Powering 2 preamps

Discussion in 'Pickups & Electronics [BG]' started by SebbyNC, Feb 25, 2010.


  1. SebbyNC

    SebbyNC

    Mar 17, 2005
    Guadeloupe
    Hey, I already posted a couple times about my project, which consists of having a magnetic preamp and a piezo buffer in my bass.
    The difficulty comes with the mag preamp (a Noll TCM-3PM) which gets its power in a way unlike most other preamps: instead of getting the power from the positive pole poe of the 9V battery and connecting bith negative poles to ground, this preamp has to be connected to both the negative and positive poles of the battery. This is done by using a 9-lug stereo jack which boasts 2 switches (to connect both batery poles to the preamp). In contrast, the piezo buffer (Graph Tech Acousti-Phonic preamp) is a regular device that gets power from the positive pole of the battery only, and has the negative connected to ground. I complicated things by running 2 batteies in series (18V, for more headroom).

    To make both preamps get along, I used the following wiring scheme, which seems to work so far:

    sans%20titre1.png

    You see that when the jack chord is in, switch#2 connects the negative battery pole to the Noll preamp, and switch#1 the positive pole to the Acousti-Phonic preamp ("bat" input pin). Then the auxilary "pwr" output from the piezo preamp sends to the Noll preamp whatever voltage is applied to its input.

    When I showed this diagram to the GraphTech tech guy, he told me that it looks like the piezo preamp is getting power only from one battery.

    Based on my diagram, what do you guys think? Am I correctly applying 18V to the Acouti-Phonic, or only half of that? I have a multimeter, if I need to check that, where should I take the readings from?
     
  2. Those batteries are wired in series for 18V, there is no 9V option.
     
  3. JackANSI

    JackANSI

    Sep 12, 2006
    PA
    Assuming 'bat' and 'aux pwr' are connected to each other on the Acousti-Phonic board and the negative from the battery is connected to ground somewhere in the Noll TCM-3PM, then yes, 18V is going to both devices.

    If, for some reason, the Acousti-Phonic is regulating the 'aux pwr' output to something other than 18V, then I don't know what is coming out of there.

    If you want to check with your meter, check the voltage from the batteries first, then move the positive lead of your meter to any of the other positive power terminals and check that it is the same. (and do it with a cable plugged into the jack).
     
  4. SebbyNC

    SebbyNC

    Mar 17, 2005
    Guadeloupe
    Thanks line6man, that's also what I thought, I guess the tech @ Graph Tech didn't read my diagram correctly.

    Anyways, now I have both the mag pickups and the piezo working together, and it sounds great.

    I know that 18V gives more headroom, but can I expect a longer battery life as well?
     
  5. bongomania

    bongomania Commercial User

    Oct 17, 2005
    PDX, OR
    owner, OVNIFX and OVNILabs
    Agreed--those batteries, hooked up like that, effectively become "an 18 V battery".

    Is the piezo buffer grounded anywhere?

    To test the power reaching the piezo buffer you'd connect one test lead to the red wire that goes to its "bat" pad, and the other test lead to the point where it connects to ground.
     
  6. bongomania

    bongomania Commercial User

    Oct 17, 2005
    PDX, OR
    owner, OVNIFX and OVNILabs
    Actually, you can't assume greater headroom. Voltage can be used in different ways by different circuits, so 18V may mean extra headroom, or it may mean longer batter life, or it may mean higher output, or any combination of those, to any degree (compared to 9V in the same circuit). You'd have to ask the designer of the specific circuit.
     
  7. SebbyNC

    SebbyNC

    Mar 17, 2005
    Guadeloupe
    I know the Noll preamp is supposed to get more headroom from running w/ 18V. I don't know for the piezo buffer though.

    Yes the piezo buffer is grounded the jack sleeve terminal.

    Thanks Bongo!
     
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