Transformer color that excites but doesn't soften/mush?

The Iron Age Audioworks Portia Street Stomp is what I reach for when that's needed. The 1:2 setting in particular brings things forward in a nice way.

www.ironageaudioworks.com/pss

Do you have the stock transformers…and what are they?
Also: matt@IAA what other transformers have you guys used with these and why / to what effect?

Mine is stock, I'm not sure what the transformers are off the top of my head.  Hopefully Matt will drop by soon to fill us in!  

@otisgreying different circuits produce different distortions. single ended will make more even order distortion, push-pull are symmetrical so they tend to have more odd order distortion products. so the circuit has a direct impact as well, though generally speaking well-behaved circuits at reasonable levels don't have really high distortion numbers.

transformers produce generally asymmetrical distortion when they approach saturation, so they provide odd-order harmonic content. This is true for all transformers. they also can have parasitic losses and can even act like a simple RL high pass filter. The larger the transformer the less this effect, and the less sensitive they are to source impedance. however there's a trade off... to get better low frequency fidelity, you usually trade off high frequency response. but just like the circuit this is level dependent.

So as an example API uses low-inductance, steel core transformers which sort of guides us to the mid-rangey, aggressive API sound: more transformer distortion in the low and low-mids, maybe even some low end roll off due to lower inductance. the 2520 op amp also tends to also make more odd-order harmonics as it gets driven, which adds to that bright feel.

In the BA283 Neve used the primary of the transformer as an inductive load that also carries DC to the output transistor, so the transformer primary is biased and the AC rides along that. as signal increases that arrangement is going to fatten up the bass, then roll it off, then go to sad times. single ended output produces more even order, hence the fat Neve bloom sound.

You can kinda start to get a feel for what to expect from different circuits based on real broad brush groups of things based on the above. hope that helps?

deaconblues  mostly just used our output transformers we use everywhere, which are steel core and low inductance (though not as low as an API 2503). We made a box with a bunch of vintage transformers for Ben Kane a while back, that was cool to play with. Hard to get a real A/B because they didn't match at level but definitely each had a unique waveform on the scope, for example. For the box I mainly wanted two things - quadrifilar to adjust ratios and low enough inductance to have a sound. the standard transformer we use fit the bill so in it went.