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Topic: JFET and D-MOSFET as voltage controlled resistor |
Keith Hilton
From:
248 Laurel Road Ozark, Missouri 65721
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Posted 14 Jun 2003 10:00 am |
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| Do any of you have any circuit diagrams of JFETs, or D-MOSFETs, used as a voltage controlled resistors? Interested in seeing different ways the gate is biased with DC, in relation to an AC signal? Also how to overcome the large differences from part to part in these devices? |
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Jack Musgrave
From:
Springfield, Missouri, USA
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Posted 15 Jun 2003 9:37 pm
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| Keith, I think that the NASA space center might have the information that you are looking for, but it is a highly guarded secret. God only knows what that kind of imformation could do in the wrong hands! |
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Michael Brebes
From:
Northridge CA
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Posted 16 Jun 2003 6:58 am
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| I'll see what I might have available. One thing to remember is that all the different varieties of JFETs are no longer available. The old 2N5457's were very good and very consistent for range, but no longer available. One key in using them as VCRs is that the signal going thru them can't be very big, otherwise it will get into the range of the control voltage and other fun things start to occur. |
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Gino Iorfida
From:
Pittsburgh, Pennsylvania, USA
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Posted 16 Jun 2003 8:29 am
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Check out www.tonepad.com They have the diagrams for the old MXR Phase 90 etc. The Phase 90 uses jfets controlled by a LFO voltage causing the sweep. I think a couple of other effects, such as the MXR noise gate etc use jfets in the same manner. I've found 2n5485 jfets to work great in this application as well.. been a while since I've been to the site so you'll have to forgive me if this isnt' what you are looking for.
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