schematic for a hum eliminator?

[darron]

seems like the conversation is going two different ways... hum from ground loops and just hum at your pickups.



just thought i'd throw this one into the mix for fun too:

http://www.muzique.com/schem/silencer.jpg

[teemuk]

http://freecircuitdiagram.com/wp-content/uploads/2008/08/hum_filter.gif

[GGBB]

http://www.beavisaudio.com/Projects/Huminator/


Shabam.

I already know that proyect, but if you notice the hum eliminator is not another filter phase for a power sypply it worck with 1/4" plugs, so you can connect it to your chain of pedal or maybe in the conection between cabinet and head.

by the way I'm talkin about this thing
Hum Eliminator http://cachepe.zzounds.com/media/quality,85/brand,zzounds/he-2_left_bottom-45f2c7549b6a89413c0fa68748190ac9.jpg

I have one of those.  It is a passive ground loop eliminator that uses isolation transformers.  There are two variations on that theme at GEO - but they are active designs:
http://www.geofex.com/FX_images/splitter.gif
http://www.geofex.com/FX_images/spltr2.gif

These will get rid of ground loop hum only.  They won't help you with mains hum, cheap power supply hum, single-coil pickup hum, fluorescent light hum, or any other type of hum including Windsor Hum.

[Nasse]

Early or mid 80´s Elektor magazine and "300 circuits" series books had such narrow notch filter, was done with op amps and it had two filters in series, one for 50 Hz and second for 100 Hz (few guitar amps go down to 50 hz)

[R.G.]

There is a problem with filtering hum out. 50H, 60Hz and their first few harmonics fall close to musical notes.

For instance: 60Hz is below the low E of a guitar at 82.4Hz.  If you want to suppress the 60Hz by 40db (1/100 the power and about 1/4 the volume) then you need to have a filter that's not noticeably losing signal at 82Hz and is 40db down half an octave a way. That's a (roughly, not doing the math precisely) 80db/octave filter, which is INSANELY difficult to do by analog means. Cauer and elliptical filters can be done to put a suppression notch in the stop band right over the desired frequency, but just the necessary precision of parts will make this very, very difficult to do reliably. The slopes on the sides of a suppression notch are necessarily steep, so if you miss the exact frequency just a ...little... bit, it not only doesn't remove the hum, it removes something else that you may want.

Worse, 120 Hz power supply ripple and fluorescent light bulb buzz is only 3.46Hz from Bb at 116.54Hz and B at 123.47Hz. Removing 120Hz with a notch and leaving both Bb and B alone is essentially impossible by analog means. It ain't easy in digital. CBS tried to do a copy protection scheme with very tight notches in the recorded material which would be detected as "protected". Seems it was obscenely audible, and they finally gave up before perverting the recorded music world even more than it is already.

Hum is in some ways like Ebola virus: it is by far better to stop it from getting in to start with than trying to eradicate it once it's already there.