Single vs 4-conductor resonant peak

[zparts]

Here are 2 graphs showing the difference in resonant peak frequencies on a 7k un-potted humbucker. One graph represents the difference between single conductor and 4-conductor. The other graph represents single conductor vs 2-conductor. Same exact pickup and lead wire lengths were used, just swapped lead wires only. I get asked from time to time how different lead wires affect the tone of a pickup. Hope you enjoy.

[Mike Sulzer]

What does single conductor versus two conductor mean? How long is the four conductor cable (before the connections are made between the two coils)? Is this a physically realistic situation, that is, loaded by a guitar cable much loner than the pickup leads?

[Mike Sulzer]

And how does the way the conductors are connected affect the response at about 1 KHz by about 20 DB?

[ScottA]

And how does the way the conductors are connected affect the response at about 1 KHz by about 20 DB?

That looks like an artifact, but the response at higher frequencies is consistent with what I've seen.

I did a thread on this a couple of years back. It was sparked by my QC observation of a performance shift when I switched 4-conductor cable vendors.

Frequency response data, not to mention AC parameters, are pretty sensitive to cable capacitance.

Unfortunately, the links in that old thread were broken when we updated our website. Here's the gist of it:



I recommend that my customers don't ground the cable shield unless they have buzz issues. From a fidelity standpoint, twisted pairs and cavity shielding are much better than shielded cable.

[Mike Sulzer]

That looks like an artifact, but the response at higher frequencies is consistent with what I've seen.

But does it make any audible difference, or significant measurable difference when the effect of the capacitance of the guitar cable is included? Remember 5KHZ is a pretty solid per limit for electric guitars.

[ScottA]

But does it make any audible difference, or significant measurable difference when the effect of the capacitance of the guitar cable is included? Remember 5KHZ is a pretty solid per limit for electric guitars.

The idea of things not being important because they get buried in the noise of the control and wiring loading is a red herring.

I study pickups unloaded because that's where you can see the detail. That detail is important installed in a guitar even if it is hard to measure at the end of a guitar cable.

There are limits of course, but that's part of the trick, too. Minimize the loss due to controls by carefully designing your control scheme, low cap cable, well placed buffers, etc.

[Mike Sulzer]

The idea of things not being important because they get buried in the noise of the control and wiring loading is a red herring.

That is not it at all. The guitar cable is an important part of the circuit. I am all in favor of measuring an unloaded pickup because you can see the most detail, but then you must judge the importance of the detail that you see. The two apparent resonances that you see (resulting from, I believe, the total capacitance across the individual coils and the magnetic coupling between the coils) are greatly affected by the addition of more capacitance across the coil (the major effect of the guitar cable). Primarily what you have then is a single resonance at a lower frequency. Yes, the details of that resonance are affected by the various capacitances in the pickup leads (how not? The exact capacitance must matter.), but this is not a very big effect. It is especially not very big if you look below 5KHz. The response of the pickup is low above 5 KHz, and the guitar speaker falls like rock around that frequency as well.

[ScottA]

The idea of things not being important because they get buried in the noise of the control and wiring loading is a red herring.

That is not it at all. The guitar cable is an important part of the circuit. I am all in favor of measuring an unloaded pickup because you can see the most detail, but then you must judge the importance of the detail that you see. The two apparent resonances that you see (resulting from, I believe, the total capacitance across the individual coils and the magnetic coupling between the coils) are greatly affected by the addition of more capacitance across the coil (the major effect of the guitar cable). Primarily what you have then is a single resonance at a lower frequency. Yes, the details of that resonance are affected by the various capacitances in the pickup leads (how not? The exact capacitance must matter.), but this is not a very big effect. It is especially not very big if you look below 5KHz. The response of the pickup is low above 5 KHz, and the guitar speaker falls like rock around that frequency as well.

