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  • Powering amps

    I used to have my amp and subs hooked up through my cd player (head unit). Once I installed my laptop and touchscreen, I completely ditched the head unit (it didn't have aux inputs). I know the way to turn the amps on is through the remote wire.

    I already know it's not safe to continually draw power to the amps, so some kind of toggle switch would be good. I already have my laptop setup with a converter from the battery. The converter has a switch that turns it on and off.

    I'm wondering how or where the best place to hook up the remote wire is to?
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  • #2
    Does your laptop have a serial port? I believe many front ends have a plugin/feature to use the DTR line of the serial port as an amp turn-on (it's 0V off, 12V on). The advantage of this is that you avoid any 'pop' associated with the pc booting up, as the amps won't be turned on until the front-end loads up.
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    • #3
      or, you can just connect it to the 'acc' wire of the cars radio harness.(use a aftermarket harness so you dont have to cut into the factory harness)

      the only reason to turn the amp on/off through the pc is if you get a pop from the audio card on the pc-- if you don't have the problem, then you don't need to rely ont he pc to turn the amps on..
      My OLD 2001 Mitsubishi Eclipse GT:
      "The Project That Never Ended, until it did"


      next project? subaru brz
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      • #4
        No serial port... very slimmed down small laptop. 2 USB's, 1 VGA, 1 ethernet, headphone, and power. No CD/DVD drive or serial ports....

        Anyways, since the amp really gets power from the car battery, I was lead to believe that the remote wire just needed something to turn the amp on/off. So, I split an extra USB cable I had and connected the remote to the +5 wire of the USB. This turned the amp on so I figured it should work.

        I then split the headphone jack into 2 RCAcables, combined them using 2 RCA->1 RCA cable, ran the one to the amps, then split it again into 2 RCA's, connecting them to the subs. I don't have the car speakers hooked up (I tested with old home theater speakers I had laying around) but had the car subs hooked up. I got no sound at all, even with the amp on. I then unplugged the headphone jack and sound was coming out the laptop.

        I know this is a crappy way of wiring, but I was thinking amp is on, speakers connected, RCA's wired like I would wire a laptop to a home theater system.

        P.S. I don't want to cut any original speaker wires/disassemble the doors, so I am planning on buying 2 tweeters and running them to the front of the car. This is essentially the same, or so I believe.

        EDIT: I am currently building my own frontend to use, I program for fun and figured I could use a good challenge. I don't know serial port programming, so that route is looking thin anyways.
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        • #5
          I tested connecting the amp directly to the car battery through a switch. When turning the switch on the camp comes on, but a new problem arose...

          Without the laptop sound barely up or muted, when plugging in the RCA cables from the laptop, I get a frequency sound that is really loud and bassy. Is this because I have it hooked to an amp for the subs? Would it play the same unbearable frequency noise if I hooked up a mid range or high range speaker to the same amp?
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          • #6
            depends on why...

            for the remote signal, i am not talking about hacking the factory harness-- this is what the aftermarket adapter cable is for-- it is a sacrificial cable-- so the factory harness stays intact--all we need is a power wire that is controlled by the ignition, and the radio harness is the easiest, most commonly documented harnesses in most vehicles.

            5v is not usually enough to power a amps trigger-- i believe some amps use the trigger line as power for the amp transistors, so low power won't allow the transistors to do their job..

            the noise could be a ground loop-- check you connections, and verify that your ground point is solid, the paint has been sanded away for a good connection. you might also need to ground the laptop power to the same spot, or it could be a issue with the power supply of the laptop--you might need to switch to a different one.
            My OLD 2001 Mitsubishi Eclipse GT:
            "The Project That Never Ended, until it did"


            next project? subaru brz
            carpc undecided

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            • #7
              The 5V info to amps is good info, and not sure if you noticed I changed it to connect to the battery with a switch installed in dash (don't want to drain battery). The amp/ground has not changed in any way. Not sure how to ground the laptop as it connects normally like a wall outlet would. Cigarette lighter power thingy that laptop plugs into.

              Do amps only accept certain frequencies? I originally had the amp and subs connected to a head unit. Without changing the amp, I tried this:

              laptop (no sound card, assuming 2.1 sound) -> headphone splitter to 2 RCA cables -> 2 RCA extensions -> amp...

              I'm wondering if the amp I have cannot accept all the frequencies being sent by the laptop? I have another amp that I will change out and try. I will report back on that.

              By the way, I changed out connections to the RCA, and noticed something weird. With 1 extension connected there is no audible frequency as I once had (also turned frequency on amp down), but with both extensions connected I get the audible frequency.
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              • #8
                being that the amp worked with a radio, you should not need to try swapping out the amps.

                a low level audio signal is a low level audio signal--weather it comes from a ipod, laptop, tape deck, or pro sound gear..

                the only reasons a amp would work with a radio and not a laptop would be because there is a issue with either the wiring your connecting it with, or the method you connected everything with.


                sorry, i misread your post on the audio connection. the way that you did it can cause problems.. the 2 rca cables coming off the deck/laptop are a stereo signal-- each one carries a different signal-- when you combined them, and then split them again, it caused the problem..

                look at the 2 rca cables coming out of the laptop as 2 pipelines-- each carrying something important, but different-- when you mix them they can cause weird issues, but keep them separate all the way through, and everything will work as they should.

                if possible, could you post either the model numbers, or pictures of the equipment your working with?

                the frequency adjustment usually has to do with the onboard crossovers on amps(changing this will allow, or block certain frequencies)..
                My OLD 2001 Mitsubishi Eclipse GT:
                "The Project That Never Ended, until it did"


                next project? subaru brz
                carpc undecided

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                • #9
                  I can get pictures posted tomorrow as well as try with splitting only the RCA's once. The wires/cables I had on hand didn't allow this, but allowed the split-combine-split again (only had 1 lengthy RCA. I will pick some up and try again tomorrow (it's dark/late, stores are closed, tired, and work in the morning)...

