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48v Phantom powered onboard preamps...

Discussion in 'Pickups & Electronics [BG]' started by ninnlangel, Jan 28, 2006.


  1. Hi,

    I was wondering, since some bass amps are starting to ship with XLR input connectors providing 48v, if it would be a great thing to standardize around, and have better on board electronics and XLR connections. I mainly use acoustic image amps, so this would be great for me. No more battery changing, and more headroom in the internal preamps.

    What are your thoughts on this ? Wouldn't it be great ?

    Ninn
     
  2. tadawson

    tadawson

    Aug 24, 2005
    Lewisville, TX
    I suggested this a while back, and think it would be an outstanding idea. For that matter, run a balanced signal, just like on MIC inputs, and then there is never an issue of having spare cables either. If the amp folds, so what if you can't power the bass, you can't hear it either, or just go direct to the PA and get power from there - and no DI needed either! Frankly, I really can't see a downside to this one, other than making the transition, and for that, a pedal-like device like Line-6 uses for the Variax to make it possible to power the instrument and then go into an unpowered amp would ease that stress as well.

    - Tim
     
  3. One downside I can see is that running off of XLR cables alone makes the use of the vast majority (possibly all, i'm not sure about the PODxt Live) of effects pedals useless unless they too were converted. I'm not crapping on dreams here, this is a technology that I'd love to see as well. The suggestion that came up earlier was to use a stereo 1/4" cable rather than XLR, and then run the bass off of either phantom power or from internal (rechargeable, maybe?) bateries for when you want pedals or don't have a phantom source or something like that.

    The only other thing I'd worry about is that you'd need to find pickups that could handle 48v. I can't think of any that do, EMG's are only good to 27v (and they really don't like anything even a little above 27v from what I've heard). The preamp would be no proble, just have one built that would run at 48v, but the pickups would be the issue. The solution that I and a couple other guys were/are kicking around is to use an external power supply box that would power the electronics at 24v (to keep the EMG's that I want nice and safe). With that, you could go so many ways it'd make your head spin.
     
  4. tadawson

    tadawson

    Aug 24, 2005
    Lewisville, TX
    Actually, from a voltage standpoint, just because you have 48v Phantom on the cable does not mean that the pickups/pre have to run that voltage. Just like condenser mics, the voltage is simply regulated down in the bass. A lot of consoles don't even do a full 48 on phantom - I have seen as low as 18. 48, is, IIRC, the maximum allowed, and pretty much any properly designed phantom powered device will run from about 18 (sometimes less) up.

    And as I mentioned, in the transition, a pedal type box to power the bass on one side, and give legacy 1/4" out on the other to use with existing stuff would be needed, and pretty trivial to build, and would solve that problem, and I did mention that in my previous post on this thread . . .

    Oh, and you couldn't do this on 2 wire 1/4", at least not as true "phantom" power, since phantom relies on the balanced connection for power transmission - it won't work unbalanced, at least not without a completely different setup, which would involve more proprietary stuff, and would pretty much negate the big plus of the XLR/phantom solution - one less type of cable to carry, and compatibility with existing pro audio gear.

    - Tim
     
  5. I might have missed a "stereo" designation on the 1/4" part there somewhere. You could run phantom down a stereo 1/4" cable (unless I'm missing something and there aren't 3 wires in stereo and XLR cables) to a stereo plug. Every now and then I forget that the rest of the world can't read my mind, and usually my family reminds me of that, but they weren't around at the moment, so...

    And I should apologize for not reading your last post closely enough.

    I'm slowly working my way through the design stage of this very thing for a unique system of my own, but its slow going and I still have to decide between having an ungodly amount of knobs on the body itself, or if I want to have a single mute switch, and then have everything else on the rack unit. Anything in between is out.

    I'm convinced that if we ask enough of these types of questions and get enough people to answer with good ideas, at some point some employee of EMG or Bartolini or some such will casually stumble upon them and *presto* instrument technology revolution. Or one of us could just start the revolution ourselves, ala Jim Bergantino.

    Whatever. Keep the ideas a'rollin!
     
  6. tadawson

    tadawson

    Aug 24, 2005
    Lewisville, TX
    Yes, you could run phantom down a TRS 1/4", but the problem is that 1/4" is NOT a standard for balanced audio with phantom - XLR is. If you were to errantly plug a "typical" instrument into the TRS phantom powered head, then you would get the full phantom voltage across either the passive ciccuitry or the active pre - neither of which would be good. In the pro audio circles, there are very few devices that run balanced XLR that won't take phantom - it's pretty much a standard. Also, on the 1/4" TRS, if some gui**** looks at it and goes "Kewl - normal 1/4!" and puts his normal guitar cord into the head, you have just shorted one side of the power supply to ground . . . . again not good. Lastly, 1/4" connectors are not that great - myself, I would love to have a locking connector such as an XLR (or mini XLR, if size is an issue) on my basses . . . . (actually, I have an Ibanez with locking 1/4" and it is nice, but XLR would be sooooo much better). And lastly, as I stated above, if you stick with XLR and the phantom standard, then you can go direct to the PA desk without the need for a direct box . . . . kinda nice if your amp takes a total dive in the middle of a show . . . . Your "proprietary" 1/4" solution would not allow that . . . .

