2005 GM TNR Low Level Audio Out split = degrade?

To add an amp for a subwoofer, I want to splice into the Low Level Audio Output signals in between the GM factory touch screen navigation radio (TNR) and the separate factory Bose amp. The factory TNR and Bose are not Luxury (ie not Y91).

I want to send the full range low level signal of all four channels (LF, RF, LR, RR) to the new subwoofer amp, rather than using a LOC on the pre amplified subwoofer outs from the Bose.

However, I'm concerned about potential signal lose to the original Bose amplifier, due to having Y split the low level audio outputs in order to feed both amplifiers.   Should I be concerned? What would be the best practice?

Use line output converter.

i am an idiot wrote:

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Use line output converter.

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I assume you mean using some speaker wires?

There are no speaker wires coming out of the head unit, only low level audio (line outs). The speaker wires come out of the Bose amp, already crossed over and frequency cut.

It seems to me like using the LOC would be a step backward... converting high level speaker wires that have already been converted from low level audio signals... back to low level audio signals again.

I'd rather just send the new amp low level audio signals.   The new amp doesn't have RCA inputs either, just wire harness connections. I'd have to convert from RCA to harness connections anyway, creating more connections that introduce noise and signal loss. There doesn't appear to be much advantage to me using an LOC, in this case.

Unless there is something I don't yet understand, which is entirely possible.   My concern in this question though is what are the ramifications of splitting the low level audio signals.   Some aftermarket amps do this, with pass through line in line out arrangements. That, in effect, is a Y split, which is what I'm considering with my headunit's existing low level audio outs.

I did the same on my 2013 impala that had the bose system. I located the low audio signal input that feed the bose amp and cut/soldered spice two sets of RCAs and feed my amp. Worked great. Although, I used the optional "line output" on my 4ch amp to feed my sub amp. Worked great. No need to use a LOC or splitter . The stock OEM unit fed the bose amp with full range low voltage sound and the bose amp separated the signals to 6ch output. Just locate the low audio input signal and directly tie in some RCAs to feed the amp. You can also just run new speaker wire to bose amp and disconnect output side and tie together from new amp, no need to run new wire all the way up front to door speakers.

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Go BIG or go Home                                    it might not be broke, but lets fix it anyway

TalarChevy...

Thank you for your report!

Did your Chevy head unit also have a "mute" wire?

My GM head unit has a "Radio Mute" wire, and it goes to my main amp (GM amp). However, my add on Sub amp does not have a provision for a "Mute" wire.   My current best guess in this scenario is that when the Radio commands "mute", my main amp will be silenced, but my sub amp won't.

I was curious if you encountered this situation in your installation?

What do other installers and do it yourselfers do when only adding a sub amp using the full range low level line outputs from the head directly from the head unit, instead of converting preprocessed high level speaker wires?

My stock head unit still had full functionality of its features, mute, steering wheel controls, etc. I only had one bose amp to bypass. The bose amps turn off and on through GM data(I forget what it's proper name is) and stills mute, etc. Are you sure the wire you're looking at is confirmed radio mute? I had no problems with setup when I bypassed it except for the louder amplified GM door chimes. You can lower the chime volume through the DIC control menu.

By the way, I first bypassed the bose system and just added my JL audio 4ch to power the stock bose speakers and they sounded great. Then I eventually installed Focal components in doors, but the bose performed well.

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Go BIG or go Home                                    it might not be broke, but lets fix it anyway

I apologize, I re read your post. Yes no matter what, when you mute the stock GM head unit, it will mute the low voltage input signal feeding your bose amp and the low voltage signal you spliced into feeding your sub amp. (same signal) just be sure you are feeding the sub amp off of the low voltage input feeding the Bose amp. If you find the sub output feeding the stock bose subwoofer and use that to feed your sub amp, then yes you will need to use a high quality LOC.

