Italian Made Gaglio Pickups And The Fantasma System

[Mike Sulzer]

Mike,

I'm just curious what happens to PHASE is this scenario? Would adding the pot allow some phase shifting? That could be useful when combining the output with a piezo saddle.

If you are using a piezo with a preamp, you might as well use an active filter to set the relative phase.

[David King]

Interesting.. But when I ask people about that they say it's not that easy because the phase shift isn't consistent across the frequency range? Maybe because it's easy to shift the phase 180º but we actually need a 90º phase shift
since the piezos are at the end of the string and the mag pickup is approximately 1/4 of the way from the end.

I'm beginning to suspect the the Villex bass pickups are bifilar, capacitively coupled pickups like the Fantasma system. They don't show a DCR so they must have a cap in there somewhere. They also have three leads coming out instead of 2 or 4 and he has a passive midrange pot setup.. Then again it could just be a choke and a cap under the epoxy.

William Villex aka Villen Khanagov has a number of patents including the concept behind the Lace alumitone I believe.
See this discussion on low impedance pus http://forum.ampage.org/forum.php?cmd=vt&tid=5081

[David Schwab]

Interesting.. But when I ask people about that they say it's not that easy because the phase shift isn't consistent across the frequency range? Maybe because it's easy to shift the phase 180º but we actually need a 90º phase shift since the piezos are at the end of the string and the mag pickup is approximately 1/4 of the way from the end.

Right, using an all-pass filter to shift the phase will result in a notching of the spectrum. This is how phase shifters work.

I'm beginning to suspect the the Villex bass pickups are bifilar, capacitively coupled pickups like the Fantasma system. They don't show a DCR so they must have a cap in there somewhere. They also have three leads coming out instead of 2 or 4 and he has a passive midrange pot setup.. Then again it could just be a choke and a cap under the epoxy.

William Villex aka Villen Khanagov has a number of patents including the concept behind the Lace alumitone I believe.
See this discussion on low impedance pus http://forum.ampage.org/forum.php?cmd=vt&tid=5081

That's him, he invented the Transsenssor pickups, which is also the concept used for the Alumitones (only with aluminum and not copper)... so I suspect he's using a similar setup with a transformer, which is also how he has these passive boosters and tone controls.

I have a set of Transsensor P pickups here. They sound pretty good.

[Mike Sulzer]

Interesting.. But when I ask people about that they say it's not that easy because the phase shift isn't consistent across the frequency range? Maybe because it's easy to shift the phase 180º but we actually need a 90º phase shift
since the piezos are at the end of the string and the mag pickup is approximately 1/4 of the way from the end.

There are all pass networks that shift phase with out changing the amplitude as a function of frequency. But this is not simple because in general each string harmonic needs to be shifted by a different phase. I think the phase shift that you need increases linearly with frequency (because it goes up with the harmonic number, or am I over simplifying it?) A phase shift that increases linearly with time is a constant time delay; you can build filters that have approximately constant delay over some frequency range. So this could work for the open string strings. But I think the phase function is different for each fret (think of the effective pickup location moving), so you would have to figure out what is most important. Does this make sense, or is there more (or less) to it?

[David King]

At that point a DSP make a lot more sense...

There's no "passive" phase shifter that does exactly what we want?

[Mike Sulzer]

At that point a DSP make a lot more sense...

There's no "passive" phase shifter that does exactly what we want?

If what I wrote above is correct (and that is a big if), a digital solution would be a lot more practical for doing it exactly. But if you are interested in an approximate solution with a single time delay, that probably could be done analog. (But I am not convinced that I really understand the problem that well!)

[Joe Gwinn]

I do not see the claimed mechanism by which the high frequencies are boosted. This appears to be a way of filtering out lows, with the pot somehow selecting how much are filtered out. (Joe Gwinn, do you see how this might work?)

It strikes me that there will be significant mutual inductance between the windings, although Gaglio makes no mention of this, and may well not know of such things.

Having significant mutual inductance means that the pickup acts like a 1:1 transformer, simultaneously with the capacitance effects. One consequence is that at low frequency with the pot at minimum resistance, the inductance will be four times that at high frequency with pot at max resistance.

