of your power amp will obviously extend its life expectancy.
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Old 06-03-2016, 08:23 AM
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...
Old 06-03-2016, 08:32 AM
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Originally Posted by David Analog View Post
Quote..."Keeping it simple since your set up seems pretty easy...
1. Put the external amps remote on/off in a toggle switch. Don't use the one from the radio. Hook up all the speakers to both the HU and amp. When you don't want to use the amp just turn it off via the toggle switch. This might not work on all head units."

Dock,
You just can't do the above (hook up all speakers to both the HU and amp) for any number of reasons.
I pulled the option to not cause him any harm. I have seen it work in an older system but not sure if it was using line level inputs or some other way of making it happen but there were no relays etc.
I think it's a bad idea all the way around and a lot of work for a limited benefit.
Old 06-03-2016, 05:36 PM
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Originally Posted by Dockholiday74 View Post
I pulled the option to not cause him any harm. I have seen it work in an older system but not sure if it was using line level inputs or some other way of making it happen but there were no relays etc.
I think it's a bad idea all the way around and a lot of work for a limited benefit.
I agree with you. It is a bit confusing wiring up relays for a non professional. Not to belittle the capabilities of boat owners. I can only gauge competency by the nature of the question.
He asked about a device and I advised him on it. I also agree in this case it maybe as you say "of little benefit" although that's for him to decide.... I have used this system on noisy Ski Boats for another reason.

By using this method through the ignition switch, when the engine was shut down the amp shut down and the speakers automatically switched to the head unit with a pre set lower volume level. This enabled verbal communication between driver and skiier. So the volume increased and decreased as the engine was stopped or started.
Apart from the obvious benefits, the driver is usually too busy to operate the sound system due programming the Wakeboard ballast system like Perfect Pass. Skiing is a very busy job for the driver. Many Ski boats have the stereo in the glove box on the other side of the boat and the observer has to operate it which means he ain't doing his job.
Old 06-03-2016, 07:24 PM
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Originally Posted by isitstuffed View Post
I agree with you. It is a bit confusing wiring up relays for a non professional. Not to belittle the capabilities of boat owners. I can only gauge competency by the nature of the question.
He asked about a device and I advised him on it. I also agree in this case it maybe as you say "of little benefit" although that's for him to decide.... I have used this system on noisy Ski Boats for another reason.

By using this method through the ignition switch, when the engine was shut down the amp shut down and the speakers automatically switched to the head unit with a pre set lower volume level. This enabled verbal communication between driver and skiier. So the volume increased and decreased as the engine was stopped or started.
Apart from the obvious benefits, the driver is usually too busy to operate the sound system due programming the Wakeboard ballast system like Perfect Pass. Skiing is a very busy job for the driver. Many Ski boats have the stereo in the glove box on the other side of the boat and the observer has to operate it which means he ain't doing his job.
Krypt has a control box that does that now that I think of it. I think I learn more from our answers then the op's do. 🤔
Old 06-03-2016, 10:01 PM
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just leave the amp on...
Old 06-04-2016, 06:19 PM
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Originally Posted by smac999 View Post
just leave the amp on...
This and get a house battery for all accessories. Enjoy the amp.

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