[sdiy] 4069 vco gives v+ noise?

[Magnus Danielson]

From: Karl Ekdahl <_nial_ at yahoo.com>
Subject: Re: [sdiy] 4069 vco gives v+ noise?
Date: Mon, 12 May 2003 16:25:06 +0200 (CEST)

> I use the same pinning as in the schedule you sent but
> it's still giving noise (in the v+ line). The noise
> seems like a 50hz wave with some minor disturbances
> riding on it that seems to be the osciallating tone. 
> 
> The minor noise can at high frequencies be eliminated
> trough adding a 10uF cap at the v+ line but I can't
> reduce the major noise (the probable 50hz) without
> putting a resistor inbetween ground and gnd pin on the
> 4069. And that - as i said - makes the square out die.
> 
> The odd thing is that the noise only occurs if i add
> more modules to the same powersupply, for example a
> ASM lfo. The powersupply should be able to drive both
> modules (at least i think so) without any
> distrubances. It's based aroun 78xx, 79xx and 6800uF
> caps and uses the standard layout found in most
> powersupplies.

Look at the powersupply lines, compare any AC with the AC from the transformer.
If they don't handle it well you doo have a too weak powersupply.

Also look at the rectifies voltages and see if they dip too low on higher
load. If they dip too low, the regulator doesn't have the voltage margin it
usually burns up to keep a steady voltage.

Cheers,
Magnus