The Moog Rogue is similar to the Prodigy but came out a couple of years later. The keyboard current source circuit is almost except for a few differences.
- The op-amp is a 353 instead of 4558. The 353 has JFET input stages. This means much smaller input and bias currents (more than 1000x smaller). However the input offset voltage is 2-3x higher.
- There is no longer a resistor connected to the + input. I guessed that that resistor used the bias current to compensate for the input offset voltage. The smaller bias current means that won't work.
- The resistor between the trimpot and - input is 130k instead of 301k 1%. This seems like a counter-intuitive change. The current can now be adjusted between 12/14.3-12/130 = 0.747 mA and 12/14.3+12/130 = 0.931 mA. This makes it harder to adjust the trimpot for the 0.833 mA. My theory on why this change was made is compatibility. According to various sources, the Micromoog originally had a pitch CV of 0.9V/oct that could not be adjusted. The Rogue allows for a range of 0.896-1.11 V/oct.
The Moog Rogue is similar to the Prodigy but came out a couple of years later. The keyboard current source circuit is almost except for a few differences.
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