mdw33333

OK, update here. I did some trouble shooting and found out what was going on. I feel like a moron. After ten years in this business, I still make silly mistakes. I had my left side converter inputs out of phase (backwards). I reversed them and now I have a good strong signal coming from the converter.

I took my turn-on wire straight to an ignition hot source and all is good. No turn-on/turn-off "thump," and no "bass hum."

After reseaching and toying with this, my conlusion is that the "preamp" leads going into the Bose amp SHOULD NOT be tapped unless you're using a line level converter. I metered them at putting out less than 1V. Cactus found out the hard way that these signal leads are very sensitive and are "strained" by tapping them and using them as pre amp signal for another amp.

Like I said above, I could tell no audible difference between tapping in before or after the Bose amp. Everyone's best bet is to use a line level converter whether you have the Bose system or not. This will assure you the life of your factory head unit.

I also believe in the "head room" concept. Give yourself plenty of power. More power means you can keep your gain control turned down, thus lessening distortion and noise. Keeping gains down minimizes any turn-on/off noises or thumps.

Now that I'm content with my signal, and my wiring is done, it's on to choosing equipment, and finishing the cosmetics. I'll being posting pics of my install and my enclosure. I've got a nifty little plan for the removable trunk access panel in between the rear seats. I'll be building a custom enclosure that butts right up to the opening between the seats. It'll be a single 10" or 12." I'm basically going to cut a hole in that removable panel, allowing the sube to fire straight into the car. I'll then cover the panel with multi-layers of black grill cloth, so the hole isn't visible. It should turn out nice.

Bob The Eskimo

so you did have a 1v signal from the head?????

mdw33333

Yes, less than 1V.

mohrt

So can these "preamp" leads be tapped into from the trunk, or does this need to happen right at the HU? (in other words, where is the bose amp?) If I'm just adding subs, it would be convenient to wire in the line-level converter in the trunk and use the rear-seat cigarette lighter as the turn-on wire. Then the only wire that needs plumbed is a heavy-guage hot wire to the battery (???)

mdw33333

The Bose amp is under the rear deck between the rear speakers. You can tap in to the rear speaker outputs for a safe signal. It's actually easier to run an turn-on lead up along with your 12V power lead to the front. Tie your turn on lead into an ignition hot source in the driver's kick panel, or in the fuse box.

When tapping the rear speakers, use these colors:
Left Rear + is Purple
Left Rear - is Pink
Right Rear + is Black/Blue
Right Rear - is White/blue

mohrt

Just for clarification, you are saying to tap the line-level converter into the rear "preamp" wires just before the bose amp, correct?

As for wiring, where is the best place to run wires, right through the console? If so, is that easy to disassemble? And the lead wire, is there a convenient place to get through the firewall? I haven't seen this info in any thread, so if I missed it please point the way

mdw33333

No, DO NOT tap into the leads before the amplifier. Tap in to the speaker level leads going out to the rear speakers. When I get home from work this evening, I'll take pictures of my install and I'll show you where to run the wires and where to go through the firewall. I'll post the pics tonight and give a detailed explanation of what to do.

mohrt

That seems a bit odd to me. Wouldn't the output from the HU be a much cleaner signal source for an aftermarket amplifier?

You are suggesting this:

HU -> bose amp -> line-level converter -> aftermarket amp -> subs

Wouldn't this be better?

HU -> (line converter/conditioner?) -> aftermarket amp -> subs

XeRo

typically yes..but not in the case of our Bose system..

mohrt

This thread shows how someone successfully tapped into the HU outputs for his amp & subs:

https://www.rx8club.com/showthread.p...5&pagenumber=1

So will that setup work, or is this something that will eventually fry the HU output?

Bob The Eskimo

Mohrt,

This is something that is up for discussion. No one knows for sure either way.

mdw3333 has tested the voltage of the HU signal at 1v so most (if not all) RCA's will be able to handle this. eXcentrics set up in my mind will work perfectly. On the other hand, the setups here should work perfectly as well.

I have done some homework on this in the past days because I am at the stage to hook up my Fiberglass sub enclosure to signal and am dying because no one knows for sure what is true. I will give you what I have discovered in the past few days.

