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Also diodes will reduce signal level by about 10-12dB depending on Vf.

I would favor adding clipping earlier rather than later in the signal path. Prior to IC3A and IC4A. If the opamp clips rails I can't imagine diodes are gonna soften that.

The aion fx is doing some real weird stuff. Looks like there's all pass filters in it. Wonder why, maybe notching when summing the bands.

Becomes like the xb driver from tech21. They make great stuff

I should revisit that schematic. This does not have a clean blend or two band drive but it has a pre drive mid boost that measures flatter as gain is turned up. I haven't found the mid boost to be overly thinning though I do like tight bass tones so ..... It wouldn't be hard to design a two band...

I've been chipping away at a bass AIB solution but I am finding that the desired post drive EQ curve changes with drive settings. I'm experimenting with boosting tube-screamer style in front which helps but then there is a hi-mid nasal quality. Do you find that overdrive structure affects...

Have people here found protection zeners to be finicky about current limiting. I have one with a 10r limiter in series but I was not sure if it's necessary? The series resistor and zener are collectively in parallel with the rails.

Maybe move LEDs to feedback loop. If you want two hard clippers in series (which is an interesting idea), add a resistor between them. Specifically place it between SW1 and SW2. Place the lower Vf diodes after the higher ones. Lower the vmid voltage divider resistances. On the order of 10k each...

However, midband interaction is a known issue of baxandalls so simulate first or maybe move the whole tonestack with a 4pdt switch to move the treble and bass caps as well.

Need a DPDT to switch C3 and C6. While you're there, create 3 mid frequencies by using an ON/OFF/ON and switching between two sets of parallel C with an off position for the "base" mid frequency.

The series resistor generally acts to limit current. With a big 220u there, it's more than likely just preventing the current draw upon plugging in from being so much as to turn off other pedals or the supply. It's also useful for protecting diodes from being over-powered. Many schottkys and...

One caveat actually, larger capacitance means less impedance at inrush which leads to high inrush current. Some supplies and other pedals don't like that. Could add a small series resistor like 10r in supply but eh..... I know 470u has given me this issue. Not sure where the cutoff is

More capacitance is always better. Look at the footprint size and find the largest capacitance per diameter. Then ensure voltage rating is at least ~1.5x expected DC. So 16v input cap for 9v pedal, 12v for vmid etc.

I see a lot of unnecessary AC coupling in circuits. You can save components and board space by continuously referencing to virtual rather than true gnd. The kicker is ensuring that there is nowhere for DC to go to create DC drops. Pots only generate thump when there is DC DIFFERENCE ACROSS them...

Awesome! So pretty straightforward. Have you found issues with minimum line width for the footprint?

I thought Road Head would be a funny name.

Sorry to revive the thread but how do you remove the copper and mask layers? Outside of selecting a thinner board what other decisions are made when sending to the fab? This is what I'm looking at but I don't trust it yet.

Though I wonder if more drive in produces better SNR for the system

True

I bet even a lm380 could work.