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Utilize factory subwoofer and speaker amps

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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!
    Celeron 2.53 Ghz Processor
    512M ddr memory
    Mimo 7" USB Display
    XM Direct Tuner
    mp3car.com XM Direct USB interface box

    1999 Mustang GT Convertible Supercharged

  • #2
    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...

    2006 Mazda 3
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    • #3
      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.
      ** Denotes an "in car" post
      In-Car posts made from passenger seat - Be safe, Don't Post and Drive.

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      • #4
        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!
        Celeron 2.53 Ghz Processor
        512M ddr memory
        Mimo 7" USB Display
        XM Direct Tuner
        mp3car.com XM Direct USB interface box

        1999 Mustang GT Convertible Supercharged

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        • #5
          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
            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.
            Celeron 2.53 Ghz Processor
            512M ddr memory
            Mimo 7" USB Display
            XM Direct Tuner
            mp3car.com XM Direct USB interface box

            1999 Mustang GT Convertible Supercharged

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            • #7
              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.
              ** Denotes an "in car" post
              In-Car posts made from passenger seat - Be safe, Don't Post and Drive.

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              • #8
                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!
                Celeron 2.53 Ghz Processor
                512M ddr memory
                Mimo 7" USB Display
                XM Direct Tuner
                mp3car.com XM Direct USB interface box

                1999 Mustang GT Convertible Supercharged

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                • #9
                  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.
                  ** Denotes an "in car" post
                  In-Car posts made from passenger seat - Be safe, Don't Post and Drive.

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                  • #10
                    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?
                    Celeron 2.53 Ghz Processor
                    512M ddr memory
                    Mimo 7" USB Display
                    XM Direct Tuner
                    mp3car.com XM Direct USB interface box

                    1999 Mustang GT Convertible Supercharged

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                    • #11
                      Alright, I tried the simple mixer today, but it didn't seem to work. I don't know if the electronics store gave me the wrong part, but I asked him for 2 10Kilo ohm resistors. He pulled some out of a drawer and I paid like 50 cents for both of them. The don't say anything on them, but they are colored. They are light blue with red, orange, black, and brown stripes on them (shaped like a small capsule). What could have gone wrong? There is no sound out of the woofer (if there is any, its too low for me to hear) when I use the resistors.
                      Celeron 2.53 Ghz Processor
                      512M ddr memory
                      Mimo 7" USB Display
                      XM Direct Tuner
                      mp3car.com XM Direct USB interface box

                      1999 Mustang GT Convertible Supercharged

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                      • #12
                        The resistors you have are indeed 10kohm. The resistors that you use I believe depend on source, 10k is probably average. I believe it depends on the source's "output impedance" as to the size of resistors you use. I'm not sure how to measure that or calculate it, but you may want to try smaller resistances - perhaps 5k or so.
                        Other than that, maybe post a picture of your circuit so we can take a look.

                        There is an issue with this simple mixer system. Because you are using resistors to mix the signals, the output will always be less than what you had to begin with. Normally you would just turn up the gain on the amp to counteract this affect, but because you are using a factory amplifier the gain adjustment is fixed - you cannot adjust it. If you end up with enough bass for your taste, then you are OK, but if there is less than you like you may have a problem. You might be able to boost the bass on the winamp equalizer to overcome this, but the best solution would be to remove the mixer and simply use only the left channel to drive the amplifier.

                        Peace.
                        ** Denotes an "in car" post
                        In-Car posts made from passenger seat - Be safe, Don't Post and Drive.

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                        • #13
                          That's what I'm going to do. I'm just going to most likely replace the factory amp with an amp that accepts two inputs. For now, I'll just use the left or right channel to drive the amp. I don't have my computer in the car yet (finishing the bezel for the dash and had to gut the original radio to do so), so I'm using an IPOD for my music. That could have something to do with it.
                          Celeron 2.53 Ghz Processor
                          512M ddr memory
                          Mimo 7" USB Display
                          XM Direct Tuner
                          mp3car.com XM Direct USB interface box

                          1999 Mustang GT Convertible Supercharged

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                          • #14
                            So did you get the 4 channel amp working ok? Mine seems to generate a LOT of noise until the carpc boots up & initialises the sound card.

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                            • #15
                              Ok, completely cured all the noise with a pair of ground loop isolators. It's working brilliantly now.

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