Speakers and tubes will affect the transformer match I suppose. I always figured this control was to control the reflected impedance of the speaker load, but rather than being given an ohms impedance or turns ratio, we’re just given a number.
Like if you wanted to simulate a 16 ohm cab attached to the 8 ohm tap, or 4 ohm cab attached to the 8 ohm tap, you could adjust this control.
I think this is also one of the things you should change if you want to swap tube types in the axe FX. I’m just going off memory now, but I think it was said at some point that when you change tube types in the axe FX, some other settings change automatically that would not, were you to (for example) put EL34’s into a 6L6 amp in real life. At least from what I remember, I think the transformer specs in the model change to match the ‘ideal’ impedance for that selected tube type. Someone please correct me if my understanding is wrong.
So for example, say a pair EL34’s want a reflected impedance of 2.5k to 3.5k, whereas a pair of 6L6’s want 4.5k to 5.5k. Let’s assume you’re using a 6L6-based amp model and it is modelled with a 5k primary on the output transformer. My understanding is that if you flip to EL34’s in the model, the ‘virtual output transformer’ primary impedance then changes to the correct impedance for EL34’s (say, around 3k).
Obviously in a real tube amp, the primary reflected impedance remains the same at 5k, and the EL34’s get to work with this impedance. So to simulate swapping tubes without an OT swap we would need to adjust Xformer Match.
Again this is just what I’ve picked up from reading the forum over the years, unfortunately it is difficult to find all these random little tidbits. And things do change, sometimes significantly, when firmware is updated so maybe the behaviour has changed.
This is a good video breaking down how output transformers function.
