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Discussion Starter · #1 ·
in stock form, the bass from the Bose system is somewhat dissapointing, not loud enough, too much midbass, etc. if you think the stock sub is doing nothing and the front speakers are making as much bass, youre wrong. disconnect the sub harness and see for youself. the bose engineers at least made sure that we have the illusion of up front bass, which is a good thing.

the amplifier itself appears to be of the switching type, and while there is a potentiometer on the circuit board, it does not control the gain. keep in mind that the amp is running off of 12v supply, it does not have a power supply to step up the voltage as do most aftermarket amps, so dont expect hundreds of watts from it. i decided to make a simple preamplifier, rather than replace the system, and have had great results on my speed6. ive had a few requests for the circuit, so here it is. i usually keep the bass control to -2, and this gets rid of the midbass hump that muddies everything up. you may need more or less bass cut depending on the type of music you listen to.

the circuit is very easy to build, schematic is attached at the bottom. all parts are easily obtainable from radioshack, these are parts i had laying around, so it cost me nothing :D

gain with parts shown is just over 4. i built it on perforated veroboard, and used jumpers to make all the connections. the preamp was taped down to the amplifier with a few layers of tape on the bottom of the circuit board to prevent shorting out the connections. keep the wiring as short as possible, and twist the signal wires to prevent inducition of rf noise. values are not all that critical, but the capacitors need to be rated at least 25v. you can use 1/4 or even 1/8 watt resistors if you choose. and before people say "ewww a lm741", keep in mind that the slew rate is more than adequate for bass, and is dirt cheap. if you choose, you could swap it out for the tl series jfet chips.

Connections (on my speed6, may be different for other cars)
12v power can be tapped on the amp harness: orange wire
ground: tap black wire
in+: cut purple wire, connect harness side to preamp input, amp side to preamp output
in-: tap yellow wire

also, because this is and inverting preamplifier, you will have to cut the speaker wires (green and red wires) and connect green wires to the red wires, and vice versa, or you could swap the connectors at the ends of the wires with new ones. otherwise the sub will be out of phase in relation to the other speakers. i tried the circuit non inverting, but it didnt work as well.
ive been running this circuit for a while, have no problems with ground loops or noise, it was one of the best free mods i have done. if you dont have any of the parts, it will likely run less than $10. dont expect to have ground pounding bass but it is adequate for my use.

if you have any doubts on building circuits or if the above schematic looks like greek to you, DO NOT build the circuit as you could damage your car, start a fire, fry the amplifier, etc. i assume no responsibility or liability for this information. use at your own risk!
 

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are you inverting all the speaker connections to get the speakers in phase with the sub?

and could u take a picture of the board you made?
 

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are you inverting all the speaker connections to get the speakers in phase with the sub?

and could u take a picture of the board you made?[/b]

+1

I'd feel more confident trying this with a pic.
 

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Discussion Starter · #4 ·
are you inverting all the speaker connections to get the speakers in phase with the sub?

and could u take a picture of the board you made?[/b]
since the signal gets inverted by the preamplifier, the output of the amp also needs to be inverted to bring the signal back in phase with the rest of the speakers. i dont have a digi cam, so sorry no pics. like i said before, if you have doubts of building the circuit/wiring it up, then DONT attempt it!
 

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since the signal gets inverted by the preamplifier, the output of the amp also needs to be inverted to bring the signal back in phase with the rest of the speakers. i dont have a digi cam, so sorry no pics. like i said before, if you have doubts of building the circuit/wiring it up, then DONT attempt it![/b]
can't u just invert the output to the sub rather than the output to all the speakers? as for the picture, id just like to see how you set it up, but it's fine if you don't have a pic.
 

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can't u just invert the output to the sub rather than the output to all the speakers? as for the picture, id just like to see how you set it up, but it's fine if you don't have a pic.[/b]
That is what he is saying. He has just reversed the wires from the sub amp to the sub itself. This will put the sub back in phase compared to the others speakers in the car.
 

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k, got it. i thought he was talking about inverting the door speakers to match the phase of the subwoofer. anyways, i'm building the circuit and i'll try it out.
 

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this pre-amp works very well. cleans up the bass quite a bit. very simple to make and is very inexpensive. great mod for those who don't want to add an aftermarket amp and wolfer, or keep the sub on the shelf.

mods should sticky this thread.
 

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Discussion Starter · #9 ·
this pre-amp works very well. cleans up the bass quite a bit. very simple to make and is very inexpensive. great mod for those who don't want to add an aftermarket amp and wolfer, or keep the sub on the shelf.

mods should sticky this thread.[/b]
good to hear that you like it. with as cheap as this thing is, it definately makes an improvement for those that dont want to replace the bose system. what year/model is your car? i know you said that your wire colors are different. post them here so that others that have the same car as yours will know how to wire it up.
 

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good to hear that you like it. with as cheap as this thing is, it definately makes an improvement for those that dont want to replace the bose system. what year/model is your car? i know you said that your wire colors are different. post them here so that others that have the same car as yours will know how to wire it up.[/b]
i have a 06 ms6. actually, my wires are the same as you described. i just didn't realize you were talking about the sub amp and i was looking for the wires at the 4-channel amp. very straight forward instructions. thanks again 808.
 

