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question of impedence

Discussion in 'Pickups & Electronics [BG]' started by On The DL, Sep 6, 2008.


  1. On The DL

    On The DL

    Apr 1, 2008
    KC
    ok, this may be a dumb question..

    Is there any difference to the gain or "hotness" of a signal using active bass (onboard pre) compared to using a passive bass with an outboard pre, such as a Bassbone or Sansamp DI?

    This may not be the correct terminology, but both essentially serve the same purpose and gain the signal stronger right?

    I'd like to know what the differences, if any

    much thanks
    DL
     
  2. Rick Auricchio

    Rick Auricchio Registered Bass Offender

    The resulting signal at the amplifier will be pretty similar. Different preamps (whether in the bass or outboard) may have more or less gain, and different tone options, but otherwise they're similar.

    The big level difference is between preamp and no-preamp. (Active and passive.)

    That said, if you're using an outboard preamp with a passive bass, you don't want a mile of cable between bass and preamp. If you need a long cable run, put it after the preamp---between the preamp and the amp head.
     
  3. spode master

    spode master

    Jan 21, 2007
    Yah Like rick said.

    Cable LCR will be more of an issue with a passive bass and an external pre, unless you have something unusual with low Z pickups.

    Internal pre amp will pretty much ensure that cable LCR has minimal effect if any as the output impedance of most pre amps is very low.

    (Wonders what the benfit of any external pre is unless its to plug into a mixer or something else with a low input impedance. Most instrument amplifiers have a 1Meg ohm or greater input impedance. Seriously if your amp doesn't have enough gain it wasn't designed properly. Normally active pre's are used for LOWZ pickups that need more gain.)
     
  4. bongomania

    bongomania Commercial User

    Oct 17, 2005
    PDX, OR
    owner, OVNIFX and OVNILabs
    A preamp does not necessarily add any gain. I have even used one preamp that was below unity (the signal was lower level when switched to 'active' than when switched to 'passive') and no, it was not a low battery ;). All active preamps will lower the output impedance; most active preamps include EQ controls; and most (not all) will increase the output level, but it could be by any amount, a lot or a little. This is true whether the preamp is onboard or external. IOW there is no one answer, you have to take any preamp on a case by case basis when asking about the signal gain.

    Spode, the benefit of an external pre is if your bass and amp don't have the switching or tone shaping functions you want- e.g. maybe your amp is a very clean Markbass, and you use a Sansamp to provide a different tone than the MB could provide on its own. Also some pre's have useful functions like a mute switch, or a DI that's better quality than the one built into some amps, or A/B instrument input switching with adjustable level per channel, etc. Also he was asking about the difference between an active bass and a passive one with an external pre; if you're going to say there is no benefit to an external pre, you are de facto also saying there is no point to an active bass.
     
  5. spode master

    spode master

    Jan 21, 2007
    Of course, If you need a little tone shaping than the pre is basically a glorified EQ circuit, hopefully with a good quality Di to boot.

    When it comes down to it any active effect you put in the chain adds another "pre-amp"

    Certainly understand why active electronics are used on board. I think they're most useful for lowz pickups, and I can see even Hi Z pickups benefiting from onboard pre (or if its unity is it considered a buffer) to drop the output Z and make the instrument less susceptable to long cable runs.

    I guess the point of external pre's is not necasarilly to add more gain or "Hotness" (Thats what Lingerie and makeup is for), though for low Z pickups, extra gain from an active Pre is essential.
     
  6. On The DL

    On The DL

    Apr 1, 2008
    KC
    Thanks for all the input guys, I'm mostly interested in more options for tone shaping than a passive bass can offer, but I was curious about the amout of impedence with active vs passive and appreciate all the info.

    thanks again,
    Steven
     
  7. SGD Lutherie

    SGD Lutherie Banned Commercial User

    Aug 21, 2008
    Bloomfield, NJ
    Owner, SGD Music Products
    Gain and impedance are two different things. A preamp could have a high impedance output like a passive pickup, but that partly defeats the purpose of having an on board preamp. By having a low Z output, your tone will stay the same whether you are plugging into a bass amp or a mixer. This is because the preamp has taken the load off the pickups, which are presented with a high Z input.

    As bongomania pointed out, a preamp can be a unity gain buffer, with no extra gain added. Active tone controls will add gain when you boost, and some preamps add gain in general.

    You don't want too much gain. A very hot output can clip the input on some amps. But a little more gain is good.
     

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