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The Art of Balancing Gain Structures

Discussion in 'Amps and Cabs [BG]' started by PhilaCPJ, Jan 11, 2006.


  1. Until I bought a Spector Euro 5 with its obscenely hot TonePump (can't wait until my EMG pre-amp comes in), I'd never really paid attention to setting up the gain structure between the bass and the amp. Trying to tame the unruly TonePump has proven to be a formidable battle, especially with a pre-amp and a separate amp.

    I'm curious as to how the rest of you go about setting up your gain controls, as well as how much your crank up the volumes pots with onboard active electronics. With my SVP-Pro, Ampeg recommends turning up the gain until the point where the clip light flickers periodically with your most aggressive attack. Depending on how high I have my pup volumes, this point varies significantly -- anywhere between 8 o clock and 4 o clock. The pre-amp master out and my power amp master are both somewhere in the middle -- I generally use both to adjust my overall volume. Is there an optimal way to set the gain? Leave the amp wide open and just use the pre master, for instance?

    Interestingly enough, I've been talking to PJ at Spector and he told me the gain difference between the TonePump and the EMG is +20db vs. +/-12db. 20db on a bass pre-amp just seems absurdly high. It overdrives EVERYTHING, even with all the controls set flat. I've had some success in not hating my tone by using an Aphex Punch Factory to buffer the output from my bass and squashing it so I have more headroom for gain on the pre. But it still isn't far from clarity to a kind of slightly-distorted tone which sounds like it's covered in a blanket or something. Drives me nuts. And that styrofoamy mid range. Ugh. Still trying to kill it.

    So, please, post any tips you have on getting the right gain settings!

    .cpj
     
  2. As suggested by the manual, I would set the preamp gain to occasionally clip with the most aggressive attack. That means you'd probably have it at 8:00, as that's your loudest attack. The rest will be in your hands, and your processing before getting to the amp.

    That seems like an awfully large range you have for input volume differences... if you're boosting a lot of bass frequencies from the onboard preamp, that might be the problem and something to consider avoiding.

    There are several threads you could search for that discuss the various opinions on the way to set your preamp output gains and poweramp masters.
     
  3. Maverick Blues

    Maverick Blues Being a Thumper is all about ATTITUDE!

    Apr 28, 2005
    Richmond, VA
    A homebrew preamp and no active basses here (yet) so this may not help you much, but:

    I crank volume and tone full up on my bass, then adjust the preamp input gain so that if I lay into the strings just as hard as I reasonably can (as in, "harder than I'll be playing"), I just barely light the clip light. That's a "set and forget" for any given bass.

    That approach insures I'll never clip the input stages plus gives me enough room to apply a pretty good boost with the parametric and still not hit the rails.

    These days I tend to run the bass about halfway open normally, so if the band takes a spontaneous leap in volume I can crank up without having to reach for my rig.

    I have a level trim on the preamp's back panel that I use to match the preamp to the power amp. Settings of it and the input pads on the power amp depend on the amp; I basically adjust them so all LEDs lit on the preamp VU gives me full rated power on the amp with minimal hiss. I treat those as "set and forget" too (haven't touched them since I racked the amp).

    I then control total rig volume with the output level control of the preamp.

    Hope that's of some help.

    'rick
     
  4. pogipoints

    pogipoints Custom User Title Holder

    Dec 5, 2005
    Atlanta
    I have the same problem with my Euro 4 and SVP Pro. I usually have to use the input pad (-15dB, iirc) to get it to not clip the preamp stage, since I generally run the volumes on the bass at full, with just a smidge of treble & bass.

    Then when I switch to a bass with a more reasonable output, I unpress the pad button.

    But, like you (and the manual), I also basically set the preamp gain to clip at peaks occasionally.

    If only TonePump had an output level trim or something...
     
  5. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    The general idea in optimizing gain is to have a reasonably hot signal from as early in the signal chain as possible. This allows the use of low to moderate gain in later stages to avoid a big buildup in the noise floor.

    However, there's a caveat: each stage along the way still has to put out a signal that the following stage's input can handle. Obviously, driving the next stage into heavy clipping is not generally a desired technique. This is the issue presented here, I think.

    If you have an active bass with a fairly hot on-board preamp output, that's great, except if the input of the following preamp or head stage is made for only instrument-level signals. Then, if the pre or head doesn't have a less sensitive input for active basses, you must either turn down the gain on the bass or use some sort of resistive pad to attenuate the signal before it enters the next stage (or mod the input with a pad).
     
  6. Here's what I've got going on:

    I'm running a passive bass with extraordinarily hot Barto P/J pups. I've always plugged into the padded input of any amp I've used, which is fine. However, since I'm now using the BBE Bmax, I don't have a clip light to rely on to set the gain. Should I turn the master volume down low on the Bmax, set the gain of the power amp low as well, and tweak the gain on the pre a notch or two below audible clipping? And from there adjust the pre's master, and then I'll use the gain of the power amp to adjust my stage volume? Just making sure I'm using optimal settings for any EQ tweaking I may need to do.

    When I ran a pre/power setup years ago, I didn't know much about gain structure, and I set the pre's gain to just below clipping (light available), dimed the master on the pre, and adjusted the power amp to taste. I was pretty close, I guess, but this time I don't think I'll pin the master on the pre, JIC.
     
  7. cb56

    cb56

    Jul 2, 2000
    Central Illinois
    I know you posted this a couple months ago but if you haven't bought that EMG preamp I'll trade you one for that Tonepump. I have the Tonepump in my Spector and love it!