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Ryceboi,

Can you take a pic of yours? I have done lots of stereo stuff, but I have not built a preamp before. I think I can handle it, but I would love see a finished example.

I also plan to have a fire extinguisher on hand just in case :)

Thanks
 

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Ryceboi,

Can you take a pic of yours? I have done lots of stereo stuff, but I have not built a preamp before. I think I can handle it, but I would love see a finished example.

I also plan to have a fire extinguisher on hand just in case :)

Thanks[/b]
i'll try to get one later tonight. i want to take it apart to solder the connections anyways. i just twisted and taped all the connections outside of the breadboard just to try it out.
 

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Discussion Starter · #15 ·
looks deceptively simple...thats because it is. it only has 5 components. i did that for a reason, so that it would be easy for people to make.

if i get bored one day i might build some eq for the circuit, and if really bored, maybe even add a low pass filter as well. the only problem is that we are somewhat limited by the supply voltage. with a 12v supply, the most you could get is +/- 6v, but in actuality there are losseses within the op amp that limit the output voltage quite a bit more. oh well...
 

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looks deceptively simple...thats because it is. it only has 5 components. i did that for a reason, so that it would be easy for people to make.

if i get bored one day i might build some eq for the circuit, and if really bored, maybe even add a low pass filter as well. the only problem is that we are somewhat limited by the supply voltage. with a 12v supply, the most you could get is +/- 6v, but in actuality there are losseses within the op amp that limit the output voltage quite a bit more. oh well...[/b]
amazing contraption here. thanks for sharing it with us. the reason i used a breadboard instead of a perfboard was so that i could easily switch the circuit out in the case you design something new for us :). i cant describe how great the music sounds. now if only i could fix the staging in the rear cabin, ill be happy.
 

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this sounds like an awesome MOD... im pretty savy when it comes to doing simple wiring, but never done anything on a circuit board like you have done... never studied anything like that, i think its great but wouldnt dare mess with it...

Is there anyway to get a kit to have this done with some step by step instructions?

honestly i dont really understand what the resistors and stuff do... and cant begin to really understand... but would love to seperate my bass a bit to create a bit more thump..

If not i guess I'll have to wait for some "syflex" style plugin kit...

Great job guys.. thanks for the info..
 

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this sounds like an awesome MOD... im pretty savy when it comes to doing simple wiring, but never done anything on a circuit board like you have done... never studied anything like that, i think its great but wouldnt dare mess with it...

Is there anyway to get a kit to have this done with some step by step instructions?

honestly i dont really understand what the resistors and stuff do... and cant begin to really understand... but would love to seperate my bass a bit to create a bit more thump..

If not i guess I'll have to wait for some "syflex" style plugin kit...

Great job guys.. thanks for the info..[/b]
the diagram 808 provided is probably the best you're going to get. i suppose being able to read it will require an electrical engineering or physics lesson. :D i'll make a schematic tomorrow that shows you what i did on the breadboard that may help you build the circuit. for now, go get the parts.

-breadboard (solderless) or perforated board (solder)
-thin gauge wire
-15K ohm resistor (1/4W or 1/8W)
-4.7K ohm resistor (1/4W or 1/8W)
-1uF capacitor (>25V)
-100uF capacitor (>25V)
-LM741 op amp
-electrical tape

i suggest you get a breadboard if you're new at this. from radioshack, total cost was ~$20. i had to buy a 50 pack of resistors and breadboard which doubles the costs of 808's original $10 estimate.

stay tuned.

edit:
actually, reading the resistors is quite a chore if you've never read one before. lol. but like i said, i'll try to help out as much as i can. maybe you guys should just have 808 build some circuits and sell them to you guys. :D
 

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ok, here's an attempt at walking you through this. please note the colors in the attachment because the colors correspond to the wire color you will need to splice or tap. the only wire that needs to be spliced will be the purple wire. all the other wires just need to be tapped.

please note the 100uF capacitor direction. the capacitor i used has an arrow on it. it indicates the side of the capacitor that connects to the negative (-). the 1uF capacitor is usually bidirectional.

i've also drawn out an example of a breadboard in case someone doesnt know how to use one. if you look at the drawing you'll see the lines labeled 1,2,3,A,etc. those lines means that all the points on that line connect. so everything on line A is connected and everything on line B is connected, etc. all the pts on the GROUND line are connected as well.

here is a link on how to read resistors:
http://www.elexp.com/t_resist.htm

if u still have trouble building this thing, just take a picture after you've completed the circuit and post it. i'll take a look and tell you if it's good or if you need to change anything.

good luck guys.
 

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Discussion Starter · #20 ·
thanks for making a drawing ryce, i was too lazy. anyways, look how simple it is. honestly, i think anybody can build this. if you dont want to solder, then do what ryce did. all you have to do is plug parts into the breadboard!
 
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