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Cycfi

Hexaphonic Pickup Project

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On a related note, I tried a secondhand Moog guitar yesterday just for the hell of it. I suspect that this particular example was badly set up, or had something wrong with it as it didn't work as well as shown in some of the Youtube videos I'd seen of it, but it was a lot of fun to play with nonetheless. Sustain appeared to be weaker, and the "mute" function only just worked. I guess the drivers weren't imparting enough "oomph" on the strings - too far from the strings? Strings were old? Not enough amplification? I notice on the Moog website that they recommend strings with a high steel content, even going as far as saying that the guitar works best with their own "specially formulated" strings.

The thing that struck me was how well it could sustain cleanly with any pickup, something that the DIY sustainer and the Ebow always struggled with. With the DIY sustainer and Ebow there is always a degree of background distortion/fuzz superimposed on the raw guitar output. From memory the general concensus during the development of the DIY sustainer was that it was largely due to the driver circuit being horribly overdriven, and the proximity of the driver to the guitar pickup inductively coupled the noisy driver signal back into the pickup. The Moog guitar had none of these artifacts, which made it so much more appealing to me as an example of an instrument fitted with some kind of infinite sustain system. I love using an Ebow, but I hate that I can't use it for clean sounds.

There wasn't an awful lot I could gather about the technology behind the pickups/drivers during my brief encounter with the instrument (the sales assistant admitted he didn't know anything much about it either, other than the pickups were based around rare earth magnets), and there doesn't seem to be much revealing information floating around on the net.

The eventual deal-breakers for me were the facts that it didn't work quite as well as the videos I'd seen of it, and the that it was fitted with a bunch of on-board filters for synth-type sounds that always seem to be applied to the guitar signal even when wound all the way back, something that I could definitely live without - if I wanted my guitar to sound like a Moog synth from the 70's I would use external processing. Because of the fancy filter/tone controls I never really felt like there was any setting that let me listen the natural sound of the guitar. I guess Moog have included it to add extra credibilty to the brand name. The implication that I need to buy Moog-branded strings to get the best performance out of it was also not encouraging. However if Moog (or some other manufacturer for that matter) could offer the hexaphonic sustain system minus the filter processing as a kit I'd buy it in a heartbeat.

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On a related note, I tried a secondhand Moog guitar yesterday just for the hell of it. I suspect that this particular example was badly set up, or had something wrong with it as it didn't work as well as shown in some of the Youtube videos I'd seen of it, but it was a lot of fun to play with nonetheless. Sustain appeared to be weaker, and the "mute" function only just worked. I guess the drivers weren't imparting enough "oomph" on the strings - too far from the strings? Strings were old? Not enough amplification? I notice on the Moog website that they recommend strings with a high steel content, even going as far as saying that the guitar works best with their own "specially formulated" strings.

The thing that struck me was how well it could sustain cleanly with any pickup, something that the DIY sustainer and the Ebow always struggled with. With the DIY sustainer and Ebow there is always a degree of background distortion/fuzz superimposed on the raw guitar output. From memory the general concensus during the development of the DIY sustainer was that it was largely due to the driver circuit being horribly overdriven, and the proximity of the driver to the guitar pickup inductively coupled the noisy driver signal back into the pickup. The Moog guitar had none of these artifacts, which made it so much more appealing to me as an example of an instrument fitted with some kind of infinite sustain system. I love using an Ebow, but I hate that I can't use it for clean sounds.

There wasn't an awful lot I could gather about the technology behind the pickups/drivers during my brief encounter with the instrument (the sales assistant admitted he didn't know anything much about it either, other than the pickups were based around rare earth magnets), and there doesn't seem to be much revealing information floating around on the net.

