Electro-Harmonix Hum Debugger

[Gilles C]

Producing noise is fun... but not 60Hz noise. You want to get rid of it.

How could we emulate this box?

http://www.gearwire.com/electro-harmonix-humdebugger.html

Check the video.

I need one, using almost exclusively single-coils.

Gilles

[KerryF]

Yea please.  I need something like this!

[R.G.]

Hum notchers have been available in PA equipment for a while. They're usually a very deep notch at the power line frequency.

The problem has always been that the power line frequency is very well controlled and the notch circuit drifts. So the PA stuff always had a tuning pot, which I don't see on the box at hand.

I'm guessing that they went to a switched-capacitor filter driven from a crystal for frequency stability.

You can do much the same thing with a variable twin-T filter and Q-enhancement (See parametric EQs, GEO) to get a very deep, very thin notch. But you'll have to leave it tunable without the frequency stabilization because ordinary Rs and Cs drift. The schemo is just the schemo for the enhanced Q twin T in the article.

[Mark Hammer]

Hmmmm...

I was gonna say that it was DSP-based notch-filtering.  A few things suggest this.  One, the pedal is bigger than one would expect for an analog device.  Two, there are no knobs to adjust sensitivity or levels of anything, yet it acts like a brickwall filter, so I'm guessing there is an intelligent adaptation to the nature of the signal itself.  Three, E-H has already taken a few steps towards DSP, why not take some more.

Having said that, Brother Keen is correct about the legacy of anti-hum notch filters that preceded DSP-based filtering.

My own instincts tell me that if one takes the analog DIY route, it would be a mistake to place too much emphasis or dependence on any one/single mechanism.  For instance, noise gates are fine but trying to control all your noise with a gate leads to mishaps with the attack and tail of notes.  Deep notch filters can take on hum, but they can be inaccurate and screw up your low end.  And, as currently discussed on the OT-Lounge forum, dummy coils can work to reduce the hum-sensitivity of single coil pickups, but they have their limitations too.

So, in the grand scheme of things, unless one has some sort of perfect digital solution, my own inclinations are to lean all these various analog methods up against each other and provide multiple redundant (but gentler) noise reduction.  An imperfect dummy coil can reduce the amount of hum fed to the effects chain.  A notch filter and very gentle gating or downward expansion can further tame any residual hum without destroying the initial attack of notes or making 12" speakers all confused.

The "ideal" gate, I suppose, has some modest notch filtering on input, detects the envelope of what comes after that, sends the signal out in a loop to one's other effects, and applies that gating action (using the input-driven sidechain) at the tail end of any and all effects.

[StephenGiles]

It may well work in a similar way to the noise reduction in software such as Cool Edit Pro as was, and currently Adobe Audition, in the digital domain.

[Gilles C]

Then for a first try, a dummy coil being effective in a guitar when used in parallel with a pickup, I am wondering if it could be installed in a box to be used with any guitar connected to that box. It would mean using a non metal box maybe so that the magnetic field is used.

Or maybe a cancellation circuit as was used in telephone circuits before, in the old time...

I was thinking about a tuned high Q circuit but you gave me a reason why it is not already used.

Some info:

http://www.analogzone.com/avt08062.htm

http://www.analogzone.com/avt08062.pdf

That could be interesting totry, with good components.

Added:

Something like this too

http://www.vtx.co.uk/video/hs2.htm

And finally, a simple passive design

http://www.edn.com/index.asp?layout=article&articleid=CA6309113&spacedesc=DesignIdeas&taxid=10536&industryid=44217

Could this be used?

http://www.avens-filter.com/avens-new/notch_filter.htm


Gilles

[Plectrum]

Then for a first try, a dummy coil being effective in a guitar when used in parallel with a pickup, I am wondering if it could be installed in a box to be used with any guitar connected to that box. It would mean using a non metal box maybe so that the magnetic field is used.

