measuring resonant peak

[Elektrometeor]

Hey,

How can I measure the resonant peak of my Pickups?
Is there any special Equipment?

[belwar]

Yes, you do need some equipment, though you can get it for cheap off of E-bay. It can not be done with a multimeter alone.

The simplest method is to have a cheap audio oscillator (range of 20-20,000hz), and a good multimeter. I'll detail the method a little later today for you.

bel

[Elektrometeor]

... like this one?
Apex AAO1 Audio Oscillator

or this one?

OMNITRONIC LH-100 Audio-Oszillator

[belwar]

Ok, first off I am no expert in this arena. I'm explaining this as it was explained to me. Before I get into how I measure it, I want to put down some notes:

- Measuring Resonance Peak is one thing, understanding it is another. As I understand it, this measurement is the point that the Inductive reactance and Capacitive Reactance are equal, showing the circuit as purely resistive.
- Lots of things can effect this point, most notably adding metal to the circuit.. i.e. shielding.
- When measuring resonance peak, you should state WHERE you are measuring it. You will have two completely different readings if you measure it at the jack versus the pickup. Joe Gwinn gave me good advise and said that if I was measuring just a pickup (outside of a guitar) that I should call it "unloaded resonant peak".

Now here is what you will need:

- A good multi meter that can measure AC voltage and frequency
- 1 mohm Resistor (in a pinch you can use two 500k guitar pots daisy chained together in series).
- Sweepable Audio Oscillator (low distortion) or Function Generator.
- A couple alligator clips help, but are not nessesary.

I would recommend an oscillator that you can sweep with a dial... It makes the process very easy. A good one might be a hewlet Packard 204AB which does from 20-40000hz. I think I got mine for 20 bucks plus shipping. It's an old 50's device that has a nice dial on the front. I later bought a proper function generator for $300 .. It's this sucker here (FRYS.com | B&K PRECISION 4012A). Both accomplish the same thing.

Now to hook it up.. Lets assume that you want to measure the unloaded resonant peak (pickup outside of the guitar). It's a little strange to hook it up the first time, as you'll have wires going everywhere but it works. Here is how you wire it.

Pickup hot -> 1mohm resistor -> Audio Oscilator Red wire
Pickup Ground -> Audio Oscillator Black wire

Now you also need to hook your multi meter to this at the same time, in parallel...

Pickup Hot > Multi Meter Red
Pickup Ground > Multi Meter Black

Next will be the actual measurement, but i'll write more tommorow, Im falling asleep as I write this.

bel.

[Possum]

.....

Its interesting to fool around with this but ultimately its only use is in designing prototype pickups and even there I'm finding it lacking. You don't just hear the fundamental peak frequency, there's stuff you don't see that has a huge effect on tone. You might make a pickup and work real hard to reduce the peak to tame some treble, but only find that the peak itself shifted and yet there can still be an annoying high treble thats still there. In pickup design its useful to use an LCR meter but that still have alot of limitations; the most useful thing is to build a test guitar you can pop pickups in and out of very quickly to make ear comparisons. And ultimately, only installing it in a working guitar and playing it will give you a final decision. One of the MLP players came up with this cool tip that I'm trying:
Quick-change pickup tip - My Les Paul Forums
I've not detected any frequency losses by using this trick, they are a little bulky to get the pickup in and out but it works and saves soldering over and over, which also can degrade vintage braid type wire bad enough to cause treble loss in itself. There may be better connectors out there that are smaller, these are RC battery connectors I think. We ought to start a new thread on making a quick test guitar rig thats as close to being actually installed in a real guitar as possible, I could sure use something better....

[Elektrometeor]

Sure, the most important thing ist the sound of the PU in combination with a guitar type. But if you just compare a few pickups without guitar, and test several winding techniques it is interesting to know how to measure it.
So I´m curious about how the measurement works...

[Possum]

....

Well try it, its fun for awhile. I tried to use it as a tool to spot some problems with treble I was having and there the method really failed completely to be of use. You need a multimeter that reads frequencies if you really want to pinpoint whats happening.

[Elektrometeor]

... and how can I measure it?

[Possum]

...

Belwar will explain it, I posted "Joe's Method" as an image on one of the recent threads where capacitance was discussed, its on a yellow sheet. Maybe you can find it in a search...

[peskywinnets]

An interesting article here...

BuildYourGuitar.com :: The Secrets of Electric Guitar Pickups (towards the bottom "Measuring Frequency Resonse")

basically they use a 'transmitter' coil to squirt a broad range of frequencies into the pickup that you want to measure ...using a scope to measure and plot the output levels on a graph.

Just a little puzzled how the resonance of the transmitting coil might impact the results - surely you'd need to know the resonant curve of the transmitting coil allow you to adjust your pickup plot accordingly? Or would it just be as simple as having one channel of the scope monitoring the sine wave across the transmitter coil too thereby ensuring it has always the same level across it? (ie adjust the waveform generator to suit)

[Joe Gwinn]

Just a little puzzled how the resonance of the transmitting coil might impact the results - surely you'd need to know the resonant curve of the transmitting coil allow you to adjust your pickup plot accordingly? Or would it just be as simple as having one channel of the scope monitoring the sine wave across the transmitter coil too thereby ensuring it has always the same level across it? (ie adjust the waveform generator to suit)

It's far simpler to design the transmitting coil to have a resonant frequency well above the resonance of the pickup under test, so this is what's usually done.

[peskywinnets]

It's far simpler to design the transmitting coil to have a resonant frequency well above the resonance of the pickup under test, so this is what's usually done.

This is a bit like one of those "How does the snow plough driver get into work?" conundrums! Therefore before using a transmitting coil to measure the resonant frequency of the pickup - you need a device to measure the resonant frequency of the transmitting coil to check it's above the resonant frequency of the pickup

[Possum]

Joe's method post....

Since no one is posting the method I went back and dug through the capacitance measuring thread:
http://music-electronics-forum.com/t15286-3/
scroll down and you will see that I posted a yellow thumbnail, click on that, you'll get the page that Joe sent me and others on how to measure rez peak. It works...

[Joe Gwinn]

This is a bit like one of those "How does the snow plough driver get into work?" conundrums!

Knowing that the storm is approaching, he keeps the plow at home and drives it to work?

Therefore before using a transmitting coil to measure the resonant frequency of the pickup - you need a device to measure the resonant frequency of the transmitting [drive] coil to check it's above the resonant frequency of the pickup

One can use the how-to-measure-self-capacitance method to measure the resonant frequency of the drive coil all by itself, but it really isn't needed if the drive coil is at most a few hundred turns of heavier wire and one is trying to measure a pickup coil with 10,000 turns of fine wire.

[peskywinnets]

Knowing that the storm is approaching, he keeps the plow at home and drives it to work?

You must work in the snow clearance industry?!!

Knowing that the storm is approaching, he keeps the plow at home and drives it to work?

One can use the how-to-measure-self-capacitance method to measure the resonant frequency of the drive coil all by itself, but it really isn't needed if the drive coil is at most a few hundred turns of heavier wire and one is trying to measure a pickup coil with 10,000 turns of fine wire.

As it goes, I'll be using that very method to measure the resonant frequency of one of my sustainer driver coils over the next day or two (just out of curiousity really) ...hey, there might even be a market for using them as 'transmitter coils' so people can plot the frequency response of their pickups!!! (ok, ok, so I know you lot can all wind your own anyway 'transmitter' coils anyway!)