Forgive my layman understanding of amp design, but what is the purpose of the OP-AMP buffer in this context and is it an uncommon design for some reason?
Just to start off, the diagram will be updated after this reply. Somebody dropped some information my way so I needed to correct it again.
As for the op-amps, Mesa would have the answer for that question. They did it with the ED and the clean channel on the RA100. If you were to compare the clean circuit to a Mark amp, it is using one less preamp triode. The op-amp buffer would not be required since they already had a free triode they could have used (V2B). If unity gain was the objective here, perhaps a plate driven output stage was not desired and the op-amp buffer was the way to go? Signal Balance between the channels? Not really sure. The Electra-Dyne has the same circuit following all of the tube stages. RA100 only implements this on the clean channel. There is something missing from the schematic but is present on the PCB assembly. There are a total of three TL072 op-amps. However only two are shown on paper. I have found the one that follows the clean channel as it is located very close to the V2 socket. The one for the reverb is also identified as rev-in. The one on the front end is a mystery. TL072 and 4558D are both dual op-amp devices. It is one of those usual Mesa omissions either intended to confuse or make you think this is not the actual schematic.
This is the TC50 where the input is located. You can see the two op-amps side by side. The TL072 is on the left and the 4558D is on the left. I will not bother to speculate what the TL072 is doing here, it was left out of document I received recently.
This is the same circuit but on paper.
The TL072 in the picture is not identified in the document. I will not show any more than this.
I was also wrong about the reverb circuit. The reverb input signal is pulled from one side of a 68K resistor and the return is on the other side, but in front of the FX recovery stage. Thinking the TC was similar to the RA100 (it is) the feedback I got with the FX loop set in open circuit and turned on, was due to parasitic oscillation caused by the open circuit on the FX return. That noise rattled the reverb but not the way I thought it would.
