|What makes a pickup a pickup?
Basically wire and a magnet. We all know how to measure the resistance of a pickup -- get
out the old volt-ohm meter and check it out! However, how do we check the strength of the
magnet(s) in the pickup? Doesn't matter? Critical? I decided to find out.
Luthiers and repairmen measure the strength of magnets with a device called a Gaussmeter (teslameter in Europe). A gaussmeter measures the gauss of a magnet, and can tell you whether the magnet you are checking is oriented north or south.
I started pricing gaussmeters on eBay, and I got sticker shock. They were in the neighborhood of $200-500 for a cheap one, and multiple thousands for the expensive ones. There had to be a better (cheaper) way because I just wanted to establish baselines with famous pickups, and use those as standards for my pickups.I started searching the Internet, and found a great site. This site will show you how to build an inexpensive measuring device for magnets.
The URL is -- http://my.execpc.com/~rhoadley/magmeter.htm and the fellow that built the site shows the layman how to measure the relative strength of a magnet. This is very important -- as stated in Guitar Electronics for Musicians by Donald Brosnac, more windings and lower gauss lowers the resonant frequency of a pickup, while fewer windings and higher gauss raises the frequency. Mr. Larry Dimarzio states that resonant frequency is a great predictor of how a pickup will sound. Well, if you don't have a gaussmeter or some way to measure gauss, how can you adjust the sound of a home made pickup? The answer is painful, slow-paced experimentation, which I'm not in to right now.
I decided to take the plunge and build the base gaussmeter model first. I ordered the parts from Parts Express, but they backordered the perf board and wouldn't ship the rest of the items. Frustrated, I then ordered the parts from MCM Electronics. Ironically, both orders shipped the same day even though I tried to cancel the Parts Express order! I took them both, and started soldering!
I bought the Hall Effect Sensor from Radio Shack last summer when I was in the States. It was the more expensive model that came with calibration charts. Using the calibration charts, I believe it reads pretty accurately.
Assembly was easy and exciting, and here is what I've found so far (NOTE: You may know all of this already):
1. Pickup covers do affect the magnetic field that the strings vibrate in. The most pronounced drop in gauss is over the slug polepieces. The adjustable polepieces have significantly more power than covered ones.
2. Strat magnets can have a significant difference in gauss in the same pickup.
3. All magnets are not the same, and PAF pickups have a significant difference in gauss from pickup to pickup.
4. The Dimarzio PAFs have almost exactly the same magnetic characteristics of a Gibson PAF.
The bottom line is that if you are interested in pickups, build your own attack gaussmeter and start assessing those pickups!
|This is a photo of the gaussmeter. The volt-ohm
meter is a combination VOM that can read capacitance and inductance. It has been a
good one and forms the core of the pickup measuring universe. Inside the little blue
box is a power supply for the Hall Effect sensor and the wires that go to the VOM and the
"probe". In the foreground you can see the wooden probe with the sensor
attached to the end (on right side -- see the white dot). I used a broken paint
brush to hold the sensor to avoid any magnetism.
Operation is easy: plug in the battery, set the VOM to read dc voltage, move the sensor toward the magnet and start measuring! The VOM gives the reading and I plug the numbers into an Excel spreadsheet to arrive at the gauss numbers.