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Thread: Gettting more power from your standard MPS stereo

  1. #1

    Default Gettting more power from your standard MPS stereo

    Ok, so I know I'm new here, but I feel I can contribute with a cheap and easy mod you can do to both the MPS3 and MPS6. I wasn't the person who thought of this or the designer, but I do know a little about electronics and I can explain how it works.

    With the standard Bose stereo, you will find that to get some decent bass you need to give turn the bass setting up on your dash to + 2 or 3. Unfortunately, when you do this, it limits how loud you can get your system because your door speakers start to distort when the volume is in the low 20's. However, the subwoofer is not being used to it's full potential. This little mod turns the volume up on the sub so you can decrease the overall bass setting on your dash which does 2 things. 1, Allows you to turn the stereo up louder, giver you stronger treble with less bass from the doors. 2, At lower volumes, the midrange is reduced giving the bass a 'punchier' sound.

    The circuit is simple, only 5 components and can be built by anyone who can solder really. I have a wiring diagram, I cant take the credit for it, I didn't draw it. I have attached it below.

    I bought all the components from Jaycar, you will need,

    1 15k resistor
    1 4.7k resistor
    1 100uF Capacitor
    1 1uF Capacitor
    1 LM741 OpAmp
    1 Small solder board to build it all on.
    1 standard spade terminal.

    Once you have built the circuit you are ready to put it into your car. It is wired in just before the sub amplifier. Open your boot and have a look at the sub mounted in the parcel shelf. The black box underneath it is the amplifier. Unclip the lead going to it, and undo the 1/4" bolts holding it to the sub, carefully lower it down and disconnect the red and green wires to the sub. Be very careful, the sub terminals are very fragile and will break easily, dont let the amp dangle from the sub. Once you have it removed the amp, you can install the circuit. The wiring is as follows. Connect the +12V source to the orange cable on the amp (splice it in). The ground source is the black wire (splice it in aswell). Splice the -Signal wire into the yellow wire. The purple wire needs to be cut, once cut, the wire that comes from the plug is your +Signal source, the wire that goes into the amp it your Signal output.

    When you have connected everything up, wrap it all up in electrical tape neatly and find a good spot to stuff the circuit. The circuit inverts the signal coming from the dash, so you need to swap the wires onto the sub. you will need to replace one of spade terminals so that you can swap the wires, one is bigger than the other.

    Connect it all up and bolt it back in. Get in your car and test out possibly the best stereo mod I have ever seen. If I have missed anything or you have any questions, just ask. Also, if people aren't confident with this sort of stuff, I would be willing to build and/or install these for people for a small fee.
    Attached Files Attached Files

  2. #2
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    Nice write up luke! Cheers.

  3. #3
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    I removed all the Bose stuff. It was really really bad. Installed Alpine speakers and a 4ch amp and a powered sub in the boot. Much much better.

  4. #4
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    Similar, 4 Polk Audio door speakers, Focal Powered sub under passenger seat and sound deadening....10 sheets of it...$1000 fitted.

  5. #5
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    Is anyone able to re-upload the pdf with the wiring diagram on it. The one in the post is blank as far as I can tell.

    Or I could just try to buy one from kmh001 if available.

  6. #6
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    Default Yes please luke

    Hello luke, i like the sound of your mods excuse the pun i would like you to make up one for me . You can install it as well if you are thinking of a holiday in Cairns Far North Queensland .pm me with price ,my mps has the sports pak optional bose unit is that ok . Do you think i would get some one up here to install it if you don,t take up my holiday offer Col
    THE COLON FILES
    Coming soon

  7. #7

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    Not sure about the trip to Cairns lol, but an auto elec could easily fit it. I will try to upload the PDF again when I get the chance, and I should be able to knock one up for you aswell fastaz.

  8. #8
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    Quote Originally Posted by mymps3 View Post
    I removed all the Bose stuff. It was really really bad. Installed Alpine speakers and a 4ch amp and a powered sub in the boot. Much much better.
    I agree, Alpine gear is better - will eventually replace all mine as well.

