Hexaphonic Pickup Project

[cycfi]

Their differential circuit, along with shielding, producing an extremely quiet pickup. These are about the only pickups I have ever used that do not pick up noise from lamp dimmers. They also allow you do disconnect the string ground, which does not add any extra noise. I used them for about 15 years on both guitar and bass, and they are dead quirt in every situation. Other instruments with conventional passive humbuckers still produced noise in the same environments that the EMGs were dead silent.

That's exactly the same noise performance I get with the balanced hex coils. The tests I have are hands free and string ground free. Dead quiet! Will I get the same performance with a singe-ended design? That's what I am about to find out.

At any rate, with a single-ended, single-stage, FET or BJT design, I am trading off more than that. There's also linearity, THD, and more importantly superb PSRR and independence from temperature. These can be mitigated to some degree, but you'll end up with a complex discrete design.

[Mike Sulzer]

You will need the string ground. I guess this is a minor safety issue. My experience is that the degree of magnetic hum reduction you get by cancellation is still the limit, and that adding electrostatic canceling is not necessary if something else is the limit. It is a nice way to do things, but I think the limit is how close you can make the magnetic cancellation.

That's exactly the same noise performance I get with the balanced hex coils. The tests I have are hands free and string ground free. Dead quiet! Will I get the same performance with a singe-ended design? That's what I am about to find out.

At any rate, with a single-ended, single-stage, FET or BJT design, I am trading off more than that. There's also linearity, THD, and more importantly superb PSRR and independence from temperature. These can be mitigated to some degree, but you'll end up with a complex discrete design.

[David Schwab]

When you load one of the coils more heavily at high frequencies you do not get more harmonics; you lose high frequencies.

No, you stop the high frequency phase canceling from having matched coils. People have been mismatching coils, either with different amounts of winds, or different gauge wire for a while now.

They use a cheap noisy op amp and a circuit that does not do what they claim. Let's not mistake sales lingo for engineering.

They aren't noisy pickups. The older models used the LM4250 because it has low current consumption. The newer X series is using something else. I make bass preamps based on the original Musicman Stingray preamp, and that uses the LM4250. It's not noisy at all. Not even with the treble cranked all the way up, and it has a lot of treble boost. There are better op amps on the market now, but it's not a bad op amp. It has its own characteristic sound.

And where is the resonant frequency? With no capacitance to replace the cable capacitance, and a conventional number of turns, it should be quite a bit higher than a normal humbucker. Maybe this is the justification for the claim of "more harmonics" compared to a passive pickup. But it is not what they say.

Have you ever used EMG pickups? Doesn't sound like you have. The guitar models sound just like what they are targeting. The older 58 and the 85 that replaced it are very PAF sounding. The 58 is a very nice sounding pickup. The 81 is edgier sounding. I have an old mini humbucker that they don't make anymore that has a narrow aperture and sounds a lot like a Firebird. I used that in a guitar along with one of their SA Strat pickups at the neck for many years. I prefer their guitar pickups to their bass pickups, but they are not bad sounding pickups, and extremely quiet. As I said you can remove the string grounding and you don't get any buzz when you aren't touching the strings.

Regarding the resonant frequency, they used to list all that stuff. From a 1999 catalog (they also have frequency graphs for some models):

EMG 81
SPECIFICATIONS:
Logo Color: Silver
Resonant Frequency (Khz) 2.25
RMS Output Voltage 1.25
Peak Output Voltage 1.75
Output Noise (dBV) -91
Output Impedance (Kohm) 10
Current @ 9V (Microamps) 80
Battery Life (Hours) 3000

EMG 85
SPECIFICATIONS:
Logo Color: Gold
Resonant Frequency (Khz) 2.55
RMS Output Voltage 1.25
Peak Output Voltage 1.75
Output Noise (dBV) -89
Output Impedance (Kohm) 10
Current @ 9V (Microamps) 80
Battery Life (Hours) 3000

