Helmuth Lemme?

[Jeff Callahan]

Searches in this forum have got me interested in Helmuth Lemme, especially his frequency analyzer. His website (in German) does not help. I'm interested in making (or buying) something like it, but don't know where to start. Also, are there any English copies of his book(s)?

Thanks for all the expertise in this forum,
Jeff

[Joe Gwinn]

Searches in this forum have got me interested in Helmuth Lemme, especially his frequency analyzer. His website (in German) does not help. I'm interested in making (or buying) something like it, but don't know where to start. Also, are there any English copies of his book(s)?

Thanks for all the expertise in this forum,
Jeff

Lemme does have an English version of much that is on his website, or at least he did when I last looked.

[belwar]

The thing with frequency analysers is that there is no set method for driving the pickup. I think some have tried driving it with a low impedance coil in the magnetic field of the test pickup, others use a frequency genertator into the wires of the coil, while others still have invented thier own ways. I had a conversation with Audere Audio recently, and the owner build a whole custom setup to uniformly measure pickups repeatibly (This guy is a serious engineer and knows his stuff). Seymour Duncan has a really cool method of driving the pickup (which I wouldnt divulge without permission) which on paper seems to be the most sensible way of performing the test.

bel

[Mike Sulzer]

The low frequency driver coil provides a time varying magnetic field that results in a flux through the pickup coil. This is fine for measuring the circuit properties and comparing the sensitivity of different coils. (The circuit properties alone can be measured more easily by driving the coil with a current or voltage source, or an I-V circuit.)

But it does not involve the permanent magnetic field of the pickup at all. Since this field magnetizes the string, this aspect of the pickup performance is not tested. For example, if the magnets of a pickup became partially demagnetized, this type of test would not accurately indicate this.

A complete pickup measuring test is not so easy.

[Steve Conner]

I think some have tried driving it with a low impedance coil in the magnetic field of the test pickup, others use a frequency genertator into the wires of the coil

What do you think the difference between those two methods would be when testing a pickup with a cover?

I wonder, because I tested a covered humbucker the other day, just driving the coils. There wasn't much difference in Q and resonant frequency when I took the cover off, certainly not as much as I'd have expected from what people say about the tone of covers.

But maybe it makes more of a difference when the signal has to fight its way in through the cover.

[David Schwab]

Here's the English version of his site:

BuildYourGuitar.com :: The Secrets of Electric Guitar Pickups

He shows the pickup analyzer and says it's a commercial product, but never seems to have it for sale.

You can also use Google to translate the German site:

Google Translate: www.gitarrenelektronik.de

[David Schwab]

But maybe it makes more of a difference when the signal has to fight its way in through the cover.

The signal doesn't fight its way through the cover... the covers introduce eddy currents which tend to flatten the resonant peak.

[Mike Sulzer]

The flattening of the resonant peak is the easiest effect to measure, but there are more subtle effects also. These effects are are more significant from the cores rather than the cover since the cores are made from permeable steel. For example, Lemme shows that there is a dip in the response of a humbucker somewhere, I believe the lower middle. This agrees with what I found the the thread "A new model for....".

How thick would a moderately conductive cover have to be to significantly reduce the signal passing through? I do not know, but Joe might have a calculation or measurement handy. I am guessing that the effect is weak with a good thin cover since generally a highly permeable material like steel is involved in magnetic field effects at audio frequencies. At rf, that would be another matter.

The lack of significant effect is also supported by the observation that a thin metal box is not very good at shielding out magnetic hum, for example from a transformer. (It is, of course, quite good at getting rid of electric fields.)

The signal doesn't fight its way through the cover... the covers introduce eddy currents which tend to flatten the resonant peak.

[fieldwrangler]

Folks -

Forgive me for bringing this up; I'm reasonably sure it's been discussed before, but is a bit difficult to search for.

This idea of driving pickups with a consistent source did occupy much of my energy for awhile. For a time I was spinning a small file (with ovoid cross section) over the top of the things with a flex drive/collet thing driven by my Dremel.

Then I set up a feedback driving pickup as far away from the Device Under Test as possible. Eventually this yielded to the really bonehead version I have now, which is a test axe lying on its back with a clear plastic platform above most of the free string span. I just drop pickups face down onto the platform wherever along the scale I want; the platform establishes a consistent distance from the pickups' faces to the strings. Then I drive one string at a time with an E-Bow. The E-Bow's height can be adjusted by slackening the adjacent strings on which it rests, and you can move it to different antinodes in order to listen to different string overtones. You can quickly swap a known pickup into the "pole position" for comparison.

Not what you'd call a real "frequency response" test (plus it doesn't give transient response information) but a combination of ears on the amp and eves on the scope combined with the use of reference pickups has really helped steer my stuff in the direction I want it to go.

Bob Palmieri

[Joe Gwinn]

How thick would a moderately conductive cover have to be to significantly reduce the signal passing through? I do not know, but Joe might have a calculation or measurement handy. I am guessing that the effect is weak with a good thin cover since generally a highly permeable material like steel is involved in magnetic field effects at audio frequencies. At rf, that would be another matter.

The lack of significant effect is also supported by the observation that a thin metal box is not very good at shielding out magnetic hum, for example from a transformer. (It is, of course, quite good at getting rid of electric fields.)

The theory of shielding is fairly well developed. At audio frequencies, the magnetic fields mostly get through, so a cover acts as a kind of low pass filter, but one that has a different attenuation-versus-frequency curve than a RC filter. A cover probably differs from a baseplate in effect because what doesn't make it through a sheet is reflected, although some is absorbed. I'll try to summarize the effects, which will require some research.

[Joe Gwinn]

The signal doesn't fight its way through the cover... the covers introduce eddy currents which tend to flatten the resonant peak.

Eddies to the Right! Eddies to the Left!

Into the Valley of Damping Rode the Music!

[David Schwab]

Eddies to the Right! Eddies to the Left!

Into the Valley of Damping Rode the Music!

[Electricdaveyboy]

Yo

Oh yes.
Read the book from Helmut wehn I was 15( 1987), playing a Johnny Pro II guitar and learing to re-wind E-motors.
The book was named `Die E-Gitarre´, great stuff in it but I lost it over the years / never got it back ( from my buddy Jan)and then it was discontinued.
But resin and capacitors wount make a crap pickup sound nice........
Had my experience.