'07 Mazda 3 GT Custom Sub Amp Questions

[00MJR]

What I have :

Mazda 3 GT with a Bose System
10" 8 ohm sub in a Tuned Ported Box

What I want:

Increase the watts going to the sub.

The Story:

I took the stock Bose Woofer out from under the passenger seat. It's a 6" 2 ohm speaker enclosed into a VERY secret(Bose) tuned plastic enclosure.

I ran the signal that was hooked to the Bose woofer back to the trunk where my 10" sub is. The loudness of the bass has dropped due to the enclosure of the trunk and since I just changed the way Bose designed it.


The question:

I'm looking into just making a little amp that I can power with the +12v battery. I want to have this amp attached to the sub enclosure in the trunk which then I will need to amplify the sound already coming from the Bose amp.

I have tried turning the direction of the sub in different ways to increase SPL or just to get SQ.

What I'm going for is SQ, which it does sound a little better then the Bose sub BUT the loudness just isn't there now... I'm not going for a really loud thumper...

1. I'm trying to find a chip I could use to run off the +12v power and that won't take up a lot of room(attaching it to the enclosure). Placing a sub enclosure in my already small Mazda 3 trunk sucks enough...



LMK if you have any ideas on chips or designs. Just pointing me in the right direction would be cool enough. I do have experience with electronics repair but just not so much in design.

Thank you for your time!

Best,

Matt

[00MJR]

Ok, Well I went out to the car. Set the EQ and volume where I usually like it. Ran some different frequencies through the system. I got the following voltages across the sub speaker terminals.

*I went ahead and converted to watts*

20Hz - .766 vac rms - 0.146689 watts

40Hz - 8.86vac rms - 19.6249 watts

60Hz - 9.11vac rms - 20.74802 watts

80Hz - 8.74vac rms - 19.0969 watts

100Hz - 7.96vac rms - 15.8404 watts

120Hz - 3.06vac rms - 2.35162 watts

160Hz - .922vac rms - 0.21252 watts

Will it looks like it may be using a TDA7240 to get the 20w maybe... not sure since it's BOSE...

Hmm... Funny thing is I was thinking it would be less then 20w, so I would just use a TDA7240 since it runs off +12v for the supply.

Any ideas to get more power? I know most car amps use step-up power supplies but I've never made one of those...

Overall I'm trying to just keep it as a project. I know I could just go buy an amp but I would like to make one from scratch and not spend a lot of $.

Thanks,

Matt

[Perry Babin]

To get more power, you either have to decrease the speaker's impedance or increase the available voltage.

Building an amp is almost always going to cost more than buying one, especially if you only build one.

[00MJR]

Has anyone taken a Bose Amp Assm apart? Wondering what chips their using...

[Perry Babin]

All of the Bose amps that I've seen (not many) had class D driver ICs driving discrete FETs. The ICs had Bose part numbers instead of generic part numbers so I don't know what IC they were using.

[00MJR]

Well, I think just buying a amp will be the better route, though I may tear the bose amp out and look at it for the hell of it. The speaker I have in my 35hz tuned box(11.5x16.5x8) is a 10" 200 watts rms 4ohm sub woofer.

I don't want to spend alot of money and a 2 ch. amp bridgeable or mono that would do 75 watts rms through 200 watts rms @ 4 ohms would be great.

Any ideas, suggestions on a brand or model?

Thanks,

Matt

[Perry Babin]

I'd suggest a Rockford amp but if you're looking at the cheapest option, that won't be Rockford.

[00MJR]

Alright I went ahead and ordered a amp. Small little 2 ch. bridgeable that I can mount on the sub box in the trunk.

Here's my final question.

The input for the new sub amp I bought... should I use the HU output or the bose sub out?

Would there be any advantage for running it before it goes into the bose amp? I was just thinking I could make a simple voltage divider circuit and use the sub out of the bose amp that I already have ran back in the trunk. I would think this would cancel any chance of hum/interference since its at a speaker level impedance.

Thanks,

Matt