CactusGeorge

Things were working fine for a few weeks, then these little fluttery noises started appearing when the HU was off and the amp was on. Then one day, no more sound

I'm trying to find an oscilloscope to verify that the HU "preamp" outputs have fizzled, but that's my best guess at this point. If it's true, others who have connected their amp to the connector before the Bose amp may want to investigate other options.

System Setup:

HU "Preamp" connections made at HU connector (see photo) then directly to amp.

Amp: Soundstream Edge 5700 (marketed to accept OEM floating ground inputs--resistance between the amp input RCA-shield contact and ground is 29.5 ohms )

Focal 165 W's in front, 690CA in back, no sub

CactusGeorge

Safeguard options moving forward:

1. Only use the + connection from the HU, connect the RCA shield to ground (for example, use RF+ and Ground going into the amp). This is assuming that RF- is a differential lead that cannot drive 29.5 ohms at the Soundstream amp)

2. Use a line converter between the HU and amp (I'm not sure what type of circuitry is in a line converter, but it may provide additional resistance to protect the HU outputs.)

3. Tap into the HU circuitry at a true pre-amp connection (Anyone have any schematics/pictures of this circuit?)

Other ideas?

CactusGeorge

Clarification:
If the HU is plugged into the amp, the fluttering noises play through the speakers (not a constant sound, start and stop).

If I disconnect the HU, no sound plays through the speakers...

mdw33333

Well, you're steps ahead of me on this. I'm considering an audio upgrade as well. The problem is that the outputs coming out of the head unit are "low wattage," not "low voltage" outputs. So it isn't a true preamp signal. Whether you tie in before or after the Bose amps, you have to use line level converters. The only way you could tap a true preamp signal is to find it inside the head unit, and that's just not an option I'm willing to explore. I've never been a fan of line level converters, so at this time, I'm going to pass on upgrading.

CactusGeorge

I'd like to know more about the personallty of the "preamp" signal--do you know the voltage level.

Next question is, can the - lead of the differential output drive 29 ohms (not sure what the impedance is...)

If your amp has adjustable sensitivity and can handle a high voltage RCA level signal, a line converter may not be necessary.

I'm still not quite sure what the cause of the current failure was/is

If I do get a line converter, it will probably be a Soundgate or a David Navone brand--they seem to have the highest focus on signal quality.

mdw33333

The voltage level of an average preamp signal is around 1.5v-2v. Alot of aftermarket radios have higher voltage preouts though. Some are 4 volts and higher.

CactusGeorge

I just talked to David Navone about the FMS/Bose setup and how to tap into the system.

Unfortunately, it looks like taking the signal directly from the HU to the Soundstream amp probably over-taxed the HU outputs and caused them to fail
Anyone have recommendations about where to get the HU repaired, or where to buy a new one?

David recommends his N774V four channel converter tapped into the OUTPUT of the rear-deck Bose amp. His recommendation is based on:
1. The HU output is probably about 2 Volts, whereas the Bose amp is at about 10 Volts--this provides better S/N at the Soundstream.
2. The Bose amp does not apply any Bose-specific equalization because it's cheaper to keep the amp linear.

I know some sub installs tried tapping in before and after the Bose amp, and at least one person commented that the sound was better before the Bose. I don't know what to make of this conflicting info.

Rotarygod, Overload, Mr Wiggles, XeRo or any other technical/experienced types care to expand on the pros and cons of line converters and where they should be placed in the RX-8 audio chain?

CactusGeorge

I'm going to move this discussion to its own thread so that anyone who is planning to add an aftermarket amp can easily find the discussion...

RX^7

I enter all my RX7's in DB drags (Decible drags) 1ST thing is REMOVE the head unit, and get a better unit Alpine,Kenwood.ALSO I always install 2 boxes , 1 a FUL range box (kicker,or JL audio.THEN a sub box (JL kicks A**) i use a Tripple 12 inch sub box jjust for bass.You will need a EQ that controls bass, like the Kenwood 642A, it has a sub Crossover (lower and inceses bass.my budy Owns a HIGH end shopo where the average install is around $20.000,but you dont need to go crazy.All my mazda's use a Self powered speakers...DISCONECT THEM!!!they usuallt have a ampp to drive both back soeakers, and an amp to drive both fronts,DISCONECT THEM AS WELL.I won 3 RX7's now and all 3 hitover 130DB (LOUD!!!). With the 642A eq you can turn of the sub it its too loud,
My friend does ALL the NY knicks sound systems.He is located in Bedford NY,His # is 914-244-o900 Tell HIM Jef PARADISE Sent you!!!
.He also does NAV systems,,17 inch monitors.And in in CAR AUDIO AND ELECTRONIS at leats 2-3 times a year.ASK for BILL WIDMAN~~Remember you dont need to spend that much,but DUMP that factory radio!! any 1 of mu RX's have won 5-7 Decible trophies.
JEFF
PS dont let anybody talk you in 2nd rate audio gear (MTX)(POLK)they are just OK and sound that way,
JEFF
Feel free to call him or i,My # is 914-420-5339

