@Tim: WRONG! No, relax, I'm joking ... ;)
@all:
May I ask you by the way how you like the sound of the diode-ladder filter
I mean do you find it more or less musical than the transistor-cascade e.g. for bass sounds or leads or so
Last question: Does the Doepfer transistor ladder filter really sounds like the Moog filter
I've read your paper about the comparison between the diode- and transistor filter, Tim. Good work!
Ollie
--- In
Doepfer_a100@yahoogroups.com
, "Tim" <timothy@...> wrote:
>
> Hi Mick,
>
> > Can someone tell me if my A102 filter is acting correctly - The resonance seems to be set really high. The filter will self oscillate with the resonance set to just 4 (when the cut off is set between 3 and 6).
> >
> > Is this normal
>
> Yes, both mine behave similarly - basically there is way too much gain around the feedback loop.
>
> > Is there any way to adjust the resonance to a more usable range
>
> I tried a couple of things very quickly (the first one was spectacularly ineffective!). However the following seemed OKish: between C10 and Q7 there are 4 resistors - the 2k2 amongst these is R24 (the 'bottom one' if you hold the faceplate nearest you); swap this for a 5k6 say, which will cut the gain to a third, so it won't resonate until the pot is further round. A 4k7 may not be enough of a difference, and a 6k8 (I temporarily added a 4k7 to the 2k2) may restrict the range of frequencies at which it will oscillate. Unfortunately it will also reduce the output amplitude somewhat.
>
> To do the job 'properly' would mean re-vamping the entire 'gain regime' around the loop, which would require considerably more thought, and replacing maybe half-a-dozen or so resistors. My initial idea was to *double* R5 (the 10k in the middle of the only group of 5 resistors, central to the board), but this seemed to have little impact, mainly I think because the resonance pot is a 'law C' ('rev log'), and so naturally 'all the action' is in the first part of its rotation.
>
> Let us know if you have any success with this!
>
> Tim
>