[sdiy] Top Octave Chips?

Batz Goodfortune batzman at all-electric.com
Wed Jun 19 05:23:30 CEST 2002


Y-ellow Lothar 'n' all.

At 06:15 PM 6/18/02 -0700, Lothar Cantare wrote:
>Hey Diy-ers...
>Has anyone played around with top octave chips before?
>(S50240)
>Are they even available anymore?
>I was just looking at an old book of schematics and
>thought that might be fun, stacking up lots (30-ish)
>of these chips, and building kind of an organ/chorusy
>cheesy thingy. :^)
>Thanks for any info, L.

Mmm. Cheesy things. That sounds like my department.

Quick answer: "Yes" and "no"

Long answer:  These things haven't been made in years. I'm led to believe 
that our jaols are full of one-time organ enthusiasts who have been 
convicted of beating other organ enthusiasts to death to get hold of just 
one of these chips. On the streets of London I'm led to believe that there 
are gangs of youth who do a roaring trade by breaking into homes where an 
organ made with these things is known to exist and pulling the chips out. 
Some are so clever that they actually wire in a cheap casio keyboard and 
the owners may not realize they've been broken into until months later. 
There are unconfirmed reports that some Peruvian peasant farmers are 
replacing their crops with chip fabs because these things are worth more 
than cocaine on the black market. And before you ask, sure I had one once 
but it was made redundant by a court ruling when I split from my defacto 
spouse in a very ugly settlement. Where the court ruled that the chip be 
split in half 50/50.

In fact you only need to use one of these chips if you can find them. The 
general principal is that you have a clock which drives the top octave 
synth. This is usually much faster than you can hear. The reason they call 
them top-octave synths is because they produce twelve tempered clocks 
across an octive which is then divided in half for each octave on the way 
down. Typically you'd use something like 12 CMOS 4040s. One on every output 
of the top octave chip.

On one keyboard I use to play, - dubbed "The Roland RSI piano" because it 
had an action like a house brick.- I once spilt half a cup of coffee into 
it. The result was that I lost all the "C" keys down the length of the 
keyboard. Fortunately a bucket and a mop fixed the problem. Another old 
piano type instrument was easily converted into a string synth by removing 
the bleed resistors that caused it to envelope-out when the keys were held 
down. Had a lot of fun with that box actually. Eventually someone was so 
impressed at what I'd done that they bought it from me for that soul 
reason. About 15 years later I was told that the keyboard was still out 
there and still impressing people. Imagine how impressed these people would 
be if they ever met a porta-tone?

There was a crumar synth, err DS something it was called. Claimed to be the 
world's first digital polyphonic synth. In fact it was just a fairly 
mediocre mono synth with a top-octave section. Still I remember feeling a 
slight bulge in my pants whenever I fondled one of these things in the 
shops. But I was just a bit of a kid then and had never been out with a 
REAL keyboard.

I'm not sure what hoops you'd have to jump through to re-create a top 
octave synth with logic these days but I'm sure it wouldn't be worth it. 
Suffice it to say that if you were really that keen, you'd probably want to 
use a PIC or an AVR or something. Or perhaps just buy something from the 
Peruvians and dream about the old days.

Hope this helps.

Be absolutely Icebox.

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