The PCB for the NGF VCO Core one (based on the Elektor Formant) with the corrected footprint for the uA726 finally arrived this week. I stuffed the PCB and wired them up to the front panels.

NGF VCO Core one (Elektor Formant based)

They worked as expected. No faults. No problems. I only made some minor changes for the next PCB run. I added a trim-pot to make the output voltage adjustable and put a 5p6F capacitor in parallel to the feedback resistor of the output OpAmp.

NGF VCO Core one PCB

You can see my “wind shield” on the left and the added small capacitor on the low right site. For measuring the temperature for the uA726 it is a must to use heat transfer paste. Otherwise your figures are way of.

NGF VCO Core one PCB temp measuring

I did this to determine what resistor to use for the heater temperature control. In the datasheet 75kOhms with 15V are used. The Mini Moog used 49k9Ohms with 10V. I decided to use 160kOhm (15V) with a “wind shield” used to avoid airflow around the heated uA726. This keeps the temperature well above room temperature and gives lower thermal stress for the device. Which hopefully makes for a longer life.