    Have you sen Jenx's install and custom Sub holder??
    Bloody brilliant!!

  9. #9
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    actually depends on your ears and your budget...I have heard high end Bose gear (not whats in the Maz) and it is miles above Alpine.

    After hearing different brand speakers I will never buy Alpine ever again haha Focal, Hertz, MB *drools*

  10. #10
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    Quote Originally Posted by tricache View Post
    actually depends on your ears and your budget...I have heard high end Bose gear (not whats in the Maz) and it is miles above Alpine.

    After hearing different brand speakers I will never buy Alpine ever again haha Focal, Hertz, MB *drools*
    I was just sitting here thinking the same thing, Hahaha. Alpine? What the hell... I've never had an issue with my Bose stuff. They're not ridiculously loud, but +2 Treble and +1 Bass saw an easy and crystal clear 114dB when I checked it new.

    Also, I can't open the PDF, but the circuit you posted is undoubtedly an active, low-pass filter. Just be careful using anything with a gain >1 as any distortion seen on the input, or caused by the circuit itself, will be amplified on the output and seen by the Sub/Amp. You run the risk of damaging your sub and amp if this happens.

  11. #11

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    See if that works?
    Attached Files Attached Files

  12. #12
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    Quote Originally Posted by Luke View Post
    See if that works?
    Nope

  13. #13

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    pdf views fine on my mac....no probs

  14. #14
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    Quote Originally Posted by zippymps3 View Post
    pdf views fine on my mac....no probs
    Yeah, you and the other 3 guys

  15. #15
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    And here it is for the rest of us...
    Attached Files Attached Files

  16. #16

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    Doh.. Pulled the sub out from under the passengers seat of the 3MPS, but doesn't look to be the amp there. Must be different to the 6MPS.

    Had the circuit made and all!
    Last edited by nath; 15-11-2009 at 06:32 PM.

  17. #17

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    This looks like a fairly poor mod designed by somebody with a dangerous knowledge of electronics.

    Firstly the circuit is a high pass filter, with a cutoff around 35Hz. This is not what you want for a sub woofer, since the amplifier is now trying to remove low frequencies.

    Secondly the voltage rails supplied to the opamp are +12V and Gnd, however the signal that requires amplification will (probably, haven't tested many line level speaker signals myself) contain +ve and -ve components. This circuit will remove any negative component as the lowest the opamp will be able to pull down to is about 1V. This will effectivly cause massive clipping.

    Thirdly (and far less important if the other 2 issues don't bother you) the LM741 is a fairly 'pedestrian' general purpose opamp. Not good audio quality.

    Fourthly this circuit will put an odd phase shift on the signal (depending on frequency) which 'may' be notice...

    For this to work well a properly biased amplifier circuit or dual (+-12) voltage rail would be required.


    What is the sub woofer audio quality like after this mod? Sure there is a gain setting on the amp that would be so much easier to adjust!

  18. #18

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    You seem to know more about electronics than I do so I wont try to contradict anything you say, but I can vouch for it's effectiveness. I would be fairly confident in saying that I am getting sound levels below 35Hz, I've not noticed anything missing in the low frequencies. What does a high pass filter circuit look like?

    On you second point, as far as I'm aware, 1 of the singal wires is a permanent ground, the other only goes as low a 0 volts, but I've not tested and stand to be proven wrong.

    Although the LM741 is relatively poor, I was under the impression that the fact we are only working at low frequencies means it's floors dont show.

    I know that this Circuit reverses the signal, and as such the wires need to be swapped on the speaker, are you refering to this or a more subtle shifting??

    I'm all ears, as I said I only know a little about electronics, so I would love if you could clarify those few points I made and if you had a more effective system in mind, I would be interested in trying it out.

    BTW there is not gain control on the little amp, it's just a 'toy' one.

