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  #1  
Old 04-07-2013, 05:59 PM
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Dual amp power on-off

I have been running a subwoofer with amp to supplement the sound from my aftermarket head unit. The blue wire from the head unit signaled the subwoofer amplifier when it was supposed to turn on and off. So far, so good.

I then got a second amp to power the other speakers and installed it next to the subwoofer amp. I then jumped a little blue wire from the remote turn-on terminal of the sub amp to the remote turn-on terminal of the main amp, but with the blue wire daisy-chained from the sub amp to the main amp, the sub amp stays on all the time and drains the battery.

I've learned that in certain cases it might be possible to:

1 - Hook the blue wire to the switch terminal on the main amp.
2 - Connect main amp OUT to sub amp IN (using "Y" connector for 2x mono signal).


But I think the sub amp would need to have the capability to sense a signal and turn itself on automatically. From what I understand, it's rare that amps do that, and I am not certain about mine.

As it turns out, any time I connect the two amps via the remote turn-on terminals, the subwoofer amp switches on.

Is there a remedy for this?

Extra info:

The amps are both MB Quart.
RAB 1450 Reference Mono subwoofer amp
REF 4.80 Reference amplifier

There is no "slave" setting on the subwoofer amp.
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  #2  
Old 04-08-2013, 09:28 AM
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A suggestion - use a double pole relay to isolate the head unit from the amplifiers.

The blue wire from the head unit goes to the relay coil, wire the other side of the coil to ground.
Tap the main power wire from your amp with a 1 amp fuse, then connect to one side of the relay contact. Wire the other side of the relay contact to the turn on input of the amp.

Repeat for the other amp.

Now both amps have their own isolated turn on signal.
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The OM 642/722.9 powered family
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)
2008 ML320 CDI (Older sonís DD)
2008 E320 Bluetec (Younger son's DD)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech
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  #3  
Old 04-08-2013, 08:35 PM
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Honestly, I don't know ANYTHING about electronics. Searching with google, I see there are double pole, double throw? What is a "throw" anyway? Are there different ratings on relays? Any kind of insight would be helpful.

I asked the people at SonicElectronics, and they suggested I use a second battery exclusively dedicated to running the audio system. The car's main battery will not drain that is true, but won't the second auxiliary battery always be drained, then? What's the point of that?
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Last edited by 1983/300CD; 04-09-2013 at 03:30 PM.
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Old 04-09-2013, 09:40 PM
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Sorry for the technical jargon, I'm a controls engineer and I forget not everyone knows the language.

The number of poles is the number of independent circuits that can be switched by the relay. Normally there are from one to 4 circuits in the relays used in the automotive world. Most are single or double pole.

The "throw" refers to the possible state of the contacts. All relays are at least single throw, which means the contact blocks power from flowing when the coil is off and passes power when the coil is on. Some relays are double throw, which means that the relay contacts have 3 points, a common, a normally open, and a normally closed. Power passes from the common to normally closed if the coil is off, and from the common to normally open if the coil is on.

What you want to do is use the 12 V signal from the car stereo to turn on a relay coil and then use the relay contacts to switch the turn-on signal to the amplifier. If you have a double pole relay then you can use one relay to turn on both amplifiers. If you have only single pole relays, you will need two relays.

There are many different ratings but for your application you only need a relay with contacts rated at least 1 Amp. And you want the coil to be 12 Volts DC. Radio Shack might still have something suitable.
__________________
The OM 642/722.9 powered family
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)
2008 ML320 CDI (Older sonís DD)
2008 E320 Bluetec (Younger son's DD)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech
----------
gone but living on
1983 240D (body to greazzer, engine to t walgamuth)
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  #5  
Old 04-10-2013, 03:29 AM
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What do you think about this one?

Normally Open Relays - Dual 87 Contacts

It's 30amp, but it seems to have the features I need.
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