hello all,

just learning about calculating attenuators with respect to different
impedances etc., since i want to build some myself. i don't think that
i quite got it though, so maybe someone can help me out?

example: the 20db input pad of the jensen mic-pre schematic.
- assuming an mic output Z.out of 150 ohms and a preamp input Z.in of
1500, that would give me a 10:1 ratio equalling 20db from the preamp
p.o.v.
- with the pad in (matched 619R in both of the balanced lines plus
169R connecting between both lines) i calculate the following:

total Z.in = 169R parallel to 1500 = 152 ohms
total Z.out = 150 + 2x619R = 1388 ohms.

now here are my questions:
- if i now compare Z.out to Z.in, i get a ration of 1:0,11 equalling
about minus 20db. however, compared to the ration without the pad in,
that would mean a difference of -40db instead of -20. what am i doing
wrong??
- i suppose the parallel resistor (169R) is for maintaining the
correct overall impedance. without the pad in that would be 150 (mic)
and 1500 (pre) = 1650. but with the pad in it's only 1388+152 = 1540.
does that matter?
- what is the normal Z.in of line devices? 600ohms? or also up to 1 or
2K? which Z.in should i assume if i wanted to calculate a *line*
attenuator instead of a mic attenuator?

thanks a bunch to you all, peace,
volker

Volker,

now here are my questions:

I'm not sure if you'll find all the answers, but some of them are covered in
my article "Mike pads and other small gadgets", about half way down the
list, he

www.ethanwiner.com/articles.html

There's even a little DOS program that can calculate the resistor values for
you.

--Ethan

ethan,
very interesting. thank you!
volker