EMG 60
SPECIFICATIONS:
Logo Color: Gray
Resonant Frequency (Khz) 2.95
RMS Output Voltage 1.0
Peak Output Voltage 3.0
Output Noise (dBV) -89
Output Impedance (Kohm) 10
Current @ 9V (Microamps) 80
Battery Life (Hours) 3000

EMG-SA
SPECIFICATIONS:
Logo Color: Gold
Resonant Frequency (Khz) 3.75
RMS Output Voltage 0.6
Peak Output Voltage 0.85
Output Noise (dBV) -90
Output Impedance (Kohm) 10
Current @ 9V (Microamps) 80
Battery Life (Hours) 3000

EMG-S
SPECIFICATIONS:
Logo Color: Silver
Resonant Frequency (Khz) 4.35
RMS Output Voltage 0.6
Peak Output Voltage 0.85
Output Noise (dBV) -90
Output Impedance (Kohm) 10
Current @ 9V (Microamps) 80
Battery Life (Hours) 3000

EMG-T
SPECIFICATIONS: EMG-FT (neck)
Logo Color Gold
Resonant Frequency (Khz) 4.85
RMS Output Voltage 0.52
Peak Output Voltage 0.75
Output Noise ( dBV ) -89
Output Impedance (Kohm) 10
Current @ 9V (Microamps) 80
Battery Life ( Hours ) 3000

SPECIFICATIONS: EMG-RT (bridge)
Logo Color Gold
Resonant Frequency (Khz) 3.70
RMS Output Voltage 0.75
Peak Output Voltage 1.0
Output Noise ( dBV ) -90
Output Impedance (Kohm) 10
Current @ 9V (Microamps) 80
Battery Life ( Hours ) 3000

[David Schwab]

That's exactly the same noise performance I get with the balanced hex coils. The tests I have are hands free and string ground free. Dead quiet! Will I get the same performance with a singe-ended design? That's what I am about to find out.

At any rate, with a single-ended, single-stage, FET or BJT design, I am trading off more than that. There's also linearity, THD, and more importantly superb PSRR and independence from temperature. These can be mitigated to some degree, but you'll end up with a complex discrete design.

I have a '73 Rickenbacker 4001 that I had done a lot of mods to over the years. At one point it had an old Bartolini Hi-A pickup at the bridge, and a rewound Gibson EB-0 neck pickup, coil switching options for both pickups, and a JFET buffer. I had the bass totally shielded with copper tape, and no string ground. It was dead quiet. I only had one instance where I picked up a minimum amount of noise in a very noisy bar. I expect all my instruments to not hum or buzz because I was doing a lot of recording at one time.

So it is possible to get a single ended circuit to be noise free. I shield all my bass pickups for the same reason.

[Mike Sulzer]

I have a '73 Rickenbacker 4001 that I had done a lot of mods to over the years. At one point it had an old Bartolini Hi-A pickup at the bridge, and a rewound Gibson EB-0 neck pickup, coil switching options for both pickups, and a JFET buffer. I had the bass totally shielded with copper tape, and no string ground. It was dead quiet. I only had one instance where I picked up a minimum amount of noise in a very noisy bar. I expect all my instruments to not hum or buzz because I was doing a lot of recording at one time.

So it is possible to get a single ended circuit to be noise free. I shield all my bass pickups for the same reason.

That is right, use a even single ended preamp, and the effect of a missing string ground is much reduced. But it is even quieter with the string ground in place. I think that is what cycfi will find in his measurements, since he is comparing with the best of the best, differential input, but who knows until he reports?

[Mike Sulzer]

No, you stop the high frequency phase canceling from having matched coils. People have been mismatching coils, either with different amounts of winds, or different gauge wire for a while now.

If you load a 1H inductor with an effective value of 15K you lose more than 6db at 3000 Hz. That is simple circuit analysis. And what is this "high frequency phase canceling"? I do not think that this exists.

