BPSSC supposedly eliminates 60 c/h. Insights?

[CheshireCat]

This is a new circuit and system from John Suhr that ostensibly eliminates 60-Cycle Hum with single coil guitars, particularly strats, or strat clones (or anything that works with a backplate).

Any insight into this? Has anyone tried one, or heard anything about it? Also, any insight into the workings of it?

I ask because I thought it was an innovative idea, and I was just wondering a few days ago if anyone would come up with such an idea, so I suppose it's time has come.

However, what I don't dig on is the $325 price tag. Ergo, I'd like to make one, or perhaps determine if it's worth it.

For instance, if I did the QTB mod, would this couple with that and create an even more pronounced hum-canceling effect, or if I already QTB'd my guitar would this not really be any more beneficial?

Also, obviously I could try to work out some way of always having my guitar in humbucking mod, but there are some cases where that is not possible, particularly with the middle pickup, and the neck pickup split.

Any thoughts? Insights?

Chesh

PS - Incidentally, I'll be contacting them eventually, but I'd like to have more insight before I dive in.

[jester700]

It's a dummy coil system, but the advantage of using a large coil is that you can use few windings, so it won't load the system and thus decrease your output and high frequencies like many "stacked" pickups do. This one has a trim pot that allows you to "tune" it to your pickup to get the most noise cancellation.

There was discussion over at AMPGE about this - some others have played with the idea before, and thought that Suhr's was a good implementation but yeah - very expensive.

[CheshireCat]

jester700 said:

It's a dummy coil system, but the advantage of using a large coil is that you can use few windings, so it won't load the system and thus decrease your output and high frequencies like many "stacked" pickups do. This one has a trim pot that allows you to "tune" it to your pickup to get the most noise cancellation.

There was discussion over at AMPGE about this - some others have played with the idea before, and thought that Suhr's was a good implementation but yeah - very expensive.

Got a link?

Also, I notice all the grounds run to (or from) the Adjusting PCB, which leads me to think that I wouldn't be able to do my integrated switching in the UUSS, with all the series combos and phase inverted stuff. That would be a draw back.

Any ideas if that effects it?

Incidentally, if I was to dummy coil my Duncan Tele Antiquity, and the single coil version of the Duncan Franken'59, would that pretty much recreate the same effect?

[sumgai]

Chesh,

Yes to your question about building your own dummy coil for your Tele Antiquity, etc.

The business of running the pickup's nominal ground wires to the pcb infer that after installation, no series switching will be taking place, only parallel. After a few moment's cogitation, I think that this limitation can be gotten around, but that's just a theory.

While technically speaking this is not a "smoke and mirrors" thing, there are some questions of design that should be addressed. For instance, putting a coil (of any sort or description) farther away from the signal coil changes the phase relationship between the time the 60Hz hum peak hits the main coil, and the time it hits the dummy coil. In point of fact, this is exactly why the original humbuckers placed the two coils as close together as possible - the cancellation was as near total as possible, and didn't require any adjustments. Doing the remote bit is why they have an "adjustment pcb" - they need to compensate for the time difference in when the peak hits each coil.

IMNSHO, if a guitar is shielded correctly, and quality pickups are installed, then this is a waste of money.


sumgai

[CheshireCat]

sumgai said:

IMNSHO, if a guitar is shielded correctly, and quality pickups are installed, then this is a waste of money.

Well, if I was to do the dummy coils for the single coil of the Franken'59 and the Tele Antiq, what would that need to look like? An almost identical coil (which may be tricky), or just something with the same resistance?

Also, would this additional coil also need a magnet as well?

And if it needed further tweaking, do you think I'd need to do the Adjustment PCB, or rather some version of that?

Chesh

[jester700]

cheshirecat said:

Got a link?

I can't find the one on AMPGE, but I think those go away when they roll off the bottom of the list; they're gone after a short while.

Here's one from the Duncan board, though:
www.seymourduncan.com/forum/showthread.php?t=75915

[sumgai]

Chesh,

IMNSHO, if a guitar is shielded correctly, and quality pickups are installed, then this is a waste of money.

Well, if I was to do the dummy coils for the single coil of the Franken'59 and the Tele Antiq, what would that need to look like? An almost identical coil (which may be tricky), or just something with the same resistance?

Also, would this additional coil also need a magnet as well?

And if it needed further tweaking, do you think I'd need to do the Adjustment PCB, or rather some version of that?

Chesh

For openers, a coil that needs to generate a current (or voltage, if you prefer) can't do so without a magnet, so Yes to that part of your questions.

Resistance, and impedance for that matter, is/are not the issue here. They will play a role in the overall tone, impedance being an integral part of the frequency response formula, but what is at issue here is the physical alignment of the two coils. As noted since the dawn of humbuckers, one magnet must be opposite the other in terms of polarity. (One has its north pole facing towards the string, the other has its south pole facing the string.) For practical purposes, so long as the proper coil alignment is maintained, as above, then all we need to do is compensate for the difference in the signal strength of the hum between the two coils. BTW, this explains why one cannot use an RWRP pickup in the middle position of 3 pickup guitar - that pickup's magnet will not be properly aligned with the one found on the backplate.

A dummy coil is defined as one that will never be used to sense a valid signal (a plucked string). Given that, all we need from such a coil and magnet is some generated voltage that will work against the main coil's hum. Fortunately, we can do that without having to resort to lots of windings of very fine wire (that breaks every 3.8 seconds of a winding job). In fact, we can use active electronics, and amplify a small coil's output to exactly equal the 60Hz signal coming from the main coil, and Voila!, the hum is history. A side benefit is that we can eliminate the imposition of the coil's impedance in our frequency response - the active circuit isolates the coil for us. Nice, eh? But without that active circuit, we would indeed need to nearly match the number of windings in order to get enough voltage of the opposite polarity to cancel the hum. Sadly, the added impedance will be a factor in our final tone.

A final observation, but this is just my opinion....... The close relationship between the two coils and the magnet of a standard humbucker is not just an accident, it was well planned. Lover tried many different layouts along his path to fame, and one thing he found was that coils and magnet constitute a magnetic circuit. Along with that, it became obvious that the further apart you spread the parts of that circuit, the more deleterious the effects of that spread. IOW, if you don't have a good close coupling of the three parts, your results will suffer. When you factor in a fourth part, another magnet for the new dummy coil, you now have what we engineers would call an abomination - the two magnets are not even close to each other, how could one expect to have the same flux current flowing all the parts of the circuit? It isn't likely to happen. (Although I suppose that with strong enough magnets, distance could become less of a factor.)

This is probably the main reason I wouldn't bother with such a toy. It might work on some level, but at what price? For the non-nerd, maybe. For the guitar-geek who knows what QtB means, I don't think so.

But as Hastings would make me say, YMMV! ;D


sumgai

[CheshireCat]

sumgai said:

But as Hastings would make me say, YMMV! ;D

First, "YMMV"?

Second, I'm thinking about this idea. What would that look like? You say a smaller coil that could be ramped up to the right frequency. What would that need to look like? I could possibly imbed such a coil near each pickup, just under the surface of the guitar face. As far as preamping goes, I already have a large multifunctional hub that I'm working on which will involve an octave divider and some other circuits, and this might be something that could be factored in. What would that look like?

Chesh

[sumgai]

Chesh,

But as Hastings would make me say, YMMV! ;D

First, "YMMV"?

Just trying to cover my butt, that's all.

Second, I'm thinking about this idea. What would that look like? You say a smaller coil that could be ramped up to the right frequency. What would that need to look like? I could possibly imbed such a coil near each pickup, just under the surface of the guitar face. As far as preamping goes, I already have a large multifunctional hub that I'm working on which will involve an octave divider and some other circuits, and this might be something that could be factored in. What would that look like?

