Even though I'm a total beginner at electronics, I've decided to build a 6-channel piezo pickup buffer/mixer unit, for a stringed instrument. It should fit into a typically sized electronics cavity, and be powered by a 9 volt battery. Gain boost is not necessary, but I'll take it, if possible 🙂
One of my questions, is how to best sum 6 of these circuits together.
Before summing the outputs together, I was thinking of adding 50k trimpots, to allow for level adjustments.
Ideally, the summing/mixing section, would also be jfet based (j201).
I've built the stratoblaster circuit before, and was wondering, if that could be used as a mixing stage?
All very naive assumptions, I know 🙂
So, any suggestions would be greatly appreciated. Thank you.
Best Answer
Almost all modern opamps are CMOSFET input, which will provide the same picoAmpere input currents that JFETs achieve.
To select an opamp, determine if you need
Rail_to_Rail inputs (such as 0v to +3.3v)
Rail_to_Rail output (often spec'd as "within 0.01v of rail, for 10Kohm load)
unity_gain stable (needed if you only use for Gain = +1) and for 100pF Cload
of adequate slew_rate ( 2 volt peak_peak output at 20,000Hz needs more than 120,000 volts/second , or 0.12 v/microsecond). So pick the default of 0.5v/uS , or faster.