[sdiy] Played My Fist Tune.....

[Magnus Danielson]

From: James Patchell <patchell at cox.net>
Subject: [sdiy] Played My Fist Tune.....
Date: Fri, 28 Nov 2003 21:33:46 -0800
Message-ID: <5.2.1.1.2.20031128212657.00b14d50 at pop.west.cox.net>

Jim,

> 
>          .....on my latest synth project...I finally tuned up the 
> oscillators today....what an experience.
> 
>          I spent several hours chasing my tail, I just could not get the 
> tuning to converge...I kept didling with the gain resistor trying to get 
> the scales to converge with no luck...I finally sat down, took some careful 
> measurements and determined that the original value for the gain was 
> correct...after making several more careful observations I discovered what 
> the problem was....because of the way I have the CVs biased and what not, 
> my tuning algorithm was backwards from what it normaly is...after I 
> reversed it, then it converged...the only other problem was for some odd 
> reason I thought the voltage reference for the DAC in the midi->CV 
> converter should have been 8.192 volts...but again, after sitting down and 
> doing a careful calculation, I discovered it should have been 10.667 
> volts...I have met the enemy, and he is I....
>          Anyway, it was good to hear a tune come out of the thing, even if 
> it was "Turkey in the Straw"... :-)

Well, you're not the first to encounter this problem. The filter-tuning of the
OB-8 is like that... too. The thing to learn is that you need to know when the
keyboard voltage make the input of the expo zero volts and when not. This could
be in any point. Doing it in the wrong direction and it will not converge but
rather diverge... or as the say: Been there, done that.

Cheers,
Magnus - OB-8 owner