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Power active pre-amp through TRS cable?

Discussion in 'Pickups & Electronics [BG]' started by delonybro, Nov 17, 2010.

  1. delonybro


    Nov 17, 2010
    Abilene, TX
    Would it be feasible to power an active pre-amp through a TRS cable while still sending the bass signal as well instead of using the battery? Possibly via breakout box of sorts on my pedalboard?

    Does this make sense?

  2. FunkMetalBass


    Aug 5, 2005
    Phoenix, Arizona 85029
    Endorsing Artist: J.C. Basses
  3. delonybro


    Nov 17, 2010
    Abilene, TX
    Thanks! I'll try searching with the addition of phantom power. I hadn't used those terms and came up empty in a search. Thanks!
  4. Phantom power would be running both the signal and the DC power together, not on separate conductors.
  5. it is possible, you have to take noise into consideration though, using batterys is alot lower noise than power supplys
  6. Not necessarily.
    9VDC at a few milliAmps would be easy enough to filter the **** out of to eliminate any ripple.
  7. delonybro


    Nov 17, 2010
    Abilene, TX
    Well I'd appreciate it if anyone has any god ideas, I'm not finding anything in the search except, "yea, it's possible!" No one is bothering to explain just how. I am fairly well-versed with a soldering iron and have built a few effects pedals, I'm just not familiar with how I'd go about re-wireing or building a phantom box. Thanks for the input so far, though.
  8. Rick Auricchio

    Rick Auricchio Registered Bass Offender

    I see a few drawbacks to doing this.

    1. You always need your breakout box---in working order---to play the instrument. A malfunction or loss of the box could leave you stuck.

    2. There is the potential for hum pickup along the DC line. Maybe not, but why take the chance?

    3. You will always need a three-conductor cord (or two plus shield). A broken or cut cord will leave you stuck.

    4. You probably will need another power outlet for the breakout box/power supply.

    5. You have to modify the bass. It can only be used with your breakout box unless it is restored to the original wiring configuration.

    Most bass preamps use only a tiny bit of current, so is this really a problem that needs to be solved?
  9. darkstorm


    Oct 13, 2009
    Its doable but not worth the hassle. A 9 volt battery will last for months in the bass. Rick Auricchio says it well imo.
  10. tubby.twins

    tubby.twins Amateur Pickup Reviewer Gold Supporting Member

    Apr 15, 2009
    If you decide to use the breakout box and modify the bass, then you'll need to send a voltage to the bass via one of the conductors of your TRS cable. This means you'll need to be careful not to bump it against any conductive object when unplugged, which might cause a momentary short circuit to ground (or to your amp's input). The power supply in your breakout box would need to be able to protect against this.

    Alternately, you could build this into a "stompbox" with a foot switch that allows you to mute the signal AND disconnect the voltage at the same time.

    Another idea: if you have to modify the bass anyway, build a small relay into it which acts as an active/passive switch. When voltage is supplied from the breakout box, the relay switches from passive mode (bypass onboard pre-amp) to active mode. This allows the same bass to be used with your breakout box (assuming that the voltage comes in on the "ring" of the cable's plug) or an ordinary amplifier.

    If you are going to buy the parts to build a breakout box, it's easier to buy extra parts up front and build two or three of them. That way you can build several and carry a spare.
  11. ZolkoW


    May 8, 2006
    Hungary, EU
    I like the phantom power idea (although if it isn't the right name for it).

    1, 3 : you can play it passive, if your bas has a bypass switch, with any regular cord

    2: yes, there may be some hum problems, if the onboard preamp is not designed to work on wall supplies, the filtering must be better. no problem, if they considered to be used this way.

    5: you only need a stereo output jack, which is probably included, if it's already an active bass. and a diode across the battery terminal. (I think, that's all, but maybe I forgot something)

  12. :confused:

    First off, there would be no battery if you are phantom powering. This is the point of phantom power.

    Second, if you had a battery, you run into issues of how to switch it on and off through the jack, because the positive DC voltage is coming in on the ring terminal, which is normally where the negative terminal of the battery would connect.

    Third, putting a diode across a battery or power supply equals a direct short, depending on which direction the diode is facing.
    Where were you getting the idea to put a diode in the bass?
  13. FunkMetalBass


    Aug 5, 2005
    Phoenix, Arizona 85029
    Endorsing Artist: J.C. Basses
    I put a diode in every circuit that I can. It's the hip thing to do these days.
  14. I had a chat with SGD Lutherie last night regarding people that are gullible enough to buy anything because they think it will improve their tone, and I said I could probably get at least one person to fall for this, so here goes:

    The key to great bass tone is to rig up your bass with some zero-Ohm resistors, not diodes. They are magical jumper wires that improve your output and tone by 56%. The problem with traditional connections between pots with wire is that wire can sometimes be very resistive. Something like 10 milliOhms would not be uncommon. Zero-Ohm resistors are specifically designed to present exactly zero Ohms resistance to the flow of current. Your highs will be very clear and present, and your lows will also sound fuller. These components were handmade by children in China. I'm going to offer them to the fine gentleman of TalkBass for the low price of $27 each. I accept PayPal, and am offering free shipping worldwide. PM me if you would like to buy some.
  15. FunkMetalBass


    Aug 5, 2005
    Phoenix, Arizona 85029
    Endorsing Artist: J.C. Basses
    So there's literally a 0.000% tolerance?

    I may be interested.
  16. No, it's even tighter than that! These are spec'd for a 0.0000000000% tolerance (+/- 0.00000000000%)
  17. FunkMetalBass


    Aug 5, 2005
    Phoenix, Arizona 85029
    Endorsing Artist: J.C. Basses

    Do you provide bulk pricing discounts?
  18. Sure, I stole these from the children in the sweatshop anyways.:bag:
  19. FunkMetalBass


    Aug 5, 2005
    Phoenix, Arizona 85029
    Endorsing Artist: J.C. Basses
    How's that 32-band quantum onboard preamp coming along?
  20. rumblinbass


    Aug 22, 2003
    Wimberley, TX
    I've been wanting to do this for years and have thought of a way that can work...

    I found some inspiration when I stumbled across ZamPower and how they do it. They do it without mod'ing your bass, by using with a dummy battery. It just shorts the battery terminals but fits in the battery compartment. So if you ever want to go back to using a battery you can.

    AFAIK the ring connects to the (-) battery terminal. The sleeve goes to the (-) power connection of the preamp. So, with the dummy battery the ring has a direct connection to the (+) power connection of the preamp.

    You want to bring in power on the Ring and GND on the Sleeve.

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