We now can do a rough Spice model, if Spice allows one to specify inductances (primary, secondary, and mutual), and self-capacitance. (There are multiple levels of Spice, the better ones costing money.) It will never be precise because Spice assumes discrete components, whereas this pickup has distributed capacitance. But it can be instructive despite the differences.

The stuff on Gaglio's website about deepest bass and highest highs may be figures of marketing speech exaggeration.

I think the quickest way to figure this out is to build a test pickup and do some listening and make some measurements.

[Mike Sulzer]

Thanks, Joe. Building one is a good idea.

Would expect a multi-layer coil with an open core to have an intermediate level of mutual inductance. With that number at hand, one could indeed do the model. That seems like a better approach than working out the whole thing from the fundamentals!

[David Schwab]

It strikes me that there will be significant mutual inductance between the windings, although Gaglio makes no mention of this, and may well not know of such things.

That's a good point, and was actually the way I figured the pickup functioned, more so than through capacitance.

Bill Lawrence has made use of mutual inductance on several pickup designs, where he has a tuned coil to influence frequency response, presumably by lowering the Q of the string sensing coil.

I'm sure these things were discovered by accident, like many other things... one of those "I wonder what this would do?" Then you try to find out why after the fact. You can't measure things you don't know exist, so sometimes you have to trip over them first ...

[Robert M. Martinelli]

That's a good point, and was actually the way I figured the pickup functioned, more so than through capacitance.

+1 Dave, I have read the explanation and he doesn't take inductance into consideration even when talking about the loss of high frequencies....he says that the loss of highs is due to stray ( or parasitic ) capacitance, while we know that inductance is involved in that too....( res. F=1/(2pi*sqrroot(L*C)) ). The pot should serve to alter the Q factor thus widening or narrowing the frequency response ( Q= 1/R*(sqrroot(L/C) ).

AFAIK Mr. Gaglio is a well known luthier, but reading the "tech talk" on his site he looks like he doesn't have an "electronic" background....though I could be wrong.

Regards

Bob

[Joe Gwinn]

Would expect a multi-layer coil with an open core to have an intermediate level of mutual inductance. With that number at hand, one could indeed do the model. That seems like a better approach than working out the whole thing from the fundamentals!

With a true bifilar winding, the coupling between windings should be almost perfect. With a near bifilar, the coupling will be merely near perfect. So, I would start the modeling effort now, without waiting for the experiment.

[Possum]

...

Why dont one of you with time on your hands (not me...) just wind a simple strat pickup and feed two spools of wire into the wind, wire it up like the patent and see what it sounds like in real life, its not that hard a deal, would be more useful that a Startrek holodeck version :-)

[David King]

Well where's the fun in that Possum?

Meanwhile how do we define "bifilar"? Do the strands need to be twisted or merely adjacent?

[Joe Gwinn]

Meanwhile how do we define "bifilar"? Do the strands need to be twisted or merely adjacent?

True bifilar requires the two wires glued together, like zipcord (and/or twisted), and this is required for many RF uses. At RF, the bifilar wire acts as a transmission line, and the spacing between the wires must remain constant to reduce reflections. People building baluns (transmission line RF transformers) usually twist the wire together, then use the twisted pair to wind the core. Of course, a big winding on a balun is ten turns, and a low frequency is 1 Megahertz.

However, at audio frequency, it's sufficient if the wires are adjacent, and I bet that Gaglio just feeds two wires from two spools through the winder.

[Mike Sulzer]

With a true bifilar winding, the coupling between windings should be almost perfect. With a near bifilar, the coupling will be merely near perfect. So, I would start the modeling effort now, without waiting for the experiment.

The bifilar winding means that the flux linking turn n of winding 1 and winding 2 is the same. But is this enough to imply large M?

For a large mutual inductance M = k sqrt(L1*L2), k (which varies between 0 and 1) is 1 (or nearly so). From Close, The analysis of linear circuits, page 335, we have "Physically, this corresponds to the case where all the flux links all the turns of both windings."

The bifilar winding does not mean that turn n of winding 1 has the same linking flux as turn m of winding 2. With the open core, we do not expect this to be the case. I think we have to determine, rather than assume, M.