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jnuaury
Joined: Feb 28, 2008
Posts: 161
Location: chicago
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 Posted: Tue Jun 10, 2008 11:44 pm Post subject:
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| doctorvague wrote: | | Here's my 'Two Simple Filter'. Parts count: 2. |
do vactrols require a current limiting resistor like LEDs do?
im assuming your "sort of" vactrol vca might work better if you put a 100k resistor where the cap was... i cant make any guarantees though as my batch of vactrols is still on its way |
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Mooger5
Joined: May 02, 2007
Posts: 199
Location: Portugal
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| Posted: Wed Jun 11, 2008 10:22 pm Post subject:
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| v-un-v wrote: | | doctorvague wrote: |
Without some of kind of summing, any attempts to introduce feedback would simply short the input and output, yes-no??
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yep that would make sense.
A diode in the chain? would that help at all?
I'm trying to balance electronics with architectural visualisation (don't ask  ). Perhaps I should be the vague one?   |
I think you´d have to add a little gain for the emphasis to work so it would be an active device, but you could always route the filtered signal through a mixer module.
Hey a diode will only pass half wave, either positive or negative(remember it´s not dc; music signals travel back and forth). It can actually sound interesting  . If not in the feedback path, try it at the filter input. You could then run it in paralel with say the unfiltered signal passing through a diode facing opposite direction....
There will be a little attenuation due to the diode. |
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zonkout
Joined: Oct 12, 2006
Posts: 33
Location: ozztin, teggsitz
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| Posted: Wed Dec 31, 2008 2:04 pm Post subject:
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| v-un-v wrote: | Hey Zeb! Been a while!! 
Howabout a potential divider between -15v and +15v, with a pot in the middle? Some wild sweeps can be achieved here. This, although really simple can yield some wild sounds when feeding oscillators into ringmods.
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How might this be constructed in a passive manner (no power supply connection at all)? I want to make a rack panel with some simple passive circuits for my MS-50 and SQ-10.
A trigger mixer would be passive too, right? Each input going through a diode before hitting a single output? |
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doctorvague
Joined: Mar 14, 2007
Posts: 281
Location: new mexico
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| Posted: Thu Jan 01, 2009 7:28 am Post subject:
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| zonkout wrote: | | v-un-v wrote: | Hey Zeb! Been a while!!
Howabout a potential divider between -15v and +15v, with a pot in the middle? Some wild sweeps can be achieved here. This, although really simple can yield some wild sounds when feeding oscillators into ringmods.
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How might this be constructed in a passive manner (no power supply connection at all)? I want to make a rack panel with some simple passive circuits for my MS-50 and SQ-10. |
It can't be powered and passive at the same time.
| Quote: | | A trigger mixer would be passive too, right? Each input going through a diode before hitting a single output? |
Yep.
http://en.wikipedia.org/wiki/Diode-or_circuit |
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machine.cuisine
Joined: Jul 20, 2007
Posts: 61
Location: ks
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| Posted: Mon Jan 05, 2009 2:48 pm Post subject:
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| doctorvague wrote: | Here's my 'Two Simple Filter'. Parts count: 2. The NSL mp3 uses a NSL-32SR3 and other mp3 is using a VTL5C3. Lacking vactrols you can always use an LED and photocell. You can also put 2 vactrols in series, parallel and of course try different cap values, or use a rotary switch to switch between caps (increases parts count tremendously, though)
Sorta works like a VCA with no cap at all: Parts Count: 1
I only feed the CV input with positive voltages, like an envelope and haven't blown up a vactrol yet.
Cheers
Phil |
Man, this makes a nice little ghetto VCA! I replaced the capacitor with a 10k to gnd - it's pretty damn quiet when off. [I'm using a VTL5C3/2 with the wiper tied to input side.] It also works good gating LFO inputs (not just audio).
EDIT: When using bipolar CV Input - I have a diode blocking negative portions.
I'll be doing some more experiments with this stuff tonight - maybe with highpass configurations (I didn't like the lowpass). |
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machine.cuisine
Joined: Jul 20, 2007
Posts: 61
Location: ks
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| Posted: Tue Jan 06, 2009 1:36 pm Post subject:
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Well, here are some audio samples of what the little "VCA" (or as I see it, the "all pass gate") can do.
Again, this is simply a VTL5C3/2 wired up as the doktor prescribed above, only the cap is replaced by a 10k to gnd.
I think that this is a very handy and insanely simple circuit. And I will probably throw one of these in every panel I make from here out (if there is room). VCA's aren't just for VCO attenuation...
Sample descriptions (#1, it sounds like a SID )
1. An LFO "gated" by an LFO which is FM'ing a VCO.
2. A VCO "gated" by an Envelope which is audio output.
3. An LFO "gated" by an Envelope which FM'ing a VCO.
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vactrol gate LFO LFO mod.mp3 |
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1428 Time(s) |
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vactrol gate as VCA.mp3 |
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1403 Time(s) |
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vactrol gate EG gates LFO FM2.mp3 |
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562.55 KB |
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fonik
Joined: Jun 07, 2006
Posts: 3950
Location: Germany
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| Posted: Tue Jan 06, 2009 6:22 pm Post subject:
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| machine.cuisine wrote: | | I think that this is a very handy and insanely simple circuit. And I will probably throw one of these in every panel I make from here out (if there is room). |
you would only need one switching socket, normalled to 10V, i think. this way your "VCA" would be open as long as no CV applied. nice idea.
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doctorvague
Joined: Mar 14, 2007
Posts: 281
Location: new mexico
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| Posted: Wed Jan 07, 2009 5:53 am Post subject:
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I've always limited the voltage to the LED side to 5V and made sure it was positive voltage, and I haven't blown up a vactrol yet. 10V with no limiting resistor might be too much. +5V will fully open a VTL vactrol so no need for normalling to 10V really.
