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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. jayadev

    jayadev Esperto

    Messages:
    1,057
    Kannur, India
    Kannur
    Grande Punto 1.3 90 HP
    The shielded cable i have used contained two wires as core; red and black . In order to reduce channel crosstalk i used two cables separate instead of same red and black for both channels.
    So the red and black wires in each shielded cable is intertwined . now it is red black soldered to 12 and red and black soldered to 14 external shield mesh of both cables joined for ground or common.

    I forgot , i will check tomorrow morning and let you know. it is too late now to get out of home.


    2 channels for front and 2 channels for rear speakers. Though it is just parallel connections but DSP have attenuators aka "FADER" by which we can control front vs rear. so if one is keen on using fader functions or rear speaker you can pull out feed for 12 and 15th pins.
    Additionally if those feeds are sent to sub amp you get a pre-out for sub woofer too , where you can control the subwoofer levels using fader control.

    I lifted pin 12 and 14 of the power amp ic. now power amp stays idle, no feed to its input. and i take(hack) the same feed from the circuit board(pcb)

    Certain other models of blaupunkt with same DSP processor have Variable subwoofer output, plus 4-ch preamp outputs which needs additional controller or switches .which are being omitted here .those areas which I have pointed do not have needed components for additional features.
    we can tap pre out from there too but without any actual or original controls or comands as controlling circuits are omitted . look carefully in the pic you can observe circuit tracks for an IC and couple of components missing.

    crooked way is in the above bold ,underlined sentence.
    2nd way is gentle and standard way- you dont need to (should not) adjust or alter subwoofer settings once setup is done. subwoofer is just for lower range of bass tones to extend the range of normal loudspeaker. so subwoofer amp is fed with stereo front or rear channel signals which is further processed by mixers and filters inside the amplifier. i hope most of the modern subwoofer amps have filters and rca inputs with internal mixers
    Last edited: Aug 12, 2011
  2. Italia-Linea

    Italia-Linea Staff Member Janitor

    Messages:
    2,123
    Pune
    thanks a lot for the explanation. now i got your point.
    So now you have just 2 channels. one is front left and other is front right. so say the front left is red and front right is black. that is why you interwined one red and one black and soldered it to one pin i.e 12 and one red and one black of other channel to 14.

    so i need to do the same for pin 11 and pin 15 for rear out.

    i would prefer rear out RCA and connect it to sub amp so that fader control works for sub. this will give the user the capability to tune the bass for every other song as per his liking using fader control.

    i was browsing some forums where these kind of RCA hack is done. i am not able to understand why are they soldering a capacitor across the RCA wires?

    so now what kind of sound quality you get :) i mean the climax?? cheers and kudos to your DIY !!
  3. jayadev

    jayadev Esperto

    Messages:
    1,057
    Kannur, India
    Kannur
    Grande Punto 1.3 90 HP
    When itcomes to messing around with RCA level signals you must use good quality Shielded wired otherwise you will end up with hiss,hum ,brrrr,and all sort of noise in audio system.
    generaly two core wire as in figure is good but those 2 cables ,red and black would be going together close enough creating mutual interference (crosstalk) so it is always good to use 2 separate shielded cables for each channels.

    yes if you prefer additional controls.But caution!! do not do not short circuit with other connections or whole system may go up in smoke or may damage your high power amplifiers and speakers too.

    Capacitors filters out unwanted DC contents (that is what capacitors are good for) additionally they act like low frequency cut off filter to.
    if you add 0.47microfarad capc to 22k ohm input impedance amplifier ,you will have cutoff at lower cut off at15hz.

    let me convert "hearing is believing " thing into proper words .let us discuss some more thing before we finalize.
    Else it would be ridiculous if i say, it sounds better than this and that, bass is round or square, etc etc...

    plug16.jpg
  4. johnny

    johnny Regolare

    Messages:
    437
    Greater Noida
    Greater Noida
    Grande Punto 1.3
    Great work Jayadev.

    It is good to read posts from 'experts'.

    Regards
    Johnny
  5. jayadev

    jayadev Esperto

    Messages:
    1,057
    Kannur, India
    Kannur
    Grande Punto 1.3 90 HP
    Thanx johnny, I am no expert but just a TFI member.
    Last edited: Aug 12, 2011
  6. anoop

    anoop Superiore

    It is a pleasure to watch this kind of DIY. Glued to this thread.
  7. royj

    royj Esperto

    Messages:
    1,306
    Trivandrum
    You are the expert member in TFI for this domain :D
    Thanks for sharing your Gyan..
  8. jayadev

    jayadev Esperto

    Messages:
    1,057
    Kannur, India
    Kannur
    Grande Punto 1.3 90 HP
    Hmm.
    Truth I realized, deeper I go, lesser I know. so cant agree for expertise.

    What is the first thing one should do if he or she want good sound in present linea or punto .
    As we all know change the speakers.
    Yes those speaker are crap. Either they will blow off themselves or take away your head unit to hell sooner or later. ( i have no idea what made fiat to compromise on speaker quality to this level).
    I used polk audio db650 comp speakers in front doors.

    How does it sounded with oem HU amp.
    sounded mellow, (I think those speaker are little less than being flat sounding but they are not bright -very good!). highs and lows were lethargic.
    I investigated the reason.- lack of power! those internal amplifier delivered nothing more than 12 to 16 watts at full volume.
    (internal Amps are AB class bridge amplifier which could deliver 12 watts X 4 from 13 volts battery. )

    I added an amp.
    Excite stereo amp . it was laying in home since long time, 2x60 watts..viola!!!
    Last edited: Aug 12, 2011
  9. Italia-Linea

    Italia-Linea Staff Member Janitor

    Messages:
    2,123
    Pune
    ok jaydev, sorry for so many questions but here i come again with another one.
    does the power amp ic do all the trick of reducing the bass as the volume increases to protect oem speakers or is it the DSP that does it?

    again to the suspense!! what do you think how much voltage does the RCA you tapped drive? i am asking this to guess what gains you need to set on the amp to match these voltages
  10. darkshooter

    darkshooter Amatore

    Messages:
    153
    Navi Mumbai
    Can't we replace TDA7385 with TDA7560 for better amplification?

    First pic is 7560 and other one is 7385

    tda7560-audio-amplifier.jpg

    TDA7385.jpg

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