I'll give the long explanation, excuse me if this is overkill/patronizing.
This is the output stage of the pedal. The eponymously-named-dry signal is being blended with wet signal (Delay Out) before being sent to output jack.
The electrical principle of superposition is how you understand...
Found the issue. There was a dual channel dip switch modifying a portion of the wet path and a portion of the dry path. Crosstalk between wet and dry was happening inside the DIP switch.
Yeah I recently realized I could do DC transfer functions with stepped DC sources which then reveal input output transfer curve. Really cool for visualizing the softest overdrive so to speak.
OP has a point regarding when one is choosing between 2 different caps like 2n2 vs 2n7. That stuff...
Yes and no, over time you learn to associate gain plots with timbres. And properties like the abruptness of clipping can be viewed on waveforms and through FFTs.
Breadboards are undeniable evidence of how something sounds but sims can give a lot of general insight whereas the fine tuning can...
Integrator opamps take square waves and make them triangle.
Lowpassing square wave approximates sine.
Hard clipping sine approximates square wave.
Electric druid makes an LFO IC PDIP8.
The output impedance of a vacuum tube is dynamic and changes with instantaneous voltage across plate. Thus, the damping factor (think voltage division between load/SPKR and source/TUBE) varies.
The XFMR has a turns ratio that multiplies the impedance seen from the TUBE by the SPKR and divides...
The beautiful thing about audio electronics is the blending of sound engineering/mixing into an otherwise objective field.
We forget how much of the field is using your ears and having an understanding of the circuit architecture as a signal chain; same as adding EQ and clipping in the DAW...