posted
Hey guys, I was wondering if you could clear this up for me. I am well versed in pretty much all areas of car audio, and output impedance is one thing that I just have not learned yet. I fully understand output voltages of HUs, but was wondering if you could expain the second part? I know that the lower the impedance the better, but I am looking for the specific details.. more or less the physics of it. Thanks a ton.
posted
netlohcs, output impedance is kindof an odd issue, most companies ignore this spec, few people go into a store and say I want the cd player with the lowest output impedance, so they can get away with not publishing it, maybe they do it because it's high, who knows. but I'll try and get a little more into what it is and how it affects you sound. First off, we'll assume an op-amp is the last component in the head/x-over/line driver whatever which will determine the output impedance. an op-amp by design has VERY VERY low output impedance and with the right design it will only be a few ohms BUT maybe the op-amp will fry if the load gets too small ie. your rca cable shorts out and the load becomes 0 ohms well say their op-amp will drive 1k ohm without a problem so they put a 1k resistor in series with the output and now no matter what you try and do to their line out it's gonna work just fine, because the load (which includes that 1k resistor) can't go below 1k, no warranty issues it lasts a long time everyone seems happy but your not really getting the best performance possible. others put a smaller series output resistance because maybe at a 200 ohm load the op amp with shut off, or overload, but not get damaged, fix the shorted RCA and your back in business... So basically they put a resistor there to protect their product with a tradeoff of a little performance..
I'm not sure if I answered your question completely but if you have any other questions just ask
(I didn't get into the noise issues associated with higher output impedance but lower is better there too.)
------------------ Digital Designs 9515 Mmats d300hc (2) (soon) Pioneer source MB Quart fronts ADS power plate RW Audio processors http://www.geocities.com/motorcity/6128 Member of Team Hertz Canada
Posts: 736 | From: Calgary AB | Registered: Oct 1999
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posted
Thanks RW, your post helped quite a bit. I see what you mean about putting a resistor in series, and how that determines the rating. So essentially the output impedance only depends upon what size (ohm) resistor they put inline? I am upgrading from an eclipse 5342r to a 7002 (screen), and i know that my pre amp voltage will be going from 2.7 to 5 volts. also the output impedance will be decreasing from 330 ohms to 55 ohms. So, essentially, the 7002 has a far superior pre amp (Op-amp) section, allowing for higher voltages and lower impedances. Am I correct on this one? When i switch head units, how much of a change do you think I will percive as far as cleanliness and overall SQ? (I am using PPI PC amps, and eclipse pointsources). Again, thanks.
posted
Well that's pretty much the basics.. there is more to what makes up the output impedance, but basically most of it is a resistor on the output, the specs aren't too bad on your first deck, but there might be enough of a difference since you don't have a line driver or anything... I personally switched from a Pioneer Deh-p815 (0.5V preout and probably very high output impedance) to a Premier Deh-p600 (4.8V probably lower output impedance) and the difference in sound quality was amazing, that along with changing from an RF to ADS amp my front stage sounds so much better.. Let us know how it turns out and if the difference is very noticable.
------------------ Digital Designs 9515 Mmats d300hc (2) (soon) Pioneer source MB Quart fronts ADS power plate RW Audio processors http://www.geocities.com/motorcity/6128 Member of Team Hertz Canada
Posts: 736 | From: Calgary AB | Registered: Oct 1999
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posted
The lower the output impedance and the higher the input impedance at the next component the better. This way the cable has a smaller effect on the signal and the head unit can drive more amps without signal loss.
posted
JC2.. here's a little something for you to read.. it's a totally different concept in signal transfer, it's kinda weird.. and it was designed by Krell probably one of the most amazing home amp makers on the planet. http://www.krellonline.com/ click on the master reference amp then look at "CAST" let me know what you think? think that would work in a car? hehe
------------------ Digital Designs 9515 Mmats d300hc (2) (soon) Pioneer source MB Quart fronts ADS power plate RW Audio processors http://www.geocities.com/motorcity/6128 Member of Team Hertz Canada
Posts: 736 | From: Calgary AB | Registered: Oct 1999
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posted
Well I wish I had a little more info, a little more technical. It is a valid argument but I don't know if they are the first to do a current driven signal. I'm not too familiar with alot of home equipment but I don't see the cable effect being on the order of percents like they said since a cable, even a 100ft cable, shouldn't have an impedance of more than one ohm. I will have to think some more about this and let you know.
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