What are you thinking about 50Hz rejection filter in stompbox effect?
i have got a schematic:
http://www.elektroda.net/audio/schematyideowe/zapor50hz.gif
characteristics of the filter are:
http://www.elektroda.net/audio/inne/zapor50hz_wyk.gif
It's not a bad idea - just really hard to do.
The power line is usually exactly 50Hz in 50Hz countries. The tolerance of components in a filter mean that unless you use high precision resistors and caps, the filter will not be exactly 50Hz, and so it either needs tuned and tweaked periodically as things drift, or it will not completely reject the power line frequency.
seems like an ok filter... but there are better ways of stopping 50Hz from entering your pedals! Namely power supply filtering and good shielding on both your pedals and you guitar... and your cables for that matter!
I wouldn't consider this for my use, but I'm a bass player, so 50Hz is more important to me!
Plus, this filter ain't gonna stop your wah pedal from picking up AM radio! DOH! That's a bigger problem in my rig! Upper -3dB point is like 1.3MHz!!!
Hi!
I've found that usually it apears to be some distortion on the mains, as it has a lot of harmonics that also got their way into the effects, so you'll need also a filter for 120hz, and 180hz and so on. That's why the simplest way is using a low pass filter directly on the supply (the 100uf-1000uf electrolitic usually)
Good luck
Miguel
good shielding is proabbly the better idea. I have found (mainly on recordings) that 50 and 60Hz bleed-through rather often doesn't consist of a nice sine-wave at all. It won't be filtered out by killing the fundamental with a high-Q parametric EQ. This means you have to get wild with both parametrics and really precisely set gates and compressors, and still need to accept it being in there slightly. It's best to not get it in in the first place: having well-stabilised and well designed powersupplies, a good grounding network, no loops and good quality cable does just that.
Now with all digital audio editors and studio gear I believe such things are not so useful any more but very interesting anyway, notch is so narrow that it does not much color sound otherwise but around hum
I have thought how this would sound with single coil pickups and loud fuzz/amp gear onstage
I have another Elektor version of same idea in my archives and it suggests using two of these in series- but the other is tuned 100 Hz (120 Hz in some countries) -the second harmonic of mains hum