Differential signals are as Cactus George and mdw3333 have discribed above, a signal perfectly reverse phase from itself, referenced to a ground signal. The thing that does not add up in the wiring schematics is a differential signal requires three pins (+ in phase, + reverse phase, and a ground signal) all for one chanel (rear right speaker), hence, the XLR Connector. In the rx8, there are only 2 lines. A differential signal is not possible unless we are missing a third line as a ground, or a second positive line. The two lines that we know of should be unballanced, or not differential.


Now, splicing into any signal will affect the resistance that the initial source must deal with, but since we are not attaching to a driver directly, this change should be minute. Somewher in the range of a few mOHMS. In my opinion, nothing to worry about.

From what I can gather the Mazda 6 guys had this issue a year ago and ended up hooking in directly without any issue. Same headunit as ours. Also, four people that I know for sure have hooked up this way already with no issue. Cactus George is the only one who has had an issue. Not to say you did something wrong george, just that there have been no other problems reported. 3 to 1 so far.

We need a poll. Who has done it which way with success?

eXentric

I'm one of the users that has the amp wired directly into the pre-amp side comming from the HU. It's been running that way for at least three months now, but this thread has me nervous.

Honestly, I'm not too terribly happy with the install because I have to have my gain set at 100% for many songs. This means that the level comming from the HU is not very hot. I have 1000 watts (bridged to 1.5 ohm mono) and I still have to have the HU up above 17 for it to sound really good on some songs. And that volume is too loud to be enjoyable for me.

And if you're wondering how I get 1.5 ohm mono, here it is:

Two 10"s at 6 ohm each. Both dual voice coil. All four coils in parallel on the mono amp. A little strange, but when they're not starving for power it all sounds really good.

So, I guess I'll echo mohrts last question: Is this a ticking timebomb for my HU? Rotary and I played with the line converter off of the rear-deck speakers. We only hooked up one speaker and it less output then the pre-amp side did. BUT, we I realized later that the amp I have has significantly less output when only one of the two RCAs is connected.

Please advise, and thanks to those researching this.

eXentric

P.S. Rap songs always sound good with my setup. Many rock songs and some alternative songs have poor reponse. I guess my crossover settings could be off, but I haven't touched them since my last install. And the songs that sound good sound REALLY good. The songs that don't sound so good still sound really good if I crank it way up.

Dunno, maybe it's all in my head :p

mohrt

So we have a trade-off: tapping into the speaker wires may not provide the cleanest possible signal, but it also doesn't introduce fluctuation/risks/unknowns to the rest of the system (?) It would be interesting to find out if the difference in sound quality for subs is noticable or negligible.

The gain problem eXentric has doesn't sound good either It would be interesting to know if tapping into the speaker wires makes a difference.

CactusGeorge

The HU in a frying pan problem that my system experienced did not have to do with tying into a "preamp" level signal.

Many aftermarket amps tie the shield connection for all channels together. Sooo, if you plug differential signals into the RCA inputs, RF- gets connected to LF- which gets connected to RR-, you get the idea. This is where problems can occur: all of the - inputs end up fighting with each other.

I've asked for an o-scope reading of the HU "preamp" outputs, but so far no-one has been able to provide this info. Until I get hard data confirmation, I am going to assume that the HU preamp outs are differential (to be safe). I see three hookup configurations on the basis of this assumption:
1. Use a line output converter at the output of the Bose amp.
2. Use a line output converter at the input to the Bose amp.
3. Use the + signals from the HU and tie the shield of the RCA cables to GND.

I'd love to hear people's opinions of different brands of line output converters (AudioLink, Dave Navonne, Soundgate, PAC, Peripheral, etc.)

CactusGeorge

BTW, when I did tie the HU "preamp" outputs directly into the Soundstream (Soundstream sales guy said this would be OK), I had plenty of signal. The Soundstream has gain controls and is rated, I believe, to work with input signals with a max amplitude of 500 mV.

If you tie the HU preamp signals into a speaker-level input of an aftermarket amp, you may not have the same level of gain (maybe these inputs are designed to work with high-level voltages, don't know.)

