Pre-Amp Outputs Tapped on Stock Bose
 

If this is old news, then please forgive me for the double post.

So far, every audio install I have seen for the 8 simply uses a Hi/Lo converter to tap onto the speakers in the rear deck. Although this is a perfectly fine approach (and an easy one at that), it’s always better to tap a direct low-level line if possible. Several have asked if this can be done, and last night rotarygod and I managed to prove that it can.

The colors in the attached diagram do not match the wire colors (because those wire colors are two-tone). But the diagram clearly shows you which pin in the stock amp header is which signal. I’ll list the stock wire colors here also so you don’t have to look it up in the header if you don’t want to.

Also, please be aware that we never tested the rear connections to be sure, but they should be accurate (we’re going off of the Mazda wiring diagram). Please PM me if they are not. We used the front signal because the front channel drives the 9” subs. Although, it doesn’t look like there is any difference between the front channel signal and the rear channel signal. So, if you want to use the rear channel to make your subs on the rear fader with the back deck, you should be able to.


Left Front +: R / L
Left Front -: LG / R
Right Front +: L / W
Right Front -: Y / G

Left Rear +: G / O
Left Rear -: L / O
Right Rear +: GY / R
Right Rear -: BR / R

(words added for search engine: preamp pre-amp RCA)

Just thought I'd add this for fun.

To be honest, I am surprised that this connection scheme worked.

Typically the signals from head-units are differential in nature. This means that instead of L- and R- signals being connected to ground, they usually have an inverted single that is 180 degrees out of phase with the L+ and R+.

By connecting the L- and R- to the shields of the RCA cables and then connecting those cables to your amp, you should have shorted out those signals which would normally cause a variety of effects ranging from the head-unit going into some sort of protection mode, the head-unit being damaged, or the signal becoming mono or more mono for the rest of the system.

Since the Bose equipt RX-8's get the same headunit as the non-Bose RX-8's, I wonder if the headunit senses the Bose and makes its outputs single-ended and not differential accordingly.

For anyone else who tries this and doesn't get good results, try connecting ground to your two RCA shield connections.

But, hey, if it works it works.

-Mr. Wigggles

Ps. eXentric, make sure to turn your Audio pilot off now that you have subs. It screws things up at low volumes.

This would also work for non-bose system also correct?

I *think* so, but does the non-bose have the rear-mounted amp? If not, you can follow the diagrams and match the pins on the head unit. It would require the header and more work.

Sorry, I have the Bose, so I don't know what it looks like without it.

eXe

Re: Pre-Amp Outputs Tapped on Stock Bose
 

I haven't had a good look at the wires yet but are any of those in the diagram a remote turn on wire?

No. The only pins on the amplifier are battery (which is constantly on).

There has been some talk in this thread about a possible switched ACC plug on the back of the head unit, but it hasn't yet been confirmed.

If you need an easy way out, check out this thread for pictures of connecting to the accessory plug near the back seat. This will give you a switched input with the accessory on the ignition but unfortunately separate from the head unit. You may want to have a remote bass knob installed for starting the car because mine pops fairly loudly when I have the amp turned up at all and I start my car.

Thanks, this is going to come in extremely handy!

The popping noise is due to the ignition hot wire that is used for remote turn on. We could rewire it through and relay with constant power and use the ACC as the relay tripping signal. This should end the popping noise.

Rotary,

I'd like to talk about doing this when you have time. I also have a couple of other questions I'd like to ask you offline. Please PM me when you think you'll have time before or after the holidays.

FYI- the rear pin-outs work perfectly- thanks guys! I took a few pics of the wiring details and posted here as an ammendment to my custom speakerbox build post:

https://www.rx8club.com/showthread.p...threadid=19906

Thanks again for the info...

-Sean

If you've been following other threads, you may have noticed that some users had problems with this method of connecting their amps. One user even feels that this connection fried his head unit. Just to play it safe, I decided to try hooking it up the other way. It only cost me $40, and here are my results (cross-post):

I must agree. I purchased the N-774v and installed it last week. I didn't get a chance to post about it until today.

Overall, I'm actually happier with this install then I was with the direct 'preamp' connection I had before. Not only is this approach safer, but I actually do get more bass out of the system now.

Unfortunately, the bass is not as clean as it was before. It sounds a bit more 'muddy' but I still feel it's worth it. I can now agree with the people that argue the Bose amplifier in the rear deck modifies the sound from the head unit. And I think it modifies it quite a bit. Now I'm wondering if it would make a difference if I hooked up to the front speaker outputs rather then the rear ones...

One last note, mdw33333 posted this:

These are the wire colors at the speakers themselves. I used this guide, but when I connected it to the amplifier one side was out of phase. I don't know if these pinouts were backwards or if something inside the N-774v I received was backwards. At any rate, I clipped off the connectors to the Pink and Purple wires on the left side and swapped them (Pink + and Purple -) and everything got much louder.

So, all in all, I would reccommend this approach and I would recommend the N-774v.

eXe

I'd like to merge this thread with the other one. If you want to reply, please reply to the Line Converters: Adding an Amp to the Head Unit thread.

As noted by eXentric on post #12, I too was having issues with volume output from my sub / amp combo:
..
My sub/amp has a High Level input (or a built in High Level to Low Level converter). I swapped the rear left speaker High leads as described above, and now the amp works correctly.
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Thanks eXentric for the post!