TheKomoman

In a previous thread a couple of months back ( http://forums.corvetteforum.com/show....php?t=1446437 ) I posted our findings from an RTA analysis of the output of the NAV head unit from my 2006 convertible. The common assumption here was that the output from the C6 stock units was flat, but there was no evidence to back that up. Having used cmb13's thread to guide me, I installed a PAC AOEM-GM24 to splice off the low level outputs from the head and we did the analysis shown in that earlier thread. We saw a classic loudness curve and based on that I purchased and we installed a Cleansweep.

After the install my ears told me something was going on. Steve Germany was vehement in his distaste for the "noisy black box" that is part of the PAC module. The combination of something not being right and his experience led me to clip the OEM-1 part of the module out of the equation and splice in RCA's. As I detailed in a thread showing how to do that it made a HUGE difference in the sound, so we decided that re-analyzing the output was in order. Finally got to do that yesterday.

The folks that said the output was flat were absolutely right and now we have data to support it. We made a poor assumption that the PAC module was doing nothing more than splitting the signal. With that noisy black box out of the mix the output from the head looks like this:



What was particularly interesting is what we found coming from the JL's output side, post-calibration. The JL actually shows that it is boosting bass a bit at the bottom of the range.



We removed the JL and the NAV head is now plugged directly into my Alpine PDX-4.150. A couple of quick listens didn't produce a noticable difference with and without the Cleansweep. Since there isn't a difference there's little sense in having an extra component in the signal path, so out it came.

The one downside to removing the Cleansweep is that I could no longer make use of it's signal sensing capability to trigger the amp, so off we went in search of a switched 12V. Fortunatley we had the foresight to pull a trigger wire when we did the original installation! Some time spent with a multimeter produced a switched 12V circuit that was labeled "Wiper/Washer" in the passenger footwell. Tapped the wire into that and worked like a charm.

My friend took the OEM-1 module home with him. He is going to do an RTA on the output of that when he has a moment and I will post those results as well.

Isn't this stuff fun?

pentavolvo

I hope everyone reads this and realizes they dont need a cleansweep. Question how the hell do u measure that and what device do you use, im very intersted in this

TheKomoman

That was measured using the Liberty Instruments Praxis application.

http://www.libinst.com/PRAXIS.htm

My friend has the old DOS version and the hardware to go with it, which we had used the first time. This time we used the freeware version (~$800 for the front end hardware to enable the full deal) and he had a USB 6-channel sound card. I'll get the details on that for you.

TheKomoman

Here's the analysis of the PAC itself... yikes.. that loudness rolloff really is built into the module!



The yellow is a Praxis-generated reference, the green is the output from the PAC.

Pentavolvo... my buddy says the sound card he uses is no longer made, sorry. He also recommends trying TrueRTA first to get a feel for things. Praxis is very complicated and TrueRTA would give you the basis you need to understand what Praxis can do.

x-mann

I just want to say , "thanks" for the info. this is exactly what i was looking for. All the audio shops around here have been trying to sell me the cleansweep, a sumoner to recombine signals after the bose amp, and use all sorts of strange ways to do a system w/ retaining the factory head unit. It now seems evident that by tapping the wires in back of the head unit and putting a line converter to them will be the way to add a aftermarket amplifier.

thanks for all the time time you put into this!

TheKomoman

You don't even need a line converter!! The signal at the head is low level, all you need to do is tap in and put on some RCA's - here's how we did it using only the GM24 harness of the PAC module, elminating the OEM-1 box.

pentavolvo

Dont use a LOC just splice in rca jacks its line level already

Steve Germany

Great write up as usual!! Appreciate the spectum analysis!

This just goes to prove that that Bose top of the line system really can sound good... as long as you replace the amp and speakers! (can you replace the little Bose name plates on the thumper grills?)

avalonn

good thread, does the same apply to the c5 head unit?

TheKomoman

Depends on what you're talking about. I've never had a C5 so I've never done this sort of analysis on the units, nor do I know the pinouts. However the PAC OEM-1 module is what it is.. if that VET1 adapter I've seen mentioned is an OEM-1 with a different harness, well as a bonus you're getting that loudness rolloff.

cmb13

You're not gonna make me pull apart the dash again, are you?

Please, tell me I don't have to do it. Just say it.

cmb13

Btw, I used the heated seats, not the windshield wipers. I wonder if there's a difference. The heated seats don't seem to trigger at the exact same time as the head unit. How about the wipers?

TheKomoman

That was the first one we tried as you had used that one. We didn't see the voltage drop off so we just kept at it with the multimeter til we saw the voltage go away when you press off. Could be heated seats are hooked into RAP and therefore the voltage doesn't drop out til you open the door?


You don't have top open the dash Craig.



There, I said it. I'm lying, but I said it. Once more into the breach, my friend....