Adding RF filtering to 'too-simple' input.

[k brown]

Would love some ideas on how to add a bit of RF filtering to this FX Return on a Soundcraft Folio Notepad. The Tape In has the same simple circuit and values.

The 'L' and 'R' are the mix bus points to the bus amps. I like these clean access points to the mix bus, but in today's environment they seem vulnerable to 'junk' coming in.

Where would you add caps and at what values?

I'm guessing something like a 220 ohm before the pot, followed by a 100p to ground (?); or, maybe as simple as, say a 470p across the input jack?

 

[Newmarket]

There's no definitive answer to this as you will never know what RFI is lurking around. But 10s or 100s of pf in the ballpark. Imo you don't really need resistors as RFI sources are usuall high impedance but I might opt for a ferrite bead there.
Imo the important thing is to take the caps directly to chassis (or as close as practicable).
You might even consider putting them in the cable jack connectors themselves to keep RFI outside the chassis as far as possible although that then ties you to using those cables to benefit.

 

[k brown]

There's no definitive answer to this as you will never know what RFI is lurking around. But 10s or 100s of pf in the ballpark. Imo you don't really need resistors as RFI sources are usuall high impedance but I might opt for a ferrite bead there.
Imo the important thing is to take the caps directly to chassis (or as close as practicable).
You might even consider putting them in the cable jack connectors themselves to keep RFI outside the chassis as far as possible although that then ties you to using those cables to benefit.

Caps in the connectors is a good idea - the unit in question is the Spirit Folio Notepad, which is in an all-plastic case! I've long considered adding a grounded thin sheet if metal inside the bottom of it (like Yamaha did with the MG-series).

 

[Newmarket]

Oh yeah - I have one of those though not used atm. Forgot it was plastic bodied unlike the larger Spirits. I haven't taken it apart. I was thinking it might have metal behind the plastic ?

 

[k brown]

Oh yeah - I have one of those though not used atm. Forgot it was plastic bodied unlike the larger Spirits. I haven't taken it apart. I was thinking it might have metal behind the plastic ?

Nope. At least the aluminum top panel is grounded!