Plug bass directly into power amp?

Discussion in 'Amps and Cabs [BG]' started by Speedbird, Jul 16, 2000.

  1. Speedbird

    Speedbird Supporting Member

    Jul 10, 2000
    Northern Virginia
    Since I received my new bass last month I've been playing with the EQ flat, so today I just pluged straight into the "power amp input" on my Peavy Combo 115 (bypassing the whole pre-amp). IT SOUNDED AND WORKED GREAT! I was able to adjust with the on-board eq and volume knobs. It sounded much better than normal. But, even my 18v Bartolini pre-amp could only push the amp to about 1/2 volume.

    So heres the questions:
    Is this safe?
    Is the crappy Peavy "DDT" limiter bypassed?
    Anyone else try/use this?

    Most importantly:
    I was planning on an amp upgrade, like a pre-amp/BIG Crest power amp/ Acme Low B-4 cabinet setup. Unlike my peavy the Crest has adjustable power-amp sensitivity and a built in limiter, so I should be able to reach full volume & have some protection, right? I can get 3 or 4 distinct sounds out of my bass alone and would be happy with that. Also I could save a $500-$600 while keeping things simple. Any feedback would be appreciated.

  2. 1. Yes this is safe, the power-amp is used to getting a signal already amplified by the pre-amp, so a bass shouldn't come anywhere near overdrive, ( I think ).

    2. No you won't bypass the DDT, is the last thing on the signal chain before the power-amp, after the power-amp in jack.

    3. Yes I tried it, but since I have a passive bass, I couldn't get the gain.

    Go ahead and try it on the Crest, it would probably work. The only thing is, if you are using the onboard electronics as a defacto pre-amp, then you might go through batteries kinda quick.
  3. Rockinjc


    Dec 17, 1999
    I don't know what you 'should' do but here's my experience.

    When I originally got my Acme cabinets, I used a blue tube rack mountable preamp with two sections of preamplification. This was designed for guitar, but since I already owned it, I thought it was worth a try. Unfortunately, it was introduced a lot of noise into the system, however I was able to circumvent this problem with a Rane dual compressor (DC-24) with crossover by the use of heavy gating on the highs.

    Mostly out of curiosity and for the sake of opening up some real estate in my 4-space rack, I removed the Blue Tube preamp replacing it with a Korg SDD-2000 Delay. Now my signal chain goes like this; Bass, Foot pedals, Compressor, Delay, Power Amp. This compressor processes highs and lows separately allowing my some control of the tone as well. When I let someone else use my amp, I have to tell them that this knob (markup gain) on the compressor is for bass and that one is for treble.

    Other than that it was no big deal. If your power amp has a limiter, use it. Other wise purchase one, as this will inhibit DC voltages from reaching your speaker. As I recall from the Acme lit, Andy does not like DC current to reach the drivers.

    Good luck.

    [This message has been edited by Rockinjc (edited July 17, 2000).]
  4. Speedbird

    Speedbird Supporting Member

    Jul 10, 2000
    Northern Virginia
    ...Anyone else?

    [This message has been edited by Speedbird (edited July 27, 2000).]
  5. Yes, I have tried. with active basses it can work, but you miss out the EQ opportunities of the pre-amp. I have run a Boss GEB7 bass equaliser directly into a power amp, and it works as well. Just a slightly raw sound. The only time it is a real godsend is with those little Marshall bass amps, that seem to fry preamps as soon as you look at them. Then, being able to bypass the preamp is worthwhile.

  6. beans-on-toast

    beans-on-toast Supporting Member

    Aug 7, 2008
    No problem plugging into a power amp. BUT -- plug in first, then power up the amp. You don't want a spike, which can happen when you plug in, going through to the speakers. Some amps are designed to limit signal spikes, best not to push your luck.

    Power amps require a certain signal level to drive them to full power. If your bass doesn't put out enough voltage, you can try a clean boost pedal between the instrument and the power amp in.
    Killed_by_Death likes this.
  7. Rick James

    Rick James

    Feb 24, 2007
    Pro power amps do have input attenuators, but they still need a pretty high voltage input to drive them to full output, usually a lot more than an active bass can deliver. You also need a high pass filter to keep out thumps, something that bass amps have built into their voicing.
  8. Speedbird

    Speedbird Supporting Member

    Jul 10, 2000
    Northern Virginia
    Thanks for the feedback. It's been a while since I was gunning for a big modular power amp set up. But I still have the same bass (Modulus) and the same Amp (Peavey 115). Still don't like the Peavey front-end, recently been using a Blue Tube pedal as pre-amp, straight into the power amp-in on the Peavey. I have to ask, my original post was 16 years ago, how does that come back to life?
  9. tzohn


    Apr 26, 2015
    That's even before 9/11, how many things have changed since... But the need for bass...
  10. BassmanPaul

    BassmanPaul Gold Supporting Member

    Aug 25, 2007
    Toronto Ontario Canada
    David, you a bit bored this morning? You respond to a 16 year old post, on a Sunday morning when most folks are still sleeping! Go back to bed man, you’re not as young as you once were!! LOL :D
    S-Bigbottom and wcriley like this.
  11. 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
    Most these days have gain controls and not input attenuators.
  12. DDT limiting did the trick back then and they still use it. Far from crappy. I guess they were way less uptight back in 2000.
  13. paulraphael


    Apr 13, 2006
    If you heard me play, you'd stop reading what I write.
    Someone in another thread mentioned plugging a bass straight into the effects return on a Tone Hammer 500. This sounded like an unlikely proposition, but I was bored and tried it. Damn if it didn't work. I had to turn the master down to keep it from rattling the apartment.

    The bass was a G&L, which has a pretty hot output, but still. It's not hot enough to require the input pad on the preamp.

    I wonder if there are potential tone issues from there being an impedance mismatch. I'm assuming power amp inputs are much lower impedance than instrument inputs. But I don't know if this makes a real world difference with an active bass or a hot passive one. In my 2-second experiment, there was no obvious problem, but take that with a grain of salt.

    edited to add: I tried this again. The gain plugged into the effects return seems equal to being plugged into the instrument input with the gain all the way counterclockwise—a setting a lot of people use for a clean tone. According to the specs this is -30db.
    Last edited: Aug 24, 2016