[sdiy] TOGs and Vibrato/Pitch bend (was Vibrato range)

[Richie Burnett]

> I have dreamed up a complicated method of using a PLL and a processor to 
keep the clock in tune, but is it necessary?

Not if you use a DDS chip. 

-Richie,

Sent from my Xperia SP on O2

---- Tim Ressel wrote ----

>Hi,
>
>Many thanks to everyone who joined the discussion and sharing your 
>knowledge about vibrato.
>
>It has been a frustrating journey trying to replace the venerable 
>MK50240. My original take was to use a CPLD programmed with the same 
>divider strings as the 50240. It worked well enough but the solution is 
>big due to the size of the CPLD chip and the need for level shifters 
>(the CPLD is a 3.3V device). Also the CPLD is a bit pricey at $7.25 and 
>also a surface mount device (I have a kit in mind). On the positive 
>side, the CPLD can be clocked at way higher rates to allow for 
>downstream octave dividing (think waveform generators). Also doing 
>vibrato and pitch bend is as possible as it is with the MK50240.
>
>I have another solution that uses little processors to create the divide 
>ratios. I can only do one note per chip so it takes a sea of processors 
>to pull it off (if anyone knows of a small cheap proc in a dip package 
>that has more than one 16 bit timer please let me know). The max clock 
>rate is limited to 8x the 50240 which is enough for waveform generation. 
>And it can do vibrato and pitch bend. Also this solution can do Just 
>Intonation, in case anyone cares.
>
>The third idea is to use the SI5351 clock generator IC. It has an 8 
>output version so only 2 chips are needed at $2 each. It turns out they 
>cannot go quite low enough to generate the top octave directly. 2x is 
>the lowest they can go. Also I still do not know how fast they can be 
>updated. They use I2C at 400 KHz, need several values per output 
>updated, and all 8 outputs need to be written during a pitch change, so 
>it seems unlikely. Still, it may be a good choice for a static TOG. It 
>would not be a kit, but it would be pretty cheap. A board would need a 
>small proc, the 5351s, level shifters (another 3.3v part), and possibly 
>dividers to bring the output down to the top octave. So about $10 in parts.
>
>Now that the windy prelude is complete, it is time for the reason I am 
>gassing on: How to pitch bend and stay in tune.
>
>It is easy enough to rig a 4046 as a VCO and use it to do pitch bends 
>and vibrato. The hard part is this: how to keep it in tune? Is it enough 
>to simply use low temco timing components and provide a fine tune knob? 
>I have dreamed up a complicated method of using a PLL and a processor to 
>keep the clock in tune, but is it necessary? I kinda hope not, because 
>it is techically cool but hugely complicated (I tend to over think things).
>
>
>-- 
>--Tim Ressel
>Circuit Abbey
>timr at circuitabbey.com
>
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