They aren't noisy pickups. The older models used the LM4250 because it has low current consumption. The newer X series is using something else. I make bass preamps based on the original Musicman Stingray preamp, and that uses the LM4250. It's not noisy at all. Not even with the treble cranked all the way up, and it has a lot of treble boost. There are better op amps on the market now, but it's not a bad op amp. It has its own characteristic sound.

When I crank up a preamp with 40 nanoVrootHz noise I hear hiss. For reference, a 12AX7 is about 5. The best solid state is about 1, but needs a lot of current and would have short battery life.

Have you ever used EMG pickups? Doesn't sound like you have.

You want to make this personal again? Why not stick to the technical aspects, and lay of the Argumentum ad Hominem?

The guitar models sound just like what they are targeting. The older 58 and the 85 that replaced it are very PAF sounding. The 58 is a very nice sounding pickup. The 81 is edgier sounding. I have an old mini humbucker that they don't make anymore that has a narrow aperture and sounds a lot like a Firebird. I used that in a guitar along with one of their SA Strat pickups at the neck for many years. I prefer their guitar pickups to their bass pickups, but they are not bad sounding pickups, and extremely quiet. As I said you can remove the string grounding and you don't get any buzz when you aren't touching the strings.

Regarding the resonant frequency, they used to list all that stuff. From a 1999 catalog (they also have frequency graphs for some models):

A resonance requires a 180 degree phase shift between the two elements. Ls and Cs each shift 90 degrees in the opposite direction. With normal pickups, the coil provides the L and the guitar cable provides most of the C. Eliminate the cable and provide no other C (as they apparently do not) and the resonance is higher. As I pointed out above, they do lose high frequencies from loading one coil, but that is not a resonance. Perhaps in those specs they are using the term resonance to mean "this is about where our pickup starts to roll off." However, it is not a resonance; there is only one 90 degree phase shift.

[rjb]

Nattering Nabob of Negativaty

I realize you intend to neutralize string crosstalk with DSP- but for hacks like me who might want to use the pickup to do nothing more than send the signals from the lower strings to an octave doubler box, I fear the pickup's inherent crosstalk may be too high.

In this post from a previous thread, it is suggested that a humbucking pair of coils be used per string- with the distance between the poles of each HB pair being "significantly closer" than the string spacing.
http://music-electronics-forum.com/t26380/#post226819

The Sixpack 1.0 uses 5mm (~0.2") Diameter magnets, with the poles spaced to match string spacing.
I'm guessing that HB pairs with ~2.5mm D magnets and coils spaced as close together as possible would be less prone to crosstalk.

In this post, a member describes a setup for triggering an octave doubler with diy low-impedance pickups, using .125"D neo magnets.
http://music-electronics-forum.com/t7149/#post56850

Back to the drawing board again?

[David Schwab]

And what is this "high frequency phase canceling"? I do not think that this exists.

You do not think it exists? Based on what? Humbuckers cancel some of the very high harmonics. This is a well known effect. If you change the distance between the two coils you can alter where this happens. You can hear it on guitars with two single coils too. Move the distance between the coil and the notch changes.

It's too late for me to look up some references, but the idea being that the treble harmonics on the string are closer together, and with the way the string vibrates over the two coils, those frequencies are treated more like common mode signals and get canceled out, but not entirely. Meanwhile you have the reinforcement of the low frequencies. It's your typical comb filtering affect.

Various pickup makers have mismatched the two coils to make the pickups brighter. One such example are the old Bartolini humbuckers. The Hi-A 2B mini humbucker I have from 1976 or '77 has a very large offset. The two coils read 4.62K & 3.4K. 4.62 closer to the bridge. Bill Bartolini stated that he used the same gauge wire on both coils.

Jazz guitarist Tuck Andress had Bill wind one with match coils to make it quieter, since he uses a large amount of treble boost, and it was too noisy with the offset coils.

When I crank up a preamp with 40 nanoVrootHz noise I hear hiss. For reference, a 12AX7 is about 5. The best solid state is about 1, but needs a lot of current and would have short battery life.

