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DIY'ing on Oem HU (strictly for/with proffessionals in electronics)

Discussion in 'Do It Yourself' started by jayadev, Aug 11, 2011.

  1. Italia-Linea

    Italia-Linea Staff Member Janitor

    Messages:
    2,123
    Pune
    whats the use when you need amplification for the amplifiers which put out 10 times more power and your speakers are connected to them?

    if you dont want to add amplifier then i can say a better power amp can be put in for more power
  2. jayadev

    jayadev Esperto

    Messages:
    1,057
    Kannur, India
    Kannur
    Grande Punto 1.3 90 HP
    From datasheet it looks like like they are pin to compatible, but i doubt if those PCB/circuit board can take additional current ,and heat dissipation also becomes serious issue for high power in OEM HU heat sinks or heat dissipating technique are next to nil, more over function of pin 25 looks bit different in both case.
    Please note additional wattage or power comes when you connect 2 ohms speaker else with regular 4 ohm drivers both will have same power (maybe tda7560 will have upper hand due to mosfet output stages)
    for any power amplifier power to speaker can be calculated with this formula

    power P= V^2 /(8x RL) voltage of battery squared divided by (impedance of speaker multiplied by 8.)
    assuming voltage of battery would be 14.4 volts.
    in case of 2 ohms speaker we will have 12.96 watts of power
    in case of 4 ohms speaker we will have 6.28 watts of power

    bieng a bridge amplifier we will have qudrapled voltage at output so final power would be
    12.96x4 =51watts into 2 ohm
    6.28*4=25.12 watts into 4ohm
    considering the fact that all these amps are class AB power amps, we get efficiency of 65percent approx
    final power delivered to speakers would be
    33.1 watts into 2 ohm
    16.32 watts into 4 ohm
    rest of the power goes wasted as heat.

    best option would be to use better power amps as mentioned by Italia-Linea
  3. Italia-Linea

    Italia-Linea Staff Member Janitor

    Messages:
    2,123
    Pune
    will there be any ill effects if we do no disconnect the legs of the power amplifier and still connect the rca cables?
  4. jayadev

    jayadev Esperto

    Messages:
    1,057
    Kannur, India
    Kannur
    Grande Punto 1.3 90 HP
    I cannot assure how much but there would be from negligible to a compromising amounts.
    Reasons:-

    Manufacturer states input impedance of 100k ohm for same ic. so you are taking out parallel connection from that impedance source. while running, the ic will get heated and chances are impedance will vary with heat. the rca cable is a conductor with capacitors at either side . One at the end of dsp and other one may be inside the amp. the varying impedance and inductive nature of rca cable "can" generate oscillations or deteriorate the sound due to capacitive reactannce.
    It is just a possible hypothesis.In reality things can get even worse. like loss of high frequency or lack of low frequency etc. hope you get me.
    It is better isolated for good!!
  5. Italia-Linea

    Italia-Linea Staff Member Janitor

    Messages:
    2,123
    Pune
    what do you think. hows the DSP on this unit? does it pass on all the frequencies or does it compensate for bass etc? hows the quality of signal that DSP generates.
    what are the gain settings on your aux amp to match to the RCA?
  6. jayadev

    jayadev Esperto

    Messages:
    1,057
    Kannur, India
    Kannur
    Grande Punto 1.3 90 HP
    It is regular audio signal. same as output of regular home CD or mp3 player.
    how i can assure you is i have tested and compared the quality of sound with various players like sony-ericson mobile(810i) output , laptop output(sony vaio),philips dvd player output, they all sound flat same as output of oem HU, now how can one question all those signals are bad compared to pre out of certain brand car head unit or cd palyer.

    There is no need of filters or compensation anywhere rather it would be silly and additional expenses for such fancies but i do agree most of the manufacturers add bass boost , presence boost and surround sound etc circuits to improve the sound, but all of them are additive to true flat sound, not much appreciable (to me at least) which may please many ears not mine.

    yes , i do agree. equalizer presets are seriously messed up. It does not sound good in any settings other than flat and user eq fed by me.
    Bass treble control is very much old school type. so just maintain it at zero level means never use them.
  7. Italia-Linea

    Italia-Linea Staff Member Janitor

    Messages:
    2,123
    Pune
    in the data sheet of TDA7385 i can see pin pin 11 is IN1 and 15 is IN3 and 12 is IN2 and 14 is IN4.
    what does this IN notify? how to verify which is front left and which is front right? what makes you tap the signal from pin 12 and 14?
  8. jayadev

    jayadev Esperto

    Messages:
    1,057
    Kannur, India
    Kannur
    Grande Punto 1.3 90 HP
    IN is short for Input.

    DIY trial and error method. I played the hu with back open and figured out the signal tracks which is which one by feeding a small audio signal from mobilephone. Before you do it mark the terminals else if you touch the mobile output feed to live terminals :-( ...!!!!
  9. Italia-Linea

    Italia-Linea Staff Member Janitor

    Messages:
    2,123
    Pune
    i dint quite get you. how did you feed audio signal from mobilephone and why?
  10. jayadev

    jayadev Esperto

    Messages:
    1,057
    Kannur, India
    Kannur
    Grande Punto 1.3 90 HP
    You can use any source of audio signal. Mobile is handy. i had a broken earphone so i cut that broken earphone leaving bare wire,and other end pin connected to audio out jack of mobile.So i can connect the bare wire to amp input which would play respective channels.Just a diy rig to identify the channels.

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