                  I thought the amps could differ as one amp I have listed Highs L/R,L/R and that was it. Figured that amp was for highs and the other 2 I have for lows, they just list L/R,L/R.

                  On a side note, my ground/power wires are thick and remote wire is thin. 2 out of 3 of my amps take small wire input, so the ground/power wires will not fit into the block of the amp where the wires are screwed on. Does it cause problems if I tape off exposing wires and just screw in enough that fits?

                  I'll update tomorrow evening.
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                  • #10
                    Originally posted by detlion1643 View Post
                    I tested connecting the amp directly to the car battery through a switch. When turning the switch on the camp comes on, but a new problem arose...

                    Without the laptop sound barely up or muted, when plugging in the RCA cables from the laptop, I get a frequency sound that is really loud and bassy. Is this because I have it hooked to an amp for the subs? Would it play the same unbearable frequency noise if I hooked up a mid range or high range speaker to the same amp?
                    "I get a frequency sound that is really loud and bassy"

                    The type of sound is expected because that amp would have X-overs set up for the sub frequencies.
                    The likely reason you are getting the sound immediately when you plug it in is likely due to an issue with the plug or cable. Kind of like when you plug in a live audio plug to an amp and get a bunch of noise when you first touch the plug to the socket.

                    Your statement below would also point to this theory.

                    "By the way, I changed out connections to the RCA, and noticed something weird. With 1 extension connected there is no audible frequency as I once had (also turned frequency on amp down), but with both extensions connected I get the audible frequency."
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                    • #11
                      Originally posted by detlion1643 View Post
                      I then split the headphone jack into 2 RCAcables, combined them using 2 RCA->1 RCA cable, ran the one to the amps, then split it again into 2 RCA's, connecting them to the subs. I don't have the car speakers hooked up (I tested with old home theater speakers I had laying around) but had the car subs hooked up. I got no sound at all, even with the amp on. I then unplugged the headphone jack and sound was coming out the laptop.
                      No sound may be caused by too weak of input signal. The amps gain control was likely set for the prior head that could have been 2v-5v based on the average head unit.

                      You now have used an already low signal level from a small laptop and split it for 2 amps. It's possible you may have to amplify the line signal if turning up the amp gains doesn't fix it.

                      When you say "split the headphone jack" I wonder if your rework is not shielded well enough and that is what is introducing the noise into your system. A car enviroment is pretty bad for stray noise to begin with and any poorly shielded or unshielded areas of the low level lines will be good candidates for the cause of noise.
                      My 2007 Ford F350 Work Log located HERE

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                      • #12
                        Originally posted by detlion1643 View Post
                        On a side note, my ground/power wires are thick and remote wire is thin. 2 out of 3 of my amps take small wire input, so the ground/power wires will not fit into the block of the amp where the wires are screwed on. Does it cause problems if I tape off exposing wires and just screw in enough that fits?
                        Its no problem other than if it has been wired with 4ga. for example and the amps only accept 8ga., there is a good chance the 4ga wire has been fused at a much higher value than the amps require. If so, you should lower the fuse rating in the supply wires.

                        Rather than tape off the excess wire, I would suggest 2 options:

                        a) The "professional" looking way would be to buy a fuse block that accepts one 4g. in and 2 - 8 ga. out (assuming this is what you are working with) and that will allow you to install independed fuses appropriate for each amp.

                        b) The "workaround" is to take the bared section of wire and start cutting away strands at the casing until the remaining copper all fits in the hole of the amp terminal. Again watch you main fuse value though.
                        My 2007 Ford F350 Work Log located HERE

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                        • #13
                          Well, I got the amp that runs the subs to work and subs are kicking, so I'm about 1/2 done. I remember seeing a diagram that supports running the power to the amp that will run the highs. Then take that ground and run it to the power of the amp supporting the subs. Then take that and ground it.

                          Hooking up the highs would be easy as well, they just take the right/left +/- wires from the speakers. However, I'm not sure about the subs. Is it possible to just wire the subs to the sub amp and all will work ok, or do I have to run some wires from the high amp to the low amp other than the power/ground? should the RCA's going into the high amp be split again and run 2 RCA's to each amp?

                          Also, being that I am only testing with one amp at the moment (getting spare wire for the other amp tomorrow), is it possible to run highs and subs from one amp with only one set of right/left +/- spots for wires?

                          Also, pictures of amps will be coming, apparently it's dark at 5pm. when I get out of work . I will have to take some before going to work.
                          Current Worklog: TBA - '05 Rav4 (Mobo Dead).
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                          • #14
                            pictures and diagrams of wiring setups will def. help-- there are as many correct ways to wire multiple amps as there are to incorrectly wire them..
                            My OLD 2001 Mitsubishi Eclipse GT:
                            "The Project That Never Ended, until it did"


                            next project? subaru brz
                            carpc undecided

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                            • #15
                              Well, I took some pictures this morning before work.









                              I'm using the black amp by itself for the time being. I hooked up some old highs I had from a theater system at home. There is an LPF switch on the black amp. When that is on, only lows play, so only bass no sounds. When that is off, only highs play, no bass.

                              I hope these pictures are ok, my camera doesn't charge and literally only lasted 1 and a half minutes off the charger.
                              Current Worklog: TBA - '05 Rav4 (Mobo Dead).
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