I’m creating a stripboard layout from the Befaco Output v3 schematics.
The CUE-IN can be controlled using a TL072 based inverting amp. The second op amp of this chip is left unused (the schematic does not mention it). North Coast Synthesis suggests not to leave it unused, but instead
“connect its inputs to voltages that would be reasonable for those inputs if the section were being used. For an op amp the best thing to do is probably hook it up as a unity buffer buffering 0V: that is, the output connected to the negative input and the positive input to 0V.”
Like this, right?
Does this apply to the unused op amp of the Befaco module? Or is there a better design?
EDIT: To be more precise: is there a better design when the first op amp of the chip is used as inverting amp?
The examples pertain to a single rail system. I don’t know whether that applies in this query, but the example labelled “good” is equivalent to connecting the non-inverting input to ground on a dual rail system such as Eurorack or Kosmo.
Good: This is the minimum recommended circuit configuration. The noninverting input is tied to a potential between the positive and negative rail, or to ground in a split supply system. Virtual ground may already exist in the system, making the resistors unnecessary. The op-amp output is also at virtual ground (or ground in a split supply system).
Eurorack power supply is a split supply system. So I guess it is fine.
All the designer has accomplished is to ensure that the op amp hits a rail, and stays there. This can cause self-heating and increased power consumption.
By “hitting the rail” I assume here hitting gnd is meant. Why would that lead to self heating and increased power consumption?
Oops I forgot to mention that the examples are for single supply opamp! In dual supply you should not connect the non-inverting to +12V or -12V, because when the output “hit the rail”, it consumes more power than being in the middle (gnd for dual supply), and also for the obvious issues if you opamp is not rail-to-rail.
