[sdiy] Real slow LFO ICs?

[Theo]

Arggg, mixed up the values for R1 and R2 when calculating.
Not as slow as advertised but about 4 times faster.
With 470n the max frequency would be 0,24 hz.
Assuming a range factor 200, the slowest rate 0,07 hz or about 13 minutes.

But there is always the trustworthy 2u2 MKT cap to come to the rescue ;)

Sorry for the calculation error.
Theo


----- Original Message -----
From: Theo <t.hogers at home.nl>
To: Troy Sheets <tsheets at atari.saturn5.com>; <synth-diy at dropmix.xs4all.nl>
Sent: Tuesday, October 28, 2003 1:50 AM
Subject: Re: [sdiy] Real slow LFO ICs?


> Why not use a "standard" Opamp based tri/saw/square LFO?
> JFET Opamp like TL072 can go quite slow.
> When one opamp is used for a 1/2V+ reference a 074 can be a nice slow
single
> supply LFO.
>
> Cook book receipt:
> Start with a standard triangle LFO.
> Take 100k & 47k for the feedback resistors around the comparator.
> Use a 10k potmeter for the rate potmeter and use it in divider mode (like
> usual),
> the top of the pot connects directly to the comparator output.
> Now add a 4M7 series resistor on the wiper towards the timing cap.
>
> In this setup even a small 470nF timing cap gives a "fastest" rate of
> 0.053hz!!!
> The slowest rate would be roughly 200 times slower,
> around 0.00026 hz or round about 1 hour period.
> This depends on the supply voltage and quality of the pot meter tough.
> A good pot and enough supply voltage can give you more than double the 200
> times range.
>
> A smaller wiper resistor and or a smaller timing cap raises the max
> frequency.
> Best to start with a smaller resistor and when down to 1M or so a smaller
> cap.
>
> Formulas:
> For the fastest rate: frequency = (1/(4RC))(R2/R1)
> Where:
> - R and C are the timing cap and the wiper series resistor.
> - R1 and R2 are the feedback resistors around the comparator.
>
> For the slowest rate: roughly 200 times the fastest rate.
>
> A diode from the timing cap to the top of the rate potmeter changes to SAW
> operation.
> However the rate doubles.
>
> Note: works best with +/-12V or more supply voltage.
> With a +5V single supply the range selectable by the pot could become
> smaller than the factor 200 stated above.
>
> Have fun.
> Theo
>
>
>
> ----- Original Message -----
> From: Troy Sheets <tsheets at atari.saturn5.com>
> To: <synth-diy at dropmix.xs4all.nl>
> Sent: Monday, October 27, 2003 10:01 PM
> Subject: [sdiy] Real slow LFO ICs?
>
>
> >
> >
> > Hi, I am looking for a super-simple LFO IC... or multiple LFOs in a
single
> > package.  sine or saw output will be fine, must be able to run in the
> > sub-1hz range.
> >
> > Anyone have any tips?  This is for an EL-wire project, not for audio...
> > so 0-5V range is OK.
> >
> > -troy
> >
> > --
>
> --------------------------------------------------------------------------
> ----
> > tsheets at saturn5.com                                  <- You have found
me
> > http://www.saturn5.com/tsheets/audio                 <- my .mp3 tracks
> > "I just don't have the discipline to be a hippie"    <- Homer J. Simpson
>