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pre-amp plus DI?

Discussion in 'Amps and Cabs [BG]' started by millard, Jan 30, 2006.


  1. millard

    millard

    Jul 27, 2004
    SoCal
    Since a DI box is intended as final step in your signal chain before hitting the PA/recording board, is it "right" to run it into a pre-amp? Isn't it already the pre-amp? Don't you sort of double or over-do some of the processing if you run through the DI and then into a pre-amp before going to your power amp?

    A little more concrete example. I have a Tech 21 Programmable SansAmp that I really like. Is it "normal" to run that into a nice pre-amp which has its own plans for your sound? If I dial something nice into the pre-amp settings, won't the SansAmp settings just mess with that, since it is trying to re-create a certain amp sound thinking it is headed for the board?

    I've been thinking of trying out a nice pre-amp (Aguilar DB680), but I don't want to lose some of my other tones and I don't want to lose a chance to switch between my tone at a touch of a switch. We do songs from rocky ballads to bluesy rock to almost metal and I like being able to match my bass tones to the song when we play live. I realize there are a coulple of footswitchable options on the Aggie but it seems to be geared towards a dirty/clean channel sort of choice.

    Is it silly to throw $100 effects pedals in front of a $2,000 preamp?

    Millard
     
  2. WalterBush

    WalterBush

    Feb 27, 2005
    Yuma, Az
    It's not silly to put a $100 box into a $2000 mic pre, anymore than it's silly to plug a $5000 custom bass into a $900,000 SSL board. A DI isn't a preamp, although some have a preamp built in, and if it's the sound you want, plug whatever, wherever (no comments from the peanut gallery, thank you :) )
    A mixing board's channel strip is littered with preamp circuitry, buffers, sends, etc, and any preamp you run through before going direct is just the first in a long, long chain. I frequently use a preamp I built for less than $20 to go into a GT ViPre, costing over 100x that much, because I like how the input of the ViPre crunches slightly when it's hit hard.

    It's not really any different running into your power amp--if you like the sound of the SansAmp DI into an Aggie into your Power amp, go for it.
     
  3. Kael

    Kael Supporting Member

    Dec 26, 2004
    Oklahoma City
    Your Sansamp isn't really just a DI. It is a DI sized preamp, so what you are proposing is using two preamps. If it works for you, great, but that sounds like too much of a hassle to me. Most nicer preamps will have good DI outs on them making an external DI moot.

    note: If your preamp's DI out is not phantom power friendly (your SABDDI is, don't know about the aggie) use a DI box anyway after the DI out to prevent some moron sound tech from frying your preamp.
     
  4. PB+J

    PB+J

    Mar 9, 2000
    arlington va
    I use the avalon U5, which is basically a really really good DI with some tone shaping features. It sounds great, and I find I don't need a preamp with it. It can work as a Di and drive a power amp at the same time, which is often how I use it.
     
  5. I find it perfectly logical to use, say, a SABDDI, as a DI, then run on to your preamp. I like to use the preamp in my rig for getting the sound I need for the stage (or room if I'm recording). That leaves the SABDDI for sculpting your tone for the PA. You might for instance have 3 different distinct tones that you want to send to the PA, AND you want to send those tones to your rig, BUT, the stage is loud that night and you need to cut lows and boost mids so the band can hear you. You would need those two pieces of gear to make that happen.
     
  6. bongomania

    bongomania Gold Supporting Member Commercial User

    Oct 17, 2005
    PDX, OR
    owner, OVNIFX and OVNILabs
    DI level = mic level, which is hotter than the normal passive instrument level expected at the input of the average preamp. So it would be an issue if the preamp you're using can't take the hotter signal, if for instance it has no "active" input jack/setting. Some preamps would be more prone to distortion that way, either good or bad. As far as gain stages and eq, every stage you add increases your noise floor and potential for gound loops or electrical gremlins. However if you're only using top-shelf gear, those problems are minimized and maybe unnoticeable in a live setting.
     
  7. like bongomania said, if you use the sansamp in front of the amp preamp, you should use the active input or use a pad on the amp preamp, otherwise you will be driving it harder and it will clip easier.

    If however you like the clipping or you want to push your amp harder, then thats just perfect...
     
  8. Kurisu

    Kurisu

    Nov 19, 2003
    Saskatoon SK
    I'm not really sure this is accurate. Correct me if I'm wrong, but the above should read:

    A DI will change your intrument's impedance (very high, sometimes 10KOhm) to the impedance of a microphone (around 600 ohm, I think). This has nothing do with "hot" signals, as there are passive DI's that do not add any current to the signal (Jensen transformers, for ex).

    Now, if you have an active DI that is also a preamp (the SansAmp) you will probably have a DI out and a preamp out. The DI out should send the same level signal with the corrected impedance, which can then be plugged direct into a mixing board or any other preamp that expects a 600 Ohm impedance signal (a standard microphone preamp). The preamp out will send a signal or Line Level output which can be plugged into a poweramp or into a line level input on a mixing board, computer soundcard, or ADC input (such as a Benchmark ADC). The line level input on a mixing board does not amplify the signal again, as this would degrade the sound quality and is not neccessary.

    Also, a DI will usually convert an instrument (or microphone, if it's designed for that) signal from unbalanced to balanced. I forget how it works, but balanced will cause any radio frequency interference to affect both conductors in the cable with the same polarity, and then the receiving unit (such as the mixing board) can remove the noise that entered the signal while travelling the cable. So, if you use a very long cable from your amp to the mixing board you would want to balance that signal by putting a DI somewhere close to your source. If you don't you will pick up hum. This isn't necessary for short cable runs in the studio, and you probably wouldn't as the act of balancing usually degrades sound quality (at least as far at the picky ears of your recording engineer are concerned).

    I don't think you need to worry about putting a DI before your preamp on stage. For one, your bass preamp/head is designed to accept high impedance signals, and two, I don't know of any preamps that accept balanced inputs, so you're wasting that "feature" of a DI and adding unnecessary noise to your signal. But changing the impedence from 10K to 600 Ohms before your preamp is fine because low to high is okay. High to low is not okay, and that's the whole point of using a DI between your bass (outputs 10K Ohm) and a mixing board with a microphone preamp (expects 600 Ohm). If you do this you will notice that your high end is rolled off and it'll sound like you're playing through a heavy blanket.

    That is how I think of the problem, but anyone please correct me if I got something wrong. That would be good, because I'm setting up my studio and equipment under the above assumptions, and it would suck if I was totally off base. :)
     
  9. Kurisu

    Kurisu

    Nov 19, 2003
    Saskatoon SK
    "I don't think you need to worry about putting a DI before your preamp on stage." This isn't completely true, of course. You can add a DI between your bass and your preamp if you like the "sound" of your DI... But that's strange, because usually DI's are supposed to be as transparent as possible, and anything added is usually not something musicially pleasing.

    Unless it's a preamp/DI, like the Sansamp. In that case you may want to use the preamp out and feed it into your preamp/head because you like the Sansamp sound. You will then be amplifying the signal twice, but that's okay as long as you watch the clip light on your second preamp/head.

    You may also want to use a DI right off your bass on stage, because then you would send the DI balanced signal straight to the front of the house mixing board, and the split "unaltered" instrument level signal to your preamp/head on stage.

    Confusing, I know. Still trying to wrap my head around it.
     
  10. bongomania

    bongomania Gold Supporting Member Commercial User

    Oct 17, 2005
    PDX, OR
    owner, OVNIFX and OVNILabs
    Actually I think you're right. I have experienced distortion in this context, and I remember portable mixers and 4-tracks where the input gain knobs were labeled with mic, guitar, and line level. Which fixed the idea in my mind that the mic and instrument signals were normally at different gain levels, but now that I think about it, the impedance difference makes more sense.
     
  11. Kurisu, I've been waiting for that explanation between line balanced line level and mic signal for ages now! Finally someone who has been able to explain it!

    would it then not be a good idea to put the balanced line from my EBS microbass preamp/DI into the Mic input on a pro tools card?
     
  12. Kurisu

    Kurisu

    Nov 19, 2003
    Saskatoon SK
    Thanks, I'm glad I can give back to the TB community. :)

    Check your microbass manual, it will tell you if the DI out is line level or just balanced. I would think that it is not amplified (so, instrument level, just balanced). Then check your pro-tools manual. The mic in is the correct impedance for the DI out, but you'll also need a preamp on that input. It should have a preamp built-in. (Most "mic in" inputs do, or else it would be labeled "line in," I would think.)

    So, it should work. Try it out, and if you can't hear anything it is expecting a line level signal. But it should work.

    Look at me, acting like a pro or something. :p
     
  13. thanx kurisu.

    will check it out in the manual
     
  14. quallabone

    quallabone

    Aug 2, 2003
    I often run a bass into an Avalon U5, into my aggy 659 and then into a poweramp. If it sounds good do it.
     
  15. dunamis

    dunamis

    Aug 2, 2004
    Charlotte
    ... or the abbreviation police will come down on you!:D
     
  16. quallabone

    quallabone

    Aug 2, 2003
    I've single-handedly put their children through college. I'll call them whatever I want.

    :)