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

[Jean-Pierre Desrochers]

The following circuit comes from a 1974 Logan-Hohner string ensemble
that used a MK50240 as a TOG:

http://www.arcenson.com/public/Logan_string_MK50240_TOG_circuit.jpg

The pitch is changed using a DC voltage from a 1k pot.

JP

******************************************************************

Le 2016-06-25 18:01, Richie Burnett a écrit :
>> 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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