Temperature Compensation for the Exponential Converter


SX-150 VCO is driven by an exponential circuit that converts CV to octave scale. This circuit utilizes initial curve of transistor but it is very sensitive to temperature. SX-150 does not apply any temprature compensation for cost saving. So this page introduces how you can add temprature compensation to this gadjet.


SX-150 VCO is controlled by exponential converter that is the simplest design as following picture:

-->Exponential converter, the original design

The converter part is surrouned by dotted line, i.e. it consists of a single transistor. This circuit is very sensitive to temperature.

The temperature compensation circuit follows. The area within the dotted line replaces the original.

-->TEMPCO exponential converter

This circuit is originally designed by Mr. pcm1723. Please refer to this page for details and its theory.

Introducing this TEMPCO circuit requires some modification in other parts of SX-150 circuit as following list:
--> The SX-150 circuit (from the Gakken site)


I built the circuit on a small piece of universal circuit board using SMD parts to make it as small as possible. this extra board is attached by the main board using hot glue. I removed the original Q2 for the exponential converter. See the picture above to see where we should connect between the main board and additional one.