SV: RE: [sdiy] Ratio switching!

[karl dalen]

My attempt is to make a ratio switcher for a trough zero VCO that scales
similarity to the ratio of a DX7 osc. The switcher is a 12 way so some ratios 
have to be sacrificed, however since the switcher shares and are buffered by
opamps almost any number of VCO's can be driven from it.

I have figured that ratio 1:4, 1:2, 1:1, 2:1, 4:1 and 8:1 can be made from 
one resistor string and ratio 3:1 and 6:1 are made from another string
these two has equal resistor values and then the remaining 5:1 and 7:1
ratios are made out of a third string with unequal resistor values. And the
twelfth ratio 1:3 are sacrificed for a LFO range.

All in all it would take 10 resistors 0.1% or better. Two 5% for the LFO
range and 1 trim pot to set absolute top voltage to the exact millivolt
in the buffer of the string driver.

However i assume the pot and the buffer will decrease the string accuracy! :-( 
Well, at least the pot will,

Ideas folks?


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