We covered some of this in that older thread I mention above. The secondary resonance you see in the pic I posted in this thread comes from the 4-C cable capacitance being introduced between the two sets of three coils (in my case. The way I wire it, two of the 4C wires tap into the D and G coils respectively to do the series/parallel split). Under the right conditions, you can see the same thing in a two coil humbucker. The one above and a conventional humbucker are both relatively low Q pickups, so the secondary resonance gets a bit muted. In a higher Q design, there is a more complex secondary structure that you can see from the 6 coils interacting with each other, even with two individual conductor wiring (or for that matter, connecting directly to the wire connection points). It's not as pronounced in amplitude as the peak you see here, but the structure is more well defined. I can see repeatable differences in that structure when I use different winding levels/string gauges in the individual coils for example.

In the data I show above, there are easily discernible differences in the 1-5 kHz range. In practice, these kinds of changes are what you hear in the "high end air" for lack of a more scientific term.

I can tell you that the difference between the red and orange series (i.e. the two 4-C cable vendors) looked like a different pickup in my final QC metrics. Definitely outside the control limits. That's what sparked me to do this analysis in the first place, response to an out of control event.

(In Capt Kirk voice) Must...have...assignable...cause...

[zparts]

The idea of things not being important because they get buried in the noise of the control and wiring loading is a red herring.

That is not it at all. The guitar cable is an important part of the circuit. I am all in favor of measuring an unloaded pickup because you can see the most detail, but then you must judge the importance of the detail that you see. The two apparent resonances that you see (resulting from, I believe, the total capacitance across the individual coils and the magnetic coupling between the coils) are greatly affected by the addition of more capacitance across the coil (the major effect of the guitar cable). Primarily what you have then is a single resonance at a lower frequency. Yes, the details of that resonance are affected by the various capacitances in the pickup leads (how not? The exact capacitance must matter.), but this is not a very big effect. It is especially not very big if you look below 5KHz. The response of the pickup is low above 5 KHz, and the guitar speaker falls like rock around that frequency as well.

I test pickups unloaded just to keep things consistent with how I test everything else. The reason I don't bother with adding variables is because I can't control them once the pickup is in someone else's hands. This graph simply demonstrates how connecting the coils together in series through the length of a cable can change the resonant frequency. Now connect the coils at the pickup in series and just use 2 of the 4 wires of the 4-conductor wire for a hot and ground, and the frequency won't shift much or any at all compared to any other lead wire of similar length and gauge.

[Mike Sulzer]

I test pickups unloaded just to keep things consistent with how I test everything else. The reason I don't bother with adding variables is because I can't control them once the pickup is in someone else's hands. This graph simply demonstrates how connecting the coils together in series through the length of a cable can change the resonant frequency. Now connect the coils at the pickup in series and just use 2 of the 4 wires of the 4-conductor wire for a hot and ground, and the frequency won't shift much or any at all compared to any other lead wire of similar length and gauge.

Great way to test for consistency because it shows up small differences. But that sensitivity cannot be used as an indication of how much things change with a guitar cable in place. Suppose we have two situations:

A. unloaded

B. loaded with guitar cable

Suppose the loaded capacitance is 5 times that of the unloaded. (With a humbucker the capacitance from the series combination (two caps in series have half the capacitance) might be 80 pfs. 400 pfs with the cable cap added is not that unusual.) Suppose we add a small capacitance in parallel in both cases. Suppose that in case A the resonance shifts by x Hz. Then in case B the resonance shifts by about x/10 Hz.

You can see this from these calculations assuming a 3 H inductance.
In [37]: 1/(2*pi*sqrt(3.*80e-12))
Out[37]: 10273.407401024997


In [38]: 1/(2*pi*sqrt(3.*81e-12))
Out[38]: 10209.794359662816


In [39]: 1/(2*pi*sqrt(3.*400e-12))
Out[39]: 4594.4074618482673


In [40]: 1/(2*pi*sqrt(3.*401e-12))
Out[40]: 4588.6751982787782

Or you can find the derivative with frequency and see that it varies as C**(-3/2).

