To attenuate 30db, I found this equation:
+Line level (input) -----R1----+-- +Line level (output)
|
+----R2----+
|
Ground (input)----+--------------- Ground (output)
The attenuation of the circuit is determined by equation:
attenuation (in dB) = 20 * log10 ( (R1 + R2) / R2 )
Plugging in 30db attenuation and an R2 value of 100 ohms, R1 is 3.062 Kohms, where the closest standard value for R1 appears to be 3.09 Kohms 1% +/-
Sound reasonable? I kind of like running everything through one box, but would it be wiser to consider the following option: I could just build a selector box and attenuate my sources directly: Chime built in attenuation, Cornet II which could be attenuated directly per recent post here, and Yamaha t-1 tuner, which has a variable output.
Matt