[sdiy] using a vactrol for a voltage divider?

[Dan Snazelle]

this is some great information!

i just might switch to the ASM2 lfo. it does look a little bigger than what i am using though.

i have a few questions: ( i will use the ASM-2 schematic as reference)

1. you said " The output of the schmitt trigger goes to the input of the integrator via a variable resistance"
is the schmitt trigger U552a and the integrator u551c? so i could use r560 as a pot?

2. is this p553?

3. how does 3 work? i dont see any OTA's here so i am interested in understanding this method.

the LFO design i was working with didnt have number 3 so i figured a vactrol was the only way.

HERE IS A LINK to what i have on my board. any ideas for adding VC?

http://www.diystompboxes.com/smfforum/index.php?topic=68582.msg548699#msg548699

(its a redraw of a roland lfo from their modular system i think)

i had to mess with the resistor values a lot to try to get the triangle louder.


THANKS



--------------------------------------------
check out various dan music at:

http://www.myspace.com/lossnyc


http://www.soundclick.com/lossnyc.htm


http://www.indie911.com/dan-snazelle
(or for techno) http://www.myspace.com/snazelle


> Date: Sun, 20 Jul 2008 17:17:07 -0700
> From: nicolas3141 at yahoo.com.au
> Subject: Re: [sdiy] using a vactrol for a voltage divider?
> To: synth-diy at dropmix.xs4all.nl
>
> In a standard triangle core LFO there are three main ways the freq is controlled.
>
> 1. The output of the schmitt trigger goes to the input of the integrator via a variable resistance (ie the R of the RC can be variable). This variable resistance is normally a pot, but could be easily replaced with a vactrol.
>
> 2. The output of the schmitt trigger goes through a voltage divider to ground and this variably reduced voltage goes to the input of the integrator via a fixed resistance. This voltage divider is normally a pot, but may be what you are talking about replacing with a vactrol+resistor. Probably easier to do 1 above instead.
>
> 3. The freq control is as per a VCO, where the output of the schmitt trigger is used as a +/- multiplier to alternately flip the sign of the incoming control voltage which then goes through a fixed resistance to the input of the integrator. This allows voltage control which is more instantaneous and more linear than any vactrol based method.
>
> So unless you really want the slow response and non-linearities of a vactrol, method 3 is probably the best way to do it. The VCLFO in the ASM-2 is an example which can be conveniently built from a TL074 if you ignore the offset trimmer on the integrator and leave out the LED driver stuff.
>
> http://www.elby-designs.com/asm-2/lfo/lfo2-asm2-cct.pdf
>
> Cheers,
> Nicolas
>
>
>
> --- On Mon, 21/7/08, Antti Huovilainen  wrote:
>
>> From: Antti Huovilainen 
>> Subject: Re: [sdiy] using a vactrol for a voltage divider?
>> To: "Dan Snazelle" 
>> Cc: synth-diy at dropmix.xs4all.nl
>> Received: Monday, 21 July, 2008, 3:00 AM
>> On Sun, 20 Jul 2008, Dan Snazelle wrote:
>>
>>> or is there a better way to approach changing the
>> pitch of an lfo.
>>
>> Yes. A normal triangle core VCO should work fine as an LFO.
>> Chances are that the voltage divider even simulates a
>> current source, so
>> replacing it with a voltage controlled current source would
>> be rather
>> trivial.
>>
>> Antti
>>
>> "No boom today. Boom tomorrow. There's always a
>> boom tomorrow"
>> -- Lt. Cmdr. Ivanova
>> _______________________________________________
>> Synth-diy mailing list
>> Synth-diy at dropmix.xs4all.nl
>> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
>
>
> Start at the new Yahoo!7 for a better online experience. www.yahoo7.com.au
>
> _______________________________________________
> Synth-diy mailing list
> Synth-diy at dropmix.xs4all.nl
> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy