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Passive vs active driving long cable

Discussion in 'Pickups & Electronics [BG]' started by manchild, Feb 9, 2014.

  1. manchild

    manchild

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    I play through DI only in our wedding band and after reading a lot on our forums about how an active bass (or certainly one with a buffer) will lose less signal quality/high end than a passive when the cable is over 20 feet long.

    My question is this:

    Given that this is the case, id like to get some perspective on this. If you had two idential basses except one has no onboard preamp, how much volume and treble frequency are you going to lose using - say, a 40/50 foot cable? What frequency range is the passive going to filter down to and how many db of volume are you losing. More importantly what is the extent of the perceivable loss?

    Thanks.
  2. line6man

    line6man

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    It depends on the signal impedance, and capacitance of the cable.
  3. walterw

    walterw Supportive Fender Gold Supporting Member

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    i'd say real-world the passive bass will just sound a bit duller. i don't think you'll lose overall volume that much.

    remember, something as basic as a TU2 stage tuner in-line makes the signal "active" from there on out, fixing the issue.
  4. manchild

    manchild

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    So with the right cable would there be no difference?
  5. manchild

    manchild

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    Would it be considerable duller like turning the tone nearly half down on a P/Jazz bass? Or very subtle?
  6. Jazz Ad

    Jazz Ad Mi la ré sol Gold Supporting Member

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    The loss of treble can be heard very easily with more than 5-6 meters of cable.
    The test is super easy to do. Plug you bass into the console using a 10 meter cable, then do the same using a 3 foot cable then a DI.
  7. manchild

    manchild

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    What is the max length of cable that should be used before the DI for a passive bass so that any loss is absolutely minimal?
  8. Jazz Ad

    Jazz Ad Mi la ré sol Gold Supporting Member

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    Ideally, zero. Which is why active instruments were invented in the first place.
    Practically, I'd say under 10 feet it will be difficult to hear a loss.
  9. RobbieK

    RobbieK

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    Are you talking about a 40-50 ft lead from the DI to the desk? Is the DI active or passive? If it's active (battery or phantom), then it won't matter. If your DI is passive, you will hear a huge difference with an active bass. Passive DI's usually only have an input Z of around 50K. That will dull a bass significantly even before the long cable run. If you use a passive bass and a passive DI, a simple fix is to run a boss pedal or something similar (non-true-bypass) between your guitar cable and the DI input. Even on bypass, this will buffer your signal.
  10. manchild

    manchild

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    Thanks jazz. Thats good to know. If using a wireless system, is it a case of making sure the impedance of the input of the wireless has a higher number than the output of the bass. Thus creating no 'cable length deterioration'?
  11. manchild

    manchild

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    I am meaning the cable from the bass to the DI :)
  12. khutch

    khutch Praise Harp Supporting Member

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    I made a brief effort to find cable capacitances on the web and got values between 15 and 45 pF per foot. I don't know if those numbers sound the limits of what is out there or not. I ran a simulation using a typical P bass setup: pickup, volume, tone, and amp input resistance. At 15 pF you get a cutoff frequency of 5.8 kHz. At 30 pF it drops to 4.2 kHz. At 45 pF it is down to 3.5 kHz. All of those are for 50 feet of cable. Those results are fairly significant for a guitar, less so for a bass. The 10th harmonic of the 24th fret on your G string is 4 kHz and I am not sure how much the 10th harmonic contributes to either the tone or the volume and of course many basses don't have 24 frets. If your bass has six or more strings perhaps you have more to worry about.
  13. manchild

    manchild

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    Thanks Khutch.

    So looking at the figures it would seem that even with 45pf, not a lot of audible treble will be lost given the 10th harmonic is 4khz? With 15pf losing next to nothing? My Ashdown speaker cab only goes up to 2khz :/ how does that figure with the audible results?
  14. lowfreq33

    lowfreq33

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    Disclosures:
    Endorsing Artist: Genz Benz Amplification
    Going wireless eliminates any issues with cable capacitance.
  15. RobbieK

    RobbieK

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    If you record a few instruments all playing the same pitch, then remove the attack of the notes in protools or something, it's surprisingly difficult to tell which is which. IOW, the attack transients of musical notes define the tone colour to a very large degree. Even with old strings, and fingerstyle instead of a pick, the attack transients (and fret noise etc) of an electric bass extend much higher and lower than 4Khz. But more importantly, they are magnitudes more energetic than the sustaining part of the note. I would think most bassists would easily hear the difference between 20 and 40 foot guitar cables of similar quality on a passive bass, even with old strings, and especially if feeding a PA, with its HF drivers.

    If you are using a DI, I can't really understand why you need a long guitar cable. The job of a DI is to buffer, then balance and drive long cable runs to a mixing desk. (And also possibly cut earth loops.) You should use a short cable into the DI, because you can use just as long a (mic) cable as you like from the output.
  16. walterw

    walterw Supportive Fender Gold Supporting Member

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    yep; wireless automatically = active.

    so much so that systems like the line 6 relay have settings to reintroduce the sound of some cable to make things more "normal" for passive instruments.
  17. manchild

    manchild

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    Thanks for the replies guys. So with a wireless system making things active, should I be looking for any other specs about it or do all wireless systems take out 'cable length'?
  18. line6man

    line6man

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    The wireless system doesn't really do anything. It's just the fact that you only need two or three feet of cable to get to your input that minimizes the accumulation of parasitic capacitance.

    One factor that may or may not vary amongst wireless inputs is the input impedance. For a passive instrument with high impedance magnetic pickups, 1M Ohms is standard. Lower values, such as 500k, are becoming common on modern gear, because buffered (low impedance) signals are increasingly popular. These lower input impedances minimize thermal noise, which is proportional to resistance, however, they may cause slight losses with high impedance signals.
  19. uOpt

    uOpt Supporting Member

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    This is purely capacitance driven.

    If this is important to you track down some Belden 8410 which is 108 pF/m. That's 70-50% of random cable material so you can go substantially longer for the same total capacitance.
  20. manchild

    manchild

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    Given that old school sound tends to have less treble than modern and that even with up to a 50 foot cable you may lose down to 3.5 kHz with 45pf, isnt the whole active vs passive for cable length a bit of a red herring? Especially given that a lot of speaker cabs without tweeters only go up to 2-4khz??? :bag:

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