Aftermarket Subwoofers on non HK GT?

[DevLF]

So I have a question that I can't quite seem to understand regarding how I'm going to splice into the factory amp to send to an amp for my subwoofer. I want to splice into the S/PDIF, as I understand it:

I need to purchase a digital to analog converter, splice into the copper SPDIF wires, hook the splice into the DAC, and then DAC to the aftermarket amp input.
But where I get confused is since the SPDIF has three wires (SPDIF +, SPDIF -, SPDIF Ground) which wire(s) do I come off of? Do I use a Y cable RCA and hook the two ends one on pos. one on negative and then the single side into the DAC? I've made a crude image to how I think understand it works when splicing off of SPDIF.



I do understand it's possible to go with a line output converter and splice AFTER the factory amp but I want to grab the signal before the factory amp touches it.

Appreciate greatly any help in advance.

 

[mfenske]

From what I understand (and please note that's purely hypothetical) you tap the positive and negative SPDIF leads which you could connect to a 75 ohm cable in to the DAC (or Digital Signal Processor). The main drawback as I understand it is that you could (and likely will) lose volume control at the source and any chimes, etc. For simplicity's sake it's probably easier to tap the speaker level signal.

That said, depending on what direction I go with my system I may try tapping the SPDIF signal just to see how it works (which will likely be a few months away).

 

[RedCal]

Agreed, I would go post amp, it's simpler, and less likely to give you issues, the last thing you want is no control of the sub volume
I had a look at the pin out, and the SP/DIF is labeled high, low, and ground... which makes it quite different...

 

[DevLF]

Just curious how I would lose chimes by tapping off of SPDIF? My amp also has a seperate control knob for volume so controlling sub volume isn't a concern for me at the headunit. I do understand its more simple tapping post amp, but the signal is processed by the factory amp at that point. Then I'm dealing with potential high pass/low pass filters and EQ being applied. Which id prefer controlling separately for the woofers

 

[DevLF]

From what I understand (and please note that's purely hypothetical) you tap the positive and negative SPDIF leads which you could connect to a 75 ohm cable in to the DAC (or Digital Signal Processor). The main drawback as I understand it is that you could (and likely will) lose volume control at the source and any chimes, etc. For simplicity's sake it's probably easier to tap the speaker level signal.

That said, depending on what direction I go with my system I may try tapping the SPDIF signal just to see how it works (which will likely be a few months away).

So do I tap it the way that I drew or is there a different way I do it? Just trying to understand the exact wiring configuration

 

[mfenske]

Just curious how I would lose chimes by tapping off of SPDIF? My amp also has a seperate control knob for volume so controlling sub volume isn't a concern for me at the headunit. I do understand its more simple tapping post amp, but the signal is processed by the factory amp at that point. Then I'm dealing with potential high pass/low pass filters and EQ being applied. Which id prefer controlling separately for the woofers

Well, you'd be disconnecting the factory amp and I think that's where those are processed. Not sure though if it's similar to other cars I wouldn't be surprised.

 

[TheBusch]

Well, you'd be disconnecting the factory amp and I think that's where those are processed. Not sure though if it's similar to other cars I wouldn't be surprised.

If he did lose chimes and volume control, it would only be on his subwoofers.

 

[DevLF]

So I'm ending up just going to go the LOC route after some more research. I originally planned on basically just Y splicing off of the SPDIF but didn't think about how putting two loads in parallel is going to halve it and idk how the head unit would handle half the impedence.

 

[G-731164]

I see nowhere how you make that RCA cable with 3 wires, i need it on a RME card, OUT+ OUT- and GND with a single RCA.

Pin assignment of the 9-pin D-sub connector, breakout cable SPDIF / AES
Note: The digital breakout cable is identical to the one used in the DIGI96 series.
Pin Name Pin Name Pin Name
1 GND 4 AES Out + 7 SPDIF In -
2 SPDIF Out + 5 AES In + 8 AES Out -
3 SPDIF In + 6 SPDIF Out - 9 AES In