note accuracy question - individual notes out

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31Hz
 
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note accuracy question - individual notes out

Post by 31Hz »

hi,

i'm unclear on how accurate tuning can get - for example, when looking at my CV, i have a couple pitches that are outside far enough to swing it enough to be problematic - for example, i have 1.009, 2.025 . 2.996, 3.999, 5.006

that c at 2.025 is amost 30cents off the upper octave above as it swings the opposite way in drift. i'm assuming the reason for so much drift is due to differences in the resistor network tolerances?

my cal and power voltages are exact. perhaps i'm missing something? please advise w/ any ideas

thanks

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antto
 
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Re: note accuracy question - individual notes out

Post by antto »

the CV relies on properly calibrated 5.3333333... reference voltage (TM6)
then, it's down to the resistor network
the bom suggests 1% tolerance resistors
you might want to use multi-turn trimpots for TM6, and the VCO pitch tuning (TM4, TM5)

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mmm
 
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Re: note accuracy question - individual notes out

Post by mmm »

Usually the resistor network is to blame for this. 1% tolerance is not sufficient.

Try resistors with 0.1% tolerance for R74 to R90. If I'm reading the schematic correctly the TB-303 also used 0.1% resistors for this network.
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altitude
 
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Re: note accuracy question - individual notes out

Post by altitude »

+1 on the 0.1% parts. That's what I used on all my builds

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