adjustable filter tracking ?

[truvc]

has anybody got some ideas for filter tracking ? that would be such a cool feature.

i tried the following from the wiki:

1:1 Filter tracking would be a simple matter. Just connect CV out into a 100k resisitor, and then into q10, like the CV for cutoff mod above. You will probably want to wire in a switch between there.

i took the CV at J6 if i recall well. the result was just that hi pitch notes only would be heard, and loudly (as the cutoff would be very open). maybe i did the mod wrong, but if not it was not really to my taste.

anybody got experience to share there?

also, from the wiki, the following would be great:

For DevilFish like filter tracking, this is a little more complex, as we need to scale the voltages. This would probably mean using a pot as part of a voltage divider, and possibly multiplying the CV in before going through the divider.

how could i do that ? anybody with some rough ideas i could experiment with ?
thx!

[booster]

Anyone got any ideas on this one?
Adjustable filter tracking would be a great mod.

I wanna try it!!

[guest]

where did you connect the cv on q10
im guessing it should go to the emitter
you could try using a larger resistor
and keep the cutoff knob pretty low

[booster]

Hi guest,

This original post/thread is actually almost a year old, I found it whilst searching for info on filter tracking and thought I would see if anyone had any extra info on how to make an adjustable mod for filter tracking; Devilfish style!
The Wiki talks about making a switched filter tracking mod (on or off), but also implies that there must be a way to make an adjustable filter tracking mod by scaling voltages?

I just thought I would dredge this post up again and see if anyone had any ideas.

[kroffe]

I've been planning to do this mod and I think the right way to do it would be to connect one end of a pot (let's say 100k) to CV out and the other end to earth. The tip goes via an on/off-switch and then connected to a 100k resistor that goes in between where Q10 and R73 meet. I'll probably try this one out tonight.

[kroffe]

I tried it out and it works very well.
I took CV from where pin 7 of IC11B and R107 meet. Only thing I would wish for is to have the CV even more stretched - maybe you could amplify it thru a OP-amp or something...

Future plans: to be able to use an external CV-source via a break-in jack..

[guest]

you could try reducing that 100k to q10
that might stretch it out some more

[booster]

Future plans: to be able to use an external CV-source via a break-in jack..

I ended up installing the x0xio rear panel mod kit. This includes a jack for filter-CV in. You can route the CV out into the Filt-CV, or use an external source.

I use it a bit in this following video:-
http://uk.youtube.com/watch?v=qxd_W14VLZ4
CV from the silver x0x is controlling the filter of the black x0x from around 0:17 onwards.


The full x0xio kit has adjustable filter-tracking I believe.

[bcbox]

For best results with filter tracking you'll need to scale the cv output before sending it to the filter cv input.
The quirk in the 303 is that the filter cv has a resting voltage of 3.25V.
Anything lower than 3.25V and the cutoff freq is lowered. Anything higher than 3.25v volts and cutoff freq is raised.
A cv of 3.25V is equal to note D#3, so if you send pitch cv straight to the filter cv input the cutoff freq will go up for any notes about D#3, and down for any notes below it. A lot of the useful range of a stock x0xb0x is below note D#3 so ideally you would like to set the 'transition' note for filter tracking to something like an octave lower, so that your cutoff freq goes up for something above say D2 and down for something below D2, so that normal basslines are effected more. This can be done by getting crafty with a non-inverting op-amp and setting it for desired gain and biasing the input to some arbitrary DV voltage that you find that works. You can also use this op amp stage to amplify the cv so that you have a bigger voltage swing so you can do over-tracking (filter freq increases more than one octave per octave of pitch cv), and then follow it with a pot to control the depth so that you can set the tracking to any amount.