working mod- VCO out/VCF in

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controlvoltage
 
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working mod- VCO out/VCF in

Post by controlvoltage »

So I had this idea- a TRS jack on the x0x that had a raw VCO output on the ring contact and a filter input on the tip contact. This way you could use a Y-cable and have a pre-filter effects insert, or plug in a regular instrument cable and interrupt the VCO signal, to have a pure external audio input to the filter/VCA. Here is how I have done it so far; after a bit of troubleshooting it seems to work extremely well.

Refer to the mainboard schematic if necessary:

cut trace on top side of mainboard between C17(-) and R70/Q12 junction;
Wire C17(-) to Ring contact of 1/4" TRS switching jack
Wire switching side of Ring contact back to R70/Q12 junction.
Connect Tip contact of jack to a 100 uF 50V bipolar electrolytic capacitor (or the +lead of a polar cap).
Connect the other/negative lead of the cap to the R70/Q12 junction.

using the filter input this way is the most wonderful liquid analog "trance gate" effect... total audio headcandy! I don't have a y-cable yet to test it with fx inserted, but I plan to make one shortly.

Has anyone else done this? If not I highly recommend it... gives the x0x a whole secondary purpose. I have a ton of other modifications affecting the filter, so it is an extremely dynamic sequenced (and MIDI-syncable!) filterbox at this point.

Back to go tweak it some more... :D
/\/cv

stevenclements
 
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Post by stevenclements »

very cool idea!!!

Got and graphics of this? Pictures as it were?

again... fantastic idea!!!

gzifcak
 
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Joined: Wed Oct 26, 2005 3:46 pm

Post by gzifcak »

i believe the devilfish uses a stereo jack for this too. i did the same thing with 2 mono jacks, just so i don't have to use an adapter. the coolest thing i've found so far is running the oscillator through a delay pedal set in the audio range, then back through the filter. awesome slap bass guitar type sounds through the 303 filter - "wow"!

greg

bcbox
 
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Post by bcbox »

yes it's like an insert. I've done this on my 303 mods and have heard of others doing it well before me. It's certainly works very well.
Just to note you don't have to cut the trace to C17 if you don't want to mark the PCB just remove C17 and move it over to where the jack is and use the older solder pads from C17 for your connections.

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controlvoltage
 
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Post by controlvoltage »

aha, clever! wish I'd thought of that. ;)

evilxsystems
 
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Post by evilxsystems »

this sounds like a very easy yet badass mod...can one of you guys give me step by step instructions for what you would do if you pulled C17 and did it that way??? I'd be very greatful :)

Is this a pretty safe mod? It sounds BANNED awesome, but I don't want to kill my x0x...

-jason

bcbox
 
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Post by bcbox »

Note the switch in the pic is simply depicting a switched jack, normally closed (opens when plug is inserted)...

Image
Last edited by bcbox on Sat Oct 14, 2006 3:19 pm, edited 1 time in total.

evilxsystems
 
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Post by evilxsystems »

awesome...thanks!

What is the purpose for the cap connected to the tip, is there a way to put a variable cap or a pot here to control the input level?

-jason

evilxsystems
 
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Post by evilxsystems »

also does somebody have a Rat shack part number for the trs switching jack, I tried to find one but I couldn't, a Mouser part number would work too but I'd have to wait for it to be shipped :(

-jason

gzifcak
 
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Joined: Wed Oct 26, 2005 3:46 pm

Post by gzifcak »

if you put a pot between the tip of the jack and the filter, you can use it as a level control and overdrive control. you have to remove or reduce the resistor people are swapping for overdrive, then wire the pot so that the middle lug goes to the filter input, the clockwise lug goes to the jack, and the counter clockwise lug goes to ground. a log pot will give you smoother results.

if you can't find a stereo switching jack, you can use two mono switching jacks instead. then you don't have to use a special insert cable. that's what i did. 1 jack for oscillator out, one jack for filter in.

hope that helps,
greg

bcbox
 
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Post by bcbox »

the cap is just for ac coupling. You never know what someone will plug into that input...10uF is ideal, 1uF is probably fine. If you go smaller you'll start hi-passing the signal into the audio range (sometimes desireable)..
Last edited by bcbox on Thu Feb 22, 2007 2:38 am, edited 1 time in total.

brizzlescratch
 
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Post by brizzlescratch »

So excited to do this mod. I have a modified DS-1 distortion pedal that already sounds great after the XOX, but I think it will sound even better pre filter. Plus I can't wait to run everything I own thru the VCF.

But before I begin, just have a small question...
VCF Audio In

Use any panel mount jack, and connect the sleeve to ground. The tip should be connected to one side of a 100K resistor, the other side is connected to the negative side of a 1uF capacitor, and the positive side connects to the point where R70
The "official" VCF In mod talks about using a 100K resistor and 1uF cap, where as this mod recommends no resistor and a 100uF cap. So which is best. I don't want to hipass into the audible frequency range. What would be the purpose of the 100k resistor and why does this mod not use it?

cheers

Tenine
 
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Joined: Mon May 21, 2007 11:37 am

Post by Tenine »

I might do this when I get my x0x.
An external Sub-osc / Octave down pedal would be awesome :)

bcbox
 
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Joined: Thu May 25, 2006 1:30 am

Post by bcbox »

use a 1uF cap and a 22k resistor - that gets you right around the input level you need and the 1uF is big enough to cover the frequency range of the x0x. Make sure you put the (+) side of the cap at the input to the VCF...so the tip of the jack goes to a 22k resistor then the resistor goes to the (-) side of the 1uF cap and the (+) side of the cap goes to R70/C17

JRock
 
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Re: working mod- VCO out/VCF in

Post by JRock »

How did you wire the two mono inputs? I would much rather do that than get a splitter, plus I already have two mono switch jacks. I want one for vco out and one for vcf in. The schematics for the one stereo input is up on the wiki but I'm new enough that I'm not sure I can figure out how to convert it to 2 mono.. Thanks......
Got it!!!

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