Doepfer

Dear Owners of A-110 Standart VCO,
I'm writing in connection with the stability of the described 
VCO:maybe somebody has made some records of these things and has 
specific data?
I.e. i play the note A(440Hz) and the generator gives the 440hz freq.
Is it possible for the signal(on the same note) to change after a few 
hours of continuos work? 
what are the possible tracking faults?

Best Regards,
Alexander