Running speaker level inputs to amp (Also question about best sub/amp combo)

carl_lazlo · 09-09-2009, 10:35 AM

I just had my amp installed yesterday and I had a quick question for you all. The installer tapped into the wires that run from the factory amp to the subs under the seat and ran the tapped wires to the speaker level inputs on the alpine sub.

Will this cause any problems since the factory subs are still connected to those wires? (Impedance mismatch, etc.)

I'm back off to the shop today because after about an hour of playing, the system is not working. The blue light on the alpine amp is flickering and there is no sound from the sub. I think there may be some loose power connection to the amp since that blue light shows when the amp has power, but the amp itself may be bad, not sure yet.

Technic · 09-09-2009, 10:51 AM

What aftermarket amp is this?

carl_lazlo · 09-09-2009, 11:09 AM

Alpine M-350 with speaker lvl inputs. If the amp is bad I will be replacing it with the new Alpine M-500. I guess if the amp is bad I don't ahve to go with an alpine amp, are there better sub amps for the money that have speaker lvl inputs?

Also, I have a 10" alpine sub with this setup. Are alpine subs good or is there something better for the money?

Technic · 09-09-2009, 11:54 AM

The OEM amp puts out a peak of 40W into each woofer, so it is more or less in line with what the MRP350 amp can take at its high level inputs. Those high level inputs in the MRP350 have an input impedance of 40K ohms, so from the point of view of the OEM amp there's nothing connected other than the OEM woofers at its outputs.

In other words, your MRP350 should be working fine the way it is connected.

What could be happening is that the OEM remote is borderline acceptable as the turn on for this amp, so it swithes the amp on and off intermittently. This is not unusual for the OEM remote, as its operational voltage is between 10 to 12V.

Use a relay to really be sure that there is a solid 12V swiching signal as your remote. Your installer should know how to wire a relay to the OEM remote to accomplish just that.

AWM3 · 09-09-2009, 04:16 PM

Quote:

Originally Posted by carl_lazlo

I just had my amp installed yesterday and I had a quick question for you all. The installer tapped into the wires that run from the factory amp to the subs under the seat and ran the tapped wires to the speaker level inputs on the alpine sub.

Will this cause any problems since the factory subs are still connected to those wires? (Impedance mismatch, etc.)

I'm back off to the shop today because after about an hour of playing, the system is not working. The blue light on the alpine amp is flickering and there is no sound from the sub. I think there may be some loose power connection to the amp since that blue light shows when the amp has power, but the amp itself may be bad, not sure yet.

What is the frequency response of the factory amp output to the underseat speakers? Does it have attenuation of low frequencies below 50 Hz? If it does, that will significantly degrade the performance of your subwoofer.

If you have a power problem, you should have used the switched 12V from the center console for your remote turn on, like I told you to do yesterday.

cassey · 09-10-2009, 01:41 AM

Check the ground wire for the amp.

09-09-2009, 10:35 AM	#1
carl_lazlo Doctor of Journalism 28 Rep 352 Posts Drives: E 92 335i Sapphire Black Join Date: Nov 2006 Location: Jersey iTrader: (0)	Running speaker level inputs to amp (Also question about best sub/amp combo) I just had my amp installed yesterday and I had a quick question for you all. The installer tapped into the wires that run from the factory amp to the subs under the seat and ran the tapped wires to the speaker level inputs on the alpine sub. Will this cause any problems since the factory subs are still connected to those wires? (Impedance mismatch, etc.) I'm back off to the shop today because after about an hour of playing, the system is not working. The blue light on the alpine amp is flickering and there is no sound from the sub. I think there may be some loose power connection to the amp since that blue light shows when the amp has power, but the amp itself may be bad, not sure yet. Last edited by carl_lazlo; 09-09-2009 at 11:10 AM..
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09-09-2009, 10:51 AM	#2
Technic Lieutenant General 2288 Rep 13,001 Posts Drives: 2021 i3S, 2024 i4 M50 Join Date: Apr 2005 Location: Florida iTrader: (18)	What aftermarket amp is this?
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09-09-2009, 11:09 AM	#3
carl_lazlo Doctor of Journalism 28 Rep 352 Posts Drives: E 92 335i Sapphire Black Join Date: Nov 2006 Location: Jersey iTrader: (0)	Alpine M-350 with speaker lvl inputs. If the amp is bad I will be replacing it with the new Alpine M-500. I guess if the amp is bad I don't ahve to go with an alpine amp, are there better sub amps for the money that have speaker lvl inputs? Also, I have a 10" alpine sub with this setup. Are alpine subs good or is there something better for the money?
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09-09-2009, 11:54 AM	#4
Technic Lieutenant General 2288 Rep 13,001 Posts Drives: 2021 i3S, 2024 i4 M50 Join Date: Apr 2005 Location: Florida iTrader: (18)	The OEM amp puts out a peak of 40W into each woofer, so it is more or less in line with what the MRP350 amp can take at its high level inputs. Those high level inputs in the MRP350 have an input impedance of 40K ohms, so from the point of view of the OEM amp there's nothing connected other than the OEM woofers at its outputs. In other words, your MRP350 should be working fine the way it is connected. What could be happening is that the OEM remote is borderline acceptable as the turn on for this amp, so it swithes the amp on and off intermittently. This is not unusual for the OEM remote, as its operational voltage is between 10 to 12V. Use a relay to really be sure that there is a solid 12V swiching signal as your remote. Your installer should know how to wire a relay to the OEM remote to accomplish just that.
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09-10-2009, 01:41 AM	#6
cassey Private First Class 5 Rep 181 Posts Drives: 2008 335i Sedan Join Date: Jan 2008 Location: Las Vegas iTrader: (0)	Check the ground wire for the amp. __________________ 2008 Monaco Blue E90 335i 6MT. Mods: 19" ITC Euro SD's, E46 ZHP shift knob, Matte black grills, Black Lines, 12" Infinity sub.
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