Car Amp - n00b question

isaacmacdonald

Platinum Member
Jun 7, 2002
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I have a single 10" sub in a ported tube. It's dual voice coil rated at around 75 watts (per channel?). Anywho, I previously powered this with a 100 watt amp and it was fine. My question is, is it really necessary to run a seperate wire from the amp directly to the car battery? I mean, the stock stereo is 200 watts, so you'd think the unswitched power line would be fine for another small amp (~75-100 watts). I ask this because, it's a huge whore to run an additional wire through the firewall and such.

suggestions?
 

minendo

Elite Member
Aug 31, 2001
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Originally posted by: isaacmacdonald
I have a single 10" sub in a ported tube. It's dual voice coil rated at around 75 watts (per channel?). Anywho, I previously powered this with a 100 watt amp and it was fine. My question is, is it really necessary to run a seperate wire from the amp directly to the car battery? I mean, the stock stereo is 200 watts, so you'd think the unswitched power line would be fine for another small amp (~75-100 watts). I ask this because, it's a huge whore to run an additional wire through the firewall and such.

suggestions?
Amp power is 12volt. The power it puts out is not the same as what is necessary for it to turn on. How are you powering the first amp?
 

isaacmacdonald

Platinum Member
Jun 7, 2002
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Originally posted by: minendo
Originally posted by: isaacmacdonald
I have a single 10" sub in a ported tube. It's dual voice coil rated at around 75 watts (per channel?). Anywho, I previously powered this with a 100 watt amp and it was fine. My question is, is it really necessary to run a seperate wire from the amp directly to the car battery? I mean, the stock stereo is 200 watts, so you'd think the unswitched power line would be fine for another small amp (~75-100 watts). I ask this because, it's a huge whore to run an additional wire through the firewall and such.

suggestions?
Amp power is 12volt. The power it puts out is not the same as what is necessary for it to turn on. How are you powering the first amp?
err... aren't all the car components 12v dc? I have a standard indash reciever/mp3 player that puts out 50 watts/channel (I pressume it draws the same amount as the stock reciever because it was rated the same). I want to solder on a wire from the unswitched 12v line that goes to the reciever and use it to power the ~75 watt amp (the previous amp was in a different car). I think the manual advised running a direct line because it assume the standard 12v line for the reciever is too high a guage (perhaps true for 10 watt/channel systems?).
 

minendo

Elite Member
Aug 31, 2001
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The smallest wire I would power an amp with is 8 guage. The power wire running to the deck is no where near that. It really is not that hard to run a power wire from the battery.
 

isaacmacdonald

Platinum Member
Jun 7, 2002
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Originally posted by: minendo
The smallest wire I would power an amp with is 8 guage. The power wire running to the deck is no where near that. It really is not that hard to run a power wire from the battery.
why though? I mean, isn't the reciever an integrated amplifier that's putting out considerably more (in the order of 2x) than the other non-integrated amp that I want to add? Is there some other difference that makes the ~75 watt amp consume more power?
 

sohcrates

Diamond Member
Sep 19, 2000
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you should NOT run an external amp off the unswitched line powering your head unit. you'll most likely blow a fuse or even worse

if you don't want to go to the battery you might be able to find a good gauge cable that comes from battery and goes to fuse block which you can tap into
 

isaacmacdonald

Platinum Member
Jun 7, 2002
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ok. I guess I'll run another wire. Last time, the only way I could see to make it past the firewall was to go through a rubber gasket looking thing close to the pedals. Is this the normal place people run them through?
 

sohcrates

Diamond Member
Sep 19, 2000
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Originally posted by: isaacmacdonald
ok. I guess I'll run another wire. Last time, the only way I could see to make it past the firewall was to go through a rubber gasket looking thing close to the pedals. Is this the normal place people run them through?
yes. easiest thing to do is run through existing rubber gasket

you may need to cut a hole in it, or possibly drill through firewall.

just look for a place where there's at least a little room to work
 

Gunslinger08

Lifer
Nov 18, 2001
13,234
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You'd also be wasting a speaker, as only 4 power wires come out of your typical headunit, and it sounds like you don't have the most high end stuff. So you'd have to not use one of your rear speakers and re-route it to the amp on like 20 guage wire. Think about it.
 

edro

Lifer
Apr 5, 2002
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I am using 2 gauge for my power, which goes into a distribution block and into my two powerful amps... I definately wouldn't run it off the power to your head unit.
 

SenorBlanco

Junior Member
Jul 9, 2003
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You have to be really careful when comparing power ratings between different pieces of audio equipment. For instance, a manufacturer may claim that an amp is 50W per channel - but that may be only when the amp is fed 14 volts instead of the standard 12 - or it may be into a 2 Ohm load (instead of a 4 Ohm load) - or it may be measured with a test signal fixed at one certain frequency (instead of a spread-frequency signal) - or it may only be when one channel is active. They have all sorts of ways of fudging their numbers to sound impressive.
 

isaacmacdonald

Platinum Member
Jun 7, 2002
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Originally posted by: joshsquall
You'd also be wasting a speaker, as only 4 power wires come out of your typical headunit, and it sounds like you don't have the most high end stuff. So you'd have to not use one of your rear speakers and re-route it to the amp on like 20 guage wire. Think about it.
err... wtf are you talking about?

I'm talking about the 12v feed, not the speaker out. As far as the audio inputs, that's simple enough (headunit thankfully has rca outs).

anywho, I got the amp today (POS pioneer for ~70.00). I'm just going to go through the rubber gasket and leave it at that.

-cheers all and thanks for the advice.
 

jlee

Lifer
Sep 12, 2001
48,511
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Pioneer isn't *that* bad...heh -- what model did you get? I have a 760w, and it's more than enough for the pair of JBL 6.5s it's running now..
 

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