VL1 phat philter envelope idea/question...

Dj Task Manager · December 20, 2011, 11:20:25 AM

Hi!

does anyone know if the vl1 has an envelope point you can tap into ala the sk-phat philter mod...? might be a nice addition seeing as it has got adsr

Mike x

Circuitbenders · December 21, 2011, 12:59:57 PM

Now this is where you need a scope

Page 6 of the so called 'service manual' does suggest that the envelope is accessible, but it appears to peak at -1.2v and drop to -3v

http://www.warningwillrobinson.com.au/manuals/Casio%20VL-1%20service%20manual.pdf

Thanks to gmeredith for the manual.

Dj Task Manager · December 21, 2011, 02:25:49 PM

well that sounds promising, I fear I havent got the skillz to make this work... I suppose you would have to convert the -3v ---> -1.2v signal into something more useful.

Dj Task Manager · December 21, 2011, 02:26:09 PM

...Hey just a thought, could the output of it (or indeed any device) be used directly as a cv to do a similar thing?

Dj Task Manager · January 12, 2012, 03:14:36 PM

...I'll answer that, you need an envelope follower you dummy.

Circuitbenders · January 12, 2012, 05:06:25 PM

yeah, what you said

or maybe you could stick the envelope from the VL into an inverting opamp to make it positive and boost the levels a bit. I suspect you'll probably have to power the opamp with a dual rail supply though, which could make things tricky.

gmeredith · January 13, 2012, 03:18:39 AM

Hey I go away for a holiday and all the good stuff happens...

That would be really cool to get my filter going on the VL. As I recall when building the Phat Philter, I think the Casio SK only put out about a 1V signal to drive the filter open, so the VL should do it if you can invert it to a + signal. The sensitivity of the filter is simply governed by a resistor, so you could adapt it to handle any CV voltage within reason.

Quote...Hey just a thought, could the output of it (or indeed any device) be used directly as a cv to do a similar thing?

Well the CV voltage output by the VL (and SK's) isn't a CV in the sense of an analog synth CV, where the higher the V the higher the pitch of a note, so if you're meaning can you hook the output to an analog synth and have the VL play notes on your SH101 for example, it won't do it, since it's an ENVELOPE CV, not a ptch CV. But it would certainly give some interesting results if you did

Dj Task Manager · January 13, 2012, 05:40:47 PM

interesting.... I'll do some research into how to invert a signal...

I think I was just wondering if you were to pump the output audio signal (or more precisely tap a bit of the audio signal with a simple passive mixer) into the 'cv in' of the phat philter would it affect it in a desirable kind of envelope kind of way?...

if routed in a certain way it would also sort of form a kind of feedback loop which would probably make it tend towards either silence or ridiculous audio destruction. Make sense?

(Im quite prepared to cast into the noob dungeon on this one!)

....................

One mod i have planned that im pretty confident will be success is swap out the low, mid, high octave select for a drag contact jobby ala gijs (http://gieskes.nl/circuitbending/?file=casio_ct-660) for appeggio good times. (or maybe even make a 4017 sequencer for the same purpose)

By the way this is all speculative. I havent even plugged it in yet!

And on that note I recon I'll go fire it up!

Bogus Noise · January 13, 2012, 07:05:00 PM

I've been playing with something similar for a different keyboard here this week. Getting an envelope signal from a keyboard matrix was harder than I expected! Taught me a bit about voltage manipulation though...

But anyway, it sounds like your envelope is at -3v when idling and -1.2v when triggered, is that right? In this situation you can probably mix the envelope output with a bit of offset voltage from the +3v terminal to get a signal that starts at 0v and peaks at 1.8v. A 10k resistor between +3v and the envelope output could do it, but you can test the output signal with a multimeter and use a pot in place of the resistor, and turn it about till you get 0v when there's no keys being triggered. Then you should get something like 1.8v when you press a key.

If that all works out, you may not even need to use the opamp.

Dj Task Manager · January 14, 2012, 04:16:37 PM

Quote from: Bogus Noise on January 13, 2012, 07:05:00 PM
I've been playing with something similar for a different keyboard here this week. Getting an envelope signal from a keyboard matrix was harder than I expected! Taught me a bit about voltage manipulation though...

But anyway, it sounds like your envelope is at -3v when idling and -1.2v when triggered, is that right? In this situation you can probably mix the envelope output with a bit of offset voltage from the +3v terminal to get a signal that starts at 0v and peaks at 1.8v. A 10k resistor between +3v and the envelope output could do it, but you can test the output signal with a multimeter and use a pot in place of the resistor, and turn it about till you get 0v when there's no keys being triggered. Then you should get something like 1.8v when you press a key.

If that all works out, you may not even need to use the opamp.

That sounds like it could work, I'll have a poke around. Do you think this tinkering would stop the envelope from shaping the voice? Though perhaps it wouldnt if it was implemented deftly, or at least with a switch to return it to the original functionality. I guess I will have to stop speculating and break it open...

Bogus Noise · January 15, 2012, 09:59:30 PM

Well, the adjusted envelope signal wouldn't trigger the VL1's envelope correctly, but you wouldn't need to disconnect the original signal. The way I'd do it is to take the envelope signal from the envelope generator section, and put a diode in to block any of the +3v offset voltage and tweaked envelope signal from going back the other way.

But yeah, at this point it's probably time to bust out the screwdrivers and get stuck in

gmeredith · January 15, 2012, 10:53:00 PM

If you were to run an audio signal into the phat philter CV input, you would get a modulated filter!! Changing the frequency of this "CV" signal would change the filter modulation frequency - like an LFO - although I think the negative part of the wave would be clipped, so it would sound partly square wave LFO. If ithe CV audio frequency was low - like 20Hz or less - you would get discernable VCF modulation. For example, if your "CV" source was a synth, if you played a really low bass note, it would be an obvious wow-wow-wow filter sound on the target synth. If you used the pitch bend wheel on the CV synth then you could do on-the-fly dubstep wobbles

Dj Task Manager · January 16, 2012, 01:17:26 PM

great tip with the diodes! I'll have a go with 'audio signal ---> cv in' and if it is radical it could be added in as another variation. Bangin'

Circuitbenders · January 17, 2012, 02:19:31 PM

It might be an idea to read up about DC blocking caps before you go wiring an audio signal straight to a CV summing point. Presumably there will already be some kind of DC offset at the CV input?

airburst · October 25, 2012, 04:00:45 PM

Just wondering of anyone has made more progress on adding a simple VCF to the VL-1 since previous postings.

I'm contemplating something similar and I noticed a couple of potentially useful things about the analogue circuit board of the VL-1.

First, the LA6355 op-amp chip (which I is marked as IC2 in a circuit diagram I have and which is described in the service manual as "Divider 2") is a dual chip which has one half unused. I'm wondering if this can be employed in the filter circuit?
If it can be used then surely that ought to simplify things a little as the chip already has power connections sorted.

Also, the board has a group of unused holes on it - almost as if Casio intended to make it friendly to hackers in need of a kludge area. I'm hoping it's possible to get all the needed extra components on there.