Bugle Resistors?

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highendman

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Bugle Resistors?
« on: 9 Oct 2003, 09:58 pm »


Is it possible to eliminate R(in) and R(out) -- that is R12 and R7? What is the purpose of R(in)?
Thank you.

hagtech

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You can, but don't
« Reply #1 on: 10 Oct 2003, 06:24 am »
Every part in that design has a purpose. Since this is an opamp based design, I use R12 to form a low pass filter with the input capacitance of the opamp transistor & packaging. Merely for RF rejection. We're getting rid of MHz stuff. You just don't need to pump that stuff into an opamp that might amplify some of it. I also specify JFET input opamps to further reject AM radio pickup.

R7 is to decouple an unknown output load (cable capacitance), which if placed directly on the opamp can cause instability and oscillation. You MUST get off of anything that will add phase shift to the feedback network. Let the opamp do it's job without interference from the outside world. And again, R7 also forms a low pass filter with the interconnect to keep any RF from progressing onto the linestage.

Good question. I realize some things look odd in a schematic.

jh :)

highendman

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Thanks again. :)
« Reply #2 on: 10 Oct 2003, 01:06 pm »
nt.  :)