JUST SAY NO TO MTX,,LMAO
JL also make GREAT door panels.my friend also makes custtom door panels.111
CHEERS
JEFF
GOOD LUCK
ALSO look for MB QUART~
SORRY FOR SPELLING!!!!!!!!!!!!!!!ive been offline for a month LMAO
JEFF

Tamas

iTrader: (1)

Great suggestion - now would you please tell us HOW exactly are we supposed to get rid of the factory head unit?

Do you know how the stock setup is in the RX-8? Didn't think so...

Also, you might want to look at what you write... English is my third language, but I could not make this many spelling and grammatical mistakes even if I wanted to :p

RX^7

REMEMBER the new Ford taurus???
Trust me i enter DB drags all the time.
Just because the radio has secondary controls, that just means you leave those in the radio.BUT
ALSO they make harnesses for EVERY CAR!!!

PS i own-an RX8 (Yellow spoiler) now with a Kenwood head unit,3 Zapco amps ans 3 12" subs~




They can install a head unit ANYWHERE, EVEN by Welding it in the Roof, or int the Glove box.
Remember the (New ford taurus??with e Oval radio??You can keep the Stock radio, BUT you can Hide the EQ in the glove box, or =under the dash.We were able to weld a Amp Rack to the headliner (LOOKED SAWEET!!!!)with 2 of the humongous Phoenix gold amps (the 3 foot long Limited edition),ALSO they can make an ABS plastic enclosure the rear that hides it, and retains all the other functions.that gut.My friend specialize in Relocation,and ABS,There isn't must involved in it really.Put it this way, the MAZDA dealer bring all his cars to him!
I know it sounds like it can me done but TRUST me it can!!!Remember as long as you can use the remote it can go anywhere!!Trick is to leave the head unit where it is just so the dash looks good!!and the other features work.But the stock radio sux....
JEFF
If your serious call him or 1, BUT plan on a few$$ because its not cheep!
JEFF
I predict it will be on Car audio and electrons~






JEFF

bureau13

How about some pictures of that Kenwood in your RX-8?

jds

mdw33333

I'd like to see them too.

G8rboy

Yeah- I'm sure welding an amp rack to my roof will retain that subtle factory look

Seriously though, with regards to this thread... I've been using the pre-amp connections with no line-level converters with my custom box for about six weeks now and it's working great. How fast did the degraded audio conditions appear? Do you think certain amps might have some kind of protection for this?

CactusGeorge

Worked great for about 3 weeks. Sounded pretty good.

The Soundstream amp does not have speaker level inputs, just RCAs. If you've tied into speaker level inputs on an amp, you may be OK.

The Soundstream also ties the "shield" connection on all inputs together, so for the HU this means L- is shorted to R-, which is probably a bad thing.

I had contacted Soundstream before connecting to the HU, and they at first said they only provide info to installers, then they informally gave me a "nod" to proceed with the connections.

Without some test equipment around I can't detail the HU signals (I've asked OverLOAD if he would look into this so the info can be posted...)

G8rboy

Interesting- I originally had used the speaker level connections on my Alpine (when I was tapping into the speaker wires coming out of the amp), but when I found the correct pre-amp wires, I switched to the RCA line level inputs.

Another difference to note is my amp is just a small Class-D (digital) mono amp (I tapped into both L and R rear connections, although it probably wasn't necessary). Sounds like your SoundStream is a lot bigger puppy (4 channel?) if it's pushing all your drivers... I wonder if that contributes to the strain on the HU.

CactusGeorge

The subwoofer setup has some important differences, but power output of the amp should not matter.

When you connect to your sub amp, L+ goes to the center RCA conductor and R- goes to the shield conductor (or whatever). If the shield conductor is grounded in your amp, this would ground the R- signal, and this could definitely be a problem. However, if your shield amp connection is not shorted to ground, this setup is probably OK.

