[sdiy] ASM-1 VCO LM311 Question

[Magnus Danielson]

From: "David Reichert" <sysyphus at sympatico.ca>
Subject: RE: [sdiy] ASM-1 VCO LM311 Question
Date: Sat, 2 Feb 2002 18:22:41 -0500

> While we're on the topic of the ASM-1 VCO, I'm having trouble with the
> 2N4856. I don't seem to be connecting it correctly. I can't find a data
> sheet anywhere and have to idea which pin is which. I could figure it
> out if it was a BJT, but for an FET I don't know how to go about it.
> 
> Can anyone help with this?

Please read the note that I put on the ASM-1 homepage, in the VCO
section:

Note:
It is a common confusion about the FET in the VCO, the PCB footprint
matches that of a PN4391 and not of 2N4391. The difference is that the
Source and Drain is interchanged in position. The best cure is to bend
the Gate of the 2N4391 diagonally to the empty corner of the
quadrat-shape that the pins touches three of the corners. If in doubt
check your FET up in a databook and compare against schematics and
PCB. This caused my VCO to keep quite :(

Knowing that you actually have the pinout of the PN4391 should help
you with using any other FET and wiring it up.

I learned it by picking up the 2N4391/PN4391 datasheet as I was having
trouble myself.

Cheers,
Magnus