Power Conditioner? Furman?

[chipaudette]

Hi All,

I'm getting really sick of intermittent hum/buzzing in my guitar amps. It comes and goes depending upon the day and depending upon the time of day. I have two guitars (Strat and Les Paul) and two amps (both tube). On a bad day, all permutations of amp/guitar will have the problem.

Things that I've noticed that get rid of the noise: When I unplug the guitar, the noise goes away. When I roll the volume down on the guitar, the noise goes away. When I touch the guitar cable, the noise goes a way.

So, my question is, is it likely a problem of radiated noise that is being picked up by the guitar? Or, is it more likely noisy power in my crappy old house?

If you think that it is noisy power, has anyone used power filtering products like those from Furman ($90 and higher) or from Eb-tech (HumX, $70). Did they solve your problem?

Man I'd like to get rid of this annoying, intermittent noise problem.

Thanks all,

Chip

[Steve Conner]

Any lamps with dimmers?

I had an intermittent buzz like this in one place I lived. It was always strongest when sitting in the middle of the floor.

Turned out the room below had a ceiling light hooked up to a dimmer switch, and the buzz was strongest when I was sitting on top of the light fixture. It was intermittent because when someone turned the light off, it stopped altogether.

In another place it was an electrified railway line, my guitar would start to buzz 3 minutes before a train passed. But only with single coils in that place, whereas the dimmer affected humbuckers too.

A power conditioner wouldn't fix either. My gut feeling is that it won't fix any interference that disappears when the guitar volume is turned down, because this means that it's noise picked up by the guitar.

If grounding your body (say by touching the strings) makes the noise less, then it's capacitive pickup, and shielding the guitar's control cavity will help too.

[teemuk]

What Steve said.

Plus a power conditioner is not even a hum eliminator to begin with. It's just a set of filters to remove everything but the 50/60 Hz cycling away from the mains, plus a bunch of MOVs to cut off the occasional current / voltage transients in the mains.

Most also have some sort of monitoring feature (like a bunch of LEDs) and some higher quality equipment (usually referred to as "power regulators") may also have some sort of regulator circuitry to keep the voltage at a steady level despite variation in the mains.

[Neo5Bass]

I think the 60 Hz is related to single coil pickups not having the ability to cancel (e.g. Hum-buck) common mode signal. If it is as you say, then a 60 Hz notch filter in line with your guitar output will knock it down. The reason it goes away when you touch the metal parts of the guitar is that you are making an AC divider with your bodies capacitance and the neutral side of your power supply.

This is also what you should be very careful about if mixing power connections. It is rare but if someone has mis-wired AC hot and neutral on one outlet and not on another if your PA is plugged into one and your guitar the other you run the risk of a nasty shock.

The standard conditioners are pretty lame for much more than:
1.) Having useful lights you can see by and
2.) A convenient place to turn on and off power mains

A true 60 Hz. Regulator at least the one I know of is a ferroresonant isolation transformer where there is a third winding on the common core. Placing a capacitance in parallel with this third winding forms a tank circuit. When you run current through the main part of the transformer the core will resonate courtesy of the tank. This makes for a pretty good rejection circuit because crud coming in on the mains gets damped by being out of the resonant frequency.

I have been amazed at what people will spend on power conditioners like the ones at Best Buy. Remember if something like power line noise is "suddenly" getting your attention there is usually something basic going on.

[wrathfuldeity]

Idk, and not sure if my ears really notice any difference, but other electrical devices in the house turning on/off don't have an effect on the amp and it seems to rock steady....but I got one of those old computer filter... battery back up things at a garage sale/thrift store, took the spent battery out and just use the conditioner outlets...$5.00...seems to work well...can't imagine that a Furman does all that much more.

[ThermionicScott]

I think the 60 Hz is related to single coil pickups not having the ability to cancel (e.g. Hum-buck) common mode signal. If it is as you say, then a 60 Hz notch filter in line with your guitar output will knock it down.

Have you had much experience with this? I've toyed around with building a "twin-T" notch filter pedal, but haven't gotten around to it yet. I worry that it would scoop out neighboring notes if I don't get the frequency right or the notch deep enough.

- Scott

[Neo5Bass]

60 Hz woes...

Have you had much experience with this? I've toyed around with building a "twin-T" notch filter pedal, but haven't gotten around to it yet. I worry that it would scoop out neighboring notes if I don't get the frequency right or the notch deep enough.

