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Patents on Parade #3

Another simple patent that illustrates once again how duplication is possible when simple solutions to common problems are devised.

US Patent Number 5,585,767 is a jfet amplifier for guitar or other musical instruments. The jfet amplifier is imside the plug housing and an external box provides power and an interface. Click on the image to view this full size. The jfet is number 24 on the drawing.

This is much the same system that some professional microphones use... the Neumann U47 FET comes immediately to mind, for example. The difference is that the fet amplifier is in the housing of the microphone instead of inside the plug. Phantom powering has of course been around for many years. More info about the Neumann U47 is available from Ethan Winer and originally published in a magazine article in 1980.

Another problem with this circuit is that Don Tillman had already invented the jfet-in-a-plug amplifier and posted the information to an Internet newsgroup in 1992... three years before the patent was filed! Don's preamp is shown below:

You can view the full page of info complete with building instructions on Don Tillman's site.

You would think that the patent office would have a subscription to Dejanews (Google News) to search for things like this.

*** I'm going to revise this page with an improved circuit to build as soon as I get some parts ordered. Stay tuned.


©2004 Jack Orman
All Rights Reserved

This page last modified on Sunday, 14-May-2006 06:52:40 PDT

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