The eventual deal-breakers for me were the facts that it didn't work quite as well as the videos I'd seen of it, and the that it was fitted with a bunch of on-board filters for synth-type sounds that always seem to be applied to the guitar signal even when wound all the way back, something that I could definitely live without - if I wanted my guitar to sound like a Moog synth from the 70's I would use external processing. Because of the fancy filter/tone controls I never really felt like there was any setting that let me listen the natural sound of the guitar. I guess Moog have included it to add extra credibilty to the brand name. The implication that I need to buy Moog-branded strings to get the best performance out of it was also not encouraging. However if Moog (or some other manufacturer for that matter) could offer the hexaphonic sustain system minus the filter processing as a kit I'd buy it in a heartbeat.

Very good points. Moog filters are nice, but having them always on? That's not good. I'm assuming it's all analog, am I correct? I'd expect that from Moog.
I believe that a pure analog approach would be difficult to achieve. Well, I know Moog did it but I also know that it can get better still. A DSP based system has the clear advantage of having the ability to analyze the sound and react dynamically. An "active-resonance" system, as I fondly call it, should be able to give just the right amount of pull (pull only! no need for push! magnets are only able to pull the strings anyway) at exactly the right time and phase. IMO, the analog approach we see in the current generation sustainers use a brute force approach that requires and wastes lots of energy. I imagine it like a swing. You need only a little nudge at exactly the right moment to get it going indefinitely. Hey, you can make even the strongest bridge collapse with just the right amount of force by tuning in on its resonant frequency. IMO, an active resonance system is the key.
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Hi!

This is part 3 of the “Let it breathe” series. For proper context, you might want to check out Part1 and Part2. This third and last part of the series concludes with actual frequency response measurements for various coil configurations of the Hexaphonic Pickup Project and with the Fender Stratocaster middle pickup as benchmark to compare against. In addition to standard windings with 500, 1000, 1500, 2000, 2500 and 3000 turns AWG 42, we also tested bifilar windings (see Alternative Ideas) with 500 and 1000 turns AWG 42. Like before, the low-power LME49726 OP Amp is used in the differential preamp stage with a gain of 5.

See this link for more: Let it breathe (part 3): Frequency Response

freq-response.jpg

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Very good points. Moog filters are nice, but having them always on? That's not good. I'm assuming it's all analog, am I correct? I'd expect that from Moog.
The typical LPF "ladder" Moog filter is offered as a switchable option, along with a resonant filter mode and an active tone control, none of which I particularly liked or really saw the need for - there was no "off" option. Not sure if it was all analogue, can't find any info on the circuitry behind it. There are a couple of shots of the instrument with it's back cover removed floating around on the net. It's definitely a complex beast and relied on external power from the included foot pedal.

I believe that a pure analog approach would be difficult to achieve. Well, I know Moog did it but I also know that it can get better still. A DSP based system has the clear advantage of having the ability to analyze the sound and react dynamically. An "active-resonance" system, as I fondly call it, should be able to give just the right amount of pull (pull only! no need for push! magnets are only able to pull the strings anyway) at exactly the right time and phase. IMO, the analog approach we see in the current generation sustainers use a brute force approach that requires and wastes lots of energy. I imagine it like a swing. You need only a little nudge at exactly the right moment to get it going indefinitely. Hey, you can make even the strongest bridge collapse with just the right amount of force by tuning in on its resonant frequency. IMO, an active resonance system is the key.

Based on what I've experienced with sustainers (DIY/Ebow/Moog et al) the biggest hurdle is the driver. Making something that only imparts the excitation signal on the string and nothing else appears to be something that is inherently difficult to overcome given guitarists desires to rely on inductive high-impedance pickups. Moog have obviously done an admirable job on their driver/pickup technology, even if they have been a bit one-eyed in their implementation of the system.

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Found this picture recently regarding another Paul Vo invention (the guy behind the Moog guitar). If you scroll to the bottom of this page you can see a blurry image of his VO96 acoustic guitar hex sustainer being tested. You can just see that each pickup appears to comprise two coils per string (one driver, one pickup?), each string pair being slightly offset from the next so that they all align properly with the strings. I guess this acounts for the Moog guitars' trapezoid-shaped pickup covers.

