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Old 17th June 2008, 04:26 PM   #1
ojcool is offline ojcool  United States
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Default current sensing relay schematic?

Sorry guys, I tried to search but so much of this stuff is over my head I can't be sure what I was looking at was what I am after.

I am adding an amplifier to my wife's Astro van and I'm just looking for a way to turn the amp on with the stereo remotely. I know I could just wire in a relay that powers up the amp with the ignition however in the past setups like this have a loud "POP" when the relay fires and I would like to avoid that if possible. Isn't there some way I can use the speaker level voltage to trigger the relay instead the way many home theatre sub amps function?

Would it be practical to use a time delay relay that would turn on after the car has started? Would that avoid the "pop"? I hate that pop sound it makes the installation so unprofessional.

Isn't there something as simple as a relay that has a low voltage threshold that would work in this respect without a ton of circuitry? And would not turn off constantly a low volume? I guess that would not be the end of the world actually since this is just for a subwoofer and at low volume you don't expect to hear the sub anyway.
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Old 17th June 2008, 04:51 PM   #2
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Using a switched power source (from the fuse box or from the rear of the radio) to switch the amp on should not cause a turn on/off pop unless the signal source is producing the noise.

Have you tried this in your current vehicle to determine if it's going to be a problem?

Are you using a good quality Line Output Converter to get signal from the head unit to the amp?

The speaker level output of the head unit is probably biased to 1/2 of the battery voltage. You could build a simple circuit (diodes, resistors, 2 or 3 transistors and a capacitor) to produce the remote turn on voltage. There would be very few instances where this would be better than using a switched power source for the remote turn on.
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Old 17th June 2008, 07:05 PM   #3
Speeed3 is offline Speeed3  Finland
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Atleast some LG:s and some other head units make popping noise, if amplifiers remote has turned on before the head unit.

Not all head units do that, try if it makes pop noise and if it does make a sircuit.
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Old 20th June 2008, 04:15 PM   #4
Dan2 is offline Dan2  South Africa
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am i getting this right??

you (currently) have the amp's remote hooked up to the ignition, so when you turn the car on the amp turns on???

so the amp is on before the head unit??

the head unit should have its own remote power supply which is usually used to turn the amp on, so the amp always tuns on after the radio. does your head unit have this?? and the amp HAS to have it.

also, are you wiring the amp up properly? the power wire should always be connected to the battery (no switches) and the remote wire should be hooked up to the head unit.

otherwise, put the relay (with a time delay circuit) on the amp outputs, so the speaker is disconnected when all the pops come through.
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Old 20th June 2008, 04:42 PM   #5
MartyM is offline MartyM  United States
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Look, this is not nearly as difficult as it's being made to be. I've installed LOTS of car stereo equipment and can tell you the following:

1. IF it is the amplifier alone (not the stereo) doing the popping, as some amps do, then you either have to live with it or go to an extreme and add replays on the speaker outputs. Not really desireable, but not hard.

2. IF it is from the head unit (stereo) itself, which is pretty common, then you can build a simple 555-based power-on time delay remote wire circuit.

The design for #2 is all over the internet, is simple, and parts are simple and cheap.

I used variations of it for a power-on delay for a vaccum tube project for the car. You can even have an adjustable time delay if desired.

Well I recommend verifying #1 is true or not, then go for it!
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