Use Saw Studio as a Way to Determine Resonance in a Guitar Pickup

[John Ludlow]

I'm doing research on guitar pickup systems. As it turns out, they have an internal resonance that is created by the inductance of the pickup coil, and capacitance in the circuit. What I'd like to do is output some pink noise from a SS recording and run it into and out of the pickup circuit and then record that result back into SS with a frequency analyzer that I put on that channel. What I'm hoping is that the circuit resonance will visually show up as an aberration to the pink.

However, I don't want to melt the pickup circuit or, you know, damage it somehow.

And I'm not very savvy about the composition of the types of electrical signals I routinely use in the studio. Up till now, I've used them and ignored what they represent. But I'm sure that, like a mic, a guitar pickup must be a relatively very weak signal and so damage to it might well be possible.

So, my question is, what do I need to do to make a signal coming out of my d/a 'appropriate' to hook up to both leads of a guitar pickup/pickup circuit?

I'm in the planning stages right now, so it would be a little while before I actually did it. But at the moment this is the sticking point in the diagram 'where magic happens'. I'm hoping there's a way that won't damage either my equipment or the pickup/circuit. Anybody feel like they understand the electrical environment at hand well enough to give me advice?

[mr_es335]

John,

May I ask "Why?" Are you wanting to accomplish this task?

What is the end result of performing this task?

Years ago now before Seymour Duncan was "famous", I actually spent hours with him discussing pickups and learnt a great deal from him. At the time he was only developing humbucking pickups - primarily for Larry Carlton and Robben Ford.

As I reflect on that conversation now - the word that comes to mind when considering what you are desiring to accomplish is "multifactorial".

Single-coils are different than double-coils, pickup wire gauge and the number of wraps[1], pickup height, pickup pole-height/adjustment, string gauge/height, plectrum type/shape/thickness, and more importantly, the "musicality/skill" of the performer. All of these elements would need to be "factored-out" in order for any kind of "scientific" analysis to be really-and-truly derived.
[1] My recent '59's are made to the very early specs - I would have to contact SD for clarification.

Unless I am reading something very wrong here?

[John Ludlow]

Hey Dell,

I won't go through the whole thing. But, it started when I listened to a video of Paul Reed Smith discussing his TCL pickups that he calls 'tunable'. And it turns out that pickups have a resonant frequency, and sometimes more than one, that is generated by the capacitance ('C') and inductance ('L') in the circuit. You can predict that resonant frequency using a formula. Well and good.

It occurred to me that maybe I could help determine that frequency by modifying the inductance, and or capacitance, of the circuit myself, additively, using separate components. After a lot of research, I don't think it's possible to do what I originally wanted because there is something sort of 'mechanical' about the LC relationship: you can't just add more L or C components and have their additive total in the circuit figure into the result.

But I have some other ideas that I'd like to experiment with that involve things like initiating my own additional resonance - particularly with a variable capacitor. That might have an effect on the inductor, which would also have an effect on the primary resonance (raising it). Or - rather than resulting in multiple hearable resonances, raise the pitch of the existing 'natural' resonance by bleeding inductance out of the coil via a capacitor that results in notes outside of the range of human hearing. So, although there would technically be multiple resonances, you would only hear the effect of the original one - but it would be tunable.

For instance, in a single coil pickup, you could use conventional means to arrive at a pickup with a natural inductance of around 2.5H (I'd have Seuf Guitars hand wind a set for me) and then bleed inductance out of it (raising the resonant frequency) using an additional variable capacitor that produced an additional resonance that was, say, above 22kH.

That's why I'm doing it. But I don't need help with that. What I need help with is being able to measure resonances in a guitar pickup circuit so I can tell what changes when I mess with it. In my forest-level reasoning there are several possible outcomes and not all of them are musical.

And what came to mind is inducing a full range of frequencies into the circuit and then, using a frequency analyzer, visually look for the frequency(s) that sticks out due to sympathetic resonance. Ergo: pink. That leaves out the whole messy plucking of strings and the additional resonances that result from that which have nothing to do with an LC circuit.

It seemed easy at first, as a forest level plan. But, the details don't work out. I can't figure out how to pull it off. I've discussed it at length with a more knowledgeable person than me and we're a little stumped. And so... I'm posting here to see whether any of the engineers know how.

[jmh]

You could try this, play a very small output to old speaker voice-coil in proximity of your pickup. Simply plug in the guitar to a hiZ input.
You could try spikes and waves... and see what you get.

A voicecoil itself may have resonances of its own being a coil - of course you could record your voicecoil too and see how your 2 recordings compare. (It seems to me a guy named Hendrix made a career by doing this brilliantly!)

