Help with Vintage EHX Micro Synth transformer

Discussion in 'Burnt Fingers DIY Effects' started by Acobberson1, Dec 9, 2019.

  1. Acobberson1

    Acobberson1 TDPRI Member

    Jul 27, 2015
    Hey everybody,

    I’m working on an old Micro Synth, the first version, and the voltages are not what they should be. The pedal has a transformer that takes 110v down to 24v, this then feeds a NE5554 that should be sending out 12v.

    There voltage coming from the transformer is about right, maybe a little high at 27-28v. However from there the pedal is not getting the 12v it should. I suspected something wrong in the power section, as the NE5554 was getting extremely hot to the touch. So I started by replacing the electro caps in the power section. This did not help, so I then suspected that the 5554 itself was bad. I replaced that and now I’ve also replaced the other caps and 4001 diode. That’s pretty much the entire power section. No help.

    Transformers rarely just fail, but after looking at the schematic I’m wondering if I can just remove the transformer and feed the pedal with the required 24v. I did this with an old Polychorus, but the ONLY reason I have not already done it with the Micro Synth is that there is also a center tap on the transformer. I’m not sure how this would be wired with just a normal positive and negative power jack.

    any idea how this might work? Here’s a photo of the power section schematic.

    Attached Files:

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