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Found this picture recently regarding another Paul Vo invention (the guy behind the Moog guitar). If you scroll to the bottom of this page you can see a blurry image of his VO96 acoustic guitar hex sustainer being tested. You can just see that each pickup appears to comprise two coils per string (one driver, one pickup?), each string pair being slightly offset from the next so that they all align properly with the strings. I guess this acounts for the Moog guitars' trapezoid-shaped pickup covers.

Woa! Nice find! My best guess is that both the pickup and the drivers are phase-inversed (humbucking style) to cancel out the actual EM being generated.

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Hi!

After countless hours experimenting and iterating over the basic design, I think I’ve reached a point where I have something that I am actually finally satisfied with. Here now, let me present version 1.0 of the Six Pack Hexaphonic Pickup. The design is modular. Visible in the xray view below, the Hexaphonic Pickup actually contains three smaller dual active pickups sitting on a main board which contains no more than biasing electronics and a micro-miniature header connector.

Assembly-Perspective-Xray.jpg

Read more about it following this link.

Features:

  1. Six low impedance coils (2000 turns, 450Ω D.C. Impedance, flat frequency response, 20Hz-20kHz).
  2. High performance, ultra low noise OPA209 (OPA2209, dual) differential Op Amps.
  3. Single supply (4.5V to 36V).
  4. Stainless steel height adjustment screws and springs.
  5. Gold plated, 1 mm pitch micro-miniature positive lock connector (Hirose).
  6. Premium 0.1% thin film low noise matched resistors.
  7. Fender Stratocaster Profile (11.8 mm height excluding connector).
Edited by Cycfi
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Nice! Looking good so far! For a low power version, perhaps there are other opamps to consider? You could probably run on less than 1mA... for all 6 coils.

I suppose your using neo magnets? If you haven't already, I'd suggest playing around with FEMM a bit to see if you can improve magnetic containment a bit. To be honest, I'm not sure neo mags are the best way to achieve what your trying to do. They can be useful, look at ways they have been used in pickup design historically. I suppose in a way this goes hand in hand with bifilar winds too.

Speaking of, did anything come of the bifilar windings? Any reason for or against it? I still have a project(on hold for the moment) based on bifilar designs.

Keep up the good work!

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Nice! Looking good so far! For a low power version, perhaps there are other opamps to consider? You could probably run on less than 1mA... for all 6 coils.

Yes. Scroll down a little bit: OPA376 is a lower power option at 760μA. Even lower power? Then how about OPA314 at 150μA. I have a list of Op Amps here: http://www.cycfi.com/projects/six-pack/op-amp-shootout/

And... in yet another development, I might be considering an alternative floating, single-ended, pseudo-differential design. For low-power, single stage discretes rule.

I suppose your using neo magnets? If you haven't already, I'd suggest playing around with FEMM a bit to see if you can improve magnetic containment a bit. To be honest, I'm not sure neo mags are the best way to achieve what your trying to do. They can be useful, look at ways they have been used in pickup design historically. I suppose in a way this goes hand in hand with bifilar winds too.

Please tell me about FEMMs and why they would be better.

Speaking of, did anything come of the bifilar windings? Any reason for or against it? I still have a project(on hold for the moment) based on bifilar designs.

It turns out that the current design is already optimal WRT noise and I was not able to squeeze more from using bifilars. A better approach, and one that I am taking now, is to take advantage of the multiple coils and have the coils alternate from north-south pole orientation, clockwise winding for the 1st, 3rd and 5th coils and south-north pole orientation, counterclockwise winding for the 2nd, 4th and 6th coils. That way, the sum of the pickup outputs will cancel some more of the noise the same way humbuckers do. It is possible to isolate the noise from the signal as well as do more advanced cross-talk cancellation in DSP.

Keep up the good work!

Thank you! I appreciate all the inputs I get.