On the Soundstream, all of the shield connections are shorted together, but they are about 29ohms separated from GND. I think the problem for the HU is having LF- shorted to RF- shorted to LR- shorted to RR- (if the HU outputs are differential, which I suspect they are.)

This got a bit long-winded, but I'm hoping that others with completed installs will contribute the details of their setups :-)

strato

You must STILL use a pre-amp level converter even though you are tapping the HU line outs in front of the Bose amp. I did mine by very carefully removing the pins from the connector, and cleanly and precisely soldering to them. Your line out device will provide RCA connectors. Try to get one with a trim adjustment (nice to have). This will isolate any loading on the existing system. In fact, it won't even know you're there. . .

I lined the well in my trunk with foil, and "molded" a sub box using fiber. Topped it off with 3/4 MDF and carpet. -- 2 nice 8" subs. Stuff the box to optimize the enclosure, and you get a nearly perfect internal volume. And you can lift it out to get to the jack and stuff. Looks great, and really doesn't use up any trunk space.

And the sound is freeking incredible!

But -- use a linel level converter -- even though you are tapping the HU outs.

CactusGeorge

strato:
What brand of line output converter did you use?

Sounds like you tied in before the Bose amp--some brands of converters recommend tying in after the amp because there is a much higher voltage (supposedly provides a great signal with little/no noise...)

strato

PAC makes an "SNI-35". Please trust me on the "before the amp" line tap. I'm an ee with lots of experience with this stuff. I read lots of forums before doing mine. I read where everyone was making errors -- even the success stories weren't optimal. I scoped everything (o-scope), used test signals, and dynamically checked crossover points.

Also, PAC makes a nice device that'll allow you to nicely switch the amp power from the trunk (no "POP"). Just use the power-in connector to the amp. The little blue wire. Its easy to get to the pins on the connectors -- just be sure to remove the "snap covers" over the connector bodies where applicable. You can make very nice, non-obtrusive connections that way.

You won't believe how nice the stereo sounds by just properly adding a sub(s). The PBX 8"s are fantastic. Soundstream amp. Be sure to fuse at the battery. You can grab a great ground under the left side interior trunk cover. If you mold into the well (highly recommend), drop cloth everything. Best wishes. . .

CactusGeorge

strato:
What are the voltage levels going into the Bose amp (say from LF+ to LF-)? If this differential is high enough, the signal should be low noise (good S/N ratio).
For a sub amp it's not so important, but I'm driving some excellent tweeters so the S/N needs to be as good as possible--ignition noise can be so annoying!

strato

I see -- for that you'll want to come right out of the back of the head unit, and use the PAC. The s/n will be fine if you're meticulous in your methods. Its a standard audio signal.

However, I'd try NOT doing that. The Bose system is a little finicky -- especially when it comes to i/o impedance matching.

I know you can always do better with aftermarket. The beeline you have to run between the always part and the do better part can sometimes have diminishing cost-benefit returns, though. For example, you may have higher quality components, but if you mess with the i/o impedances in the process of connecting them, or if you introduce some noise into the system, or, or, or. . . -- and these are all rather sensitive and noticeable parameters in the RX. . .

I had very good friend who was a car stereo installer extraordinaire (he passed away several years ago). Anyway, he had a theory he always impressed me with -- a sort of work with what you have/less-is-more theory. Anyway, what I'm saying is, as built into the RX, the Bose system isn't all that bad. . . If you work with what you have, adding only what you have to all little at a time, you WILL be impressed. I've never been into sheer volume, or curb shaking. . . But I have had some very, very nice systems -- I'm an electrical engineer/recovering musician. . . I've had systems in a few cars, some done by Luke, and some done by me. . .

This one impresses me as much as ANY of them. . . And all that has been done is the sub. Now mind you, it was done meticulously. . .

I will give in to the fact that if I very carefully added nice tweeters, the sound would improve. But my, my. . . That would take some careful amplification, as well as removal of the existing tweeters -- this might mess up the stock arrangement (and it can be a good one) by a greater or equal margin as the improvement. . .

In the end, I'd try a meticulously done sub, then I'd see. Personally, I'm just not going to mess with it. It sounds too good already. I've had a few listen, and they are blown away -- they comment. But mostly, they just listen and say very little -- And they get that funny smile that speaks volumes. . .

strato

. . .I forgot. . . Any noise you get won't be due to a s/n problem. It will come from either poor shielding or from slight ground plane differences. The ground plane problems are difficult. When you start adding wires/components at different locations, small differences tend to show up. And remember, the Bose system uses impedance matching that's probably 12-16 times lower than the standard -- Its gonna be sensitive. . .