I think no matter how you attempt to do this, you will have some difficulties in interpreting the results because the environment (for instance a moving or stationary guitar string) becomes part of the circuit.

Another thing you could try is if you have a humbucker with separate leads for each coil, you could very easily put a very small signal (maybe: line level -> impedance matching transformer -> pickup coil 1) in one and record the other.

John

[jmh]

Just saw you replied to Dell while I was writing. I think the nearby voicecoil would be informative if you played a sweep of the same amplitude. (I think you may be able to generate the waveform with sox). Now I'm curious to see what you get too. Just a non-linear response or different harmonics at various frequencies imposed by the pickup would impact its tone.

[mr_es335]

John,

OK!

What of this?: TCI Pickups with Paul Reed Smith | PRS Guitars

• His striking hand technique is rather "poor" compared to this: Larry Carlton - Emotions wound us so (live Last Nite album)
• Notice that Larry is using "up stokes" and he is able to obtains the sounds that he does.I would still like to know what the end result is of all of this research?

If you would be so kind and indulge me a bit here.

[John Ludlow]

Hey John,

Yeah! You get it. Isn't this an interesting idea? You could have a fourth knob on your Strat pickup guard that you could use to tune your pickup resonance for the key you were playing in, even.

Your humbucking solution is pretty brilliant in that it's the first one that I've become aware of that overcomes the issue that you can either produce the resonance in the pickup perfectly - or you can monitor the result - but not both. Still though, it won't get me any closer to voicing my own Seuf single coil. Plus, it would be nice to be able to plug any pickup into the rig and both determine its resonance frequency and measure what happens to it when you jimmy the system.

And the idea about having the pickup excite an external voice coil is one that was suggested by my more-knowledgeable-friend (whose name may, or may not be, Dave...) before and rejected by me for likely introducing its own artifacts.

But I'm very interested in your line-level -> impedance matching transformer -> pickup idea. That would at least solve the portion of the problem that requires moving the signal out of the converter to the pickup without destroying it. Would you mind elaborating on that? I'm not very electrically educated (-> impedance matching transformer?).

But, presuming that can be understood by someone like me, how can I record the result of playing back pink noise into the pickup without introducing more sonic variables?

[John Ludlow]

John,

OK!

What of this?: TCI Pickups with Paul Reed Smith | PRS Guitars

• His striking hand technique is rather "poor" compared to this: Larry Carlton - Emotions wound us so (live Last Nite album)
• Notice that Larry is using "up stokes" and he is able to obtains the sounds that he does.I would still like to know what the end result is of all of this research?

If you would be so kind and indulge me a bit here.

Yes - that is the very video that started all of this.

From my vantage point, his technique is immaterial to the question. You listened to the difference in sound between the two guitars using the same pickup. He doesn't say so, but the difference isn't all the pickups. But, what he's saying is that PRS can now choose the frequency of the resonance in their inherent inductance/capacitance circuit, rather than it just being whatever it turns out to be.

If you don't know (and - why would you; I didn't know, at least) there is a relationship between inductors and capacitors. You can read about it here: https://en.wikipedia.org/wiki/LC_circuit . Basically, a charge gets sent back and forth between the inductor and the capacitor at a frequency that is determined by the formula:



...where f is frequency, L is inductance, and C is capacitance.

That signal only exists when, in this case, a separate signal is exciting (and energizing) the pickup coil. But it happens separately and in addition to the signal from the guitarist. So, if you measure the circuit while it's plugged in, but not being played, there will be nothing there. But if you supply a separate signal to it (pluck a string...) the capacitor fills up and empties over and over at the frequency determined by that formula above. And that causes changes in the tone as its sine wave interferes with the signal.

Well... I tried to explain why I care about it in my previous response. Basically, it will hopefully allow one to tune one's pickups for one's application. I'm not sure I can do a better job. Can you be more specific?

[jmh]

I don't even know that you need a matching transformer to experiment, but you might want to start by breadboarding up an attenuator to be confident that you would not damage the pickup.

http://www.nu9n.com/tpad-calculator.html

[John Ludlow]

I don't even know that you need a matching transformer to experiment, but you might want to start by breadboarding up an attenuator to be confident that you would not damage the pickup.

http://www.nu9n.com/tpad-calculator.html

I looked at that page and I'm already underwater. I wonder whether a log taper pot would be sufficient? And if so, how big?

Here's something else I wonder. Say I have that pot on the end of a converter output lead that is further connected to the pickup in and out. What would happen if I connected the lead from a converter input across the same contacts? Like... simultaneously exciting and recording that same circuit? I sort of have this uncomfortable feeling it would be like crossing the streams, but it's worth asking.