[A27Hull]

The short answer is yes it can be done.

But someone more knowledgeable than me will have to help.

math wise, to figure a -6dB per octave high pass, use a little algebra on:

f = 1 / 2pi(XY)

X is an arbitrary resistance value

Y is an arbitrary capacitance value

f is the desired cutoff frequency (where the power attenuation acheives -3dB)

Using this formula, with 100 = f and 4.7uf = Y, I get a resistance of about 339Ω

Now, this is where I have to stop. I can't tell you the proper values appropriate here, nor can I tell how to implement it for a balanced line.

You may want steeper attenuation than -6dB per octave. At 50 Hz, if my thinking is correct, the attenuation will only be -6dB roughly. This will require more than a simple resistor/capacitor combination for passive implementation, maybe several back to back.

The real question IMO is whether or not it can be done practically, iow, can it be done for less that it would cost you to buy ready made items?

Good luck, and I hope to be schooled here as well.