  19. #19

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    Quote Originally Posted by Luke View Post
    You seem to know more about electronics than I do so I wont try to contradict anything you say, but I can vouch for it's effectiveness. I would be fairly confident in saying that I am getting sound levels below 35Hz, I've not noticed anything missing in the low frequencies. What does a high pass filter circuit look like?
    It doesn't instantly stop frequencies, but rather rolls off. The amp has about 10dB of gain at higher frequencies, at 35Hz it's about 7dB (and cutoff is usually measured as the -3dB point). You probably wouldn't notice it as it is still providing the signal (with gain) to the amp, but it is giving more gain to higher frequencies. It is like an equaliser, but an effect you either don't want or just don't notice/know about.

    You can tell it's a high pass filter as there is a series capacitor in the input. This is needed as a form of AC coupling, but if it's too small it will have less gain on parts of the signal you want. It's cut-off may be less than 35Hz if my analysis is out...

    A low pass filter generally has a shunt capacitance (ie signal to ground).

    On you second point, as far as I'm aware, 1 of the singal wires is a permanent ground, the other only goes as low a 0 volts, but I've not tested and stand to be proven wrong.
    One wire is almost defiantly ground. The other is either 1 of 2 things. 1) The signal coming from the HU has a DC offset. This is removed by the series capacitor mentioned earlier, which means the signal into the opamp will contain -ve components. 2) The signal coming from the HU already contains +ve and -ve components. Either way

    You may not notice this effect if you are purely going for sound/noise level, but an oscilloscope or proper listening would be able to show you.

    Although the LM741 is relatively poor, I was under the impression that the fact we are only working at low frequencies means it's floors dont show.
    It's flaws pale in comparison to other issues. Probably something you'd never notice.

    I know that this Circuit reverses the signal, and as such the wires need to be swapped on the speaker, are you refering to this or a more subtle shifting??
    More subtle shifting. But again, probably something you'd never notice.

    I'm all ears, as I said I only know a little about electronics, so I would love if you could clarify those few points I made and if you had a more effective system in mind, I would be interested in trying it out.

    BTW there is not gain control on the little amp, it's just a 'toy' one.
    I'll try my hand at drawing up a little nicer circuit, with gain control (easy enough with a POT). I'd also be worried about creating ground loops and adding hum to the system, so you may consider using one of the audio transformers/isolators on the input.

    It would be necessary to know the details of the signal coming from the HU to provide a circuit I would be confident in using. ie. What peak voltage level it is providing, operating frequency range. Whether it is a +- signal (which I would assume).

    ---------- Post added at 07:30 PM ---------- Previous post was at 06:54 PM ----------



    This circuit will bias the incoming signal with a +6V DC offset. The amplifier will then provide 1x - 3x gain on the signal.

    I have left the values of the input and output capacitor off. These need to be tweaked a bit. You can try the 1u caps you are using now, but the bigger the better. You can try polar capacitors too, just ensure the +ve is towards the middle.

    As for the opamp, just use the LM741 and nobody will care/notice.

    I also forgot, the capacitor across the 12V and GND is a good idea, you should keep that too!

    As a note: I don't warrant this circuit what-so-ever!

  20. #20

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    Quote Originally Posted by YOU LOSE View Post
    Hello luke, i like the sound of your mods excuse the pun i would like you to make up one for me . You can install it as well if you are thinking of a holiday in Cairns Far North Queensland .pm me with price ,my mps has the sports pak optional bose unit is that ok . Do you think i would get some one up here to install it if you don,t take up my holiday offer Col
    Col I can solder m8, and I work at Jaycar lol Let me know if you wana do this mod
    "THE PATH OF THE GTI-R IS BESET WITH PERIL BY THE INJUSTICES OF THE SPEED CAMERA AND THE TYRANNY OF OTHER DRIVERS. BLESSED IS HE WHO OVERTAKES THE EVO & STI THROUGH THE VALLEY OF HAIRPIN TURNS, FOR HE IS TRULY HIS CAR'S TUNER AND THE FINDER OF LOST HORSEPOWER. . . AND WE SHALT STRIKE DOWN WITH GREAT BOOST AND FURIOUS ACCELERATION ON WHOEVER DOTH ATTEMPT TO OBSTRUCT OR DELAY OUR OVERTAKING. . .
    BMW M3 Evo Coming to the R stable soon. . .

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