[sdiy] [spam] Re: Pink Tunes self-composing program.

David Manley dlmanley at sonic.net
Wed Jan 10 03:08:21 CET 2018


I can confirm the DAC was exponential, it used a custom resistor network 
from ??? (insert major US manufacturer of resistor networks - can't 
recall right now it was in a light blue ceramic package).  From memory 
there's nothing to the QuASH but a 8-bit register to latch the micro 
writes plus an analog switch demuxing the 'DAC' output to simple 
capacitor plus TL0xx output buffers.  I may still have Simonton's 
published lab notes somewhere.

-Dave


On 1/8/18 11:37 PM, rsdio at audiobanshee.com wrote:
> Thanks for the hint, Terry.
>
> I found the following to be very informative
> http://www.muzines.co.uk/articles/paia-8700-computer-controlle/2614
>
> The PAiA 8700 has a 6503, which is a 6502 with a reduced address bus. The DAC uses only 6 bits, so exponential would make sense as the only feasible utility for a mere 64 distinct output levels. There is 1 bit used to control glide between output levels, and I assume that would be an analog glide. There is also 1 bit used for Gate. In total, 8 bits are output to control the transition to a new level.
>
> I’d like to see a more detailed schematic for the QuASH component mentioned, but I suspect that if I read through the assembly source code then I could learn what I need. If such a schematic is available, then the exponential nature of the DAC could probably be confirmed.
>
> Thanks again,
>
> Brian
>
>
> On Jan 8, 2018, at 3:03 PM, KA4HJH <ka4hjh at gmail.com> wrote:
>> On Jan 8, 2018, at 5:54 PM, Jay Schwichtenberg <jschwich53 at comcast.net> wrote:
>>> Hard part is figuring out what all the hardcoded numbers are. For example are the music keyboard values directly related to a real note voltage value? Initially I'm going to assume that is true.
>> IIRC, Pink Tunes was written for the 4700 system which used a custom exponential DAC with linear VCOs. If so the output pitch values should all be linear.
>>
>> Terry Bowman, KA4HJH
>> "The Mac Doctor"
>
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