Syscomp Scope and application

[mickmutante]

Or maybe one coil of the size of the two coils of the humbucker?

[Mike Sulzer]

Or maybe one coil of the size of the two coils of the humbucker?

No, that would tend to cancel just as any field that is constant over the two coils would.

[Jeff Callahan]

Excellent analysis, Mike.
I think it's time to settle on a relatively standard driver coil and get empirical data.

Exactly my feeling, From what I've got so far, the resistors and driver coils have more of an impact to the graph than the pickup.

Sorry for the delayed response, 4 month old, buying a house, and of course work have my hands tied...

Also, thanks Salvarsan for getting me started in this process.

[salvarsan]

..Also, thanks Salvarsan for getting me started in this process.

I can't take credit for pointing out a door that you decided to walk through.
You should be giving me shit for not being more help.

Anyway, thanks for grabbing the ball and running hard.

[mickmutante]

Finally I have my Syscomp CGR-101.
Now I am going to build 2 driver coils and compare them; one with 34AWG, and other similar as Lemme describe with 26AWG (it's the wire I have).
Soon I will post some graphic to compare.

[David Schwab]

Hey, check this thing out. Anyone think it would be useful? $99.95

DSO Nano V2 - Pocket-Sized Digital Oscilloscope - SparkFun Electronics

[salvarsan]

Hey, check this thing out. Anyone think it would be useful? $99.95

Inflated specifications.
On an Oscope, a 1MHz signal bandwidth implicitly means phase discriimination at f3dB, or a 10 Msample/sec acquisition rate.

The CGR-101 is a 20 MSamp/sec device rightly claiming 2 MHz bandwidth, has two inputs and a signal gen. The DSO Nano is a 1 MSamp/sec device realistically delivering 100 kHz bandwidth, has 1 input and a signal gen.

The CGR-101 performs spectral analysis and network impedance analysis.
The DSO Nano does not.

The CGR-101 requires a host workstation.
The DSO Nano does not.

Summary: Sparkfun exaggerated the DSO Nano bandwidth by a factor of 10; it will not do impedance plots of pickups, but it costs half as much and is very convenient.

You can go broke buying good deals if they don't fit your needs.

[StarryNight]

just piping in to say this is an awesome thread. I also would agree having a standardized coil driver would be beneficial to all, and could help greatly with sharing ideas.

[mickmutante]

I made 3 driver coils.
1. 26AWG, 100turns. > Did not work (Syscomp application did "read" it).
2. Driver Coil 1: Purple line on the graphic.
37AWG, 506 turns, DCR 108.8Ω
@ 1KHz: L: 11.07mH; C: 2.282µf; ACR: 105.28Ω
3. Driver Coil 2: Red line on the graphic.
41AWG, 750 turns, DCR 638Ω
@ 1KHz: L: 21.29mH; C: 1235nf; ACR: 636Ω

The pickup I used for test it ia a Jazz with split coil hum canceling.
42AWG PE, 9500 turns, Alnico 5 rods, DCR 7.09kΩ
@ 1KHz: L: 2.803H; C: 8.97nf; ACR: 7.42kΩ

The first image (Jazz-HB-MS-drivercoil.jpg), shows how the Syscomp Scope works with the driver coils #1 and #2 with "Figure 3: Pickup Frequency Response Test Setup" shown on the Pickup Resonance.pdf posted by Jeff.
The second image (Jazz-HB-MS-MesureCircuit.jpg) shows how the Syscomp Scope works with the "Figure 1: Measurement Circuit" shown on the Pickup Resonance.pdf. I used a resistance that matches the DCR of the pickup using a 25kΩ pot.

I am trying to understand the graphics...
Is there an ideal "graphic"?

[Possum]

I think the charts in the PDF were done without a pot in the circuit. Personally I think its better to just read from the coil by itself to keep it simple. A 25k pot as you can see really darkens the pickup and there's not any resonant peak of any notice I see at all. What I discovered is that too small a driver coil doesn't work very well. Physically is needs to be a larger coil size. I am using a humbucker bobbin for the driver coil, same as Lemme did, but am filling the bobbin completely full. I am using 38 AWG wire and its about 337 ohms and works better than the 50 ohm one I wound with the same wire. The 50 ohm coil was just too small to couple very well with the pickup, or its resonant peak was much too high, I didn't measure the peak of the driver yet.
Here's a strat coil by itself. You can plainly see the rez peak and the scooped mids....

