does some know how to build a 60hz hum Eliminator which stops the 60 hz hum??

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
The one and only
Joined 2001
Paid Member
Assuming that it's the 50/60 Hz line, it's not difficult to inject some
of the line signal into a passive or active summing junction to
cancel it out. Such a system has a line sample (usually transformer
isolated) and a potentiometer which allows a +phase through
0 to -phase injection into the signal, preferrably with band-pass
filtering centered on the line frequency.

You have to adjust it at each gig, but it usually does the job.
 

taj

diyAudio Member
Joined 2005
Interesting. My experience with guitar noise is mostly buzz picked up from stage lighting dimmers. Especially when using single coil strat type pickups. It's a sharp harmonic buzz picked up as a consequence of the tiny signal level and long unbalanced trip from the pickup to the amplifier, along with the massive amounts of AC dimmers laying nearby.

So the actual 60Hz content isn't as great as the multitude of its upper harmonics, which fall right smack in the middle of guitar sound bandwidth. A sharp filter centering on the line fundamental wouldn't help too much, but it wouldn't affect the guitar sound too much either, unless it was a bass guitar, so it's probably worth trying.

I think the best approach would be preventative measures first. Stay far away from the dimmer packs (or keep the dimmer packs far away from the stage); Reduce the number of AC cables, particularly lighting cables, laying around the stage. Make sure the guitar amp is well/properly grounded and shielded; use a VERY well shielded/maintained (ie: expensive) guitar cord; shield/ground the pot cavity inside the guitar body; use humbucker pickups if it suits 'your sound'; if you use a pedal board with multiple stomp boxes, make sure all the interconnecting cables and plugs are well shielded and grounded and their internal wiring is in top-notch condition (no missing barrels around the plugs).

Then, try some Nelson Pass magic. ;)

Or take up drums. :devilr:

..Todd
 
hi,

Here is what i do on live gigs, guitar amps and stomp boxes are plug on the same power strip that is plug to a line surge/conditioner or have a ground wrist strap (the one that they use when working on an esd sensitive device) and clip it to the ground portion of your Phone plug. A bit annoying but much better than a humming FOH speakers. Hope this helps.

Best Regards,
audiomachines
 
The way I do it on the basses I build is to wind a pickup coil, but use it without a magnet. Since it has no magnetic field of its own, it does not generate a signal from the strings, however it remains sensitive to all EMF fields in the area. I then run that signal into the main output out of phase, thus canceling the hum.
Or you could just use humbucking pickups...

Grey
 
Disabled Account
Joined 2006
Suggestion: 'direct injection' box consisting of the following, in this order...

- basic differential op-amp
- low pass filter (nothing to do with your 60Hz issue, but just because you can, and because it's a good place for it, with a -3dB point about two decades above your highest desired frequency)
- 60Hz series tuned filter (= inductor in parallel with resistor+capacitor)
- unity gain buffer
- a capacitor at the output (because you are likely to have a dc offset at the output. But then again, if the amp has a cap at the input then this output cap may not be required)

The basic differential amp, even with simple 1% resistors, should get you 25 - 30 dB of attenuation, and the tuned filter should do the rest.


I also agree with the suggestions from the other guys.
 
a unity gain buffer is an amp stage (usually opamp) that is configured for a gain of 1. It has a really high input impedance that doesn't load the signal, and has a low output impedance to drive a cable or input circuit. It converts impedance, basically, without affecting gain.
 
Up to 10~15 feet of cable you should not really be getting enough pickup to be heard in normal conditions, particularly as there is often some masking hum from other sources and other background noise.

You can of course use a DI box if distances are great, but if not, ensure that the cable and connectors are of good quality and that the joints are well made. Then make sure that the same applies to the guitar, and that it is well wired with spidered grounds without loops.

Failing this effecting a cure, you might want to ask another guitarist whether he gets an unusual amount of hum when he plugs into your amp. If he says yes, have the amp serviced or possibly replace it. Otherwise you might just want to ignore it. A guitar system that evidences no audible hum when listened to close up at high volume settings with the strings damped is unusual.

w
 
mr pass ...

i am breathless .........

from all that ive read and all my field expirience the only one that stands a chance is gordy .....

presuming that everything is fine and correct with the construction and the power of the particular amplifier so it doesnt pick up any noises from plugs filtering ground connections and or ground loops ...
.........so lets suppose that everything is ok there is only 2 things to be done

A) once i had a problem quiet simular with a quitar ( well not really greek instrument looks like quitar and called laouto ) it prooved that someone in the past replaced the output jack but made a mistake in the polarity !!!!!!!!

B) and most of all in all my field expirience ( and that includes both terrible wiring and alot of dimmers ) there was no hum that resisted me after i installed a passive DI box !!!!! the particular one is called arctic and costs the astronomical figure of 8 euros !!!!!

finaly its not the instrument nor wiring nor dimmers that is sensitive to hum ..... mostly is the preamplifier input sensitive to pick up stuff like that .....

matching resistors ...... keep it too high or too low between instrument and preamplifier and then the cable becomes a wonderfull antenna that pick up anything ....

best regards sakis
 
Nordic said:
Unity gain buffers normaly deliver sliglty less than unity output...


I guess if it's not an opamp that is definitely something to consider. With an opamp, the difference is negligible.
Guitar and instruments have one of the worst interfaces in general. My strat has a lot of the buzz mentioned above when in the "non-humbucker" positions (2 and 4, I think they're usually called). I've often wondered if it would help any to build a box that would provide phantom power to an on-instrument preamp (similar to a condenser microphone) that converts the signal to balanced low-impedance. The box that supplies the power could sit right on top of the amp and convert the signal back to single-ended and go into the amp at that point.
I guess the question I've always had was whether that would make a difference or not, as the pickup might be the problem and not the cabling. How about if the pickup was treated as a floating balanced signal with a differential input to the buffer/driver?
Sorry... not trying to threadjack... just thinking out loud. This is something I've thought about before.
 
If you have a problem with hum you should try a balanced line with a transformer and at the pre amp you can bring it back with a transformer to a asymetric line. if you stil have hum you can make a L C serial connection in your pre amp , for the L you can use a gyrator made with a opamp
 
The way I do it on the basses I build is to wind a pickup coil, but use it without a magnet. Since it has no magnetic field of its own, it does not generate a signal from the strings, however it remains sensitive to all EMF fields in the area. I then run that signal into the main output out of phase, thus canceling the hum.
Or you could just use humbucking pickups...

Grey
That's actually pretty clever.
 
i am breathless .........

from all that ive read and all my field expirience the only one that stands a chance is gordy .....[snip]

How can you say that if you don't even know the cause of the hum? As far as I know, Mr. Pass' method has been in use for, ohh, 80 years? by the tube crowd to null heater induced hum. Yes I know this is not a tube amp, but the principle is the same. Tried and proven, simple, easy, effective.

jan didden
 
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.