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
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!
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
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!
