Tiny Minimoog VCF design - whats wrong?

oolfur · Joined: Oct 08, 2015 Posts: 12 Location: NY

i was excited to share with the community a tiny SMD version of Yves's minimoog filter - i've built it before using discrete through hole components and it sounds great - however, trying to make it work with SMD components has so far not been great.

what i've done is replace the CA3046 with the intersil HFA3046, and am using BC847BS pairs for the ladder section.

I've gone through the circuit schematic over and over again with no luck at all! only clue is that the BC557 transistor seems to be getting quite hot.

thank you!
-oolfur

yusynth · Joined: Nov 24, 2005 Posts: 1314 Location: France

I am not sure but if Eagle shows the PCB as seen from top and T1 is also on top of the PCB then the imprint (pinout) of T1 is incorrect and it seems E and C have been swapped. The cure unsolder T1 and replace it by a new one soldered with a 180° rotation (flat side turn toward the inside of the PCB).