Can you extend the high frequency response of a pickup with individual coils?

[Mike Sulzer]

The most common guitar pickups consist of one or two coils such that each covers all six strings. The simplest circuit model of such a coil is a large inductance in parallel with a small capacitance. The significance of the terms "large" and "small" is that the pickup capacitance is generally significantly smaller than that of the cable connecting the pickup to the amp, while the inductance is large enough so that its interaction with the cable capacitance makes a resonant circuit that determines the high frequency response of the pickup. Using too many turns lowers the resonance too much and cause a loss of high frequencies.

In a situation where the pickup capacitance dominates, true only if one uses a buffer amp in the guitar, one can raise the resonant frequency by winding multiple coils and putting them in series. This is true because both the capacitance and inductance of the smaller coil are less, and the series combination into a very high impedance load has this same higher resonant frequency. However, this is not the situation we have in the usual passive guitar.

In the passive situation where the cable capacitance is dominant, any significant increase in the resonant frequency when using multiple small coils in series would have to come from a reduction in the inductance of the series combination with respect to that of the original coil. Theory suggests that there is no such effect. Measurements verifying this follow in this post.

Following the original discussion, I have made two bass pickups, one with a singe coil, the other with four. Pictures are shown.


The steel cores are 1/4" rod, 5/8" long. All coils are #43 wire, 6,000 turns. At 120 Hz with the Extech, the single coil measures 2.438 H with an ac resistance of4.971K. The multiple coil pickup, wired for string signals in phase, measures 2.594 H with an ac resistance of 5.033 K.

These measurements are close. The multiple coil pickup has a somewhat larger inductance, and so we wood expect it to have a slightly lower resonant frequency and somewhat less high frequencies.

[David Schwab]

The multiple coil pickup has a somewhat larger inductance, and so we wood expect it to have a slightly lower resonant frequency and somewhat less high frequencies.

So Mike, have you listened to it, or are you just speculating what it's going to sound like? Let's hear it.

Also, your subject line is not what the original subject was about. It has nothing to do with extending the high frequency response. Please go back and read the thread. It was about the pickup not losing the high frequency response with the amount of wire it has. This is why I asked you to wind more wire on the coils. Your single coil would never be muddy because you didn't wind it hot enough. Another issue is that 43 gauge wire has a totally different tone from 42. It lacks some high end and has more mids.

But I'd like to hear the results of your pickup, because originally you said the 4 coils in series would be the same inductance ad one coil. Now it looks like it's more.

[Mike Sulzer]

Pure, absolute, and utter speculation! We all know that circuits with similar measured properties usually sound nothing alike, and so all theories and measurements are useless. I will get to the listening tests as time permits.

The subject line is wrong? No the subject line is right on. If you make a pickup "muddy" by winding too much wire on it, you have filtered out the high frequencies that you wanted to keep. If you can make it less muddy by using individual coils, you extend the high frequency response. The interesting thing is how and why that does or does not happen.

#43 wires does not have a "tone". Its size and resistance are different from #42 and the circuits using it have somewhat different properties as a result.

I think if you go back and read the thread, you will see the word "approximately" or equivalent used frequently in regard to the relative inductances. We are not winding ideal square coils here, and wire packs differently when you wind a long coil compared to a compact one.

As always, it is interesting to read your comments since you view of reality is so close to orthogonal to mine.

So Mike, have you listened to it, or are you just speculating what it's going to sound like? Let's hear it.

Also, your subject line is not what the original subject was about. It has nothing to do with extending the high frequency response. Please go back and read the thread. It was about the pickup not losing the high frequency response with the amount of wire it has. This is why I asked you to wind more wire on the coils. Your single coil would never be muddy because you didn't wind it hot enough. Another issue is that 43 gauge wire has a totally different tone from 42. It lacks some high end and has more mids.

But I'd like to hear the results of your pickup, because originally you said the 4 coils in series would be the same inductance ad one coil. Now it looks like it's more.

[CRU JONES]

The steel cores are 1/4" rod, 5/8" long. All coils are #43 wire, 6,000 turns. At 120 Hz with the Extech, the single coil measures 2.438 H with an ac resistance of4.971K. The multiple coil pickup, wired for string signals in phase, measures 2.594 H with an ac resistance of 5.033 K.

These measurements are close. The multiple coil pickup has a somewhat larger inductance, and so we wood expect it to have a slightly lower resonant frequency and somewhat less high frequencies.

Now, THIS is interesting

I notice you have your measurements at 120Hz. I notice you have ac resistance listed but not dc resistance. Is this foreshadowing? Or should I not read into it?

I think it could go either way...

The Multiple-Coil Pickup could have less capacitance because the winds are compartmentalized, thus have a higher resonant frequency...

on the other hand.

I think the Multiple-Coil Pickup will have a lower resonant frequency than the single wound coil. Here is why I think that:

I think the Multiple-Coil Pickup, because of how the winds are intimate to the cores, and will have higher eddy current losses. It is not just the LC that determines the resonant frequency, losses; such as the volume, tone, eddy currents, and other losses also effect the resonant frequency. So I am going to go for it and say that, when you measure inductance at 1000Hz, the inductance of the Multiple-Coil Pickup will actually be less than that of the Single-coil Pickup. So even though it may be that the inductance is LESS, and the capacitance might be LESS, the resonant frequency is still LOWER. Because of loading, the resonant frequency will be LOWER for the Multiple-Coil Pickup.

That is my final guess... Until I guess again

Cheers,
Ethan Spaulding

P.S. I'm assuming we are measuring resonant frequency with volume, Tone, and a cable.

[ScottA]

Yes.

In my experience, and I have quite a bit of it as I've been concentrating exclusively on poly-coil pickup designs for more than five years now, multiple coil pickups tend to set up at higher resonant frequencies when dialed in to have a similar output and tonal response to single or even dual coil pickups. For instance, my vintage targetted stuff is all nominally 9 k Ohms DCR (~ = 120 Hz ACR) and higher inductance typically than conventional single coil pickups (mine are in the 4-6 H range generally), but the (unloaded) resonant frequencies are typically over 10 kHz. Higher than any conventional single coil I've measured, and they're all lower L and R than my stuff.

The higher resonance contributes to an extended high frequency response.

I'll be talking more about my findings in the future. I've constructed a very well developed model that explains these responses, but I have some IP in process and I'm not ready to talk about it publicly yet.

Mike, I'd love to talk to you offline though. I've read through some of the stuff that you've done (at least what I could find) and I think we could potentially do some pretty neat stuff together. It seems we're dancing around a lot of the same physics.

Cool looking pickups, too, btw!

[David Schwab]

#43 wires does not have a "tone". Its size and resistance are different from #42 and the circuits using it have somewhat different properties as a result.

Well, pickups wound with 43 will have different tonal qualities than those wound with 42 assuming they are both wound with the same number of turns, etc. Therefore it's safe to say that thinner wire sounds different from thicker wire.

I use a certain size wire depending on the tone I'm after. So 43 gauge wire does indeed have its own tone. Same can be said for 40, 41 and 44 AWG.

Here's Seymour Duncan on the subject:

204. What effect does magnet wire gauge have on DC resistance and resonant peak.

As a general rule..using the same number of turns on a pickup and different gauges of magnet wire will give you different DC resistance’s and Different resonant peaks. Winding a coil with 8,000 turns of 42 AWG will sound brighter and have a higher resonant peak than a coil wound with 8,000 turns of 43 AWG magnet wire.

As far as the title. The idea is that the Wal pickup has enough wire in it to equate to a very dark sounding two coil humbucker. Except it's not a dark sounding pickup at all. It's also very different sounding than most pickups, which has people wanted them to get that tone. This is why I'm making them, because Wal does not sell pickups separately.

