Reply To: Input gain pad on QU16?

[Andreas]

Just some points from my side for clarification. The circuit expects a High-Z input to work correctly (reduce level by 6dB), otherwise R2 has to be seen in parallel to the input impedance. If R2 equals the input impedance, reduction will be 12dB.
-6dB Pad isn’t very much for a pad and when choosing R2=R1 you’ll get -12dB.
For symmetric signals R2 needs to be 2*R1 for the virtual ground in the “middle” of R2 to obtain -6dB, as Mervaka said.
The non-trivial problem is to choose optimal values for R1 and R2, since you also need to take into account the source impedance, input impedance and capacitance.
Anyway, I somehow doubt this is a pad issue, since level from a mic should be way below line level and the inputs allow signals up to +19dBU which I rarely saw from any device (particularly not a mic, and never from a phantom powered condenser).
I’d probably check cabling first. A broken ground or signal line on a phantom powered mic can easily produce that high spikes when shaked.