Using that particular op amp? If you haven't built a preamp with the LM4250 and used it in an actual instrument how do you know? You are guessing.

I have a Musicman style preamp in my '87 Ibanez that is my main stage bass. Even with the treble control cranked all the way up (which is a little too bright to use), I can't hear any hiss through a 500 watt Hartke amp. Not any more so than the hiss the amp makes. So your comment about it being a cheap noisy op amp doesn't seem to hold water.

You want to make this personal again? Why not stick to the technical aspects, and lay of the Argumentum ad Hominem?

I asked you if you ever tried an EMG pickup. You are making claims about how they can't work, and must sound this way or that way. Lots of people know what they sound like, because they use them. I'm asking you if you have had any real world experience with them? You probably have not. But you are telling everyone what's wrong with them and that their claims are all marketing. Right? But you have no real experience with them. So how do you know? We don't even know how accurate that schematic is.

BTW, over at one of the DIY forums, they made a PC board layout for that preamp and the members made some active pickups. So there's some people doing hands on testing of the circuit.

http://www.freestompboxes.org/viewtopic.php?f=3&t=880

You are the one with the chip on your shoulder that has to explain why everything can't work, even when it does. It gets tiring.

No one was attacking you, but you seem to feel persecuted? You come off like you are right and every one else is wrong. The people at EMG can't possible know what they are doing. They just made a very successful business making one of the first active pickups on the market.

A resonance requires a 180 degree phase shift between the two elements. Ls and Cs each shift 90 degrees in the opposite direction. With normal pickups, the coil provides the L and the guitar cable provides most of the C. Eliminate the cable and provide no other C (as they apparently do not) and the resonance is higher. As I pointed out above, they do lose high frequencies from loading one coil, but that is not a resonance. Perhaps in those specs they are using the term resonance to mean "this is about where our pickup starts to roll off." However, it is not a resonance; there is only one 90 degree phase shift.

Have you tested one of these pickups, or this is all off the top of your head? Most pickups list resonant frequency. It always means that hump before the response drops off.

Here's a few obviously not very accurate charts they included with the specs (Possum might have drawn these!). You can also see the difference in the Q on the first one. Does it match the response of the pickup? I have no idea. However, from having used their pickups in various instruments of mine, I agree with where they say the resonant peak is, which is easy to test using a parametric EQ.

EMG SV

EMG SAV


EMG T

[cycfi]

Using that particular op amp? If you haven't built a preamp with the LM4250 and used it in an actual instrument how do you know? You are guessing.

I have a Musicman style preamp in my '87 Ibanez that is my main stage bass. Even with the treble control cranked all the way up (which is a little too bright to use), I can't hear any hiss through a 500 watt Hartke amp. Not any more so than the hiss the amp makes. So your comment about it being a cheap noisy op amp doesn't seem to hold water.

Hi David,

The hiss would be audible if you crank it up a lot more. I don't think it is relevant for bass, but it will be for, say, heavy metal guitar with tons of gain through distortion pedals. I haven't used LM4250 yet, but I have used Op Amps with the same noise figures (i.e. 40 nV/rtHz measured at 1kHz). An example in that vicinity is the LM324 with 46 nV/rtHz.

The current benchmark for "low-noise" is the NE5532 (dual) and NE5534 (single) with 5 and 3.5 nV/rtHz (respectively) measured at 1kHz). These are used in almost every mixing console, and in a large number of preamps. Current generation Op Amps are even more amazing (e.g. the LME4990 at 0.88 nV/rtHz measured at 1kHz). But that comes at a price: high quiescent current. I am using the OPA209, another modern Op Amp, with 2.2 nV/rtHz measured at 1kHz. The thing is, the lower power you get, the noisier the Op Amp is. Check out my Op Amp Shootout and notice the specs.

(P.S. I am not saying that the EMG is not a good PU. It is! And I have lots of respect for EMG. I'm just surprised with the design decision).

[cycfi]

I realize you intend to neutralize string crosstalk with DSP- but for hacks like me who might want to use the pickup to do nothing more than send the signals from the lower strings to an octave doubler box, I fear the pickup's inherent crosstalk may be too high.

