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    leonm12's Avatar
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    preout impedance

    what is the benefit of lower preout impedance?
    I have Pioneer DEX-P9 HU, which have 100-ohm RCA outputs.
    and it's external Processor DEQ-P9 have 1Kohm RCA outputs.

    I am confused and don't know why there in diffrences at the preout impedance and how it is effect SQ??







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    Re: preout impedance

    The important variable is output voltage,
    not output impedance. Anything 2v - 4v is
    good.




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    Re: preout impedance

    Voltage is not rated in RMS. While playing music you will find that voltage is less then one volt RMS.




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    Re: preout impedance

    Quote Originally Posted by mcsoul View Post
    The important variable is output voltage,
    not output impedance. Anything 2v - 4v is
    good.
    no, 2 volts is ok. 4 volts is good.




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    Re: preout impedance

    Quote Originally Posted by mcsoul View Post
    The important variable is output voltage,
    not output impedance. Anything 2v - 4v is
    good.
    Kind of.

    In order to boost the S/N ratio, a low impedance output + a high voltage signal is preferred. It's about noise, really.

    Not sure if you understand, but you'll get 4V out of your P9 with a 0dB test tone and the EQ maxed out. With music, then it's not even close.

    Eclipse's technology as a reference: http://www.fujitsu-ten.co.jp/english...8_body/01.html




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    Re: preout impedance

    Yeah guys, I'd rather have 4v too. But I would not replace
    an HU that I'm otherwise happy with over it. Unless you are
    actually picking up noise over the rca run.




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    Re: preout impedance

    Think of it as damping factor for pre-amp level signals.

    If the ratio of the output impedance of the source to the input impedance of the receiving component is too small, then they can "load" and cause anomalies in the frequency response.

    And then the noise issue Fox mentioned.

    To say that output voltage is more important than output impedance is just flat out wrong. Many actually place more importance on the latter than the former. Pioneer had an old headunit that was quite highly revered, DEX-M88....only had 1V or so output voltage but it's impedance was ridiculously low, like 4ohm.




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    Re: preout impedance

    Quote Originally Posted by squeak9798 View Post
    Think of it as damping factor for pre-amp level signals.

    If the ratio of the output impedance of the source to the input impedance of the receiving component is too small, then they can "load" and cause anomalies in the frequency response.

    And then the noise issue Fox mentioned.

    To say that output voltage is more important than output impedance is just flat out wrong. Many actually place more importance on the latter than the former. Pioneer had an old headunit that was quite highly revered, DEX-M88....only had 1V or so output voltage but it's impedance was ridiculously low, like 4ohm.

    So the lower the output impedance the better. I
    learn something new every day, often from you.




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    Re: preout impedance

    Actually it's best to choose devices with similar impedences, not just lower. Having two or 3 low impedence devices would be great, but, as Squeak expained above, if one is high impedence you could have an impedence mismatch that can cause serious noise problems and even preamp failure. It would be better to have all the devices high impedence than to mix high and low.
    You want the output of one device to match the input of the next device. It's very similar to the idea of matching sub impedence to the amplifiers output. It doesn't really matter much what the impedence is, you just want them to match to get the best performance from both.
    Some devices can have very different input and output signals.
    When trying to match devices you want to match balanced/unbalanced, voltage range and impedence range, outputs to inputs for each device.
    A 4 volt unbalanced 2k ohm output signal is very different from a balanced 4 volt 50 ohm input stage and they would not match up very well.



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    Re: preout impedance

    OK then I did'nt understand what squeak was saying.

    I'm still not there 100%.

    I hope that these issues generally do not factor in
    when going from your average brand new 2v or 4v
    deck out to your relatively new off the shelf amps
    that have a variable gain, and the signal is being
    conducted by high quality RCAs.




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    Re: preout impedance

    That is correct, they do not generally factor in because most amplifier inputs are specifically designed to accept a wide range of input voltages and impedences. An inline device, like and e.q., might be a problem if there is a mismatch because they generally do not have the ability to accept such huge variation of inputs.

    Unless your HU has a strange output and/or your amp input has an unusually limited range, most amps input stage can be adjusted to accept most HU outputs.



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    Re: preout impedance

    Quote Originally Posted by DidUHearThat? View Post
    Actually it's best to choose devices with similar impedences, not just lower. Having two or 3 low impedence devices would be great, but, as Squeak expained above, if one is high impedence you could have an impedence mismatch that can cause serious noise problems and even preamp failure. It would be better to have all the devices high impedence than to mix high and low.
    There is nothing wrong with using a low output impedance with a high input impedance. this isn't RF. further, the only case i can think of where equipment would be damaged would be in the low-output, low-input impedance case.


    You want the output of one device to match the input of the next device. It's very similar to the idea of matching sub impedence to the amplifiers output. It doesn't really matter much what the impedence is, you just want them to match to get the best performance from both.
    this would seem to be the exact opposite of what happens. A typical amplifier might have a DF > 100 when used at full power. this means the output impedance of the amplifier is 100 times less then the impedance of the load. Similarly, line drivers often go for very low output impedances as well.



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    Re: preout impedance

    Quote Originally Posted by DidUHearThat? View Post
    That is correct, they do not generally factor in because most amplifier inputs are specifically designed to accept a wide range of input voltages and impedences. An inline device, like and e.q., might be a problem if there is a mismatch because they generally do not have the ability to accept such huge variation of inputs.

    Unless your HU has a strange output and/or your amp input has an unusually limited range, most amps input stage can be adjusted to accept most HU outputs.
    Unfortunately as much or little I understand the concepts,
    I still have low level alternator whine and a nasty THUMPhssst
    on turn off my HU!




  14. #14
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    Re: preout impedance

    Quote Originally Posted by leonm12 View Post
    what is the benefit of lower preout impedance?
    I have Pioneer DEX-P9 HU, which have 100-ohm RCA outputs.
    and it's external Processor DEQ-P9 have 1Kohm RCA outputs.

    I am confused and don't know why there in diffrences at the preout impedance and how it is effect SQ??
    I myself run a P9 combo and I have to say this is the quietest system I've ever had. The fact that you run an optical cable which is immune to noise and interference makes all the difference. I mounted my processor in the trunk and made 4 short runs to the amps and it's absolutely silent.

    In short, don't worry about specs. Ask yourself how it sounds.



    Source Unit: Pioneer P9 combo
    Tweeters: CDT DRT-25 Silk
    Mids: CDT ES-5 (5.25")
    Midbass: CDT M6 (6.5")
    Subs: Pioneer TS-W12PRS
    Mid & Tweet amp: Pioneer PRS-X340
    Midbass Amp: Pioneer PRS-X720
    Sub Amp: Pioneer PRS-X720

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