lter 18/24 db
Filter 18/24db

Early VCS3 and Synthi A featured a 18db/oct filter. Then it became 24db in 1974.

Technically, early filter is a 4-poles 24db behaving more like a 18db.
This mod ads a 5th pole (as on later Synthis) to the early Synthis, thus makes the filter a 30db behaving like a 24db. More info about this weird feature in this excellent article of Tim Stinchcombe.

Personnaly, I don't think this mod is very useful. It's most noticeable effect is a displacement of the cutoff point. In some complex patches it can be more drastic, but I almost never use it.

Pot to replace with a push-pull one :
- Filter "frequency"

This mod consists in simply adding a 100nF capacitor and a 100 ohms resistor in series to the filter circuit between diodes D16 and D23's cathodes.

No hole
Push-pull pots
Matrix MKI/MKII layout
Voltage controlled shape and reponse
Hi/lo range oscillators

Simple Random Voltage Generator and Sample & Hold

Documents, manuals, dopesheets, links

Filter slew/unslew
Oscillator synchronization
Attack and decay time extension
"Synthi 2" interface