TOS - Top Octave Synthesizer (or TOG - generator)
I don't know if this has been mentioned before somewhere - but now that we don't need top octave synthesizers any
more*, they have become extremely easy to make! (*as using computers we can form the output waveforms directly etc
etc). The only use I can think of is maybe to repair or improve some old organs.
Presumably a TOS may be made also using computers, however playing around with CPLDs** I programmed a few.
(**CPLD - a form of FPGA, which contain hundreds of logic cells, but also containing a non volatile memory that quickly loads the
programming of the chip on turn on). Boards with the chip already mounted can be bought from China at under £20. Load
program in, finished!
A cheap programming 'connector' from the computer to the board is necessary. Also you have to get your head around the
2GB software as well - unless of course you have the program from somebody else.
You don't even have to use optimum lists of dividers*** as the frequencies the CPLDs can run at are so high that
practically any series will be accurate enough. ***As I used for my previous boards - the last one being a 8x10cm board
with 30 SOT HCMOS chips with outputs of 5V cosmos and 1:1 mark to space ratio.
This board and all the CPLD ones as well have accuracies better than one sixth of a cent.
Using the larger CPLD it is also possible to produce the next lower 7 octaves as well from the same board, ie all 96
notes from one small chip. There is even enough 'room' on the chip to make around 5 of the octaves free phase -
although I can't imagine that the very slight differences in the frequencies (accuracies still as above) can make any
difference to the sound. (Of course one could also program much bigger differences in, if one didn't adhere to the
accuracy requirement).
CPLDs used: Altera EPM570t144 and 1270t144. Altera Quartus software (free). Outputs 3.3V cosmos, 1:1MS.
I don't know if this has been mentioned before somewhere - but now that we don't need top octave synthesizers any
more*, they have become extremely easy to make! (*as using computers we can form the output waveforms directly etc
etc). The only use I can think of is maybe to repair or improve some old organs.
Presumably a TOS may be made also using computers, however playing around with CPLDs** I programmed a few.
(**CPLD - a form of FPGA, which contain hundreds of logic cells, but also containing a non volatile memory that quickly loads the
programming of the chip on turn on). Boards with the chip already mounted can be bought from China at under £20. Load
program in, finished!
A cheap programming 'connector' from the computer to the board is necessary. Also you have to get your head around the
2GB software as well - unless of course you have the program from somebody else.
You don't even have to use optimum lists of dividers*** as the frequencies the CPLDs can run at are so high that
practically any series will be accurate enough. ***As I used for my previous boards - the last one being a 8x10cm board
with 30 SOT HCMOS chips with outputs of 5V cosmos and 1:1 mark to space ratio.
This board and all the CPLD ones as well have accuracies better than one sixth of a cent.
Using the larger CPLD it is also possible to produce the next lower 7 octaves as well from the same board, ie all 96
notes from one small chip. There is even enough 'room' on the chip to make around 5 of the octaves free phase -
although I can't imagine that the very slight differences in the frequencies (accuracies still as above) can make any
difference to the sound. (Of course one could also program much bigger differences in, if one didn't adhere to the
accuracy requirement).
CPLDs used: Altera EPM570t144 and 1270t144. Altera Quartus software (free). Outputs 3.3V cosmos, 1:1MS.