[sdiy] Tonewheel relics

[Roman Sowa]

I would start with 4046 which is more loved here for its VCO, but 
actually this part will not be used in this application.
Datasheet gives some guidelines and I'm sure everybody has 4046 in the 
drawer somewhere.

Roman

W dniu 2017-10-24 o 11:22, Rutger Vlek pisze:
> I thought about that. The gear ratio's are crucial to the tuning of the 
> tonewheel generator, and I feel that varying belt diameter (tension 
> related, temperature dependant) could become an issue. Though, I have no 
> way to quantify this instinct.
> 
> As for 3D printing, this is really a nice case where it's not perfect 
> yet, as far as I can tell. I've asked some experienced people, and what 
> I heard was basically that the composite nature of 3D printed objects 
> results in a not-so-homogene material, that has unpredictable wear 
> properties during applications with friction. Polishing changes the 
> surface a bit, but lack of internal homogenity is supposedly a problem 
> for gears, especially when running at higher RPMs (more friction). From 
> memory I recall the drive shaft of the central AC motor in the Pari runs 
> at around 1200 RPM. It connects with a belt drive to the first tonewheel 
> drum shaft, which then connects with gears towards the last (12th) 
> tonewheel shaft, progressively slowing down each drum such that 
> identical drums given a semi-tone tuning difference. The last drum 
> connects with a belt to the vibrato scanner.
> 
> As for PLL loop: I've never designed one, but it has my interest. What 
> amount of complexity am I looking at? Can someone refer me to an example 
> circuit schematic? Each tonewheel drum contains several octaves, the 
> highest octave as (I believe) 16 dents on a single revolution. So that 
> would be the preferred source for PLL feedback, I guess. The other 
> octaves automatically align. The drums are spring-coupled to the gear 
> shafts by the way, so the PLL loop may be affected by that (bouncing at 
> startup?).
> 
> I do imagine this would be a HUGE step forward for the Pari in becoming 
> tunable and way more silent than it is.
> 
> Best,
> 
> Rutger
> 
> 
> 
> 
> 
> 2017-10-24 0:48 GMT+02:00 Sarah Thompson <plodger at gmail.com 
> <mailto:plodger at gmail.com>>:
> 
>     Would belt drives work? They have huge advantages over gears if you
>     need smooth transfer with no cogging or backlash.
> 
>     On Mon, Oct 23, 2017 at 4:34 AM, <rburnett at richieburnett.co.uk
>     <mailto:rburnett at richieburnett.co.uk>> wrote:
> 
>             @roman and Richie: thanks! From my limited experience with
>             bldc's I
>             feel they would be costly, especially a 12-way driver system
>             for them.
>             Would they need hall sensor feedback to get the tuning accurate
>             enough?
> 
> 
>         Yes, probably not cheap.  I don't think you'd need hall sensors
>         to detect the field, but you would need to ramp the frequency up
>         at a controlled rate to allow the mechanical bits time to
>         accelerate up to operating speed.
> 
>             The pll sounds nice and classic. I'll look into that. At
>             present I'm
>             not sure if the pick-up  coils of the generator could handle
>             more
>             loading, e.g. As required for closing the loop. But a high
>             impedance
>             buffer would probably be ok.
> 
> 
>         Take the feedback for the PLL from the highest frequency that
>         you can.  The loop filter in the PLL has to filter out the
>         ripple in the compared reference and positional feedback
>         signals.  The higher you can make the reference and feedback
>         signal frequencies, the larger the bandwidth of the loop filter
>         can be, and the quicker the PLL speed controller will settle. 
>         i.e.  Don't use a reference signal that is just one pulse per
>         revolution, as this can mean you end up with a very sluggish
>         control loop!
> 
>         -Richie,
> 
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>     -- 
>     [s]
> 
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