Chesh

Errr, not the frequency, Chesh, that's established at 60Hz. (But perhaps you merely mis-spoke.) We only need to boost the voltage level to match, or nearly match, that of the hum coming from the main signal coil. To cancel hum, two voltages must be equal in strength but opposite in polarity. Any small signal amlifier circuit will do the job, use whatever spare or leftover stages you may have on hand. I see no reason to go to any special lengths for this, it's all very pedestrian.

I can't fault you for wanting to try this, from an experimental point of view. If you think this will be of benefit, and you are more than willing to invest the time and effort, please, be my guest. My only complaint is with companies that offer a "be all, do all" solution at a greatly inflated price for something that "is guaranteed" to work as advertised. I liken that to snake-oil salesmen, and I take great delight in running them out of town. Call it a personal quirk of mine. ;D

The real 'hidden' kicker here is, you may succeed, and that may drive you to try your invention on other guitars. If you keep succeeding, you just may go into business (maybe only a sideline, but hey....) and become a competitor to the 'high-priced' spread. IMO, that would be a good thing. (And no, they can't patent their goodie, it's been done to death - prior art and all that.) At that point, I might have to eat a little crow as you grow into a mega-conglomerate that defied my nay-saying so long before, but until then, I still think I'll sit this one out, if you don't mind.


sumgai

[ChrisK]

When you factor in a fourth part, another magnet for the new dummy coil, you now have what we engineers would call an abomination

I wouldn't actually use a magnet in the dummy coil (unless yer interested in yer belt buckle's movement aboot)! (Or unless one is tracking an inadvertently swallowed cow magnet, wait, embedded magnet afoot.)

I also wouldn't worry aboot the field sensing time lag between coils (something to do with the speed of light/electricical fields or something).

Unmagnetized core material might be best (dead magnets).

First, have identical windings in number and direction (phase is just hookup wire related, oops, here we go again....). Second, have identical inductance. Third, have fun.

A passive dummy coil will drain the signal, but cut the highs less (low pass path to common). A series dummy coil will raise the output impedance, but retard the highs (low pass path to output).

One might as well use active subtraction and get a cable buffer to boot.

[CheshireCat]

sumgai said:

Just trying to cover my butt, that's all.

No, define "YMMV". I've never heard that acronym before.

sumgai said:

I see no reason to go to any special lengths for this, it's all very pedestrian.

No, please do. I'm still not getting the concept on a comprehensive level (and, yes, I probably used the wrong term).

If this is something as simple as ramping up a bit of coil, like something akin to a cell booster or something, with a simple preamp, that's very doable. The only sacred cow in this whole equation is the Utah itself. As long as it maintains it's Utahness, everything is totally open game.

chrisk said:

One might as well use active subtraction and get a cable buffer to boot.

Explain.

Chesh

[ChrisK]

Chesh,

YMMV = Your Mileage May Vary. (Your results might vary.)


One could use a relatively identical pickup with dead magnets or equivalent core material. This pickup should be oriented in the exact same attitude as the other pickups (attitude is an aircraft term that infers the same XY orientation, Z would be the inter-pickup spacing).

Connect this coil to a preamp circuit (as in an OPAMP). Run the desired guitar signal into an identical OPAMP stage. Sum the difference in a third OPAMP stage. If the hum is bad, reverse the dummy coil leads to the OPAMP. You might want to use trimmer pots for adjustment of the subtractive hum signal.

Keep the gains low (under 5) to maximize signal headroom, on the order of 1 VAC peak output.

You now have an active hum reducing circuit, a guitar signal booster/over-driver, and have eliminated the effects of cable capacitance thru the much lower output impedance of the OPAMP.

I can help you with the topology of the OPAMP circuits if needed.

[CheshireCat]

chrisk said:

YMMV = Your Mileage May Vary. (Your results might vary.)

Ah. Clever.

chrisk said:

I can help you with the topology of the OPAMP circuits if needed.

Alright, now we're cookin'!! Let me chew on this a bit.

[CheshireCat]

Is there a way to notch filter out 60 cycle hum?

