VCF Audio mod from the mod page

[CoolColJ]

With this mod, will the original VCO will always be still sounding?

I thought that when you plugged something in the original VCOs would be cut out so you only hear the external audio. Then when you unplug the cable, everything is back to normal?

How will it work?

[Jonnay]

I think the mod on the mods page would mix in the external audio with the waveform. However, moding the mod (a metamod!) would be pretty trivial.

One idea is to change the waveform switch from a 2 position to a 3 position. (it probably has some kinda fancy schmancy name... Dual Pole Triple Throw?). Another is to use a jack with a switch connector, and wire it up so that the output from the VCO is wired to the NC position. This would override the VCO whenever you plug something in.

I think the switch would be much more elegent.

[CoolColJ]

So ideally it would like this with the 3 position waveform selector

setting it to square/sawtooth has the audio input mixed together with the VCO, and in the middle position just the external audio by itself?

[Jonnay]

No.. the way I thought of doing it, it would just be selectable between Saw, Square and External.

I have a schematic here: http://wiki.jonnay.net/x0x/vcfmods

[CoolColJ]

I just thought it might be nice to sometime have dual VCO action by mixing another VCO with the unit's existing one that's all

I want to hear my Minimoog, TX416 and SH2 getting sequenced by and run through the X0X0B0X

[CoolColJ]

been discussing this mod with the guy who's building mine -

replacing the 2 way waveform selector switch with a 3 way one,

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it would select between letting the saw pass, square pass and nothing pass

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so when the switch is set to "nothing pass" and you have a jack plugged in, you only get extenal audio

and on the other settings, you get either saw or square mixed with the external

and if no jack is plugged in, only saw/square or silent on the 3 settings

[controlvoltage]

Like, yeah...

http://www.ladyada.net/forums/viewtopic.php?t=455

this mod may be untested on the x0xb0x but I think it's pretty standard & well-tested when it comes to TB303s. The illustration of this mod which I found on hyperreal is about 10 years old now.

I'll be trying it as soon as I find the right switch.

Oh and I think you want to mod the ext. in to run directly to the third position of the switch, rather than using the existing external in circuitry.

I might even add a diode buffer network to help shield the circuit from potential nastiness... rather than a completely straight wiring from input jack to switch. This might not be necessary, but shouldn't hurt either.