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

[David Ingebretsen]

Thank you too Achim. I tried this and it fixes the problem. (I got Oren's
reply first...)

Now the question is the best way to effect a permanent cure.

David

~~ -----Original Message-----
~~ From: synth-diy-bounces at dropmix.xs4all.nl [mailto:synth-diy-
~~ bounces at dropmix.xs4all.nl] On Behalf Of ASSI
~~ Sent: Wednesday, January 06, 2010 12:12 AM
~~ To: synth-diy at dropmix.xs4all.nl
~~ Subject: Re: Why is this please???? Was: RE: [sdiy] MFB SEQ-02 question
~~ 
~~ 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]>+
~~ 
~~ Waldorf MIDI Implementation & additional documentation:
~~ http://Synth.Stromeko.net/Downloads.html#WaldorfDocs
~~ 
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