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

[Magnus Danielson]

Oren Leavitt wrote:
> 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

Seems very likely, but I am supprised of the low level of capacitance 
needed.

Cheers,
Magnus