Passinwind
Well-known member
My LTspice-Fu is strong.
I started a zillion years ago messing with tube EQ circuits and then Craig Anderton's circuits from Electronic Projects For Musicians. So by now I can recognize many of the usual suspect EQ formats and have a decent idea of what to change, and sometimes by about how much. With Spice models used in conjunction with actual measurements to confirm correlation, I can often get with a couple of percent of my target on the first try. Good enough that I usually don't bother to breadboard clean circuits, but distortion modeling is a much deeper rabbit hole.
So say I want to understand how swapping standard cap values into a simple Baxandall based EQ for bass guitar affects bass control tuning. I make my model, and a list spec'ing 15nF, 18nF, 22nF, 27nf, and 33nF, with the bass control full up. Here's what LTspice thinks that'll do:
Green trace is 15nF, purple is 33nF. Peaking frequency ranges from ~46Hz-35Hz and the hinge frequency where we start hearing tone control effect (+3dB point above flat gain) varies from ~375Hz to 225Hz. The hinge spec is often at least as important as the peak one, it really changes the play feel quite a bit. There's also one resistor in the circuit that can move that around in a similar fashion to the cap change, so we have trades we can make to meet other targets we might have. This kind of modeling is great for understanding control interactivity, and once you've seen enough of these curves you can often have a pretty good idea of how your prototype build is going to sound...until you don't!
This just took me less than five minutes to work out starting with a pre-existing model, and no actual solder fumes were ingested. So this is my preferred method of sharing designs and especially mods, but of course there would be a learning curve on your side, and many people prefer other equally valid approaches.
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