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Using a Car AMP as Preamp on Receiver?

post #1 of 17
Thread Starter 
So I have a spare Rockford Fosgate car amplifier and sub. I was wondering if it was possible to use this car amp in my home to hook up another subwoofer to my Yamaha receiver. I was watching videos on how to use a car amp in the home with computer power supply. If I do this to get the amp to power, I can inturn use it as a preamp, correct? I just wanted to double check before I went ahead and put in the work to get the amp working with the power supply.
post #2 of 17
You can't use any amp as a preamp even if it is a car amp. If you meant using the head unit - well - maybe. But not a pure amplifier.

I've been using a 10" auto sub installed in a small sealed enclosure for the past few weeks. I like to tinker! I'm driving it with a 240 watt Dayton plate amp driven by my Harman Kardon 3390. I've been very surprised at how well it sounds for music. It is very detailed and does not exhibit the boom that is so prevalent in today's car audio. Most of those are ported enclosures that allow booming bass - it impresses the street corner crowd but sounds like crap. It plays down to 35hz before rolling off - nothing to speak of past 30hz.

Get a decent power supply - a computer power supply might be ok if you don't draw too much from it suddenly - they are made for steady loads - not shock loads. Some of them are capable of cranking out 20 amps or so. Find one with a single rail - meaning all the power comes off a single side. Some are dual rail - they have in effect 2 12v sides and less amperage will be available per side. Combining them would be instant fire and sparks.

It isn't going to impress anyone with its movie performance but for music they do quite well.

My sub is an Infinity single coil 4ohm. The Dayton amp has no problems getting to work well. It'll be going into my Karmann Ghia after it gets painted over the winter. I've also got a JBL 300 watt sub amp that'll drive the sub when it gets installed into the car.
post #3 of 17
Thread Starter 
Well I guess then my question is, how can i hook this subwoofer up to my in home receiver using my car amp so that it will be a power sub and not a weak passive...cuz i'm sure its possible to make it a powered sub with the stuff I got right?
post #4 of 17
Depends on the connections to the amp. Is it RCA or speaker level inputs?

You'll need a good 12v power supply - or get a 120v plate amp and do it like I'm doing. I'm listening to classical music as I type this - sounds wonderful.
post #5 of 17
Thread Starter 
Well heres the equipment.

Trying to hook up to a Yamaha RX-V867 receiver, with a Pioneer 300w subwoofer and a Rockford Fosgate Punch 500w Amp and a standard Computer PSU (i think it's only 250w which obviously wont work cause it doesn't have enough power to power the amp and will just end up killing itself) but lets say I got a 550w [at least] comp PSU to use.....pictures below [as reference]

post #6 of 17
You'd be better off just getting a heavy duty 12v power supply. It'll have a single rail supply. Get one capable of at least 15 amps. 500W/12=41 amps. Rockford is guilty of puffery - I doubt the amp puts out 500 watts - probably 200 or so continuously on a good day. 15 amp power supply should suffice.

How does the amp get the subwoofer signal? RCA or speaker level inputs? Is the amp a mono-block - 2 channel - 4 channel?
post #7 of 17
Thread Starter 
If it isn't any trouble could you link me to what your talking about I should get, just so I dont search wrong myself? I also heard Rockford was pretty good with their power ratings, its a Punch 500a2, the older version from like 1999. Its been very good to me and still works like a champ. I replaced it with an Alpine amp thats all digital [but 175w RMS to each channel] I was thinking about bridging it to get the 2om 350w to the subs but to be honest, any more power and I think my car might rattle apart haha. I've been rocking bass in my car since I could drive and well id rather not speed up losing my hearing any faster than i am haha, but my home entertainment is a different story

the amp is 2 channel and uses RCA
post #8 of 17
Thread Starter 
Here's a picture of its inputs

125w x2 @4om
250w x2 @2om
so i guess the 500w is bridged @2om, some reviews say tho it ends up being closer to 700w
post #9 of 17
Get power supply for the rockford amp....You need to make a jumper from the remote input to the +12 volt to turn the amp on

plug rca of sub pre out of reciever to the input of this amp. Hook woofer to the amp.

It will work
post #10 of 17
Thread Starter 
Originally Posted by Vic C View Post

Get power supply for the rockford amp....You need to make a jumper from the remote input to the +12 volt to turn the amp on
plug rca of sub pre out of reciever to the input of this amp. Hook woofer to the amp.
It will work

Would something like this work? I'm not exactly which rating i should be looking at, I noticed this one is 500w

post #11 of 17
I was thinking something like this.

Even better would be this.

You'd have no power supply problems. You could get the same one I'm using on the Infinity 10" right now. Don't be fooled by the 240w rating - it'll run circles around your car amp.
post #12 of 17
Go with KNUCKLEHEAD 90's recomendation.

I was going to suggest something from Pyle they make units like that as well for bench testing car equipment. We used something like this pice to power a car stereo mounted in a hot tub a few years ago. The car head unit and built in speakers worked great for a cheep sound system that was built into a hot tub

I think even radio shack has bench power supplies for car audio...

Forget the computer supply I dont think youll get enough amps from it.

Hell a car battery charger would even work as a power supply.....
post #13 of 17
Do not use a computer power supply especially a $20 one that claims 500 watts. First off that is all rails or all voltages driven to a given level. ie. there are 5volt 3 volt multiple 12 volt rails. If you plug a 400watt device into one rail and that rail only has 100 watts that is all you will get from it or the power supply will try to provide the power and could catch on fire. You would need a very good 800-1000 watt computer power supply to actually make about 500 watts on a single rail that would output to your sub... much cheap and better is a dedicated 12 volt supply.
post #14 of 17
if you look at the data plate for the power supply you want to buy it has 2 X 12 volt rails at 20 Amps each i.e. 240 watts per plug/rail. and a max of 384 watts for both 12 volt rails i.e. bywiring the amp, which I am not sure would even work with a computer power supply.

Remember this is MAX not what it can handle for a long time.
post #15 of 17
Thread Starter 
Ok, I just had one laying around and I know you can use it to power an amp [i've seen it done in person and the tons of videos on youtube] but I think i'll go the dedicated 12v power supply route. I'm not looking to spend to much, this is just cuz I have an extra sub/amp laying around not being used. Figured I'd find a way to add it to my home system since my cars system exceeds what I'm looking for already. I'll need to get a box for the sub as well so I guess the best question is, is there somewhere that sells the power supply/box together and all i'd have to do is all the amp and sub?
post #16 of 17
just sell the speaker if you are happy with your home system. a Car Sub is not meant to do the same thing as a home sub... what is the freq responce of this sub? if it doe not go down to at least 30Hz or lower it is only going to hurt your system not help... assuming you have a decent sub all ready.
post #17 of 17
I am planning to use a pc power supply Yo power my amp and sub, I have a denon receiver and it has one single RCA out for subwoofer, so my amp has two inputs(RCA) can I run a single RCA from the receiver sub out to one of the 2 L/R inputs on my amp(I have heard of this being done or should I get a 2into1 RCA adapter and run from the receiver to the amp or can I jus use the left or right channel on the amp, thx
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