Basic op amp inverting buffer questions

[kenjib]

Ah okay that makes a lot of sense. Do you know why the Rod Elliot schematic (Figure 2) still has that 100k resistor there even though it has an inverting power supply?

[antonis]

There isn't such thing like "inverting" power supply..
Inverting or non-inverting configuration locates the signal input/output phase (180^o or 0^o/360^o..)

In following figure:


Pins 3 & 5 DO need some kind of bias.. For a symmetrical dual supply (+/- 15V), this is supply midpoint (zero volts or GND)..
This is obtained via R101/201 resistors for SW1 in Normal mode..
(in Reverse mode, pins 3 & 5 are directly grounded..)

Now, in your circuit, UnA output (pin 1) plays the role of R201 (connection of pin 5 to GND) in Rod Elliot's schematic..

P.S.
In case of DC blocking cap existence right after UnA out put, R42 should be essential..!!
(now, it's just redundant..)

[kenjib]

Sorry I meant dual power supply.    Thank you for the explanation. Now I realize that when I copied that circuit I set up the inverting and non-inverting supplies to the op amp backwards.  If I switch the inputs to UnB I still need to remove R42 due to it pulling bias from UnA still right?

[PRR]

So I guess R42 is a bias resistor. Do you think it might be the wrong value?

In abstract, you "may" need it, to set the DC bias.

HERE, you are direct connected to another amplifier. The bias IS set. So waste of 11 cents.

[kenjib]

Okay I think I understand the biasing difference now. Thanks again! How does this look?

[antonis]

Much prettier than previously..