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FEMM 4.2 is a free magnetic modeling program. While limited, it can be very useful in visualizing magnetic fields and relative strength. I would suggest researching noiseless stacked coils for some examples of use of neo magnets. Lace pickups also have many interesting concepts, though many remain patented.

As for the bifilar coils, I'd be more interested in output vs size (sensing area related) Of course, these coils would have little effect on noise ratios from a design standpoint, and would need to be wired as you are doing with sets.

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FEMM 4.2 is a free magnetic modeling program. While limited, it can be very useful in visualizing magnetic fields and relative strength. I would suggest researching noiseless stacked coils for some examples of use of neo magnets. Lace pickups also have many interesting concepts, though many remain patented.

As for the bifilar coils, I'd be more interested in output vs size (sensing area related) Of course, these coils would have little effect on noise ratios from a design standpoint, and would need to be wired as you are doing with sets.

Thanks! I just googled a bit after relying. I'll definitely look into that. For now, I'm quite satisfied with the coils and it serves its purpose well. There are still bigger fish to fry and I need to move on.

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...and they're definitely the guys to be doing it! I was very much in agreement with RedHouse's statement on how we have gone through decades of iterations on losing the noise and perhaps trading off some of the "positive faults" inherent in old noisy gear. There are only 24hrs in a day and between building we should at the very least be playing too. I certainly spend far too much time hunting for better tones in my gear instead of improving my chops :-)

That isn't to say that this will not be a fantastic project. Maybe it'll make some of that old noisy vintage gear sound a little less so!

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I like it a lot! Very clean.

I'm still not convinced on the neo magnets though, and you could still improve the magnetic design aspect a bit. If you can squeeze a bit more output from these coils then that would be less noise out since a big source of noise is from amplification. Also, narrowing or manipulating the magnetic field will improve issues with noise and crosstalk.

Do you have room under the pickup to place magnets? Or room for a small and compact enclosure system around the coil sets?

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...and they're definitely the guys to be doing it! I was very much in agreement with RedHouse's statement on how we have gone through decades of iterations on losing the noise and perhaps trading off some of the "positive faults" inherent in old noisy gear. There are only 24hrs in a day and between building we should at the very least be playing too. I certainly spend far too much time hunting for better tones in my gear instead of improving my chops :-)

I agree 100%. We should play the instrument more :) Thanks for reminding!

That isn't to say that this will not be a fantastic project. Maybe it'll make some of that old noisy vintage gear sound a little less so!

Thanks. Well, I haven't deviated from my original goal: to create new sounds. I'm tired of the old vintage sounds, to be honest.

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I like it a lot! Very clean.

I'm still not convinced on the neo magnets though, and you could still improve the magnetic design aspect a bit. If you can squeeze a bit more output from these coils then that would be less noise out since a big source of noise is from amplification. Also, narrowing or manipulating the magnetic field will improve issues with noise and crosstalk.

I'd definitely love to incorporate newer/better ideas, but I also want to get this out the door sooner rather than later. So, for this project, I'd say I've satisfied all my initial requirements. I don't consider noise an issue anymore as I've far exceeded the desired SNR (>80db). I also no longer consider crosstalk a problem as I am confident that this can be mitigated through cancellation in the DSP.

Tell you what: how about collaborating on a new PU project with your ideas in mind?

Do you have room under the pickup to place magnets? Or room for a small and compact enclosure system around the coil sets?

Yes, we can probably squeeze in some more room. What do you have in mind?

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It's fairly rough, but as you can see there may be something to gain. A tighter field will result in less noise in, less string pull, less crosstalk, and in this case more output since the coil's core is now increasing the inductance. Less noise and more power in the pickup stage means less power can be used in the amplification stage and maintain a low noise level.

