Tube Amps / Music Electronics
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|8/10/2005 8:56 AM|
|Max Weinhall||Joe Gwinn's Inductance Measurement|
I am new here, plus I am an electronics novice, so please forgive if I show bad manners or laughable ignorance.
I am looking at Joe Gwinn's homebrew test instruments ( http://home.comcast.net/~joegwinn/ ). First of all - THANKS! I will have no problem making the "Simple Hall-Effect Magnetic-Field Meter".
I am keen to try the "Maxwell-Wein Impedance Bridge" for measuring inductance, but I don't have a signal generator. I would like to use a PC soundcard based signal generator - could that be made to work? I think getting the correct frequency is no problem, but what about voltage? Can I just test AC voltage with my DMM and move volume sliders up and down until I'm very close to 1.0V? Or would I need a a specialized measurement tool for that route, like an AC Millivoltmeter?
If that's no good, what about building a simple transistor-based generator like in my personal EE college, a kids' edu-toy breadboard kit/illustrated book? E.g. http://www.redcircuits.com//Page13.htm -Would that do the trick?
I'm mainly want to compare pickups and be able to reproduce the same thing. I have been winding for a few months and already all my friends want copies of some of the serendipitously great pickups I've made. Most of them are assembled from parts of old junker pickups, so I can't just go buy another magnet or bobbin or anything to match. Also I have a cheap Korean ceramic humbucker that I LOVE and I would like to be able to make my own, slightly darker version. So I just need consistency for comparing pickups side by side, not absolute, perfectly-calibrated, team-of-101-scientists type precision measurement.
I have seen the Extech meter that is mentioned on this forum - added it to my Amazon wish list - but I'd like to do this on a super low budget - even lower than $180. Plus I really like making my own tools - gives the hobby an old world luthiery vibe.
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|8/10/2005 9:10 PM|
On 8/10/2005 2:56 PM, Max Weinhall said:
The cheap analog signal generators, which have a big mechanical frequency dial and cost a few hundred dollars, will also work.
Or, look for "wein bridge" oscillators.
|8/13/2005 4:54 PM|
An afterthought. The two potentiometers (R1 and R2) need to be either ten-turn types, or to be composite (two pots in series, one 3% the resistance of the other), or it's too hard to adjust to the null manually.
The trick is to get everything nicely nulled (DMM reads less than a millivolt), disconnect the signal source, and then use a DMM to measure tha actual values of resistance and capacitance.
|8/13/2005 9:33 PM|
Joe Gwinn wrote:
Links to sound card test sites are at:
It occurred to me that you could get the inductance of a guitar pickup in a voltage divider by plotting its output from a frequency sweep below its resonance point. Shouldn't be too awfully difficult with a sound card, a couple of cables and a resistor near the DC resistance of the coil.
A freeware sweep generator for sound cards is at:
Marchand electronics has a few mpegs for test tones and a frequency sweep over at:
|8/19/2005 10:18 AM|
Hey thanks for the great info guys. I was away on a very rare vacation since I posted that question, and I only just now ordered the remainder of the parts I need for these gagdets. I'll report back how it works out.
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