Mxr block logo phase 90 schematic11/4/2023 These variations between transistors with the same name are due to being made by different manufacturers or to belonging to different transistor batches made by the same manufacturer., we buy transistors in big batches from the same manufacturer to be sure that they have similar parameters. Check the voltage in the source pin with a voltmeter for each transistor and then get the four that have the most similar values (the absolute value doesn’t matter). You can build a circuit with a small resistor voltage divider to set the gate voltage to around 2V, a 10k resistor between DC and drain, and a 10k resistor between source and ground. ![]() Anyway, if you can get a bunch of them and select four that are quite similar, you’ll get better results. ![]() ![]() Nevertheless, this is not as important as the trimmer setting (we even got our first Phase 90 working with different JFETs). As the filter has four identical stages, it’s advisable to use transistors with similar gain parameters so they react the same way.
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