The idea above is first use a ferrite core in the inductors and then shape the field using neo magnets. There is plenty of experimentation to be done to see output and noise levels with different configurations. A neo magnet has a lot more pull to itself and thus the relative usable field isn't projected as far, well sort of. This is good and bad. Another good thing about experimenting with this is the only modification needed to the original design in order to experiment is a change to stock coils rather than the neo coils. Another way to help shape the field is through the use of fins, or even small poles or rods, to give the magnetic field an easier path back to the other magnetic pole. This can also be good or bad. Good if balanced with your needs, bad if it removes most of the usable magnetic field.

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It's fairly rough, but as you can see there may be something to gain. A tighter field will result in less noise in, less string pull, less crosstalk, and in this case more output since the coil's core is now increasing the inductance. Less noise and more power in the pickup stage means less power can be used in the amplification stage and maintain a low noise level.

The idea above is first use a ferrite core in the inductors and then shape the field using neo magnets. There is plenty of experimentation to be done to see output and noise levels with different configurations. A neo magnet has a lot more pull to itself and thus the relative usable field isn't projected as far, well sort of. This is good and bad. Another good thing about experimenting with this is the only modification needed to the original design in order to experiment is a change to stock coils rather than the neo coils. Another way to help shape the field is through the use of fins, or even small poles or rods, to give the magnetic field an easier path back to the other magnetic pole. This can also be good or bad. Good if balanced with your needs, bad if it removes most of the usable magnetic field.

Thanks for the explanation. Isn't that the same idea presented here: http://music-electronics-forum.com/t26380/ ? That project was plagued with weak signal and too much crosstalk. Maybe his inductors are too tall and his magnet too weak?

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Well, no.

I imagine you will still have crosstalk relative to the original design, just to a lesser degree. It depends on how well the original design performs. Another factor to consider is how close the pickup can get. The closer the better, however if it's at the neck position this won't be possible. Also, if placed near the neck you will need to worry about string bends and the magnetic field. It's a lot of trade offs and balancing once things are refined, but the general applied concept could improve things.

Basically, a larger magnetic field will have a bigger, possibly wider, sensing area but will be more susceptible to noise(magnetic) and crosstalk. A smaller field needs to be positioned more carefully. A stronger magnetic field relates to output, but does correlate since there are other factors to consider, largely inductance but there are a few more. Since the plan is to still use the neo magnets, the field strength may be stronger than the project above. Again, a lot of it is a balancing act of size and intended use.

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Well, no.

I imagine you will still have crosstalk relative to the original design, just to a lesser degree. It depends on how well the original design performs. Another factor to consider is how close the pickup can get. The closer the better, however if it's at the neck position this won't be possible. Also, if placed near the neck you will need to worry about string bends and the magnetic field. It's a lot of trade offs and balancing once things are refined, but the general applied concept could improve things.

Yes, I'm aware of that.

Basically, a larger magnetic field will have a bigger, possibly wider, sensing area but will be more susceptible to noise(magnetic) and crosstalk. A smaller field needs to be positioned more carefully. A stronger magnetic field relates to output, but does correlate since there are other factors to consider, largely inductance but there are a few more. Since the plan is to still use the neo magnets, the field strength may be stronger than the project above. Again, a lot of it is a balancing act of size and intended use.

Sounds good. I'll give it a try when I get a chance. FEMM is indeed interesting. BTW, are those vertical ferrite bars between the coils?

There's no space there anymore, but there might be in front and behind the coils. It's also interesting how some space between the magnet and the ferrite affects the whole.

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Sounds good. I'll give it a try when I get a chance. FEMM is indeed interesting. BTW, are those vertical ferrite bars between the coils?

There's no space there anymore, but there might be in front and behind the coils. It's also interesting how some space between the magnet and the ferrite affects the whole.

No, just steel. I know proportions and details aren't exact, but it's a rough idea. To be honest, FEMM isn't going to simulate a pickup. There are much more complicated things going on, in 3D and AC. It can help you visualize the basics though. What your looking at, there are six coils with smaller metal rods between them. The rods are much darker than the ferrite core of the inductors. The two smaller boxes on the outsides of the pickup are the adjustment screws, or a representation of them.

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