> DW Fearn states their box provides 45dB of attenuation.
So? Is that the only right-answer?
Many mic-amps can choke down 1V without coughing. Few studio sources are over 10V. 20dB pad can work. 36dB pad will output 0.15V, which I'm sure your preamps can handle. Given a more sane 2V level, -36dB outputs 30mV, which even my old Langevin could digest.
> Any idea as to what R1 & R3 have to be for that?
"Bigger", obviously.
You want numbers? Take the number you have taken: 45dB. Convert that to voltage ratio: 178. Since this is much greater than "1", it is near-enough the ratio of big series resistor(s) to little shunt resistor.
The obvious shunt is the 150r. But this may have a 2K preamp in parallel, 140r. Multiply by 178: 24,837 ohms. You want that in two pieces, 12,419 ohms. A sharper pencil says 12,348.6 ohms. IAC: Use two brown-red-orange-gold against a brown-green-brown-gold.
Input impedance is over 24K, but under 25K, a happy zone for most sources.
Impedance shown to preamp is a hair under 150r (149r), and preamps should be very tolerant 50r-500r since mikes come all different Z.
If your resistor-box is VERY skimpy: 10K-100-10K gives 46.5dB 99r, which is same-as 45dB 150r for any musical purpose.
