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Discussion Starter · #1 ·
Hi,

I am a rookie for all the mods and DIY stuff so please be patient with me. I have a 2005 Honda Accord V6 with factory radio with XM as a head unit.

I installed 2 Alpine MRP-M500 Amps with 2 10 inch E series subs. I am using the speaker level inputs on the amps so I dont have to run Pre-amp outputs from the head unit to the back. Infact I have too much of a mess around the head unit because I had a FM transmitter before and now I have a USA SPEC Ipod kit connected to my head unit. So I just tapped my rear speakers and fed it to my amps to avoid complications.

The problem is I was tuning my amps with 60hz freq sound wave, I turned the gains all the way down and was measuring the voltage output on the speaker outputs. I had kept the head unit volume control to 30 (75% of 40) and I was expecting 31.62 volts that is sqrt of (250 watts-speaker rms x 4 ohms). But I was seeing somewhere about 50V on the multimeter.

For now I have reduced the bass and turned the fader to front speakers to reduce the output under 31 volts so I don not burn my speakers down. But I am worried about them. So am I doing something wrong here?

Links to the setup is below:

http://usaspec.com/product.php?ProductID=29&forceShowProduct=1

http://support.alpine-usa.com/products/documents/OM-SWE-10_12_S4.pdf

http://support.alpine-usa.com/products/documents/OM_MRP-M500.PDF

Any help will be appreciated.
 

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Hey dude,

I don't know much about what you're working on, but I was wondering what you used to hook the factory head unit up to the amplifier? I've got the same Ipod unit you've got and was thinking of returning it to put an aftermarket radio in.
 

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Discussion Starter · #3 ·
@GunmetalV6: I hooked up my amp with the rear speaker lines. I tapped both the left and right channel wires going to the speakers. Then I connected the tapping wires to the speaker level inputs of my amp. I measured the voltage yesterday and it shows me 8.1V AC when the factory head unit is running at full volume (40). I was running a 60Hz test tone via aux in from my cellphone.

The problem was with 8V going to the speaker level inputs of my amp, it was giving out 50V AC with the gain set to the minimum. But as I already mentioned, my subs are 250 Watts 4 ohm subs. So it could only take a max of 31.62 V.

Today I talked to an electronics engineer at work and he suggested me to use a voltage divider circuit to take down the input voltage of the amp. I created a voltage divider circuit in between my tapped speaker outputs and my amps' speaker level inputs. I kept R1 as 375 Kohms and R2 at 125 Kohms. This dropped down my input to the amps from 8V to 2V.

Now I can tune the amp by adjusting the gain knob on my amp. I tuned my amps now and by keeping my gain setting at about 11 o clock and I get 31.62V out at the subs. Let me know if you need any more details on the voltage divider circuit. This is a real nice tutorial http://en.wikipedia.org/wiki/Voltage_divider :yes:
 
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