[UnklMickey]

yes............................and no.


it would require an extremely sharp notch.

the low E on a guitar (E₂) is much less than an octave above 60Hz (B^b₁~B₁). just slightly more than a perfect 4th.

so unless you want to have a very weak bottom end on your guitar, or use Nashville tuning, the notch must be very sharp to be effective in reducing 60Hz.

sharp filters usually sound bad near the notch so even if the bottom notes are nearly normal in amplitude, the distortion will probably be undesireable.



bottom line:

it's more practical to cancel, than to filter.



unk

[ChrisK]

One could do a notch filter, which would preserve any subharmonic effects going on (unk, the fundamental is at play here as well).

One could also do a high pass filter, but due to the closeness of the pass band to the stop band, many stages would be needed. Certain topologies could be used to reduce this, but pass band ripple results and phase (filter phase) gets GeFooey. A Bessel topology is the best for equal phase delay, but it has the softest cutoff of any topology.

An active filter would be required due to the significant insertion loss from a passive.

I don 't remember which city I left my A. B. Williams filter book in, but it doesn't appear to be this one. I can rapidly determine the order and topology needed, but only with the shortcuts in this book. Longhand is, well, much longer.


Although, if you were to relocate to Europe (50 Hz) it would be easier. ;D

Or like, remove the low E string like on MacGiver or whatever name Keith Richards gave to his Tele. ;D ;D

Heck, I had enough trouble getting around to naming my children. ;D ;D ;D

[CheshireCat]

chrisk said:

One could do a notch filter, which would preserve any subharmonic effects going on (unk, the fundamental is at play here as well).

One could also do a high pass filter, but due to the closeness of the pass band to the stop band, many stages would be needed. Certain topologies could be used to reduce this, but pass band ripple results and phase (filter phase) gets GeFooey. A Bessel topology is the best for equal phase delay, but it has the softest cutoff of any topology.

An active filter would be required due to the significant insertion loss from a passive.

I don 't remember which city I left my A. B. Williams filter book in, but it doesn't appear to be this one. I can rapidly determine the order and topology needed, but only with the shortcuts in this book. Longhand is, well, much longer.


Although, if you were to relocate to Europe (50 Hz) it would be easier. ;D

Or like, remove the low E string like on MacGiver or whatever name Keith Richards gave to his Tele. ;D ;D

Heck, I had enough trouble getting around to naming my children. ;D ;D ;D

So, if you had that book, you could come up with a workable model that would have no ill or undesirable effects?

[ChrisK]

No, I could come up with models, workable will be determined by ear since the stop band and pass band are sooooo close.

[CheshireCat]

chrisk said:

No, I could come up with models, workable will be determined by ear since the stop band and pass band are sooooo close.

How involved would the circuits be, and would they be more involved than doing it the other way with the active pickup and the dummy coils if we were to factor in phase inverting as a sonic option?

[ChrisK]

Well,

I found my filter book. Standard filter topologies will be untenable due to the closeness of the stop band to the pass band. For a 1,000 to 1,300 Hz ratio, an elliptic topology (ripple in the stop band as well as the pass band) with a pass band ripple of 0.2dB and a stop band floor of 60dB will require a 7th order filter (7 reactive elements). This infers three OPAMPS.

By comparison, a Butterworth topology will require a 27th order filter (13 OPAMPS).

The order can be reduced by increasing the allowable pass band ripple (non-linearity) and the stop band floor (less 60 Hz rejection).

I'll look at some inter-relationships and get back to you.

Numerical evaluation of elliptical filters is somewhat difficult without a significant "engine".

[ashcatlt]

I'm glad we got over the idea of needing magnets. We're not trying to build a transducer, we just want an antenna. A couple of turns of wire should do it.

Since you mentioned the QTB deal, I'll point out something that should be rather obvious. If the dummy coil is inside the foil shielding from your QTB mod you shouldn't get any noticeable cancelation.

