My first console was a Chilton QM3, which also turned out to be my first major restauration and recapping project.
I loved the preamps in that thing, instant 70s vibe, and instant feel on anything I put through them. Over the subsequent years, I have done a number of recreations, each time varying the design a little, improving it from my point of view, possibly just changing it from someone else's
When I felt like the design of the preamp had come home to the place where I wanted it to be, I put some thought into implementing it in a recording channel, and decided to pair it with the BAX design I had already crafted earlier (with the wonderful M100D discrete opamps. from Silent Arts).
It is the best recording channel I can think of.
Gut shot with M100D Discrete Opamps (DOAs)
"The rainbow-shaped path created by the missile as it moves under the influence of gravity, subsequent to the engine's deactivation"
The name, Gravity's Rainbow, refers to the novel by Thomas Pychon. The cover of my copy of the novel inspired me a great deal for the visual aesthetics on the units I design.
The original QM3 design did not sport modern amounts of headroom, to say the least, but every attempt to raise the bar of the headroom, also lowered the bar of the sound and vibe of the preamp.
So I concluded that the strength and the weakness of the circuit had to be mediated, rather than solved, and worked from that as a premise.
In response, I came up with the idea of switching the input transformer into various headroom and impedance modes, and after implementing it into the working prototypes, I gave it to my test engineers and told them to "see how you like it", without going into technical details.
There is a primary x flip, and a secondary x flip on the front panel. They will give you some interesting flavours, and they will react differently at different loads and levels.
I suggest you use the non-flipped unit as a starting point. Thats the "correct" implementation of the Lundahl transformer on the input.
I also suggest you flip through buttons, and I predict youll crack a smile once or twice while you do.
When this circuit starts clipping, it does so asymmetrically.
If you push it really hard, your waveforms will come out a bit loopsided because of this.
You can monitor clipping on the headroom monitoring meter mode (push the button on the front panel), or you can use your ears. To some, it will sound a lot better than symmetrical clipping.
Measuring Gravity's Rainbow clipping on the scope