Tweakers' Asylum

Hagerman Bugle Question

67.21.91.65

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

Sure, if you want - Jim Hagerman 21:42:45 10/09/03 (1)
But 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 & packagting. 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 questions. I realize some things look odd in a schematic.
jh
- Thank you for the thorough response. :-D nt. - highendman 05:57:50 10/10/03 (0)
  nt.
Re: Hagerman Bugle Question - Perphenazine 11:29:54 10/09/03 (0)
I don't have an answer, but wanted to say that Hagerman has their own section over at audiocircle.com where you can get answers from owners and the company directly.

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