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Active/Passive input & Visa Versa

Discussion in 'Amps and Cabs [BG]' started by Bassman 100, Nov 2, 2010.

  1. Bassman 100

    Bassman 100

    Apr 4, 2008
    When using an acoustic bass guitar with 9V pre-amp, do you use your active or passive input to the amp?

    I am guessing we should use the active input.

    Question; does it matter, will you do any harm by plugging an active acoustic, or any active bass into the passive input OR visa versa?
  2. First, no harm will be done either way.

    Active inputs (for the most part) are just a padded down input that should only be used if you are hearing distortion in the preamp even when the input gain is set at very low levels. This is totally driven by the output of an instrument and the technique of the player. Some passive instruments can have VERY hot output, and hence need the padding of the active input, and some active instruments (i.e., onboard preamps) are set to mimic a classic passive output level, and have very low output.

    Similarly, some players have 'gorilla technique' and need the padded active input to keep the hot signal from overdriving the preamp, regardless of the inherent level of the bass output.

    In rare occasions, the active and passive input can have different input impedances, but that is rare, and with an active instrument, it doesn't matter.

    In your case, many buffered piezo pickup driven instruments have extremely hot output, and you might need to use the active input.

    Always start with the passive with any bass (since it is the purest signal path without the extra capacitor or whatever to lower the signal). If it sounds good, you are good to go. If you hear that preamp clipping, and turning the gain down doesn't work, switch to active input... or engage the -10db input pad switch, depending on the amp.
  3. Bassman 100

    Bassman 100

    Apr 4, 2008
    Thanks for this excellent information.
  4. Depends on the amp, so try it both ways and use what sounds best. I've found that most of my basses sound best with my amp in the passive mode, the basses with the 18 volt pre-amps are the exception.
  5. Just FYI, the 18 volt thing does not impact output in most cases, but rather headroom (i.e., the ability of the internal preamp to handle extreme volume peaks transmitted through the pickups.

    Also, many preamps have internal volume/output trim pots. So, virtually no correlation any more between active/passive or 9 volt/18 volt and instrument output.

    One of the hottest output basses I've ever played was a passive Reverend bass (that almost blew through the -15db pad on my amp), and one of the lowest output basses I've ever played was a Jerzy Drozd with an 18 volt Aguilar OB-3 preamp.
  6. Bassman 100

    Bassman 100

    Apr 4, 2008
    Geez first time I've heard of 18v. Is there any advantage with 9V Vs 18V ?
    Is it a "Tone Thing" - "Volume thing" or a "compensation thing" Or am I on the wrong track?
  7. There are some preamps that can run 18volt. Unless you have very aggressive technique or extremely hot pickups, I never really noticed much of a difference between preamps running 9 and 18.

    Again, not really a 'volume' thing... it isn't that the increase voltage translates to a hotter output. It is more of a 'headroom' thing..... i.e., a cleaner, less compressed tone coming out of the preamp if there are VERY hot signals going into a preamp.

    It is a bit like amplifier headroom... another 100 watts (or and additional 9volts in this case) won't necessarily sound any different 90% of the time, but when really pushed, will possibly result in less distortion/compression on the peaks.

    I would never bother to modify a 9volt cirtuit to 18, and I would never buy a preamp based on its ability to run at 18volts. However, if you are one that REALLY digs in, and also has hot output pickups, it can result in a slightly more open, cleaner signal going into your amp.

    IMO and IME.
  8. Bassman 100

    Bassman 100

    Apr 4, 2008
    Great to know thanks. I have a Fender Jazz (American Passive) It's volume is SO weak compared to a cheap active "i Fretless Bass" that I have. I thought it was the 9V that was giving me the "power" obviously not ! Sometimes I think of going for a Gibson SG Bass, it seems SO Hot compared to the jazz. I'm not a hard player, I only play jazz finger style - But I like lots of head room, espcially if playing wedding receptions.
  9. That's what the amps gain control is for. Basses and preamps massively vary in output, but once you get your amp's gain control set correctly, these differences in instrument output become pretty much a moot point.

    And, the headroom you are talking about has more to do with the ratio of your amp's power output to the size and SPL of your speaker than anything else.

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