Top Octave Divider - the hard way!

The Top Octave Divider IC is a brilliant component when you want to make a polyphonic instrument: You feed it with a stable 1 or 2 MHz master frequency and based on simple integer division it calculates a complete chromatic scale.
But what if all supplies of this IC was suddenly dried up and there wasn't any microprocessor based options available? Then we would have to make it using good old 1970's digital counters and gates.
This is what I am doing in this video: Constructing a Top Octave Divider using nothing but counters and gates. It's not exactly difficult - it's just quite a lot of work for just twelve notes.
I might be tempted to say: WARNING: Don't do this at home - it's way too much hassle!
The music is a silly little waltz I put together on my Casio WK-1800.

[@KJagdAmbient]

I am very impressed with your projects 👍

[@BadChizzle]

Really Cool! You’re gonna have so many things to put together to make an amazing unit. Add this and your 555 synth… and wow!!

[@timothyverbist5795]

Hey Flemming, can you play Jump (from Van Halen) on your Entry-Level Casios?

[@qbqbqdbq]

i've been wanting to make one of these with a pair of atf16v8's

[@synthnerd4539]

EDIT: I think KZbin deleted my comment as I had a link in it. Try again! This is interesting. I'm intrigued by your divider design, combining the binary output of the 393 with the ripple output of the 4024 - and taking the desired signal from a counter pin. That's something I've not seen before. I guess the RC after the AND is to compensate for the propagation delay on the ripple output? I've been planning this week a 440 tuning reference using the same idea, with a 2MHz xtal and a 4040 to give 880Hz, with a 4013 f/f after to take that to a neat 440. Give or take a little sharp or flat, but close enough for music. I did a deep dive into the Korg Lambda a few years ago (on my synthnerd wordpress blog if you're interested) and the master osc for the dividers was a little over 2MHz. Thanks for this video :)

[@organfairy]

Yes, the RC is there to prevent premature resets caused by one counter pin changing before the others - like when 7 advances to 8 and needs to reset on 11. Instead of showing 0111 -> 1000 some counters do 0111 and then shortly 1111 followed by 1000, and given the speed of modern components it can trigger on this very short 1111. The RC delays are not necessary on all counters but I decided to build them anyway to be sure that everything worked. Sometimes the problem can be solved by using slower gates - like 74LS21 instead of 74HC21, but I happened to have a lot of HC gates so that's what I used.

[@AlainHubert]

You do know that an inexpensive Arduino Uno can do that very easily these days, don't you? But I admire your patience and perseverance.

[@organfairy]

Yes, I am totally aware of it. This is one of those project that is just as much a "method over result" thing, just to see if it is possible. First time I saw a microprocessor solution to the Top Octave Divider was in the late 1990's where someone had done it in a PIC controller.

[@AlainHubert]

@@organfairy This project reminded me of a similar one I had done as a teenager in the early eighties building myself an electronic organ using Mostek MK50240 and twelve CD4024 used as octave dividers. I had stumbled on the fact that I could use my fingers as a switch to play notes, so I had soldered metal thumb-tacks to the wires and only had to touch them to play the 'instrument". I called it the Thumb-Tack Synth (TTS)! 😆

[@timothyverbist5795]

Hey Flemming, can you try to cover a 1980s hit on your keytars?

[@timothyverbist5795]

Can you also try to Show us how to clean a Casio CT-380? It's just in case i got a dirty Casio from a jumble sale & stuff.

[@PracticalCat]

Very cool! Love all this divide down stuff. I once read somewhere that those TOS ic's didnt actually give you a proper chromatic scale. Something about it not being possible to get the propper divisor? Apparently it was very close but not axact, not sure if its true. Also I have noticed organs that use a single master oscillator and TOS ic sound very bland and small compared to those that have 12 free running master oscillators. Years ago I got a gem rodeo 69 cheap from a trash and treasure market, when I got it home and pluged it in I was horrified how bad it sounded. That one had a single master osc. That being said the tone filters where piss poor also.

[@organfairy]

Tuning can be a very deep 'rabbit hole' - there are so many opinions on what tuning is the "correct" one: There are people who believe that we should go back to the medieval Pythagorean tuning or the Meantone tuning simply because they believe it's more 'musical'. The scale that we get from a divide-down system will always be a compromise between perfect tuning and what is possible with the given technology. As an example the Hammond organ was depending on the number of teeth that could be cut in the driving gears in the tonewheel generators. The integers that is used in my dividers has a maximum deviation of 0.079% or 1.35 cent from the perfect pitch. That's on the note D. All the other notes are 1 cent or less apart from perfect pitch. In classical music a deviation of 3 cents are normally accepted - or maybe that's just what could be obtained by classical instruments. I don't think your Rodeo's bad sound was caused by a divider based tone generator. I have had several organs that used this technology and they sounded fine to my. But I do know that some people believe electronic organs should be made with individual tone generators - not only for each key but also for each voice! The first electronic organs that were made was basically build like church organs but with oscillators instead of pipes. This meant that they had hundreds of individual oscillators in a big rack and because none of them were in perfect pitch the organ sounded almost organic....... an organic sounding organ. That was a long pile of words, but as I wrote in the beginning: This is a deep rabbit hole!

[@4estral]

@@organfairy@PracitcalCat I agree slight variation in tune is partly what makes old analog synths sound more organic. I just saw the other day that someone was saying on old Hammonds some vibrato would mask most tuning differences. Of course if you are designing sounds with ensemble-ing layers, a small tuning variation is desirable.

[@PracticalCat]

@@organfairy The "imperfect" tuning is definitely not noticeable and not responsible for a bland sound. I just find organs that use single oscillators to sound rather dull because there isnt any movement between notes (beating) The hammond organ that technically has one oscillator in terms of phase relation (ie all tone wheels are fixed to the one shaft) is the only exeption. I dont think there is a "correct" tuning I was just curious about what I read regarding TOS ic's having aproximate divisors for the cromatic scale. I personally cant hear the diference but the phase locked aspect of the notes can be a little tiring. I like multiple oscillators in organs for the beating and movement you can get, not to achieve some ideal tuning relationship between notes. Multiple oscillators make the tuning less perfect which I prefer.

[@PracticalCat]

@@4estral Hammond organs have no tuning variation between notes as the tone wheels are fixed to a single shaft and thus cant spin independently. Vibrato will give you pitch modulation for every note at tje same time. For some reason to me hammond organs sound good even though the oscillators are fixed like In a single oscillator divide down organ.

[@Dablioton]

há um erro no lugar de hef2024 é hef4024