- Scott

Hi Scott;

In a word, "maybe" I used to design filters for a living. As far as real-time filtering goes a notch is pretty good. A Crystal tuned notch has Q's in the thousands if I remember correctly, ( OK,maybe hundreds, certainly less than 1 Hz bandwidth) . If 60 Hz is really excessive, you may have a funky shield or crappy cables. To narrow it down remove as much stuff from link from the guitar to the amp as possible, even try one of those shorty cables to link effects and go straight into the amp with that. Does the 60 Hz go away? Try the amp in a different room, any improvement? If yes to either you might have a bad cable (bad being not really very well shielded like only a few of the shield wires making contact with the sleeve pin on the connector). An ohm meter can tell you if this is the case.

[ThermionicScott]

Hi Scott;

In a word, "maybe" I used to design filters for a living. As far as real-time filtering goes a notch is pretty good. A Crystal tuned notch has Q's in the thousands if I remember correctly, ( OK,maybe hundreds, certainly less than 1 Hz bandwidth) . If 60 Hz is really excessive, you may have a funky shield or crappy cables. To narrow it down remove as much stuff from link from the guitar to the amp as possible, even try one of those shorty cables to link effects and go straight into the amp with that. Does the 60 Hz go away? Try the amp in a different room, any improvement? If yes to either you might have a bad cable (bad being not really very well shielded like only a few of the shield wires making contact with the sleeve pin on the connector). An ohm meter can tell you if this is the case.

Well, my main problem is my insistence on using single-coil guitars and basses. I use a 3ft George L's cable most of the time, but I think my house wiring may be noisy as well. There are a couple of needless dimmer switches.

After seeing this, I thought about building a filter, even got most of the way through designing a tube version, but I never followed through with it. Electro-Harmonix makes a "Hum Debugger" pedal, but from what I gather, it filters out the frequencies digitally and adds a slight lag to the signal.

I think if I could just knock down the hum by several dB, I could be happy. A little background hum never killed anyone.

- Scott

[Neo5Bass]

Notch filter design

My only reservation about a filter done in this way is the active elements are only functioning as buffers and not an integral part of the topology. Since all analog filters are termed "resonant" you can never improve the notch function by anything other than the perfectness of the reactances and the ability to match each "T" with this design. That is a real world limit. Even with an unlimited budget you would be hard pressed to get really really high Q's out of it. You would be even more hard pressed to do it for 10 or 20 of them as well.

[ThermionicScott]

My only reservation about a filter done in this way is the active elements are only functioning as buffers and not an integral part of the topology. Since all analog filters are termed "resonant" you can never improve the notch function by anything other than the perfectness of the reactances and the ability to match each "T" with this design. That is a real world limit. Even with an unlimited budget you would be hard pressed to get really really high Q's out of it. You would be even more hard pressed to do it for 10 or 20 of them as well.

Yeah, my intent wasn't to make a production thing out of it. Just one for myself, for those occasions when the noise level is too egregious to be managed through positioning myself and riding the volume knob.

I have to admit, the performance of the TB-5 filter with its Q of 50 looks pretty good to me on paper. A Q in the thousands with a <1Hz bandwidth is probably overkill for my needs.

- Scott

[Neo5Bass]

Overkill

Probably right. If you do build this, your results will be proportional to the match you get on your caps. If you can, use NPO's. Use a LOT of them if you have to. That way if you get the whole thing working, it will act the same 5 even 10 years from now.



Happy playing.

[Steve Conner]

Don't use a notch filter!

1. It'll sound awful.

2. Hum is not just 60Hz. The leakage flux from transformers is rich in harmonics, because of the non-linearity of the iron. So you need a comb filter.

3. Hum is not always 60Hz. The power line frequency can vary +/- 0.2 of a Hz over the course of a day.

[Neo5Bass]

power line leakage

I was trying not to get too geeky but you are right of course. You would have to use a tracking filter to deal with the load dependent rotational variation.

My advice on noise and 60 Hz annoyances is try to keep them out of your high impedance signal chain in the first place.

[Rigpa]

One of my friends once told me that after he went wireless, his noise and hum disappeared almost totally.

[Neo5Bass]

Wireless and Hum

I would guess that would be because of a cabling problem then rather than single coil pickup. I can't comment on wireless for Guitar since I have never used one, but I have noticed a real lack of headroom for a wireless Bass.