    - Tim
     
  7. tadawson

    tadawson

    Aug 24, 2005
    Lewisville, TX
    Oh, one last thought. At least in my mind, what I am thinking would take minimal modification to the instrument. Simply add a center tapped line transformer to the output, which would isolate the phantom for the pre output, and you can take the power off the center tap. Output level can pretty much stay the same, since going to a PA desk, they can treat it like a MIC and have plenty of gain, so all you would need to do is take the phantom power derived from the transformer CT to ground, regulate it, maybe add a small cap for some final filtering, and feed it to the pre. Done. For a passive instrument, you still use the transformer, but don't use the CT (no power) and the transformer isolates the power from the pickups, and makes the output balanced as above. Simple, cheap as sin (the miniature line transformers suitable for this are big time cheap - and we don't really need to worry about high freq. response, like in a channel strip, so can probably go a bit lower in cost there too. I would guess that you could probably do one-off mods to a bass for under $10. On the amp, the same thing applies - once again, use a line coupling transformer, and feed phantom . . . the only other thing needed there is a current limiting resistor in case the phantom gets shorted to ground. Yeah, there are active solutions that can be used to avoid the line transformers, but the transformers are simple, reliable, and frankly, tend to be regarded as some of the best sounding (look at high end sound desks - the better ones tend to use transformers.) Oh, and the transformers I am thinking of are typically the size of a nickel to a quarter - should fit right into most bass routings with no mods . . . .

    - Tim
     
  8. I'm liking where all this is heading. True, yeah, we have to think about keeping the guitarists safe, they need all the help they can get on that side of things. ;)

    A locking connector wouuld be nice, and XLR is good because it is shallow, so that when someone stands on your cable and then you accidentally turn, you wouldn't put as much strain on the jack as you would if it was a nice long 1/4". I'd rather pull the guts out of a jack on accident than bend a plug and crack the wood or strip some screws or something. Smart thinking.

    Like I said earlier on it would be nice, though, to be able to use 1/4 inch mono (and run off of internal batteries) for when the unexpected happens. That'd be my big seling point for 1/4", but that's just me, I'm paranoid.
     
  9. tadawson

    tadawson

    Aug 24, 2005
    Lewisville, TX
    Well, for your "safety" case, you could always setup the bass to also accept an internal battery, and then just use your basic XLR to 1/4" balanced ==> unbalanced adapter into any old guitar head. Granted, and extra item to carry, but simple, and once again, and item that a lot of PA guys carry in the ditty bag all the time, so not hard to find . . . . Simple diode isolation could be used to protect the battery from phantom, if you forget to take it out and plug in, although some means of turning the battery off when not playing would be needed, since I am not aware of any XLR that has aux contacts . . . .

    - Tim
     
  10. Wouldn't the XLR - Jack combo connectors allow the jack input to connect to a battery and the XLR to connect the phantom ?
     
  11. tadawson

    tadawson

    Aug 24, 2005
    Lewisville, TX
    Not sure what you mean here. The combo jacks will take an XLR or a 1/4" - one at a time. If you mean to try to use the sleeve to ring short (as some current basses do) to switch power when running 1/4", that very well may be an option - frankly, I had forgotten about those connectors. That truly would be the "best of both worlds" in that you could go either way, with nothing more than changing the cable you connect. Now, you wanna get exotic, set it up with a rechargeable battery (lithium, perhaps? Almost zero self discharge . . ) and set it up so it charges when on phantom . . . . . I know, not good for the guy using just 1/4", but I would not think that the 1/4" would get used too much if someone bought a bass with this system . . . .

    - Tim
     
  12. Yeah that's what I meant, and the battery idea is a very good one. I'll have to talk to my engineer friend who designs high-end amplifiers, see if he's up for a project like that ! I'll start easy, 2-band EQ, killer tone. But he'll say yes and probably never have the time to do it...
     
  13. tadawson

    tadawson

    Aug 24, 2005
    Lewisville, TX
    Actually, I just thought some more about this, and it would only work if the jack had separate contacts for the XLR and 1/4" circuits, which I believe is not the case. If they are the same, the battery connection could not be on the sleeve to ground, because that would see full phantom voltage when run with the XLR and phantom. If they are separate, then fine, but I doubt it . . . . the idea was either XLR or TRS balanced, IIRC, not separate circuits.

    I think I like my original idea of an external XLR->1/4" adapter better all the time. It would not be needed much, and most sound guys carry them . . . . .

    (Quick note and edit: Just checked Neutrik, and, much to my suprise, the combo connectors DO have separate pins, as well as can be had with some aux contacts, so it looks like either idea will work after all!)

    - Tim
     
  14. amper

    amper

    Dec 4, 2002
    US
    Yes, it *would* be great, for instruments that have active electronics.
     
  15. tadawson

    tadawson

    Aug 24, 2005
    Lewisville, TX
    Balanced on passive instruments would give a lower noise level, and be compatible as well. I guess I don't see a downside to this anywhere . . . .

    - Tim