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Thread: Special audio preamp circuit

  1. #1
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    Special audio preamp circuit

    I have a chrysler with the infinity head unit and amp. I found that the amp works much like a normal audio amp, only it seems to take a slightly higher power input than just a line out.

    Past suggestions included line drivers, preamps, and headphone amps. I am looking for a more simple solutions, and I would like everyone's input.

    I opened my headunit, and found the connection where the HU feeds the audio signal into a small preamp, and through the volume control, out to the amp (in the trunk). I spliced in my lineout signal and ran it through the preamp in the head unit. Aside from a great deal of noise (i think i had bad grounding and onboard sound, buzz and fuzz), the sound seems to be at about the right level.

    I would like to build a small audio amp circuit VERY similar to the one in the head unit, but there a few more problems. First, i have yet to design and build a circuit from the ground up. Obviously, this can be a problem. Second, the volume control is not as it seemed. It is a digial knob (turn to the left acts like a vol down button being pushed, and same for turning right and vol up). With the head unit's audio signal unpluged, and the computers linout signal in it's place, the volume control did not work. Instead, turning the knob did NOTHING, until i turned it very low, at which point it would mute the output. So with my signal, it was either 1 volume, or mute.

    Does anyone have any suggestions about design and building a small preamp with similar specs and a volume control?? (I would REALLY LIKE to try to include a digital vol control, b/c i do not want to send the audio signal all the way up to the dash and back. I would like to keep everything in the trunk).

    PLEASE HELP! I have pics of the circuit boards, and I can collect any other info. I would even be willing to pay someone to make something i can use.
    System in the works:
    Celeron 850 or PIII 933, SB Live! Value into a stock 4 channel amp, ATI vid, 10.4" sharp LCD w/ allen's controller, Elo SW touchscreen overlay and controller, GPS, TV tuner, FW DVD drive, 4 port serial card, and some other stuff....

    Loads of ideas.

  2. #2
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    Hey Clay, not sure what it is you're trying to do. Are you just wanting to add a "line-in"?

    If thats it, do you want it to have its own Vol control, or controlled through the factory HU?

    I'll try to do what I can to help, but can't promise anything.

    BTW, I'm in Jacksonville, so we're pretty close. :-0

    Love that Panda Chinese buffet down your way!

    See ya, Dex

  3. #3
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    Hey dex, how are you? I should tell you that I just moved. I am not longer in Gainesville, I am now in Madison, Florida. Madison is about an hour and a half due west on I-10 (from jax). What kind of car/equipment do you have?

    Anyway, what I am trying to do is a little different than adding a line-in. I want to get rid of the head unit. In fact, I have to for 2 reasons. It is too big, and it is going bad.

    What I want to do is run my computer sound card's line-out directly into my amp. I have found that the amp needs a slightly higher power input than my line-out. So, i want to build a small amp circuit, similar to the one used in the head unit. With volume control.


    Another thought: I found a Mobile Authority MEQ-800 (i think), which is a 2 channel eq/preamp. I can get them for $30 each. If I get two of them (in order to get 4 channels) how could i control the volume of both (at the same time)? They are dash mount units, but I would put them in the trunk, and run some sort of volume control button/knob to the dash. What does everyone think of that??
    System in the works:
    Celeron 850 or PIII 933, SB Live! Value into a stock 4 channel amp, ATI vid, 10.4" sharp LCD w/ allen's controller, Elo SW touchscreen overlay and controller, GPS, TV tuner, FW DVD drive, 4 port serial card, and some other stuff....

    Loads of ideas.

