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Thread: Utilize factory subwoofer and speaker amps

  1. #1
    Variable Bitrate miwise's Avatar
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    Utilize factory subwoofer and speaker amps

    Hi, I have a Lexus SC400. . .1996 version. This car has factory amps and I've been told that i can't use these with any aftermarket system. I don't understand why not. It looks like it has pretty much the same type of connections that an aftermarket amp would (beit that they are in the form of wires and socket type plugs). It has constant 12v input, low level positive inputs and a signal ground, a ground wire, an igition 12v input, and remote input. I would appreciate it if someone could look at this schematic and see if you agree with these people. I like the factory amps and subwoofer as they are good, so I don't see spending that extra money if I don't need to. Thanks for any help!

  2. #2
    Maximum Bitrate Dennis5587's Avatar
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    Quote Originally Posted by miwise View Post
    I don't see spending that extra money if I don't need to. Thanks for any help!
    Welcome to CARPC's... the hobby based around spending money where you doing have to...

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  3. #3
    Variable Bitrate
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    I've taken a look at your schematics, as well as one that I have found:
    1996LexusSC400PioneerSystem.pdf

    It looks a little complicated to do, but I think it is possible. I haven't had any trouble interfacing with toyota factory amplifiers myself, although I have only had experience with thier JBL and Fujitsu Ten systems. I would make sure and measure the signals that you will be using - the amp turn on voltage, the line level voltage if possible - to make sure they are what you expect. If it were me, I'd go for it.

    Good Luck.
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  4. #4
    Variable Bitrate miwise's Avatar
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    Thanks for the reponse. I'm going to try and measure all of these things this weekend. All I really have is a voltometer/ohm meter. It should at lease measure the voltages pretty accurately. I'm going to go for it this weekend hopefully. Thanks!

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    MySQL Error scott_fx's Avatar
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    the problem with some stereos (namely BLOSE...ERR BOSE) is that they have external amps for only some frequency ranges to specific speakers. for instance. my car's factory amps only power the crappy 8" 'woofers' in the door, while the head unit pushes the 3" 'twiddlers' and the rear speakers.
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  6. #6
    Variable Bitrate miwise's Avatar
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    Alright, it seems that the factory amps behave EXACTLY like aftermarket ones minus the ability to adjust gain/bass and crossover frequencies. All these are preset and it seems to work exactly as it did with the radio (all speakers work. . .tweeters, mids, and subwoofer and the crossovers must have been built into the amp b/c the mids still don't have much bass, which is as it should be, and the subwoofer doesn't have highs, again as it should be). All I had to do was to jumper the ACC to the AMP 12V (A3 to A1 on my schematic in the original post at the radio amp plug). This enabled both amps.

    Now for the only problem. It seems that all speakers work correctly, but the subwoofer only has one input. I have 2 outputs from computer and don't want to cross the wires b/c it may interfere with my highs (losing the stereo effect via backfeed from these wires as they are all tied to the same plug). How can I tie both left and right to the subwoofer positive lead. I have the signal ground taken care of already. Can I use a diode on each line to prevent mixing the two channels on my highs? If so, what type of diode do I need? I'm not too familiar with diodes, but do understand what they do. I just don't know if they are appropriate for what I need.

  7. #7
    Variable Bitrate
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    No, diodes won't do it.
    You need a simple "mixer" to do what you want. Something like this:
    http://www.tkk.fi/Misc/Electronics/c...s/linesum.html

    You can buy these. Here is an (expensive) example:
    http://www.partsexpress.com/pe/showd...number=302-308

    Alternatively, you could just forget one or the other channel and not worry about it.

    Peace.
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  8. #8
    Variable Bitrate miwise's Avatar
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    Thanks for the quick reply and insight. I want to have all of my channels or some songs may sound strange. The impedence diagram seems very easy to follow. I'm going to see if I can dig some of those out of the attic. My uncle used to have loads of those things. May just go to radio shack and find some there. I didn't reallize that low level inputs are 5kohm So, this will also keep my channels from mixing for my highs and mids? Thanks again!
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  9. #9
    Variable Bitrate
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    You might also want to check out this website. It describes stereo-to-mono as it applies to subwoofer installs.
    http://www.rane.com/note109.html

    And this site describes summing amplifiers in detail.
    http://www.ecircuitcenter.com/Circuits/opsum/opsum.htm

    Good Luck.
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  10. #10
    Variable Bitrate miwise's Avatar
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    So let me get this right, the greater the resistance (of the resistor I use), the better the channel seperation, but with shortened distance capability (length of the wires). did I understand it correctly?
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