[sdiy] Inverting Amplifier as a Buffer Output.

[Oscar Salas]

Hello,

As a summary I understood that:

Case A/ 
Conveniences: better isolation from parasitic capacitance
Inconveniences: Voltage drop.
Observations: 10Ω to 100Ω Is enough so the voltage drop not significant.

Case B/
Conveniences: No voltage drop
Inconveniences: No good isolation from parasitic capacitance at the output.
Observations: Cables in a modular synthesizer not are too long. If the cable capacitance is 100 pF/meter we could have problems over 1 meter. 

But going further with three more questions :D :
1) If we add a compensation capacitor output to -input it will cancel any problem, as noise, caused because the output parasitic capacitance. so reducing or cancelling inconveniences of case B? 
isn't it?

2) And because the fact that is an inverting amplifier even without the compensating capacitor, the possible noise at the output will be gain 1, I mean it will not oscillate as if it was a non-inverting amplifier. 
Isn't it?

So I'm adding two configuration more, adding a compensating capacitor at case B, one taping the capacitor before the output resistor and other after it.

3) What performance differences do you think there will be within case C and D?

Note: David, I am also using this way of layout and I saw this you said but if you want to implement the case C you will need also the jumper. I think.








                             ----/\/\/\/\-------
                             |                 |
A)                           |                 |
                             |  =              |
                             |  =   =          |
      -----------/\/\/\/\-------=  --   =      |
                                =           =-----------/\/\/\/\
                            ----=  +    =
                           |    =   =
                           |    =
                         __|__



                             ----/\/\/\/\----------------
                             |                           |
B)                           |                           |
                             |  =                        |
                             |  =   =                    |
      -----------/\/\/\/\-------=  --   =                |
                                =           =---/\/\/\/\----------
                            ----=  +    =
                           |    =   =
                           |    =
                         __|__


 




                              ----/\/\/\/\----------------
                             |                            |
                             |                            |
                             |                            |
                             |      |  |                  |
                             -------|  |------            |
                             |      |  |      |           |
C)                           |                |           |
                             |  =             |           |
                             |  =   =         |           |
      -----------/\/\/\/\-------=  --   =     |           |
                                =           =---/\/\/\/\----------
                            ----=  +    =
                           |    =   =
                           |    =
                         __|__




                              ----/\/\/\/\----------------
                             |                            |
                             |                            |
                             |                            |
                             |      |  |                  |
                             -------|  |------------------|
                             |      |  |                  |
D)                           |                            |
                             |  =                         |
                             |  =   =                     |
      -----------/\/\/\/\-------=  --   =                 |
                                =           =---/\/\/\/\----------
                            ----=  +    =
                           |    =   =
                           |    =
                         __|__