The phase angle of the 60Hz hum induced into the dummy coil will be a little bit off from that of the other pickups. This means that you won't get total cancellation, but you can come close due to the actual lenght of a 60Hz wave. For proof of this simply consider that the distance between the neck and middle pickups on a strat doesn't have much effect on the hum-cancellation.

Theoretically, this phase difference could be compensated for by the length of the wire between the two coils. Considering the length of the wave, though, this is impractical. Oh yeah, and all that wire would have an adverse effect on the sound.

As for "notching out" the hum... Well coming from an audio engineering (as opposed to electrical engineering) standpoint, I find that unless the guitar is the only instrument in the mix, there isn't a whole lot of information that I really want in the guitar signal below the fundamental of the lowest string anyway. Many people will beg (possibly scream) to differ, but I tend to low-cut guitars somewhere around 75-80Hz, and I've found that even 100 doesn't hurt all that bad in most situations.

The problem with this is that the most offensive thing about what we call 60 cycle hum is not, in fact, that 60Hz fundamental wave, but rather the higher frequency harmonics (multiples) of 60Hz which is what gives that characteristic buzzing noise we all know and love. A tuned comb filter might do the trick, but in order to get significant reduction in the "noise" you would generally have to completely screw over your guitar.

All that being said, I'd like to mention that unless you've got a ground loop or something fairly seriously wrong with your equipment (including the wiring of your space) or are playing under flourescent lights or standing right next to a computer 60 cycle hum is usually only a problem when your standing around between songs or possibly during the quietest passages of an extremely dynamic performance.

When you are hitting the strings with any moderate amount of force the actual guitar signal will generally be loud enough to mask all of this noise.

[UnklMickey]

Ashcatlt,

(is it okay if i call you Ash ? )



most of that is spot on!

since EM radiation travels at about the speed of light ~186,000 miles per second, one degree of a 60Hz signal would be:

(186,000 / 60) * 91 / 360) = 8.6 miles (approx)

so i don't think we need to worry about the distance.



but to maintain the same harmonic content, and amplitude it would be easy if the coils have the same reactance and number of turns.

that's why Chris mentioned "dead magnets".

if you have pole pieces that are not magnetized, they will cause an identical coil to have the same inductance, but not do any string (or belt-buckle) sensing.

not only will the difference in inductance affect the relative harmonic content (lower inductance will allow more high-frequency content), it will also affect the phase angle a little bit.



so a coil that is the same as the pickup would definitely be easy to work with.

you wouldn't need to provide any active components (gain).


fewer turns and the same ratio of inductance to resistance should be workable.

the phase angle and harmonic content will be the same, so now all we need to do is add some gain.


good point about having the cancelling coil inside a shielded cavity.

definitely want it in a similar environment as the pickup we are using it with.

and oriented in the same axis.




"...60 cycle hum is usually only a problem when your standing around between songs or possibly during the quietest passages ..."

very true.

but if you are using a ton of gain, and have an electrically noisy environment, instead of dead silence at the end of the song, you have hum, until you turn you volume down.

i'm sure there are lots of live recordings that have captured exactly that problem.




this is turning into quite an interesting thread, don't you think?




unk

[ChrisK]

unk,

Regarding

fewer turns and the same ratio of inductance to resistance should be workable.

the phase angle and harmonic content will be the same, so now all we need to do is add some gain.

methinks that the phase angle won't be similar, and the (sensed) harmonic content will be a function of the LCR of the dummy coil (absolutes when it comes to transfer function). A filter with a given resonant frequency (LCR) has a different phase angle as one tuned for a different frequency at any given frequency. The signal phase angle goes thru 90 degrees at resonance for a single pole filter (the laws of physics (are)).

While one "could" take the tack that we only care about 60 (or 50) Hz, in reality it's often the EMF from other sources as well (such as CRTs or even LCDs around 15 kHz) that contribute to noise susceptibility.

