posted
Does anyone know at what impedence alpine heads put out their rated voltage? I was taught that impedence was just as important as voltage when considering this spec.
I need to know if it's anything close to the 55ohms the eclipse units offer.....I'd rather buy an alpine due to eclipse's skipping problems (my car isn't the smoothest ride).
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Posts: 156 | From: Austin/Kerrville TX USA | Registered: Jan 2000
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posted
How crucial is the impedence of the preamp section of the head unit. I know that the lower the better but how does that affect SQ and proper gain setup?
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posted
This is a quote from a friend of mine who goes by the alias chev2 on sounddomain and the PG forums. He is comparing an eclipse HU which should really be 5 or 8v @ 55 ohms, an alpine HU (4v @ 300 ohms), and the phoenix gold PLD1 line driver (which should be 8v @ 33ohms),
quote:Ok when comparing line drivers and decks for that matter the output voltage is really not that important. It's a lot of marketing junk. Voltage only tells us the potential between to points. To find out how much power where getting we need to figure out the wattage. and to do that we need the impedance. Now audio control doesn't post the impedance of there unit... But i will do a example comparing eclipse h/u , Alpine h/u and the pld. the equation is volts^2/impedance
so for Eclipse: (the have two models) 6V @ 55 ohms 6x6/55=.655 Watt's and 8V @ 55 ohms 8x8/55 =1.16 watt's
and for alpine 4v @ 300 ohms. (in power's prev's post he told use that the impedance of alpines deck is 300 ohms). 4x4/300=.053 watts
And finally for the PLD 9v @ 33 ohms 9x9/33=2.454
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Posts: 156 | From: Austin/Kerrville TX USA | Registered: Jan 2000
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posted
depends on what model of alpine deck you have... anywhere from 1.8v to 4v, i think... i'm using a panasonic w/ 4v preouts and 60 OHM impedance, sounds pretty damn good
mqqball: the lower the impedance, the cleaner the signal and you get better s/n out of your amp
hope this helps
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Posts: 1408 | From: Stacyville, IA, USA | Registered: Jan 2000
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posted
At the Eclipse products training siminar that I went to last week, they informed us of that the skipping problem was fixed and should not reappear again. It was a very difficult problem to fix because the skipping was due mainly to the vehicles and not the HU. Many shops were finding that if you took a HU out of one car and put it into another then skipping would go away. I am not sure which cars this problem was happening in but this is what they found out. This is a bit off from your main question but I think that if you wanted to go with an brand new Eclipse unit you would not run into the skipping problem. Any model that has a 5-digit model number is going to be safe. Hope this helps some people out with their decisions.
posted
Thanks for the post RDWM...I understand what all that translates to...It doesn't matter what the preout voltage is, its the impedence of the preouts that determines the strength of the signal going to the ampliefier. Therefore the higher the wattage from the deck the better.
Now that raises another question...How does this affect the gain setup on amplifiers? I know how to do it (Thanks to Wayne) but should I look for certain things when moving from head unit to head unit?
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posted
I always thought that alpine had a 10k impedence?? are we talking about the new one's here or am I missing something? I guess that equation would explain why I had to turn the sensitivity all the way up on my ppi peq114 eq/line driver. 16/10000=.0016 Is this correct?? is it really that low?
posted
The reason that many HU companies have high impedence RCA's is because if they have a low imped. and touch anything metal they short out the outputs. With many older vehicles having metal behind the dash it seemed logical for them to raise the imped. on the RCA's so that if they touch anything they would not fry the outputs. This is why some installers suggest you wrap your RCA's with electrical tape. But with so many newer cars have less & less metal materials in them the HU companies can now lowering the imped. without as much worry about them shorting out. You can bet that if this wasn't a problem then you would have never seen this issue. You must remember this is also part of a marketing scheme. Don't get me wrong. A HU with low imped. and high voltage is always a plus. But with soo many HU's out there now that are all claiming they have 4v or better RCA's they have to start to look else where for reasons why their HU is better then their competitors, and lower imped. just happen to be a good way to boost your product. I hope this might shead some light on a few things.
posted
A low source impedance is CRITICAL for good noise rejection. Ideally, the source impedance would be almost 0. (The same as a power amplifiers output impedance) and the amplifiers input impedance would be infinite (current amps are around 20K). This would allow the source unit to drive an infinite number of amps without a voltage drop and would result in less chance of induced noise.
Many source unit manufacturers insert a series resistance between the output line driver of the unit and the center conductor of the RCA "pigtail". This prevents the line driver op-amps from getting damaged when you short the center conductor of the RCA output to ground. While this may increase reliability, it has a detrimental impact on noise immunity. (Noise can be induced into the RCA cables leading from the source unit to the amps because of the increased source impedance.)
Another thing you should look at is the resistance between the shield of the RCA cable on the pigtail and chassis (power) ground. Ideally, there should be a dead short. In my opinion, there should be only one point where chassis ground and audio ground are common, and that is the source unit.
Unfortunately, many manufacturers insert a resistor in series with the audio ground before the pigtail. This is a bonus "noise generator" that you won't find in the user manual. A poor audio ground can result in all types of problems "down stream." Many products may have "floating" grounds to prevent ground loops. Without a proper ground, these products may not work correctly.
Manufacturers started adding this series resistance to increase reliability. Evidently, some installers were connecting amps with common audio / chassis grounds to radios with common audio / chassis grounds. Obviously, this creates a "ground loop" and noise results. Guess what some of the installers did? They disconnected the power ground lead to the amp. This caused the amp to source it's ground through the shield of the RCA cable AND the ground of the radio. This usually resulted in fried traces on PCB in the source unit.
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posted
so what you're saying is..........I'll have an Alpine cda7840 and a cha1214 12 disc on ebay soon and that I'll be lookin for a new deck?......right
I've had a cda-7839 for over a year now. It has served me very well, and as the first piece of audio equipment I ever purchased, it was the stepping stone to about 15 other purchasaes since. Definitely put a good car audio taste in my mouth.
It only skips when I take speed bumps or dips at 30 mph or if someone slams the door real hard. Overall a good unit, although I have no frame of reference in my vehicle.
I would buy alpine again....but would also use a line driver or two if i did. I'll probably save my money and buy eclipse.
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Posts: 156 | From: Austin/Kerrville TX USA | Registered: Jan 2000
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posted
Now I was thinking about buying a PPI PAR-245 Pre-amp but by using the formula listed above the output of the unit is 8x8/10,000 which is 0.0064W...How would this help in my setup when I can get a deck that will put out more than the preamp? Whats the sense of buying a preamp?
------------------ Knobs Rule! Keep it simple, clean, and loud!
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