However best results you'd likely get with a matched set within range. I would not recommend this even so it has been done as in for instance the Guyatone Rollophase You can ofcourse then try linearization circuits to each FET so as to drive them midways. If you use transistors with a very low Ugs, like 0V6, you might want to change the zener to say 2V7 but distortion through circuit would be worse.examples of such transistors would be 2SK30A. You might also want to try 2N5487 with a better likelyhood of finding a matching set. You could find a quartet with the MPF's as the Ugs is poorly defined but you may need a bag of them to find this: they would be allover the place likely To get each allpassfilter to sweep in the same way for deepest effect controlrange need to be the same for each transistor used If you look at the circuit you will see that the transistor works as a parallell shunt to a resistor. It will not matter what the case of the transistor says: what you want to do is operate the FET in it's resistive range, also known as triode range. Try for this circuit to match transistors with an Ugs at about 1,4 to 2V5's and a set matching within a few millivolts. BTW, be sure to check the pinout of the transistor that you choose, keeping in mind that it may not be the same as the one indicated in the Tonepad layout. Abstract: MPF-102 pin out mpf102 Application Note MPF102/D Text: MPF102 Preferred Devices JFET VHF Amplifier NChannel Depletion. Throughout its history, Motorola was known for its innovation in the field of telecommunications. It was headquartered in Schaumburg, Illinois and was one of the largest providers of mobile phones, telecommunication equipment, and semiconductors. I think the 2SK104 sounds like a better prospect, but if your friend is going to let you hang out and measure transistors, then take your time and find a matched quartet with Vgsoff close to -3V. was an American multinational telecommunications company that was founded in 1928. I liked the 22uF better, but the 10uF increased the maximum rate to something approximating a genuine Phase 90 that I played in a music store.ĥ. FWIW, I originally had a 22uF cap there, and later swapped it for a 10uF. Otherwise, use what you have, and don't worry too much about the taper.Ĥ. If you happen to come across a 500k reverse log pot, then go for it. I would (and did, as a matter of fact) just use a 500k linear pot here. If Rx = 100k and the maximum resistance of the pot is 500k, then the maximum resistance you'll get from this arrangement is 500k * 100k / (500k + 100k) = 83.3k. Less glib version: the maximum resistance of the pot in parallel with any tapering resistor still needs to be 500k. Long version: read "The Secret Life of Pots" at GEO. I have been meaning to try a larger value there, but I haven't gotten around to it. Mine ticked with the feedback resistor in place, so I removed it. In other words, looking at the Tonepad schematic, it's the 22k resistor closest to the word "Schematic" You might as well put it in, and if you get a bad ticking sound that you don't like, remove it, or try increasing the value. The feedback resistor is the one that connects pin 7 of IC3 to pin 6 of IC2.
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