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Go BIG or go Home                                    it might not be broke, but lets fix it anyway

FWIW splitting an RCA line level should not degrade the signal any more than the connections and the wire itself. This is because the amps have a very high input impedance. If you went crazy splitting out to many amps, then yes, the effective impedance could drop enough to start pulling at the signals amplitude, which I imagine would cause a horrid distortion. There is the possibility of picking up noise, especially if the run is long and the wires are unshielded.

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Build a man a fire, he keeps warm for a day. Set a man on fire he stays warm for life!

Knudsen...Thank you for the feedback on splitting low level signal lines. It sounds like just one split for a very short run shouldn't noticeably degrade signal.

TalarChevy... Thank you for your continued feedback and guidance on what you have done. My chevy is a bit older than your chevy, so I imagine that there are a few differences, but in general your feedback is helping me put it all together in my head... before splicing wires.

Because of the door chime issue, and because of the rear seat audio control issue, I've been thinking about NOT using the low level audio signals to the original Bose amp, and instead using a high quality LOC on the high level outputs to the original Bose sub, in order to get some signal into the add on sub.

This would avoid any issue with chimes, because I presume that the Bose amp filters the chime inputs from the head unit out of the subwoofer output signal.

The only problem with using the Bose sub out signals is that they are already frequency cut, and that cut off may be a lot higher than the frequencies my supplemental sub would be capable of reproducing. So that is an issue... Thoughts?

i am an idiot wrote:

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Use line output converter.

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I'm beginning (slowly) to see the real value in this advice!   

Can you elaborate more on your reasoning, given the concerns that have been raised in this thread since my original post.

If you are concerned about the crossover point being too high on the bose output, use the crossover built into your aftermarket amplifier.

To answer your last question, Years of seeing people attempting to reinvent the wheel only to later find out it rolled easy enough and did not need any improving.

It only chimes out of the front left speaker. Use rear speaker feed if you still insist on reinventing the wheel.

i am an idiot wrote:

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If you are concerned about the crossover point being too high on the bose output, use the crossover built into your aftermarket amplifier.

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I don't understand this. Isn't it true that an aftermarket amplifier can only crossover the frequencies it receives? If the Bose subwoofer output is already frequency cut, how can the crossover in the aftermarket amplifier add those frequencies back, or cross them over?

My concern was that if I used an LOC on the Bose subwoofer outs, then I would not be sending the aftermarket amplifier the full range signal.   The Bose factory subwoofer is only 5.25". It may not have the capability of reproducing the low frequencies that an 8" subwoofer might be able to reproduce. So if the Bose amp subwoofer output is only designed to feed this small 5.25" subwoofer, isn't it likely that the output frequencies are limited, and higher, than what would be desired in an aftermarket sub?

i am an idiot wrote:

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Years of seeing people attempting to reinvent the wheel only to later find out it rolled easy enough and did not need any improving.

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I'm not trying to reinvent the wheel, I'm trying to understand the wheel. I can't help it if I didn't know wheels existed. I wasn't born all knowing. That's why I'm asking questions... and believe me when I say how much I appreciate your taking the time to answer them!

i am an idiot wrote:

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It only chimes out of the front left speaker. Use rear speaker feed if you still insist on reinventing the wheel.

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My concern with using the rear speaker feed is the deafening feedback others with similar vehicles have reported when someone in the back seat presses the Rear Seat Audio enable button. I don't want to disable the Rear Seat Audio function in the vehicle, so I'm trying to learn what the best course of action is.

Yes, I agree, the RSE can be a pain. You don't need to feed all 4ch low level inputs into the sub amp, especially if it's a mono amp. Your new sub amp should have a nice built in low pass crossover, use that to filter out the highs. If you want true low pass audio input into the sub amp then I recommend using a LOC on the bose subwoofer output. There's always too many ways to skin a cat. I enjoyed messing around with my GM bose setup, trying to find out what worked best for me. Once you start, you'll want to do more. In my honest opinion stock GM bose speakers sound great with an aftermarket 4ch amp at HPF'S set to 100hz.But that's a different post thread, lol. Feel free to PM me if you want more info.

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Go BIG or go Home                                    it might not be broke, but lets fix it anyway