Not made at all presentable.. unreadable, missing stuff, yada yada. but I've been going mad for months working on this...
I'm in the middle of a build that was for the winter buildoff, that I'm now about to get around to making a new SBO thread, but I've been 99% working on this preamp the
whole time. And now it's close to finalized, so I can get back to making sawdust
I've learned so much just by being very critical and editing-focused, as well as the unique constraints that pop up in an onboard preamp.
So just to clear my throat as I turn the corner back to documenting my build (and doing some
building again), here's my messy perpetually-in-progress schematic
The BMT eq has some unique tricks to craft a particular response- namely a partly-peaking partly-shelving bass and treble, which attempts to emphasize and exaggerate the instrument's voice.. the treble opens up the string and finger noise a bit, without that (IMO) terrible airy/glassy content that gets added in with the typical amp/stereo type baxandall (or really any shelfing eq). Similarly, the bass control is centered around ~75hz, which for this instrument seems to be the sweet spot. When boosted, the peak at 75hz goes up to 12db+, but the lowest lows essentially raise as a shelf, but only at about a 1:2 ratio to the peak. So you never get the big yawny boomy dumbness, but you DO get enough near-subharmonics boosting to keep the bass natural and full sounding. The bass and treble have a shelfing response when cut. The mids are a pretty wide boost and cut centered around 450hz. Part of the checklist is that with all bands boosted fully, it sounds good. It's basically a hyper exaggerated version of the natural freq content of the instrument.
The simple mids are helped by the inclusion of some 'contour' switches. These give a subtle-but-not-too-subtle baked in 'preset' to the frequency response.
-There's a pulltec-trick type shape, with boosted lows and a veryyyyy carefully chosen scoop in the low mids. Not too low, not too high, doesn't kill you in the mix
-A classic ~800hz scoop for a very jazzbass slap sound
-a lowmid-bump to a lonnnnnnnnnng rolloff of the highs.. very motown, but detailed
-and finally, a wittle presence-boost.
These have been a HUGE portion of the time spent, and they have gone through soooo many iterations. They have also helped me grow a lot; over and over I had to be very intentional about not being precious about ideas or stubborn about certain approaches or initial designs. I spent months crafting contour controls that dialed in with a single gang pot. It was so hard, so challenging, and I'm very proud of a couple of the circuits... only to finally decide that some toggle switches would be better. The one-knob pulltec is an especially nice trophy, and its going on basically every pedal I ever make going forward.
I'll eventually make a good post in one of my threads, with a better schematic for me to blather on about.
anyhoo, just trying to get myself moving!