I'm not sure how your test, while interesting, has shed any light on this. I'm curious to hear the sound samples.

[CRU JONES]

Scott,

I figured you would chime in on this one

I too have multiple-coil pickup winding experience, unfortunately I hadn't figured my way around testing them back then! But, I do have a vague memory of it.

What are your loaded pickup resonance's? If I may ask

I can buy the series of individual LC transducers adding up to give a higher resonant frequency, but under load; I have experienced that the individual resonance's collapse and act more like one coil of much lower resonance. Adding to this is, in this case, Mike is using 1/4" steel slug's. Because of the slugs, I think it will be of increased impedance that the resonant frequency will end up being lower than the Single-coil pickup once loaded.

Measuring with a scope of 10M 10p (my scope) is a large enough load to make the pickups impedance small, misrepresenting what the pickup will end up producing.

I do like the tone of your Zexcoils! Alnico core... Hmmm....

Anyway, I'm sticking to my guns! These pickups better be measured under load! Lol.

Ethan Spaulding

[LVS]

My 2c

I think, when the question would be:
"is it, in theory, possible to extend the frequency response by replacing a single coil pickup, with a pickup having a coil for each string, and both pickups having the same total inductance",
then the answer is yes when an LCR model is used.

A number of n coils in series, each having the same L, R and C can be replaced with a single coil with inductance n x L, resistance n x R and capacitance C / n.

So on the one hand let's assume a single coil pickup with L=2H, R=5K and C=100pF.

On the other hand, a 4-coil pickup with L=0.5H, R=1K25 and 40pF for each coil, which has an equivalent single coil pickup LCR model with L=2H, R=5K and C=10pF.

Connecting a guitar cable with a capacitance of 500pF yields L=2H, R=5K and C=600pF against L=2H, R=5K and C=510pF, so the (equivalent of) the multicoil pickup reaches a higher resonance frequency according to Fres=1/2π√(LC). Even if the (total) resistances of both pickups would differ, but, a higher resistance would result in a smaller resonance amplitude.

Admitted, it's just a theoretical observation using a lumped model.

[Mike Sulzer]

The higher resonance contributes to an extended high frequency response.
Cool looking pickups, too, btw!

Thanks!

Individual coils certainly lead to a higher resonance frequency when unloaded by cable capacitance. But the practical question is what happens when it is loaded. If the cable capacitance is significantly greater that the capacitance of the single coil, then changing to individual coils is not going to make all that much difference because neither the inductance nor the total capacitance has changed all that much.

I will start measurements of impedance versus frequency tonight.

[Mike Sulzer]

I notice you have your measurements at 120Hz. I notice you have ac resistance listed but not dc resistance.

The ac and dc resistance are close at 120 Hz. This means that eddy current losses are small and that the inductance is accurate. So for a quick reliable measuremnt, I prefer 120 Hz.

[ScottA]

I do like the tone of your Zexcoils!

Thanks! We're getting a lot of good feedback lately. Now all I have to do is figure out how to sell more of the damn things!

What are your loaded pickup resonance's? If I may ask

I can buy the series of individual LC transducers adding up to give a higher resonant frequency, but under load; I have experienced that the individual resonance's collapse and act more like one coil of much lower resonance. Adding to this is, in this case, Mike is using 1/4" steel slug's. Because of the slugs, I think it will be of increased impedance that the resonant frequency will end up being lower than the Single-coil pickup once loaded.

Measuring with a scope of 10M 10p (my scope) is a large enough load to make the pickups impedance small, misrepresenting what the pickup will end up producing.

Anyway, I'm sticking to my guns! These pickups better be measured under load! Lol.

Ethan Spaulding

Thanks!

