[quote author="Viitalahde"]I've been thinking of buildind another Sontec someday, just to see if I could make it even better. The model 430 might be a nice start..[/quote]
There is one lengthy PSW thread about the 430 and the differences between the models. It seems that people there agree that the 430 series is the best one, or at least better than 250.
There are three main differences that are rather obvious:
1) addition of shelving filters using one more opamp
2) only 3 parametric bands instead of 5, thus less work for the last opamp
3) discrete opamps in the filters
Here is a redrawn and modified schemo of the 430 that makes reading easier than the one Jakob has on his site:
http://www.akustische-kunst.org/audio/sontec/sontec_schematic.pdf
(Because the original opamps had separate DC offset trim inputs I had to change the servo circuitry slightly.)
When looking at the filter section there is also a slight difference: less capacitors. Maybe this is due to the fact the unit is using switches, so we don't have to deal with scratchy pots. But on the other hand we would get pops instead when switching.
I have no idea which of this details really makes the sonic difference.... maybe we will find out. - In case I ever come to Finland I'll bring my 430 for a shootout!
Olaf
