On 20/08/11 13:32, Juergen Haible wrote: >> http://www.adambaby.com/images/tech%20pics/SH_2/sh2vco.html >>> >>> 2) Does the low frequency drift point to a typical problem? > > Try replacing IC13. > Problems at low freq. in expo VCOs often indicate leakage currents. For VCO1 it would be IC18. Cheers, Magnus