Doepfer

> > > Is it possible for the signal(on the same note) to change after 
a 
> few 
> > > hours of continuos work? 
> > Of course. This is normal for every synthesizers VCO with this 
> schematic 
> > (eg. Moog Rogue).
> 
> Are you saying the A110 is based on the moog rogue oscillator?

This view has been expressed here before, but looking at the 
schematics I would say there are more differences than similarities. 
For example, the exponential converter in the Rogue is quite 
different to that in the A-110, presumably bringing differences in 
temperature stability with it. The A-110 uses the 'transistor oven' 
method to make it temperature-stable; the Rogue seems to be using a  
voltage generated by one transistor in the chip as a reference used 
by the transistors driving each oscillator, and also that for the 
filter cut-off. How stable this makes it I do not know, I have not 
attempted to check the detail, nor how similar this is to the A-110 
stability. However from the schematics, it's clear the two methods 
are quite different.

But, whatever: designing a highly-stable analogue oscillator is quite 
tricky, and unless you spend an inordinate amount of time, effort and 
money on it, the chances are the oscillators are likely to drift over 
many hours of continual use. The trick is really to keep this within 
a level such that it is seen as 'acceptable', rather than a pain-in-
the-butt to have to keep re-tuning.

Tim