  4. #4
    Maximum Bitrate allenruble's Avatar
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    hear one i use for my set up http://cgi.ebay.com/ws/eBayISAPI.dll...tem=1942287587 It is all in one unit and it got volume control . It sounds good runing sound from my computer to my two amps . the out put of the eq is 10volts it sould be good to hook out to your amps .
    www.sounddomain.com/id/2000mp3ranger

    Mp3 player - 10.4 Allbrite Gigabyte GA-71XEH , 700 mgz t-bird , coolmaster fan , 2x 128 ram + 1 512ram , ATI-RAEON RV100 ,on bd sound , Linksys Wireless-B usb network adapter , 20G IBM TRAVELSTAR

  5. #5
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    I went and checked out that preamp, it looks pretty nice. I am going to look into the specs further, but I have another question. With a crossover, the highs and/or lows are pulled out of a signal, and sent to seperate outputs... what happens if I do not want the crossover to pull the lows out to the subs? In other words, i do not have subs. I would like the bass to go through the 4 channels. Is there a knob for that?

    Also, do you know what kind of volume control it has? I would like some sort of a control that I can hook up a remote button (without running the sound back to front and back).

    Allen, how have you been? I have not seen you around. Hey, another question. I went by your site, and I saw a weird keyboard setup. What is that laptop keyboard you are using? I have one that I would love to hook up, but i do not know how to build a custom kb controller. Let me know, i am very curious.
    System in the works:
    Celeron 850 or PIII 933, SB Live! Value into a stock 4 channel amp, ATI vid, 10.4" sharp LCD w/ allen's controller, Elo SW touchscreen overlay and controller, GPS, TV tuner, FW DVD drive, 4 port serial card, and some other stuff....

    Loads of ideas.

  6. #6
    Maximum Bitrate allenruble's Avatar
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    the eq got full range to front and rear and a sub out with all low bass .
    www.sounddomain.com/id/2000mp3ranger

    Mp3 player - 10.4 Allbrite Gigabyte GA-71XEH , 700 mgz t-bird , coolmaster fan , 2x 128 ram + 1 512ram , ATI-RAEON RV100 ,on bd sound , Linksys Wireless-B usb network adapter , 20G IBM TRAVELSTAR

  7. #7
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    I understand. So it does not 'pull' the bass out, it 'splits' it. Ok, i am going to see if i can win this auction.

    What do you know about the 4500?

    Also, is that keybaord a laptop keyboard??
    System in the works:
    Celeron 850 or PIII 933, SB Live! Value into a stock 4 channel amp, ATI vid, 10.4" sharp LCD w/ allen's controller, Elo SW touchscreen overlay and controller, GPS, TV tuner, FW DVD drive, 4 port serial card, and some other stuff....

    Loads of ideas.

  8. #8
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    Clay,
    take a look at www.audiocontrol.com in the car section. They have a Master Volume Control (MVC) which will do what you want.

    UPDATE: I went to the site after posting this, and it is no longer listed on the main car audio page They still have the manual online however: http://www.audiocontrol.com/Manuals/...s%20Manual.pdf

  9. #9
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    I see that the unit has a line level adjustment, but does it work as a preamp? I need something that is going to preamp the signal before it goes into my amp.
    System in the works:
    Celeron 850 or PIII 933, SB Live! Value into a stock 4 channel amp, ATI vid, 10.4" sharp LCD w/ allen's controller, Elo SW touchscreen overlay and controller, GPS, TV tuner, FW DVD drive, 4 port serial card, and some other stuff....

    Loads of ideas.

  10. #10
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    Jan 2002
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    Can anyone tell me if the Directed 5500 or 4500 models actually input 4 seperate channels, amp and eq them, then output those 4 seperate channels? The specs on both of them mention multiple source inputs, and I fear instead of inputting 4 channels, it is really 2 stereo inputs (CD and AUX), then the stereo is split into 4 channels.

    As for the MVC mentioned above, does anyone know if it has any amplification, and where I can get one?
    System in the works:
    Celeron 850 or PIII 933, SB Live! Value into a stock 4 channel amp, ATI vid, 10.4" sharp LCD w/ allen's controller, Elo SW touchscreen overlay and controller, GPS, TV tuner, FW DVD drive, 4 port serial card, and some other stuff....

    Loads of ideas.

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