Why is this please???? Was: RE: [sdiy] MFB SEQ-02 question

[ASSI]

On Wednesday 06 January 2010, David Ingebretsen wrote:
> Alright. I've pinned down exactly what causes the ripple in the
>  SEQ-02.
[...]
> So, what magic is the shield doing to introduce this ripple
>  regardless whether or not it is connected to ground?

Capacitive load introducing another zero into the transfer function 
and de-stabilizing the output buffer, most likely.  You can test this 
by adding a few pF-nF at the and of a cable that would otherwise not 
produce the ringing.  Shielded cable may also introduce some RF ground 
currents that would otherwise not be present, but that is less likely 
to be the culprit judging from the scope plots.

> The easy fix is to make up a bunch of single conductor patch
>  cables, but I'd love to understand why.

Try a smallish series resistance at the output of the buffer and 
before presenting any capacitance (i.e. before the jack preferably).  
But check with MFB first that the component values around the output 
buffer(s) are correct, especially those that provide frequency 
compensation (if any).


Achim.
-- 
+<[Q+ Matrix-12 WAVE#46+305 Neuron microQkb Andromeda XTk]>+

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