Individual coils certainly lead to a higher resonance frequency when unloaded by cable capacitance. But the practical question is what happens when it is loaded. If the cable capacitance is significantly greater that the capacitance of the single coil, then changing to individual coils is not going to make all that much difference because neither the inductance nor the total capacitance has changed all that much.

I will start measurements of impedance versus frequency tonight.

My primary goal in development (and also quality control) is to look at what the pickup itself is doing. The associated external components (controls, tone caps, cables, etc.) blur the response to the point that it is impossible for me to measure what I need under load. Not that the loaded measurements aren't important or relevant, I just can't see what I need to see in that mode so I don't do much of it.

Consider that you can take a humbucker and a single coil and load them both down to the point that the response will look like pretty much the same low wide frequency hump, but the single coil will still retain much of its single coil character (albiet somewhat muted) and the humbucker the same. So I counter with the perspective that the unloaded data (to me at least) is the most relevant to the pickup's basic response. The loading by external components doesn't change the basic character of the pickup, sonically it darkens it up a bit and quantitatively it just makes it harder to discern. The fundamental character of the tone is generated while those electrons are spinning around the pole piece(s) through the coil(s).

I did do a little bit of loaded measurements through cables a few months back and there was nothing in the data to indicate that the responses were being significantly skewed (relative to a loaded conventional pickup), and in a tip of the hat to David's perspective, my ears tell me that everything is OK. It's all relative really though, right? I mean, for example, my stuff sets up at higher resonance unloaded, but has higher DCR/inductance than conventional stuff so gets loaded down relatively a little more than conventional stuff, so ends up roughly in about the same place. Then you can always play tricks like using higher value pots to bring some of that back if you need to (I've found that I don't need to)...yada, yada, yada.

Anyway, my approach is to stick with basic pickup measurements, do my dialing in based on those data, then listen to things installed in a standard rig. I use my ears primarily for loaded measurements and instruments for unloaded measurements. It works for me.

[ScottA]

Scott,

I figured you would chime in on this one

I'm glad I saw this one. I haven't been coming here as much the last couple of weeks, that virus stuff scares the crap out of me. I got a bug here a couple of years ago and it took me two days to get rid of it!

[David Schwab]

I'm glad I saw this one. I haven't been coming here as much the last couple of weeks, that virus stuff scares the crap out of me. I got a bug here a couple of years ago and it took me two days to get rid of it!

Yeah, I was hoping you would chime in also. The thread started here:

http://music-electronics-forum.com/t28235/

We got on the topic discussing poly coil Bartolini and Wal bass pickups.

[Mike Sulzer]

I think we all can agree that there is some difference; the question is a practical one: given that the guitar cable has more capacitance than the pickup, how much difference does lowering the pickup capacitance make? The square root is a killer; there is usually not going to be much difference.

My 2c

I think, when the question would be:
"is it, in theory, possible to extend the frequency response by replacing a single coil pickup, with a pickup having a coil for each string, and both pickups having the same total inductance",
then the answer is yes when an LCR model is used.

A number of n coils in series, each having the same L, R and C can be replaced with a single coil with inductance n x L, resistance n x R and capacitance C / n.

So on the one hand let's assume a single coil pickup with L=2H, R=5K and C=100pF.

On the other hand, a 4-coil pickup with L=0.5H, R=1K25 and 40pF for each coil, which has an equivalent single coil pickup LCR model with L=2H, R=5K and C=10pF.

Connecting a guitar cable with a capacitance of 500pF yields L=2H, R=5K and C=600pF against L=2H, R=5K and C=510pF, so the (equivalent of) the multicoil pickup reaches a higher resonance frequency according to Fres=1/2π√(LC). Even if the (total) resistances of both pickups would differ, but, a higher resistance would result in a smaller resonance amplitude.

Admitted, it's just a theoretical observation using a lumped model.

[David Schwab]

The square root is a killer; there is usually not going to be much difference.

I already posted clips of the Wal pickup recorded passively with a 20 foot cable. It makes a difference.