Home › Forums › Help/Technical Questions › weird grounding issue with Stereo Polyphase expression pedal input

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  • February 11, 2023 at 9:27 am #197875
    mtech
    Participant

    hi there

    I just had the mode selector pot for the Stereo Polyphase replaced by a technician (EHX sent me a direct link to the correct part). The pot now works as expected – however, I now have a new issue. I damaged a couple of the sockets when trying to remove the PCB from its case (I lifted the metal tags/clips off the top of the sockets whilst wrestling with it). The tech has repaired or replaced these.

    I am aiming to use the pedal with my modular synth system, by sending Control Voltages (CV) into the expression pedal input. I have done this for years with my Memory Boy Deluxe, and understand about the correct cable and voltage range required.

    However, the expression pedal input ONLY works with Control Voltages coming from devices that aren’t grounded via the earth pin of their mans plugs. Very bizarre!

    For example, I have a number of powered Eurorack modular cases. The ones that use “laptop style” power bricks work fine with the phaser – but the ones that are properly grounded via the third pin of a UK mains plug (rather than having a plastic pin) do not work with the pedal. The module connected does not modulate the phaser’s frequency at all.

    If I move the exact same module into a case which isn’t grounded via its mains plug the module works perfectly – and you can clearly hear it modulating the phaser.

    My Korg SQ1 and Behringer CAT also work fine with it – but, again, they are both powered via adapters that don’t make use of the earth pin of the UK mains plug.

    Any ideas? I’m guessing that the socket for the expression pedal is either missing its ground connection, or has one when it shouldn’t have? (not sure which)

    Cheers, Matt

    February 14, 2023 at 2:59 pm #197898
    Electro Harmonix
    Keymaster

    Unlike the majority of our pedals, the Stereo Polyphase expression jack cannot share ground with the audio jacks. So if both audio and the CV signal come from the same instrument or from instruments that share the same ground, the Polyphase expression won’t work. When the CV signal comes from an independent device, which is perhaps battery powered, it will work.

    August 2, 2023 at 4:53 am #203035
    RyderHartley
    Participant

    It seems like the expression pedal input on your Stereo Polyphase pedal is behaving strangely, only working with Control Voltages from devices that aren’t grounded via the earth pin of their mains plugs. This could be due to a possible issue with the socket’s ground connection. It’s likely that the socket may be missing its ground connection or has one when it shouldn’t. I recommend reaching out to the technician who repaired your pedal to have them check the ground connection on the expression pedal socket for proper configuration.

    Best of luck with your modular synth system!

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