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Should i use a line driver for my carputer?

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  • Should i use a line driver for my carputer?

    Hi, I am building my first carputer and I have a few questions about the audio. (I am using a non amplified sound card; signal amplitude about 0.3V)

    1. Do i need to put a pre amplifier between the BASS output on the soundcard and the subwoofer amplifier?

    2. if so, would the pre-amplified signal connect to the high level or the low level input of the subwoofer amplifier?

    3. I built a circuit board to "pre amplify" signals from 0.3V to 2.5V; Low THD% sounds good overall.
    My Speaker Amplifier can take an input of up to 6V.
    Would my homemade circuit be sufficient or should i buy a professional line driver?

    4. Does it make a difference in distortion if I am at the high end or low end of the allowable input signal (Range 0V to 6V)

    I have searched many online resources for the last 3 days and experemented with various circuit boards and even went to the local car audio shop, no one seems to know!!!!!!!

  • #2
    1. no you don't HAVE to, but you can.
    2. you connect it to the low level input.
    3. 2.5v is average. Good enough for the BASS
    4. It depends. Usually the higher the better, but there are diminishing returns as it will start to distort..perhaps even clip

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    • #3
      I have been reading online that a pre-amplified signal should go to the high level input, because low level input will get damaged from too much voltage.
      Is that true??

      Comment


      • #4
        yeah if there is too much.. just stay at 6 or under and you should be fine.
        Hi levels are for getting a signal from a speaker wire. The application is usually for people who have factory headunits without RCA outs.. So they connect their speaker wires coming from the head unit straight into the hi-levels inputs on the amp.. as you can imagine, the signal on those speakers wires are going to be high.

        Usually the hi-level inputs on the amp will not give you the best quality, so you want to use the low-level inputs.

        Comment


        • #5
          Interesting topic. I was thinking about getting the audio control unit. My amp is old and I no longer have the manual so I can't check there to see what a safe voltage is to input. I guess we try it without first then see if it's needed.

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          • #6
            Originally posted by gibroni View Post
            Interesting topic. I was thinking about getting the audio control unit. My amp is old and I no longer have the manual so I can't check there to see what a safe voltage is to input. I guess we try it without first then see if it's needed.
            Exactly!

            line drivers are usually not needed unles the amp's input gain isn't sensitive enough to deliver full power with the amount of signal level injected into it. 99% of the time you do not need a line driver. Either way, if you could not properly match you amp gain to the signal level and acheive the output you desire then that is where a line driver comes into play.
            System always under construction


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            • #7
              another factor is how many amps you have on the line, 2.5v to one amp will be a whole lot better than 2.5v to 3 amps.
              MY NEWEST INSTALL:modded infiniti fx with big screen

              first windows carpc install........my liquid cooled LVDS screen :D

              Comment


              • #8
                I don't know if I would agree with that. The input impedance on an amp is usually high enough it won't make any difference and voltage in parallel is still the same voltage level seen at all the amps connected.
                System always under construction


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                • #9
                  hmm, this I won't argue as fact, but from my experience I've found this to be true, a bank of amps will require a higher line voltage if there all run off the same line is the impression I've always been under.
                  MY NEWEST INSTALL:modded infiniti fx with big screen

                  first windows carpc install........my liquid cooled LVDS screen :D

                  Comment


                  • #10
                    I won't argue with experience but I was just curious where that came from. I have never really ran a bank of amps so I don't know, but anything is possible if the source unit can't deliver the current if it's heavily loaded down. Similar if you split the signal a bunch of times. I have only ever used a 6 channel line driver to multiple amps.

                    I still stick with my statement of most of the time you won't need a line driver, but it does more than just increase the signal voltage

                    i.e.

                    -lower output impedance of the source = more current to input signal of amp
                    -clean up ground loops if it is properly designed (or add ground loop noise if it's improperly designed)
                    -can help lower the noise floor IF installed properly.
                    System always under construction


                    Comment


                    • #11
                      back in the day line drivers were the way to go, there was no 8v preouts or digital transmissions.it was also rare to have 3 sets of rca's out from a head, only real high end units had them. I have done installs that started out as one amp, & then added to them & in almost every case I did need to readjust the gains up to bring it to the same level when a few amps were on the line, then there would be times that the gains would need to be too high & a line driver was considered a necissary addition, the ones I've seen not affected by this is when the amp has it's own pass thru output though

                      I've also worked on vehicles with multiple amps banked to subs & from my experience if only one amp was connected the input was enough to adjust the gains fine, but when all the amps were on line the gains needed to be raised quite a bit or a line driver added. back then eqt's were the equiptment of choice for achieving this as well as eq'ing the system. later on eqt's & the like were thought to be not all they were cracked up to be, but back then they were the shet, then again, I remember when dat's were the shet too, & before that dolby b & c cassettes, metal tapes, I guess all things evolve
                      MY NEWEST INSTALL:modded infiniti fx with big screen

                      first windows carpc install........my liquid cooled LVDS screen :D

                      Comment


                      • #12
                        Originally posted by durwood View Post
                        -lower output impedance of the source = more current to input signal of amp
                        -clean up ground loops if it is properly designed (or add ground loop noise if it's improperly designed)
                        -can help lower the noise floor IF installed properly.
                        Those are reasons why a line driver can be a benifit to almost any low-Volt system. The key is to place the LD as close to the source unit as possible.

                        Comment


                        • #13
                          ^^^^ that is one of the reasons the eqt's gained a bad rep, guys would install them in the trunk, then run rca's from a 2v head all the way back, now, the line driver in the eqt's is amplifying the noise picked up as well as the signal. eqt's weren't noisey but they got a rep for being noisey because of how they were intended to be installed.
                          MY NEWEST INSTALL:modded infiniti fx with big screen

                          first windows carpc install........my liquid cooled LVDS screen :D

                          Comment


                          • #14
                            What About Trebble, Power

                            Originally posted by ironfinger View Post
                            3. 2.5v is average. Good enough for the BASS
                            4. It depends. Usually the higher the better, but there are diminishing returns as it will start to distort..perhaps even clip
                            I have an 800W (60W RMS x 4) speaker amplifier (FR, FL, RR, RL), and 2 x 12" Subs each powered by a 1200W (550W RMS) amplifier.

                            *3 Amplifiers in total.

                            So 2.5V (which is about 40% of the makimum input of 6V) is good enough for the BASS Amplifier. Does "good enough" mean **** off the Nabour Powerfull or just "good enough".

                            What about the regular speaker Amplifier (FR, FL, RR, RL) would 2.5V be good there or should i lean closer to 6V? (I Want Loud BASS and Trebble)

                            I am asking because i want the most power (with still low THD%) coming out of my little investment here!

                            Any Sugestions to input levels to my different Amplifier? (max input 6V)

                            Comment


                            • #15
                              average/good in that 2-volts is around what you normally see in aftermarket head units. It's only usually the more higher end models that you get more than that.

                              You should be good at 2.5 volts for all your speakers. But you can still add a line-driver for the reasons mentioned in the previous posts.

                              Your amps seem to be powerfull enough to give you the volume you want, but still make sure you set the gains correctly.. the higher the signal-voltage the amps sees, the lower you set the gains. I have around 7volts going to my amps and it's gains are set all the way down.

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