Output levels, SVF Cell 1 & 2

Cell 1

I've measured the output levels of three different circuits for cell 1 of the SVF.

The results are fairly stable, within approx 0.05-0.1V between cells.

Output of LP, BP, HP and Notch are all around +/-5.5V when input is +/-5.0V. 

As I mix BP with input, and the output should be 2 x BP + Input, we have to reduce the input resistor for input to boost it from 5 to 5.5V approx. 

BP output is between +/-5.3 and +/-5.4 for all cards, so gain needs to be between 5.3/5 = 1.06 and 5.4/5 = 1.08 Experimentiation showed that using a 51k and 1.8k resistor in series, combined with the 56k feedback resistor, gave a good result. The calculated gain for this is 1.06.

Cell 2

I did the same for Cell 2, testing device 2, 3 and 4 against each other, and again they match fairly well.

Raw output is around +/-3.4V with a little offset. BP, however, was too low even after the 100k/67k boost and came out around +/-3V. After some experimenting I chose to replace the 67k resistor with 4.7k + 56k, which brought BP up to the same as the others.

The output after final amplification is +/-5.4 to 5.5V which is approx the same as from cell 1. Not sure if I should adjust this back to +/-5V, as the input is 5V, I guess unity gain is a nice feature so perhaps worth the extra work.