Vactrols: which parameters matters beside on and off time?

[Funky40]

Hello, ( sorry, its somewaht longer, so i put the question into fat )

i was Today studiing the first time Vactrol Datasheets.
I was really suprised to see that a VTL5C3 and a VTL5C3/2 have not the same turn-on and turn-off times,
so i studied more of the different Types.

The VTL5C1 for example has a dynamic range of 100db and interesting on/off times with: 2.5mS/ 35mS.

My questions are now:
What Parameters beside the on/off times are from importance ?





I have recognised for example that the Fonik LPG ( which is based on the Schematics provided by Peter Grenader) goes really fast into clipping,
and that clipping is REALLY not nice,
so a higher Dynamic range would be very appreciated.


Then i have thought that depending on what you are patching,
it might be very usefull to have LPGs with different Characteristics.
I have built 5 Fonik LPGs, and one is much pluckier then the others.
I have built them all with VTL5C3/2.
This more pluckyness counts really when i drive Seqeunzers fast.
So in this Case the Turn-off parameter counts in my opinion .
Hey, the manufacturers must provide universal fitting modules, but in DIY we can go for specialised stuff



On the other side i think that for slower running seqeunzes a Vactrol with lightly slower Turn-on time would be great.
so i come again to this:
What other parameters are really from importance ? Can i go just with the On/off times and dynamic range

"Off resistance" i don't understand
"light Hystory Memory" is another one
not shure what other could be from importance



after reading the datasheets, and with my very basic knowledge, i think:
VTL5C3 is more interesting for the LPG then the dual VTL5C3/2
VTL5C1 might be the most interesting if just Dynamic range and on/off times are counting.

[Luka]

im also curious about vactrols, i posted a reply in the mfos adsr mods thread as im trying to implement cv decay with a vtl5c3. my question is that do you have to protect the line you are feeding into the LED of the vactrol? Ie you external modulation current. Do i have to put a cap or resistor in line?

[Funky40]

here is the other thread i openend not so long ago.
http://www.electro-music.com/forum/viewtopic.php?highlight=vtl5c3&t=24997
So my question i had there if the 5C3 dual and single are the same is answered now:
no, they are not !

yeah. me too belive that slower Vactrol Turn-on times give more of that sound what i'm looking for,
on the other side are longer turn-off times that what makes that i find some of my Vactrols not so plucky.
they don't close good when the Seqeunzes have a certain speed.

so the speed of running sequenzes are an important Factr5or for which you like to have, IMHO.
I will say: to have different more specialised LPGs makes more sense in my opinion .
I think this also since snme time concerning to envelopes.
Clear that Manufacturers might look for overall best use, i must not............
I'll go for more specialised LPGs then.

hope to hear from your Experiences

[widdly]

[Luka]

ok so i need a little switch transister eh.
no prob

thanks widdly

[andrewF]

and a resistor!
]treat the led in a vactrol as a normal led(which it is)
if you try to pass 15V thru it without a resistor, it will die

[widdly]

Here's some ideas from the square wave parade site...

[Luka]

great, i wouldnt have thought about the limiting resistor. thanks a bunch w.

i have a bunch of vactrols here so once i re-make my vc - a(d)sr and ads(r) faceplates ill do some testing and post some differences. i will do it in the mfos mods thread not here, sorry for the hijak funky40.

[doctorvague]

I did quite a bit of breadboarding with some different vactrols in a modified filter circuit based on Buchla/Scott Stites mutant vactrol filter. I did study the data sheets but can't say I understood all of it and how it applies, but got the general idea of the timing and curves. In my case I had good results with the VTL5C3, the VTL5C2 and the overlooked but very musical NSL-32. I had no way to directly compare the VTL5C3 and VTL5C3/2 since one setup uses 1 led and one has 2. I thought theoretically the LDR side was the same on both but apparently not.

I would highly recommend breadboarding and trying the VTL5C2, VTL5C3 and the NSL-32 and see how they actually sound and respond in the circuit in question. I've also thought of putting screw terminals on the board so these could be changed out from time to time, or you could rig a switch to switch betweeen 2 in real time which I have actually done and worked well. People will usually tell you that the VTL5C2 is too slow but I found it to be musical and sometimes preferred it depending on the CV circuit driving it. Just to complicate matters they also make a VTL5C2/2 as well which I have a few of. It may have just been the particular circuit I was using but I tended to like 2 VTL5C3's rather than 1 VTL5C3/2 even if I simulated the same LED load by using 2 of the LED's to get a match. The individual ones always sounded better to me for some reason.

I don't know what kind of vactrols Doepfer LPG uses but it was one I'd never seen before. I can't say specifically the vactols he's using are the cause, but I personally don't like the sound of his implementation myself. I plan to change out vactols sometime on it and see what happens.

I consider vactrols kind of like guitar pickups in that they have a character and response and are best evaluated on the guitar itself (or in the case of vactrols in the circuit itself). They are also quite variable individually too (as Peter Grenader has said as well) so that's another reason to evaluate them in the circuit. If you feed a known amount of current and measure the resistance individually you will see there is quite a variation there - more than we are used to with most electronic components. They are a beast to be tamed!

One other thing to consider is that your CV expo circuit does not have to be 1/V octave since there's no way a vactrol filter will ever track 1V/oct, so why not tweak the circuit for "musicality" and response time? I like it where it's a bit more sensitive than 1V/octave myelf = snappy. This is a good area of experimentation IMO as you can really change the character and response time. I'm talking filters here and not other uses, BTW.

If you want the fastest response time I'd start with the NSL-32.

Cheers
Phil

[Funky40]

[doctorvague]

[Funky40]

[Dave Kendall]

Hi.

Just curious - in the squarewave parade VC resistor schemo posted by widdly, there is a resistor from the base of the NPN tranny to GND, and in the bridechamber one, this resistor is from the emitter to GND.
Anyone know what (if any) difference that would make?

cheers,
Dave

[Scott Stites]

The 100K resistor in the Squarewave Parade schematic is acting as a voltage divider on the base of the transistor. The 1K resistor between the LED and the collector is providing the current limit so the LED doesn't go>pop<. I haven't seen the Bridechamber thing, but I imagine the resistor between emitter and ground is serving the same function - the resistor could go in either place. Through sheer force of habit more than anything, I put the current limiting between emitter and ground myself.

Cheerios,
Scott

[Dave Kendall]

Thanks Scott!

So many little mysteries - so many synthy things to fiddle with

cheers,
Dave