The only thing is, for a "perfect" humbucker to work, the two coils should occupy the same point and orientation in space, therefore in respect to the state of the local interference. As this is impossible, coils are in close proximity and the further one is from the other, the lower the likelyhood of effective cancellation.

[TELEFUNKON]

who in the box decides if you got western 60Hz or eastern 50Hz bugging you?

[Jeremy]

I don't know if anybody else has noticed, but the hum debugger runs on an AC power supply.  It takes either a 9 or 12 volt AC power input.

This is important.

My guess is that the hum debugger uses a portion of its own power supply to cancel out the 60Hz hum in your signal. 

And if it doesn't, somebody should design a pedal that does.

[Gilles C]

Exact...

Btw, in my searches, I noticed a site where they say they sample the power from the main instead of from a transformer for a correct working.

Gillles

[Mark Hammer]

In which case, that's one VERY smart product.

[joelap]

Beh... not sure how much you'd really want to emulate that box... my buddy got one and at anything other than low volumes it produces some nasty, metallic overtones to the guitar signal.  Definately not something you'd want to straight up clone, but probably something worth improving upon.  Just FWIW, if you've never tried one.

[Nasse]

I remember some old magazine article suggesting two notch filters in series, one for fundamental mains freq and other two times it (like 60 Hz and 120 Hz and 50 and 100 Hz)

[TELEFUNKON]

who in the box decides how much amplitude you need
to cancel the hum?

[zjokka]

The technology might be very intelligent, I'm hardly in a position to electronically judge.

From a practical point of view I just notice how he takes great pains to create the hum...

A demonstration of guitar hum with a double hum-bucker?   Ah he switches to single coil mode? I don't know the brand of guitar he's using, but a double humbucker axe is not devised for one single coil use. Most of those types aren't even wired for single coil mode, but anyway it's very unlikely these guitars are shielded to the extent a good strat is.

By having to select single coil mode to have hum, he proves the source of the hum is the guitar. Then he kicks in a muff to create even more hum which is only logical as everything (including the hum) is applified. Shouldn't this problem be tackled at the source rather than at the music store. If you really dig playing on one single coil on you Les Paul, shield it ... er, or buy a Strat or something. And shield it...  

maybe long pedal chains benefit from this, don't know but that's not even demonstrated in the video



no?
zj

[TELEFUNKON]

shielding:
is one sided shielding - the other sides is needed to pick up what the strings produce (and what the environment introduces)!

[Meanderthal]

they sample the power from the main

How is that possible when using a 9v battery?

[TELEFUNKON]

they sample the power from the main

How is that possible when using a 9v battery?

see reply#9 :

Exact...

Btw, in my searches, I noticed a site where they say they sample the power from the main instead of from a transformer for a correct working.

Gillles

& reply#8:

I don't know if anybody else has noticed, but the hum debugger runs on an AC power supply.  It takes either a 9 or 12 volt AC power input.

This is important.

My guess is that the hum debugger uses a portion of its own power supply to cancel out the 60Hz hum in your signal. 

And if it doesn't, somebody should design a pedal that does.

[Meanderthal]

 Yes, I read those... and that's what confused me... hence the question. With no connection to the main ac power how would they determine the exact frequency to notch? Jeeze, you were asking almost the same question.(who in the box...)

Oh, and I looked it up. It runs off a 7.5vac 200ma adaptor, or a 9v battery.

[Gilles C]

Beh... not sure how much you'd really want to emulate that box... my buddy got one and at anything other than low volumes it produces some nasty, metallic overtones to the guitar signal.  Definately not something you'd want to straight up clone, but probably something worth improving upon.  Just FWIW, if you've never tried one.

Thanks, I never tried one, but always thought it would be a nice box to own if it works. Seems it's not so good.

I normally use my Strat in positions 2 or 4 because of the hum in the other positions. And it is really well shielded. But a Strat is a Strat...

A delay is used in some systems to detect hum. What's repeating is hum. What's not repeating is signal. But I don't think it would work with a guitar.