JohnRoberts said:As I recall Steve described some exotic tricks like twisting wire leads together to make small value variable caps, to use in canceling stray capacitive coupling, etc.
Yes at first glance, but note the 4.7ohm resistor to ground in the inverting path..ricardo said:looks like a polarity switch.
But the -ve polarity has much less gain than +ve or maybe not cos on +ve, there is leakage to the -ve i/p.
I've used a much simpler version to get clean polarity swap.
yes correctamundo....PRR said:> note the 4.7ohm resistor to ground in the inverting path..
> The 4.7 ohm is a crude approximation for the JFET on resistance.
Note the one side is *10K* and 4.7r, the other side is *two* 3.3K and two FETs.
So we figure 4.7/10,004.7 is 0.000,47. The FET side must do the same with two dividers, so take square-root, 0.022 in each divider.
I figure the JFET is more like 71 Ohms. Which is a more believable value than 5 Ohms (a VERY fat JFET or a power MOSFET). > note the 4.7ohm resistor to ground in the inverting path..
> The 4.7 ohm is a crude approximation for the JFET on resistance.
Note the one side is *10K* and 4.7r, the other side is *two* 3.3K and two FETs.
So we figure 4.7/10,004.7 is 0.000,47. The FET side must do the same with two dividers, so take square-root, 0.022 in each divider.
I figure the JFET is more like 71 Ohms. Which is a more believable value than 5 Ohms (a VERY fat JFET or a power MOSFET).
FETlife said:Had another look at the schematic, they use this circuit elsewhere but with different values for the 10k, 4r7 combo!
Ah well, time to forget about this circuit me thinks! Cheers all.
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