Pre vs. Post Bose Amp and LOCs
 

Hi all, long time reader, first time poster.

I have read the a pile of the information avaliable here about adding an amp and sub to the Bose system in my 8. I am so very confused regarding the discrepancies between these two threads:

https://www.rx8club.com/series-i-interior-audio-electronics-24/line-converters-adding-amp-head-unit-23213/

and

https://www.rx8club.com/series-i-do-yourself-forum-73/diy-custom-sub-box-install-pics-plans-19906/?pp=15 particularly page 3

The conclusion I draw from that first thread, is "tap post Bose amp with LOC -> RCA into amp".
The conclusion I draw from the second thread is "tap pre Bose amp -> RCA into amp"

Now, perhaps I am missing some threads in between these where things were sorted out, but I have been searching for days and these are the two best threads on the topic, but which one is 'correct'?

I would love to tap pre-bose and not use a LOC. To me this corresponds to how it 'should' work, but if the inputs are truly differential, how can this possibly work as shown in the second thread? Isn't he sending one of the differentials to ground, thus he should be frying his HU? He also mentions that the pre-bose tapping got him better sound, and better Audiopilot functionality, which is obviously desireable.

What piece of this puzzle am I missing here? Thanks to anyone who can help put a final word on this issue.

......

If you are using a non-powered "cheaper" LOC, you must tap after the Bose amp. If you tap pre-amp, there is simply not enough juice.

If you are using one of the higher-end LOC such as the 3sixty, LC6i, or CleanSweep, you should tap before the Bose amp. This will give you the non-Bose-EQed signal most people want, but the powered LOC will be able to bump up the juice enough for your aftermarket amps.

^This.^

I would not advise hooking the pre-Bose inputs directly into the pre-amp or speaker level stage of an aftermarket amplifier unless you have enough electrical engineering know how to use an osiliscope and to design and build your own balun to convert the differential signal into a real pre-amp signal. Any sort of mistake in a setup with the HU output going directly to the amp could lead to a blown head unit. In fact, I've talked to electrical engineers that advised me it's a bad idea so I never pursued it.

Ok, those answers make sense to me, but then why does tapping the pre-amp seem to work so well for G8rboy and a couple of others in this thread? Is their amp different- ie. does it handle differential input without anyone pointing it out? Or are they just lucky? G8rboy's amp is just a basic Alpine which I don't think has differential input... why did his HU not die?

https://www.rx8club.com/showthread.p...6&pp=15&page=5

I'm not saying the LOC solution is incorrect, I'm mostly curious as to why pre-amp tapping seems to work so well when, according to the accepted data, it should rightly burn a HU?

I haven't experienced the headunit frying issue that several have discussed on here, but I have personally attempted the el cheapo LOC before the amp and it was simply not strong enough. Here's a decent read for ya?
https://www.rx8club.com/showthread.p...813#post302813

I used a LC6i and tapped it straight from the back of the radio(speaker wires)
Do the same ,it is easy.Just solder the wires and bring them back->LC6i>AMP->Spks.
There is a diagram for the connector of the headunit somewhere...

.... or you could just tap into the Bose input harness and save yourself running all those speaker wires to the rear.:Freak_ani

firebirdude, if you are going to make a good installation(new wires / speakers) then you have to tear up the whole car...so doesn`t hurt to change that wires also.
Worst thing i remember from my installation is trying to pass the new wires through the door:banghead:

I never said it would hurt your installation. But it will hurt your pocketbook from running 50ft of unnecessary speaker wire to the rear of the car, as well as waste a good deal of your time by removing the headunit when it's completely unnecessary.

The signal at the Bose input harness IS the wires output from the headunit. Are you suggesting the factory wiring installed by Mazda is insufficient?

Ok so, a follow up question:

Isn't using a LOC post-amp or using high-level speaker in on an amp essentially doing the same thing? Why would I invest in a LOC when I can use high level into an amp? I would think that the losses are going to be the same regardless...?

i had to open the radio because i changed the 6disk to mp3 player and because i use 3 amps i thought is better to change that wires also.
purpledrillmonkey : I think you have to use the LOC because of the voltage you can fry your Head Unit.

no, using the LOC after the Bose amp shouldn't affect the head unit. The LOC just takes the high-level speaker signal and drops it back to line-in level for RCAs. My question is why would I do that when pretty much every amp I'm looking at has High-level input anyway?