In this post from a previous thread, it is suggested that a humbucking pair of coils be used per string- with the distance between the poles of each HB pair being "significantly closer" than the string spacing.
http://music-electronics-forum.com/t26380/#post226819

The Sixpack 1.0 uses 5mm (~0.2") Diameter magnets, with the poles spaced to match string spacing.
I'm guessing that HB pairs with ~2.5mm D magnets and coils spaced as close together as possible would be less prone to crosstalk.

In this post, a member describes a setup for triggering an octave doubler with diy low-impedance pickups, using .125"D neo magnets.
http://music-electronics-forum.com/t7149/#post56850

Back to the drawing board again?

I'm not sure. I am already committed to the coil's design. I'll keep that in mind though.

One thing I need to know is how much crosstalk can be tolerated (in terms of db)? Early experiments show good separation as-is. Perhaps the designs are different? It seems he has quite a bit hefty inductors there and with the magnet at the bottom, I'm guessing the signal is quite weak and needs a lot of gain. It's odd that he complains about crosstalk even with the bass guitar spacing! Anyway, I'll post some soundclips showing how much a string signal bleeds into its neighbor string and I'll quantify the crosstalk in terms of db.

[Mike Sulzer]

You do not think it exists? Based on what? Humbuckers cancel some of the very high harmonics.

Oh, you mean the canceling of higher harmonics due to the spacing of the two coils of a humbucker. I did start a discussion on that not long ago, and showed that analysis, measurement, and listening all show the same thing: that the higher harmonics of the bass strings are significantly affected, but the effect becomes very small as you proceed to the #1 string. The relevant harmonics (first null is the 34th, if I remember right) are out of the range of the system.

We are primarily talking about engineering in this discussion. It is permissible to discuss various circuits with reference to their advantages and disadvantages from an engineering point of view. Also from that point of view a resonant and non-resonant filter are distinct, just as engineering and advertising copy are distinct.

[RedHouse]

...Have you ever used EMG pickups? Doesn't sound like you have....

This sounds like the (ongoing) problem.

Talk = Cheap
Experience = Priceless
Talk ≠ (!=) Experience

[RedHouse]

...You are the one with the chip on your shoulder that has to explain why everything can't work, even when it does. It gets tiring....You come off like you are right and every one else is wrong...

and so it goes, Ad Infinitum, Ad Nausium.

(Translation: on and on forever, and sick of it)

YMMV

I suppose we all do it from time-to-time ...naaa, some of us are INDEED right all the time Muahahahahahahaha!!!!!!.

[rjb]

Anyway, I'll post some soundclips showing how much a string signal bleeds into its neighbor string and I'll quantify the crosstalk in terms of db.

Huzzah.

[RedHouse]

...say, heavy metal guitar with tons of gain through distortion pedals...

There's no cure for raising the noise floor with tons of gain, even more cowbell won't do. Some things just are what they are so it's like a moot point talking low noise and excessive gain within the same notion IMO.

The 5532 (and 5534) isn't really a "current" benchmark as it's an old chip from the late 70's which has long been upstaged by newer low noise chips but for musical intrument applications it's a very good general purpose low-noise chip , I've updated/upgraded several studio consoles by replacing 5532/4 chips with lower noise modern equivalents. There are some great white-papers available on noise sources (National Semi + AD) which tend to show that currents through input resistors other than the on-chip resistors are often the "usual suspects" although we do tend to quote the spec-sheet's nV/rtHz statements as the magic number. IMHO, a badly designed circuit can always make a loud-hissy-noised slice of silicon out of a low noise chip.

We went through all this low-noise suff in the 80's/90's until we made everything as sterile sounding as possible, now 20 years later we find ourselves back-pedaling on the notion that noise is a "problem". It's more like getting a great dynamic signal down the cable that serves the end purpose the most and we can use many more devices than the ultra-low-noise devices to get us there.