[zparts]

[QUOTE=Mike Sulzer;392067]

Great way to test for consistency because it shows up small differences. But that sensitivity cannot be used as an indication of how much things change with a guitar cable in place. Suppose we have two situations:

A. unloaded

B. loaded with guitar cable

Suppose the loaded capacitance is 5 times that of the unloaded. (With a humbucker the capacitance from the series combination (two caps in series have half the capacitance) might be 80 pfs. 400 pfs with the cable cap added is not that unusual.) Suppose we add a small capacitance in parallel in both cases. Suppose that in case A the resonance shifts by x Hz. Then in case B the resonance shifts by about x/10 Hz.

You can see this from these calculations assuming a 3 H inductance.
In [37]: 1/(2*pi*sqrt(3.*80e-12))
Out[37]: 10273.407401024997


In [38]: 1/(2*pi*sqrt(3.*81e-12))
Out[38]: 10209.794359662816


In [39]: 1/(2*pi*sqrt(3.*400e-12))
Out[39]: 4594.4074618482673


In [40]: 1/(2*pi*sqrt(3.*401e-12))
Out[40]: 4588.6751982787782

Or you can find the derivative with frequency and see that it varies as C**(-3/2).

Wow great info and depth on the subject and I think I get your point. We can make something as flawless or perfect as we possibly can, but we can't control the end user which is why I avoid too many variables. Maybe they use 100ft cable with cheap pots and they can't play worth a damn. Who knows, but at the end of the day I can only make something the best way I think it should be, pouring everything I have into it, and feel really good about sending it out into the world.

[ScottA]

I look at it as loss of fidelity.

Any capacitive loading like that leads to a loss of fidelity in some sense. If I can see it in the measurements, then at the very least there is the potential of an effect on the tonal quality.

You can't control what people do, but you can give them guidance on how to get the least affect on, or coloration of, signal quality, or at least to have that option on tap.

The unloaded measurement gives what the pickup is capable of. Of course some amount of loading is usually desirable as "everything the pickup is capable of delivering" is, many times, harsher than what most people want to hear. It's also kind of "built in" to the designs anyway. I target voicings and analyze data based on the unloaded measurements, but when I'm evaluating performance I'm playing through a realistic, representative rig, albeit designed with loss minimization in mind. I use low cap cables and buffers in the right places, but I'm usually running through at least the equivalent of 10-15 feet of low cap cable as well as an optimized set of controls. That filter is built in to the design loop.

Look at it this way: The measurements tell you when you should be looking for a tonal difference, then you can let your ears tell you if you care about it or not.

My general philosophy though, is to make the sensor as good as I can, and part of that is minimizing losses due to coupling. If people want to muck it up downstream that's their business.

[Mike Sulzer]

I look at it as loss of fidelity.

Fidelity is faithfulness to an original. If you are trying to create the tone you want, then fidelity is an irrelevant concept. Fidelity to what?

If you are trying to reproduce a guitar sound from the past, then just do things the way they were done in the past, or find a new way to get the same sound. But a few pfs of C in lead cables has nothing to do with it.

[ScottA]

Fidelity is faithfulness to an original. If you are trying to create the tone you want, then fidelity is an irrelevant concept. Fidelity to what?

If you are trying to reproduce a guitar sound from the past, then just do things the way they were done in the past, or find a new way to get the same sound. But a few pfs of C in lead cables has nothing to do with it.

Nit-pick much...?

Sound quality, whatever you want to call it. Excuse me for using "fidelity" in the sense of the audiophile marketing voodoo, but I think in the context of the vernacular, we all know what it means.

The data show this clearly. Add capacitance, and the frequency response is shifted from what the pickup is capable of producing. "Degraded" I think is not an incorrect way to look at it. So in that sense, I would say yes, it is "unfaithful to the original".

Mike, you seem to be a very intelligent guy, but your condescending tone becomes tiresome.