Blog posts of '2022' 'January'

SSI2131 Prototyping Board - Scaling The Output

The output SSI2131 Prototyping Board for all three wave forms, saw, triangle and pulse, is 0 - 2.5V. In order to use this output on a Eurorack setup you're going to want to scale to 10V peak to peak.

This can easily be accomplished by using the external +5V ouput of the SSI2131 Prototyping Board, pin 32, a TL074 and some 10k, 20k resistors in a non-inverting configuration. Essentially you want to amplify the signal to +10V and offset it in a negative direction by -5V. 

Looking at the saw output in the picture below as an example:

The 20k resistor, R13, combined in parallel with 10k, R12, produces a resistance of approximetely 3k. Using the non-inverting gain forumla of Gain = 1 + Rf/Rn and substituting R11 for Rf and the product of R13 and R10 for Rn, we get a gain of 4.

4 x 2.5 = 10. 

The +5V going into the inverting input provides the -5V offset we need to complete the scaled output.

The diagram below is what I will be using in an upcoming Eurorack VCO that uses the SSIS Prototyping Board as its core.

Scaling the output of SSI2131 to 10V PtP