Active/Passive inputs

Discussion in 'Amps and Cabs [BG]' started by jazzy bass man, Jul 30, 2005.

  1. Does the active input on an amp protect the amp from a bass' active pickups or from the active circut, or both.

    In other words is it a bad idea to plug my spector legend (active pre but passive pickups) into the passive input.

    Thanks :cool:

    My amp is a ampeg ba115 if it matters.
  2. bump

    If its already been answered sorry I couldn't find it. Could you please point me in the right direction.

    Also I assume in my situation that it would be a bad idea to run my bass through a my lr baggs para di and through the passive input because that would make the signal even hotter.

    please answer, i've only posted twice and haven't really gotten answers for either, are my questions stupid or something. :( :confused:
  3. seanm

    seanm I'd kill for a Nobel Peace Prize! Supporting Member

    Feb 19, 2004
    Ottawa, Canada
    First off, if you have an active pre, it does not matter if the pickups are passive or active. The active pre "hides" the pickups from the Ampeg.

    Passive basses are high Z (impedance) devices. Active basses are low Z devices that usually have a much hotter (stronger) signal.

    So generally, you plug a passive bass into the passive input and an active bass (like yours) into the active input.

    However, as long as you do not overdrive the preamp, it is safe to plug the active bass into the passive input. I would use the active input though unless you are having problems with the input signal being too weak.
  4. that's what I thought would be the outcome of that question
  5. If you want further confirmation, I agree also.

    I go by the gain knob. If in passive, you have to set the preamp gain really low to keep from overddriving it use active. If its in active and you have to crank the gain knob almost all the way up, use passive.

    You really just want to avoid the really low end of the gain knob so you have some leeway/space to make fine adjustments.

    I never finished my Electrical Engineering degree, but I did stay at a Holiday Express Inn before. Hope that helps.

  6. seanm

    seanm I'd kill for a Nobel Peace Prize! Supporting Member

    Feb 19, 2004
    Ottawa, Canada
    When you think about it, a lot of people use effects that "effectively" (hehe) turn a passive bass into an active bass from the amps point of view, but still plug into the passive input.
  7. IndyBass


    Jun 11, 2005
    Central Indiana
    Reviving an old thread here, but I had a more technical tangent:

    Will an impedance mismatch between the bass and the head cause any noticible colorations of the signal/tone (aside from the level issues)?

    If so, would certain frequencies be more impacted than others?

  8. I've never noticed much of an impact on sound using, for example, the high versus low Z inputs on the series I and II Clarus heads.

    Also, a quick question for all of you techies.... active and passive inputs aren't necessarily the same thing as high Z and low Z (impedence) inputs from my understanding. Aren't a lot of 'active' inputs just a 10db down pad?

    I have always used the passive inputs for my 'active preamp' basses with good result.... if the above is true, it would be a more 'pure' input in that it is not 'padded down'. That's the way it sounds to me anyway... but that might be due to the impedence differences... the passive input on most amps always seems to have a little more 'sheen' to me. However... it's pretty subtle.
  9. seanm

    seanm I'd kill for a Nobel Peace Prize! Supporting Member

    Feb 19, 2004
    Ottawa, Canada
    You are correct, "active" inputs are usually just a pad. If anything, they will have lower input impedances. Since the active outputs have lower output impedances it makes sense to lower the input impedance to reduce noise.

    However, like you mentioned, most are just pads. True high Z inputs are specialized and ment for piezo pickups. You usually don't see true high Z inputs except on amps geared for the DB market.
  10. Thanks! It seemed that some posters where confusing these two issues.
  11. My basses are both active and pretty hot. Using my Demeter201S I have used the passive input with good results. I agree with Ken it does have a more "pure" nature to it. As was mentioned though, you must watch the gain since the passive is not padded. I can only turn the gain on the demeter up to like three or 9:00 when using the passive input. I can go to 6-7 or 1:00/2:00 while in the active input. Either way it works well.
  12. IndyBass


    Jun 11, 2005
    Central Indiana
    To add some data to this discussion, the specs for my SM-900 list the following:

    Passive/Active Input: 800 k-ohms
    Active Input: 60 k-ohms

    The "passive/active" term is SWR's, not mine. Plus, I just found this note in the owner's manual:

    "Using the Active input with passive basses may result in a loss of high end transients. Players who roll off their high end starting at about 2kHz or prefer a "darker" sound, may find this input more to their liking."

    I was just curious if the reverse situation (active bass into the high Z input) would also result in some losses somewhere. This is the way I've been running for years, but something just got me thinking about it recently.
  13. I always found the passive input to sound better on my old 900 with all my basses. So, in this case, it seems that it's more the low/hi Z sort of inputs versus the more typical 'regular/ -10db pad sort of thing. Interesting.
  14. seanm

    seanm I'd kill for a Nobel Peace Prize! Supporting Member

    Feb 19, 2004
    Ottawa, Canada
    No. You want low impedance into high impedance. A general rule of thumb is that you want the input impedance 10x the output impedance.

    So running a high impedance passive into a low impedance will result in losses. Running a low impedance into a high is not a problem except you *might* get more noise.