Basically I'm not looking at building a competition system here. I just want to push a bit of power into a single 10" to add some kick and fill in the low end of the Bose system without getting the sound all muddy. I don't plan on dropping a huge chunk of change on a system here, and especially not $100+ on a LOC. I just can't imagine that an average LOC is going to be much 'better' than using high level input on an amp... plus the auto-sensing turn on might even work. I'm just not super familiar with speaker level input into an amp, so maybe there's a good reason not to use it?

purpledrillmonkey you are correct that you don't need a LOC if you tap AFTER the Bose amp and use speaker level inputs. The only question is, does the amp have a flat frequency response? or is it tailored for the Bose speakers? I haven't found a definitive answer to that (but many opinions) in this forum. If the response is flat, using the speaker level outputs into an amplified subwoofer would be the simplest and cheapest way to go. If the amplifier is "tuned" for the Bose speakers, it may not give you the best sounding response with your particular subwoofer (although many others on this forum have had success doing exactly that). Unfortunately, you'll just have to try it and see what results you get.

What brand(s)/model(s) of subwoofer are you considering? I'm trying to go the same route as you to add a little extra umph without busting the checkbook. I'm considering the Kenwood KSC-SW10 mounted under the passenger seat. It gets good reviews, is not too expensive, and won't overpower the rest of the system. Has anyone else tried this? It should be a simple cable run from the rear speaker taps to the speaker level inputs and the auxillary power port in the center console for the remote turn on. The power line would be the same as all the others. Any suggestions, hints, or warnings?

You looked under the passenger seat yet?

firebirdude - luckily I looked again before replying and sticking my foot in my mouth! I definitely remembered more room than is actually there and I just noticed - are those HVAC outlets? Definitely don't want that much air blowing across the speakers - I'm now looking for a new location . . . any suggestions anyone? I would like to keep the subwoofer in the cabin, not the trunk (doesn't the sound get distorted going through the back seats?).

Any suggestions of places to purchase any of the aforementioned LOCs?

If you're just looking for the basic one, you can find them at Best Buy. $25.

Hmm....I thought the basic ones wern't worth a shit after reading through this post (and the linked ones). I was under the impression that I needed to get a nice (LC6i, CleanSweep, etc) LOC (~$100) and then use that pre-Bose amp.....and that the cheapy ones run the risk of frying the HU :-S

Socket mentioned that if you were to use the high-level inputs on the amp (as in no LOC at all), you may have issues with the headunit. As I mentioned, I've done several installs in 8's now (all using LOCs of some kind though) and never once had any issues with the headunit.

If you're just adding an amp for subwoofers, the cheaper LOC is perfectly fine. Connect it after the Bose amp. If you're doing a full on revamp with high quality equipment, sure, go with something higher-end like the LC6i, 3sixty, Cleansweep. You can buy any of them online.

Ah...good to know :) I'm going to be building a custom glass box for just 1 10" with a small amp, so I'm guessing the cheaper LOC will be just fine. I know you mentioned Best Buy...any particular model that you've used in the past that you could recommend?

I've used the "Installer's Edge" orange and grey package LOC they sell there. Never any problems. Also the Axxess products that Circuit City used to sell worked many times for me too. I'd avoid the blue Scosche ones from WalMart though. Also, a lot of people on this board has used the David Navone LOCs and swear by them:
http://www.davidnavone.com/cart.asp?14&pid=362

Oh and I'm sure PAC Audio makes several. If you happen to stumble across one of theirs, they make good stuff too.

PAC has so many models for LOCs....$15, $20, $30.....would this one work?

http://www.pac-audio.com/productDeta...&CategoryID=28

The only real difference I see in the cheaper ones is a volume adjustment knob.....

That one looks fine. As a side note, you DO want one that is adjustable. Just about all you can find anyone, but just in case.

So how will I know what 'volume' to set the LOC to....I mean the amp remote adjustment is a given, but how will I know for the LOC?

Just find a happy medium without hearing distortion. I usually prefer a stronger input signal, vice using the amp's gain knob to amplify a weaker signal. So I usually set the LOC to roughly 3/4 and let it be. It's really not an exact science. Just go at it.