PDA

View Full Version : HU Pre outs



unrated
10-28-2006, 12:03 PM
hey guys, im looking for a cd player with a good output, but i dont know what kind of impedsnce i should be looking for in a output level

Example : Subwoofer Output Level/Impedance 5V/60 ohms

is that good?!?!? Thats off a panasonic deck, or should i find something different

thx

dkguitarist
10-28-2006, 12:07 PM
buy my eclipse 3434.

PhatTonyDeMarco
10-28-2006, 12:08 PM
The preout voltage only determines where you will set your gain, if the preouts give more voltage then your gain will not need to be as high. It should NOT be a factor when deciding what head unit to buy, it will affect nothing audibley.

unrated
10-28-2006, 12:11 PM
The preout voltage only determines where you will set your gain, if the preouts give more voltage then your gain will not need to be as high. It should NOT be a factor when deciding what head unit to buy, it will affect nothing audibley.

right on thx

so i dont need to worry about the Impedance of the line then?!?!?

PhatTonyDeMarco
10-28-2006, 12:13 PM
right on thx

so i dont need to worry about the Impedance of the line then?!?!?

No..

iceteebone
10-28-2006, 12:14 PM
right on thx

so i dont need to worry about the Impedance of the line then?!?!?

lower impedence better. 60 ohm is pretty low. most preouts are 100 ohm. voltage really doesn't mean crap. with music, you will never see 5 volts or whatever the deck claims.

HCCA
10-28-2006, 12:43 PM
No..
Sorry, so very wrong! The lower output impedance, and the higher the output voltage, the better the induced noise rejection. If you want to keep alternator whine, static hiss, humm, etc, out of the signal path, you have to keep the output impedance as low as possible, and the output voltage high. 4 volts is sufficient, but it serves a hidden purpose. All 12 volt decks without a switching power supply derive their output voltage from converting 12 volt DC line in, to 2V, or less output AC signal. Without a switching power supply, you cannot gain any more output voltage. It's not possible. What's more, you will have clipping at the higher volume settings. Something you want to avoid in the setting of all other components in your system. However, unlike your other components, you cannot adjust the I/O gains to get rid of the clipping.
A switching power supply, if done right, can give you 4,5, in the case of some Sony units, 8v of output. This is clean, undistorted, non-clipped signal. It is the same concept as what your amp's power supply does. Brings in 12v DC, and after switching it to pulsed DC, rectifying it, and running it through a transformer, the voltage is stepped up to somethin like 24-36 volts. So, the output voltage aside...the clean non-clipped signal output you get from a switching power supply is all the reason you need to look at higer output voltages. Also, if you have an output impedance that is too high, say 2000 ohms, you must look at the input impedance of the next downstream device (say...an EQ). It must then have an input impedance of 10 times that amount, to drive it. That would be 20,000 ohms. Some devices don't have that kind of input impedance. With an output impedance of your HU (60 ohms), you can drive anything with an input impedance of 600 ohms or more. A zero ohm impedance would, theoretically, drive ANY input impedance device.
As another note, you cannot induce a voltage across a dead short, right? Well, zero impedance at the output of a head unit is essentially a dead short (as far as radiated noise is concerned). As output impedance drops, it becomes more difficult for radiated noise to enter the system.

iceteebone
10-28-2006, 01:18 PM
preout voltage is simply used for level matching. once you are playing music you are never gonna see a constant 4 volts anyways. if you are getting induced noise, all higher preouts do is make to where you don't need to turn up the gain and therfore not amplifying the noise. if you have noise, higher preouts is just a bandaid for what is wrong in the system

HCCA
10-28-2006, 10:03 PM
preout voltage is simply used for level matching. once you are playing music you are never gonna see a constant 4 volts anyways. if you are getting induced noise, all higher preouts do is make to where you don't need to turn up the gain and therfore not amplifying the noise. if you have noise, higher preouts is just a bandaid for what is wrong in the system

Sorry, wrong! Induced noise has to overcome, or "push through" the signal voltage to be able to be reproduced. If you think that signal voltage has only to do with level matching you have little or no education of electronic theory. The higher the output voltage, the more difficult it is for radiated noise to enter the signal path. BTW, what do you call a "band-aid fix??? If I were to use fiber optic connections in the system...Is that a band aid fix, or a better way of doing business??? Can you induce radiated noise across a fiber optic cable? Neat trick if you can. I'd pay to see that one!

"if you have noise, higher preouts is just a bandaid for what is wrong in the system" .....Just what is it that is "wrong" with a system that picks up noise, if not high output impedance/low output voltage? Yes, you can route the signal wires away fron the power wires. Yes, you can use good grounding. Yes, you can match your signal levels. And, when you still have induced noise in the system....what then??? An output impedance of 4 ohms, and a signal voltage of 5 volts...such as the M88 Pioneer unit (old school) will reject said noise. There CANNOT be radiated noise in a system with a HIGHER output voltage than said radiated noise! A higher output impedance allows noise a better chance of being picked up....almost like a magnet. A low 5 ohms, or less, output impedance will be more difficult for noise to be picked up...much, much more difficult (vs. 250-1000 ohm).

No, you will not "see" a constant 4 volts in program material. You will, however, have a higher signal voltage than any radiated noise. A signal voltage of .025 volts is no match for radiated noise of .5 volt of alternator whine!!! 4 volts of signal will push out that .5 volt, even if it dips to .5 volt on regular musical passsages. Repeating what I've said before, how do you get around clipped output from any unit without a switching power supply (which you will ALWAYS have)???? This clipping will be evident to even the most neophite novice. Said clipping will damage drivers at max volume, if amplified in an average high powered system.

Not that it's necessary, but I have 2-double master degreed engineers who agree with me. Names Richard Clark & David Navone. I also worked on guidance systems for aircraft in the military, and two years of car stereo competition under my belt....whach you got???

dleccord
10-28-2006, 11:04 PM
So are you saying that the higher voltage the pre outs are, the lower the impedence that it has? And is that a given or an example or the .5volt of alternator whine?

HCCA
10-29-2006, 12:54 AM
So are you saying that the higher voltage the pre outs are, the lower the impedence that it has? And is that a given or an example or the .5volt of alternator whine?

No...I was saying that you want BOTH higher output voltage, and lower output impedance. One is NOT the result of the other. Both together are good, however. I would limit the output voltage to 7 volts (for an output voltage from a head unit), as most amps, and signal processors, have a 7V max input voltage. Output impedance is considerd near perfect when it gets close to zero, but is not a RESULT of high output voltage.