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

[Oren Leavitt]

David Ingebretsen wrote:
> Alright. I've pinned down exactly what causes the ripple in the SEQ-02.
> 
> In essence, if I use a patch cord made from shielded cable longer than about
> 10 cm, regardless whether or not I connect the shield at either end, it
> creates this ripple when I plug it into the CV output. On the bench, in the
> rack, regardless. It always does.
> 
> If I use a single conductor wire, regardless the length within reason, to
> patch the SEQ-02 anywhere else, all is good, with one exception. If I plug
> the SEQ-02 into a multiple and plug a shielded cable into the multiple, I
> get the 2 volt peak-to-peak 400 kHz ripple again.
> 
> So, what magic is the shield doing to introduce this ripple regardless
> whether or not it is connected to ground?
> 
> The easy fix is to make up a bunch of single conductor patch cables, but I'd
> love to understand why.
> 
> Thanks
> David
>



David,
Sounds like the CV output is direct coupled to an op-amp that does not 
like the capacitive load the shielded cable may be imposing on it.
As a quick test, to isolate the issue, you can try placing a 100 ohm (or 
more) resistor between the internal SEQ-02 output and the CV out jack. 
See if that stops the problem.
My guess..
- Oren