[sdiy] New Vco (new images)

[René Schmitz]

Hi Tom!

>I got the saw...Yeah! Don't know what I did wrong the first time?

Congrats!

>> To make the tuning curve better I think I'll add that Franco compensation, 
>> its not a big deal, but I need some time to redraw my circuits. I'll all 
>> let you know.
>
>I sat your core on my expo and got almost 8 octaves 1Hz - 33KHz
>range.  It does go flat as freq reaches about 1KHz...That's a little to 
>low. 

Aha, but thats a different expo then!? So your statement musn't
neccessarily be 
valid for the circuit I proposed... Anyway I calculated the needed Franco
resistor,
 and had to include a diode so that the resistor doesn't affect the lower
threshold (otherwise it would be merely shifting the action), and to make
the discharge work properly. You might add these two parts and test again,
it worked very well for me. Shouln't go flat anymore.

Though I based the Franco resistor value on the 1uS reset figure and a rBE of 
0.7Ohms as the BC548 have, your 2SC1583 might need a little more. (Or make it 
a trimmer and have it precisely set.)

>I changed the freq-pot resistor from 150K to 100K the neg-ref resistor 
>from 39K to 33K and the current resistor from 1.5K to 4.7K
>
>> but where is the temperature compensation?! 
>
>Make that 1K a tempco....if you want....  

Well I know, but it might cost as much as the whole VCO.

Cheers,
 René
-- 
uzs159 at uni-bonn.de
http://www.uni-bonn.de/~uzs159