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Adding tweeter on/off switch, needs ampere/current rating

Discussion in 'Amps [BG]' started by Antoje, Dec 30, 2012.

  1. Antoje


    Aug 13, 2010
    Sherbrooke, CAN
    Hi all! I have a technical question here.

    I am adding a tweeter on/off switch on my Trace Elliot GP7SM 250 (80's 250W solidstate combo).

    Anyone knows the max current passing there normally? I need to know so I select a switch that is sturdy enough.


    Attached Files:

  2. 1958Bassman


    Oct 20, 2007
    How much high frequency response do you need? How will you control the level? I would use a fixed L-Pad, rather than an on/off switch. The amp sees a more stable load and the switch won't need to handle a lot of current because the L-pad will be in series, "absorbing" current. 5A would be fine unless you're pushing an extreme amount of power.

    P=IE, which means your power needs to be specified. Once that's known the current (I) can be determined. The power is calculated using the impedance and voltage (E).

    Here's a useful chart for these calculations-
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  4. Antoje


    Aug 13, 2010
    Sherbrooke, CAN
    Thanks for your quick reply, I have a spare 10 A switch i can use.

    I did not know the existence of L-pads, but I can interpret wiring schematics and calculate electrical loads: thanks for your time to show me this!

    The tweeter is already on the amp, I just want to deactivate it when I use it as a keyboard amplifier or a guitar amplifier. (This is the only amp I have at home for practice, all others are where my band rehearse.) I fear high frequencies caused by highly distorted sounds can degrade the tweeter if used for a long time.

    As we are speaking, I just unsoldered the crossover from the circuit and the amp has been doing great since. I just want to have the tweeter back on when I practice bass, since I feel it sounds better.
  5. Primakurtz

    Primakurtz Registered Nihilist Supporting Member

    Nov 23, 2011
    Denver, Colorado
    I believe the formula is 250 watts divided by 120 volts (or 240, depending on where you live). You should be fine with anything over 2.084 amps. I may be wrong...
  6. Antoje


    Aug 13, 2010
    Sherbrooke, CAN
    It seems there is already a L-pad on the crossover, so I would just have to move the SPST switch between the crossover and the Tweeter positive lug to effectively have a switch with no total impedance variation.

    Attached Files:

  7. Antoje


    Aug 13, 2010
    Sherbrooke, CAN
    No, the voltage inside the amp is not 120 V or 240 V. This would mean all european cabs would be more powerful (Impedance x Voltage = Power, and speakers are the same)

    Circuits are working at different voltages with the help of transformers.

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