In a passive only scenario, I would use exactly the same pickup as the ones that I'm trying clean up, and kill the magnets. This can be accomplished with a transwarp dewobbulator (well, a strong AC driven electromagnet where one slowly moves the electromagnet away from direct contact with the dewobbulee's pole piece). Just shutting the AC off will leave random phase-based magnetic polarity.

since EM radiation travels at about the speed of light ~186,000 miles per second, one degree of a 60Hz signal would be:

(186,000 / 60) * 91 / 360) = 8.6 miles (approx)

Yeppers!,

Based on the 2 meter amateur band having a wavelength of like 2 meters or something, a 60 Hz wavelength would be:

145,000,000/60*2 (meters) = 4,833,333
times 39.37 (inches in a meter) = 190,288,333 inches
divided by 12 (inches in a foot'ski) = 15,857,361 feet
divided by 5,280 (feet in a mile'aroni) = 3,003 miles

If yer pickup is in New York, and yer dummy is west of the Mississippi, you might have an issue. ;D


ashcatlt,

Since you mentioned the QTB deal, I'll point out something that should be rather obvious. If the dummy coil is inside the foil shielding from your QTB mod you shouldn't get any noticeable cancelation.

I would like to mention that if the pickups are located within the shielding, you want the dummy to also be so located, or you will inject more noise than you would have picked up without the dummy coil.

The problem with this is that the most offensive thing about what we call 60 cycle hum is not, in fact, that 60Hz fundamental wave, but rather the higher frequency harmonics (multiples) of 60Hz which is what gives that characteristic buzzing noise we all know and love.

It's also the NON-harmonics (unpredictable) that come from the older switching power supplies and AC phase cutting going on in the modern, new and improved world. (Hint, don't operate the Tesla coil while yer playin' aboot.)

[ChrisK]

chesh,

I spent a few hours reviewing filter topologies and realization circuits. If you want to proceed, a state-variable bi-quadratic transfer function elliptic filter may be best. This topology allows setting all capacitors to the same value and adjusting pole/zero locations by trimming resistors. (Yes trimming since an accurate and functional design requires 1% resistors AND capacitors.)

[CheshireCat]

chrisk said:

I spent a few hours reviewing filter topologies and realization circuits. If you want to proceed, a state-variable bi-quadratic transfer function elliptic filter may be best. This topology allows setting all capacitors to the same value and adjusting pole/zero locations by trimming resistors. (Yes trimming since an accurate and functional design requires 1% resistors AND capacitors.)

Interesting. How would that work? And would it eat into the guitar signal? Also, if I was to use an octave divider with a dedicated pickup for the E and the A strings, would that have an impact?

Chesh

[ChrisK]

Chesh,

While I can't really quantify "eat into the guitar signal", one can adjust each pole or zero independently with such a topology. One can also make trade-off's, as far as depth of attenuation vs pass band ripple.

When Laplace transforms are used to describe filter responses with polynomials, poles occur in the numerator and zeros occur in the denominator. For simple filters, an all-pole design is used. While simpler, their attenuation is more gradual than complex filters, but they don't have pass band (or stop band) ripple.

For a 0.2dB pas band ripple (which incurs about a 14dB gain penalty) the actual ripple is about 3+ % (which probably is nowhere discernible). Backing off to a greater pass band ripple incurs a lesser penalty. The maximum gain achievable for a given number of stages is related to the maximum topology gain minus the "penalty" for pass band ripple.

Rather than get into photographing pages of the book and posting them (copyright infringement), I can email some to you as we get further along and you need them. Tuning these filters will be another story. I usually tune with a digital meter, but then I cheat by using my stock of 1% film capacitors (which I will not part with). One can also cheat by using an LCR meter, which I also have, but they run from about $250 for a low-cost one on up. I've only found one (the BK which is out of print) suitable for pickup measurement. I got mine at Frye's in Seattle a couple of years ago.


If you are using the separate pickup for the two strings to drive an octave divider, unless the 60 Hz noise exceeds the trigger point for your divider, I don't think that you'd need a complex filter for it. Maybe something simple would suffice.