[mickmutante]

Another test, same pickup, but this time Driver Coil #1, an a new one.
Driver Coil 1: Purple line on the graphic.
37AWG, 506 turns, DCR 108.8Ω
Driver Coil 3: Red line on the graphic.
37AWG, 1300 turns, DCR 304Ω
With the same pickup (on the attachment).

[Possum]

Peter told me to check the resonant peak of the driver coil and to make sure its not way too high above a typical guitar pickup's resonant peak. I haven't checked my driver coil for that yet. But in the end you just have to pick which driver coil you are comfortable with and then only use THAT ONE and never lose it! Of course, for me the frequency chart is of minimal uses really, he calls it a "broad brush" look at the frequency response. For me the reason I bought this device is you can really get a very close fix on the resonant peak frequency of pickups. I'm only just doing this now, so how useful is it really? I don't really yet know, will take months to see how practical it is in every day uses......

[Mike Sulzer]

Peter told me to check the resonant peak of the driver coil and to make sure its not way too high above a typical guitar pickup's resonant peak. I haven't checked my driver coil for that yet. But in the end you just have to pick which driver coil you are comfortable with and then only use THAT ONE and never lose it! Of course, for me the frequency chart is of minimal uses really, he calls it a "broad brush" look at the frequency response. For me the reason I bought this device is you can really get a very close fix on the resonant peak frequency of pickups. I'm only just doing this now, so how useful is it really? I don't really yet know, will take months to see how practical it is in every day uses......

I think the resonant peak of the driver coil should be well above that of the pickup if you are using it to find the frequency response of the pickup.

When you wrote that you want to measure the resonant frequency of pickups, what do you mean? What matters is the response of the pickup when embedded in the rest of the circuit of the guitar including the cable. Measuring the resonant frequency of the pickup by itself does not give you the resonance in the circuit you use, nor would measuring it in one circuit allow you to determine the exact response in any other circuit.

However, there is another way to go about this. If you know the impedance of the pickup as a function of frequency, then you can calculate its frequency response in any guitar circuit. So if you really want to know how the pickup will respond, you need its impedance. On the other hand, you also would like to know how much output a pickup has, at least relative to other pickups. Using a driver coil can tell you something about this.

However, once you have measured impedance you really only need to use the driver coil at a single frequency: everything else you can get from the impedance. It is much easier to make a driver coil that does what you want at just one frequency rather than over the whole range. This frequency should be well below pickup resonance; that makes it easier to interpret.

[Possum]

The problem with measuring it IN a guitar circuit is that no two wiring harnesses will ever be identical. If you just measure the pickup soley by itself you don't have anything else in the way. Wiring harnesses are all over the place, any new guitar I buy I always throw it all away and do it over, as pretty much all of them detract from the pickups rather than let them breathe and do what they do best.

The other problem measuring in a circuit, just going by ears alone, is that tone caps all sound different. I just hooked up a test rig so I could clip in different tone caps in my test guitar and listen, this is the first time I've ever done this and was awestruck with how different they all sound. I used some Russian paper in oil, NOS Sprague paper in oil, some Cornell Dubilier greenies, one of those "workalike" caps from singlecoil.com, and a Jensen paper in oil. Every single one of them sounded noticeably different. So, if you have that in the mix with a guitar pickup its just too confusing for me, anyway. I think the Syscomp device may also be able to chart a frequency response of tone caps, will give that a try to see if it spits out anything useful. Pots are all different too, no two are identical, cheap pots don't sound as transparent CTS pots with much bigger carbon paths etc. Its just easier to clip a pickup directly into the device and get a simple look at what it does by itself. Even there its important that you're doing it with the same room temperature, so the DCR is the same. I'm really happy I bought this thing and think it'll be a useful tool. It was a little troublesome to get it working on the Mac but I figured it out....

The resonant peak is interesting to me because you hear it, how you design your pickup determines where it falls, in prototypes if differences are hard to hear the rez peak can help you see whats happening by making minor changes.

[mickmutante]

A wrote an e-mail (a month ago) to Peter @Syscomp asking him how to obtain a better graphic.
He answer this:
"What you would do is save the data from the network analyser response to a
file, which, if I remember correctly, you can do from one of the menus.
(Maybe Tools -> Export Waveform).

Then you would load that data into a spreadsheet. Create a new column that
multiplies the amplitude readings by 1/f. Then plot this new column."

So...
I plot my pickup with the network analyser, and then I exported.
The file had 3 columns: Frequency, Magnitude, phase, and Quality.
So I did another column with Mag*(1/Freq).
I could not re-plotted with the syscomp application, so i tried with Excel application but I think I did not have the expected results.
Maybe is the Excel app.?