With regards to line output converters, most of them take the differential signals into an audio transformer to isolate the HU from the aftermarket amp. Not sure what kind of losses happen when you run an audio signal through a transformer, but this may explain why you are not getting enough signal at the amp.

mdw33333

Ok, here's where I stand. I posted previously that I tied in (using a line level converter) BEFORE AND AFTER the Bose amp. I found there to be no audible difference between the two methods. But again this was using the same line level converter in both methods. Now, for those who have aftermarket amps with speaker level inputs, using them is NO DIFFERENT than using a line level converter. The process is the same, only it's being done inside your amp. That's why it was "successfully" done in the thread posted above. He tied in before the amp, but did so using the high level inputs of his new Alpine amp. He wasn't getting a true preamp signal either way.

Now, tapping those same Bose pre-amp signals and running them straight into an aftermarket amp's RCA level inputs is different. That's where the danger is. To get a true pre-amp signal we'd have to use no converter, and splice those signal taps into RCA cords, and plug them into our amp. Cactus tried that, and didn't fare well. I believe that this method puts to much "strain" on the HU's outputs, especially when gain controls are also a factor. Some type of "feedback" could be an issue as well. I considered tapping straight into the preouts of the HU, asnd diode isolating the HU. But, honestly, I'm just not willing to experiment that deeply.

Sure we'd all love to have a true pre-amp signal, but as far as I can tell, the costs out way the benefits at this point. And again, through the converter, I couldn't tell a real difference, before or after the Bose amp. I'm sticking with my converter and playing it safe.

I'm posting some pics of my progress so far. Previously in thsi thread someone was asking some general wiring questions, so I'll post some instructions along with my pics.

The first is my 150 amp circuit breaker installed inside the battery compartment:

mdw33333

Next is where to route your power wire through the firewall just above the driver's kick panel. There's grommet there and it's pretty easy to "poke" through.

mdw33333

Next is routing your power wire and ignition turn-on lead to the rear. It's snug if you're running 4 awg., but it can be done along the driver' door sill. Make sure to wire tie yoour power wire against the factory wire harness to keep it clean.

mdw33333

Here's pic of my Peripheral line level converter. I 3m taped it to the area at whick it's mounted. I'm big on not drilling holes. I want to be able to remove every component of my system with little or no trace that it was there.

mdw33333

Finally, my test sub, a Kicker 10" L7. I've got a new Alpine "Type X" 12" subwoofer on order. I'll have it when they're introduced in a couple of weeks. I did my testing with a Kicker amp, but I'll be using the new 550 watt Alpine mono amp, with digital input and gain settings.

I'll have my sub in this postition. The removable cover between the seats will be modified. I'm going to cut a big rectangular hole in it, and cover it with multi-layers of black grill cloth. This allow the sub to fire straight into the cockpit, but without being seen from inside the cockpit.

mdw33333

More pics to come.

Bob The Eskimo

mdw3333,
nice install. Im anxious to see the center pass through with the hole drilled and covered.

That's the same location I used for my power wire. Where did you attach your 12v on signal to?? I am planning on using the ciagrette lighter in the center console unless you have a better location.

Regarding the signal output from the HU, There are two ways to determine if it is differential or standard.

1. I have a 200w Precision Power amp that is perfect for trying out my sub with. In the manual it states that it will accept either differential signals, speaker inputs, or standard RCA, all through the RCA jack. You just need to flip a switch for speaker level inputs, to reduce it to low level inputs.

2. I will attach my voltage meter. Black to the chasiss, red to the - wire, and mark the voltage (if any). If there is no voltage then it is a ground and they are standard RCA or speaker level. If there is a voltage then there is signal and we have a differential line. If the voltage is 9v-12v then we have a Speaker level output. I will also do the same test to the + line as well. This way there will be no question.

I am opting for #2. Problem is, I may not have time to do this until this weekend. I will post the info here as soon as I have it complete.

Has anyone done this already?

CactusGeorge

MDW:

Impressive install--thanks for sharing the pics.

mdw33333

For those still in question, I spoke with the head of tech support at Peripheral today. He stated that the pre-amp outputs of the head unit ARE differential. He also stated they could be tied into, but only by using a line level converter. I asked his opinion about doing so and he stated he would prefer to tie in AFTER the Bose amp. He said the signal after the Bose amp is a stronger and would allow you to keep your input gain set a lower, therefore, creating less noise. He confirmed that the HU's signal IS NOT a true pre-amp signal, and that there would be no benefit to tapping it.

Like I said, using a line level converter, you can tap the the Bose pre-amp signal, but you are actually better off tapping after the amp for a stronger signal that will allow gains to be set lower and lessen the effects of noise.