[sdiy] minimalist resistor ladder DAC intonation

[David G Dixon]

You can do all sorts of useful things with multiple R-2R ladders and summing
amps.  I developed a matrix scanning circuit for a 12x5 matrix keyboard I
pulled out of an old Farfisa organ.   This required a 6-rung ladder, a
3-rung ladder, three opamps, and a small pile of hand-matched resistors.  In
this way, I tricked a binary system into thinking in multiples of 12 rather
than 16.  If you wanted to add or subtract voltage from each note in
proportion to the binary number, then you could use the same technique.
I'll email you a schematic of my ladder circuit.



> -----Original Message-----
> From: synth-diy-bounces at dropmix.xs4all.nl 
> [mailto:synth-diy-bounces at dropmix.xs4all.nl] On Behalf Of Jason Nanna
> Sent: Monday, December 17, 2012 3:05 PM
> To: synth DIY
> Subject: [sdiy] minimalist resistor ladder DAC intonation
> 
> Hi, I'm looking at building a minimal resistor ladder DAC as 
> an experiment with a Raspberry Pi.
> 
> I was hoping someone might have some ideas with respect to 
> temperament.  What I'd like to accomplish is a direct 
> bit-to-interval relationship, so for example the LSB would 
> correspond to a semitone, the next-LSB would be a larger 
> interval which could have the LSB added to it to achieve the 
> third pitch, and so on.  Perhaps the LSB has to be a 
> microtonal interval to 'correct' certain others.  I'd like it 
> to be 8 bits.
> 
> I don't require a general-purpose scale.  I'm looking for 
> something musically useful.  The octaves do not have to be 
> 2:1 per se, and I don't need a wide range of control voltage. 
>  The GPIO pins are 3.3v, so I presume I'm going to have to 
> scale the DAC output up to 4 or 5 volts, which would be the 
> maximum control range I'd expect.  Even 3 octaves would be 
> sufficient.  The music will (hopefully) suit the tuning, not 
> the other way around.
> 
> Hoping to get interesting ideas.  Perhaps someone knows of a 
> similar project, but I haven't been able to find anything 
> online to date.
> _______________________________________________
> Synth-diy mailing list
> Synth-diy at dropmix.xs4all.nl
> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy