Saturday, September 10, 2005 - 08:03 am, by: Jason Kingsmill(Jason_k)
Another question for you Mark...
I have finally got off my ass to start installing the CarPC, and just had a few more thoughts...
The TV tuner plug where you tap into the audio and video(not with the Tuner mod, unplugging the tuner and wiring directly to the plug)...what audio line voltage would be expected there? I think the PC's audio line out only puts out 500mV... Does Jaycar sell a Line Driver with line isolator built in? I have only managed to find the line isolator AA3085.
Does the factory volume control drive a pre-amp, or is it somehow tied into the main and sub amps?
Simply, is it possible to just replace the main amp with a standard car amp and retain the factory volume control, while using the TV input? And would you expect any loss of quality using the TV input compared to a direct input to an amp? Either through induced noise, or (if it uses pre-amp),
Sorry for all the questions....I don't want to stuff around doing it one way then totally changing it!
Saturday, September 10, 2005 - 09:54 am, by: Mark Paddick(Sparks)
I don't know for sure what the sensitivity of the TV input is but it is relatively low; 500mV will be plenty to drive it and you shouldn't need any line drivers or matching. This is the same for the TV mod too as it simply switches that same audio point. The audio from here goes straight to the radio receiver so leads are short. The factory volume control is digital and connects through the tape player which in turn controls the radio receiver pre-amp stages. This is the reason why you can't easily remove the tape player; it does input switching too. The factory amps connect to the radio receiver and use fairly standard line levels so you can easily swap amps. The only function you are likely to lose is the mute function as most aftermarket amps don't have one. This is only a problem if you have a mobile phone car kit; you won't be able to automatically mute the stereo on phone calls without a bit more modifying. Nearly all amps, including the factory setup, use a 12v line to enable the amp. This can be used with a relay from the mobile mute line to acheive the mute function with aftermarket amps. The sound quality of the preamps in the radio is pretty good and the noise isolation is better than most. You probably won't hear a difference between the direct amp connection and the preamp connection, except for the effect of the factory auto-loudness on low volumes. The factory amps are pretty good too. I have replaced the sub amp in mine because of the new sub but I still use the factory 4-channel amp. In fact i use two of them and electronic crossovers. The main advantage is power drain from the battery. The factory amps run from 12v directly; most aftermarket amps use a DC-DC converter power supply to get higher power levels and hence have higher input power requirements. I find that the factory amp working over a reduced frequency range has plenty of headroom and sounds much better because of that. I don't think replacing them would achieve much for me and two 4-channel aftermarket amps would be a pain to fit in whereas the factory amps both sit under the stacker on factory brackets (Sat/Nav removed and TT brackets used for second amp which fits where the Sat/nav would normally be in a TT). I do use a 1F capacitor, mainly 'cos I got it cheap and it helps with noise suppression, and this has definately improved the low end performance of the factory amp.
Saturday, September 10, 2005 - 11:14 am, by: Jason Kingsmill(Jason_k)
Thanks for the great response Mark....Certainly explains the whole system a lot better. Muchly appreciated.
I managed to test the audio using my sisters iPod...when at full volume, it is only slightly quieter than playing a CD, although there is a small amount of noise. Yet to determine if it is just the poor quality amplifier in the iPod causing it or not.
I tested the video input with my camera...works! The only thing so far that annoys me is the relatively poor brightness and contrast of the factory screen. Would amplifying the video signal help with the brightness at all, or would it simply distort the picture? (I have never studied LCD principals, only CRT unfortunately)
Other than that, would it be possible to upgrade the backlight(s) to help?
Or could it simply be just that my screen is too far gone (you saw the amount of dead pixels!) and requires replacement?
Saturday, September 10, 2005 - 12:12 pm, by: Mark Paddick(Sparks)
The noise is probably the iPod.
Poor contrast/brightness is usually the backlight not the best. I have a couple of pretty good EMVs at the moment with much better screens and backlights, $200 to $300 exchange, depending on screen quality. I would need your EMV first as i don't have working touch screens (yet).
Jaycar have a video amp with brightness and contrast controls (QC3437 $69.95)
Saturday, September 10, 2005 - 06:19 pm, by: Jason Kingsmill(Jason_k)
Ok, well finally got the PC hooked up and running.
I don't think the composite screen is gonna handle the job...resolution is just too low to read any of the text. Brightness is much better than from the camera though.
Audio level seems pretty good, although there's pops and crackles everywhere, so I guess I might need an isolator.
Guess I'm gonna be more out of pocket, now that I gotta buy the VGA touchscreen And it's gonna be a lot more work...
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