Adding one SPDT switch to switch between cap and resistor would switch between 'VCA' and 'VCF' modes but it doubles the parts count! 
How about a PC board run for this?
Seriously adding a 2 transistor CV expo converter is easy and makes it a lot more usable. Without it, it sort of pops on and off around 1.5-2V or so. With a converter circuit it has a smooth response to CV. Still fun to make noise with only 2 passive parts though and works fine for simple stuff. As with any vactrol circuit you can only modulate with audio-rates in low ranges as vactrols are too slow for higher audio-rate modulation. Seems like around 1K is the limit IIRC, but it would depend on the vactrol, modulation wave, etc.
Fun!
Phil
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machine.cuisine
Joined: Jul 20, 2007
Posts: 61
Location: ks
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| Posted: Wed Jan 07, 2009 8:50 am Post subject:
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| I ended up adding a resistor (<1K) to the CV input - to smooth the rise/fall response. I haven't been using a diode on the CV input, negative swinging (LFO) signals seem fine so far. As far as adding anything else (transistors, etc), forget it. The thing works just fine for me as a simple VC-gate. |
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funkyfarm
Joined: Jan 21, 2007
Posts: 583
Location: France
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| Posted: Sun Jan 11, 2009 4:42 am Post subject:
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HI PASS FILTER
For sure the point between 10k resistor and J3 connector (6) is connected to ground ?
Nice passive HPF as on Roland System100M filter M-121
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funkyfarm
Joined: Jan 21, 2007
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richardc64
Joined: Jun 01, 2006
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Location: NYC
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doctorvague
Joined: Mar 14, 2007
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Location: new mexico
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droffset
Joined: Feb 02, 2009
Posts: 515
Location: London area
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j.dilisio
Joined: May 19, 2009
Posts: 200
Location: baltimore
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| Posted: Mon Mar 22, 2010 5:13 pm Post subject:
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I'm intrigued by this vactrol filter.
Is this how you would make an ultra simple voltage controlled high pass filter?
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ezekiel
Joined: Oct 17, 2009
Posts: 30
Location: Columbus Ohio
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| Posted: Fri Mar 26, 2010 7:33 pm Post subject:
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| For passive highpass filter, just swap the resistor and capacitor in a passive lowpass filter circuit. The input signal should pass through the capacitor and then that output should go through the vactrol's resistor to ground. |
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j.dilisio
Joined: May 19, 2009
Posts: 200
Location: baltimore
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| Posted: Sat Mar 27, 2010 8:36 pm Post subject:
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Like this?,..
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blue hell
Site Admin
Joined: Apr 03, 2004
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Location: The Netherlands, Enschede
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| Posted: Sun Mar 28, 2010 3:54 am Post subject:
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Just to be sure ... there must be a resistor in series with the VTL5C3 LED, just putting 5V over it will kill it.
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Jan
also .. could someone please turn down the thermostat a bit.
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jnuaury
Joined: Feb 28, 2008
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fluxmonkey
Joined: Jun 24, 2005
Posts: 708
Location: cleve
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| Posted: Fri Jun 18, 2010 5:38 pm Post subject:
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| jnuaury wrote: | heres a david tudor phase shifter
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i dont understand how this would be connected? where's the input/output?
b
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jnuaury
Joined: Feb 28, 2008
Posts: 161
Location: chicago
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| Posted: Fri Jun 18, 2010 5:42 pm Post subject:
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| bbob wrote: |
i dont understand how this would be connected? where's the input/output?
b |
my assumption is that "red" serves as both the input AND the output and that black is ground and the change is frequency response is largely depends on the impedances of the circuitry that comes before and after
havent had a chance to try it yet though... i'll report my findings when i do
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jnuaury
Joined: Feb 28, 2008
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| Posted: Fri Jun 18, 2010 5:48 pm Post subject:
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im also assuming that the two separate drawings have their "reds" and "blacks" connected so that the capacitors on the left drawing are switched in and out to change the value of the total capacitance when combined with the vertically arranged capacitor on the right side
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LektroiD
Joined: Aug 23, 2008
Posts: 1019
Location: Scottish Borders
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| Posted: Sat Jun 19, 2010 2:08 am Post subject:
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| jnuaury wrote: | | bbob wrote: |
i dont understand how this would be connected? where's the input/output?
b |
my assumption is that "red" serves as both the input AND the output and that black is ground and the change is frequency response is largely depends on the impedances of the circuitry that comes before and after
havent had a chance to try it yet though... i'll report my findings when i do |
If it's not too much trouble, I'd be really interested to see your schematic with the ins and outs, once you have it up and running too.
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jnuaury
Joined: Feb 28, 2008
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Location: chicago
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| Posted: Sat Jun 19, 2010 2:24 am Post subject:
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| LektroiD wrote: |
If it's not too much trouble, I'd be really interested to see your schematic with the ins and outs, once you have it up and running too. |
well if it works as i think it will... the input and the output are the same point within the circuit! and that point has capacitor(s) going to ground which cause the "phase shift" The drawing does some some inconsistencies in the way it represents capacitors but i think if anything is tough about the schematic... its that it is too simple! i think its pretty much just throwing some caps to ground inside of a floop to see what happens... but im sure tudor thought of it atleast slightly differently
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jnuaury
Joined: Feb 28, 2008
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| Posted: Sat Jun 19, 2010 5:35 pm Post subject:
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okay i tested it out and it works although i need to do more experimentation to find the best cap values to use
i used .1uF caps and occasionally clipped in another .1uF capacitor or two
im going to try it again later with some capacitors that are a little smaller
also you can give it an easy bypass switch by using a SPST to lift all the caps from ground
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