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Thread: gadget schems

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    gadget schems

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    I am delinquent in that I promised somebody a drawing of a pot box (sorry, don't remember who!) and have not delivered.
    I have therefore attached same together with some related circuits that peeps might find useful.

    The first diagram is merely a potentiometer in a tin to control the level from say a "pro" mic pre amp, mixer etc, to an AI or other device that might not be able to handle pro, +20dBu levels.
    The pot can be any value but 10 kOhms log is a good choice, if driven from a low, source impedance the worst case output Z is about 3k which is reasonable but the device should be as close to the controlled device as is practicable so that the cable is no more than 3mtrs of so and HF is not impaired. This precaution always applies to attenuator circuits.

    Points...VR1 is shown with tags top and bottom. This is for clarity, in practice the top tags would hide the lower ones. Convention (from tape days) means "upper" is the left circuit. You can of course just us a single pot/jacks for mono. Also the 4 jacks could be two stereo ones (I have shown stereo jacks. Always buy them the cost difference is trivial) Both the layout and the schematic below are shown.

    "X'" Shows a point where an earth lift can be inserted (the circuit can be used for re-amping). The switch breaks the ground path for the output but C keeps a ground at RF. A double pole switch is shown since almost all you see are min' DPDT but you could combine the earths and just use one switch and cap.

    .................High Z Attenuator...................
    I see a lot of posts where folks find their AI cannot handle the full output of their guitar or bass. With the values shown you get about a 10dB loss and the input Z is still about 1 meg. These figures assume the AI has an input Z of 1 meg as well. The output lead for this box really wants to be no more than 1mtr to avoid "tone suck".

    ......................Dim/Boost Box.................

    This was designed to allow a music source to be "dimmed" for voice overs. When S1 is closed the pot allows the amount of cut to be set. Opening the switch defeats the pot and full welly busts forth. R1 ties the track to ground so that should there be any DC leakage from any device it will be drained an so avoid any click.
    The circuit could be inserted in a guitar amp's FX loop as a boost (the inverse operation) or as an attenuator to allow the pre amp circuits to drive harder or to tame a **t or bust volume pot.

    Any questions, always about. Any requests, all currencies happily....I am kidding! Just fire away!

    Dave.
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