DI confusion with active/passive bass

Discussion in 'Recording Gear and Equipment [BG]' started by Cue Zephyr, Sep 25, 2017.

  1. Howdy folks,

    I'm confused. I have a Radial ProD2, which is essentially two ProDIs stuck together. It's a passive DI and the economically-priced and built alternative to the JDI.

    I also have a Radial PZ-DI. It's essentially a J48 with some extra options. It's an active DI and the more economically built and priced alternative to the PZ-Pre.

    My PZ-DI doesn't really care what signal it gets. I can plug passive piezo pickups into it, all the way to my super-hot active bass setting.

    Here's where it gets interesting. My ProD2 likes the active signal. I get a strong and rich tone from it. However, when I switch the bass to passive, it saturates the transformer. Super cool, but why?

    I understand it has something to do with low (active) and high (passive) impedance but I'm puzzled by how the lower output passive setting saturates the transformer.

    I know there's some voltage/current relationship that gets altered when you change from active to passive but I'm not really sure what actually happens.

    Does anybody care to explain?

  2. silky smoove

    silky smoove Supporting Member

    May 19, 2004
    Seattle, WA
    What are you experiencing that equates to "saturating the transformer?" What specifically about that is correlated to passive basses?

    If you're using a passive bass into a low Z input you might see some reduced high frequency content because of the less than ideal impedance, but that's commonly about it. Is there a high Z switch you can use to have a better impedance match?
  3. Geri O

    Geri O Endorsing Artist, Mike Lull Guitars and Basses Gold Supporting Member

    Sep 6, 2013
    Florence, MS
    I'm not sure that "saturating the transformer" is the term that's applicable here.

    A passive signal is typically lower in gain than an active signal. And a saturated transformer means an overloaded transformer. You might be experiencing an impedance mismatch with the passive instrument.

    As with the previous post, I'm curious what you are hearing that leads you to the saturation conclusion.
  4. ofajen


    Apr 12, 2007
    92.4W 38.9N
    It seems totally implausible that a properly functioning passive bass mode would provide enough signal to overload that DI, and then of course, it has a switchable 15dB pad to keep from overloading the unit on the most powerful input signals (which a passive bass most definitely is not).

    OTOH, the ProD2 does specify a 140 KOhm input impedance at 1 KHz, which is not actually super high. Perhaps it’s simply a loading issue on the passive setting?

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