PTBM (passive bass/treble/mid) for bass guitar

[ssstonelover]

Frets recently posted a PTBM for HH guitars which then led me to ask if she had any ideas for a bass guitar oriented version. She jumped on it and had actually wired one up in the past, so created a rough drawing I could use as a basis for my project.
We collaborated with me asking questions and troubleshooting issues and now the design has been thoroughly troubleshot and tested on my 5 pot version to full utility.
I also revised her 3 concentric pot version to bring it up to the same standard, so that should be good as well (and suitable for tighter space cavities using mini pots, found on many basses).


Features:
1. I have wired each of those 3 pots directly to the volume pot, not to each other, so any further modification (such as cap value) would be more surgical. Other approaches were tried (tied in to the other tone pots) and will work, but I liked compartmentalizing each pot for the reason stated above.
2. Bass control wiring does not go to ground, but only between the volume and blender (or between volume -> other tone pots -> then blender as alluded to above, another valid approach}.

Note:
* The cap cut points Frets gave seem fine.
* Be warned that cutting bass "all the way" kills most volume so just move that control a little to 'season' the sound. Cutting all 3 controls kills virtually all volume, so once again, don't overdo things.
* I show A250K as the volume pot. In the end I used A500K, the value recommended by Frets for all pots to keep a more controllable taper and I think that may be more ideal to batter sweep from bright to 'dark' as you have a ton of control now especially as the treble cut is quite light and warms up the sound nicely as it is.

For the future, or future builds, I'll look for a C500K anti-log pot for the bass control, as the control currently works in the opposite rotation, compared to the other 2 tone control in terms of 'cut'. However that small current inconvenience is a minor price to pay to try out the bass cut feature.

5 pot wiring: (tested, implemented and fully functional). A500K actually used on the volume pot (I had it in stock) ...but I expect A250K is fine too.





3 pot version: (wire leads revised to to match the 5 pot design)

[ssstonelover]

There may be questions about the Xicon transformer. 
You use the 2 outer legs on the "Primary" side. All other legs can be clipped off.
I got a 1.1H reading.

[ssstonelover]

I revised the bass cut pot finally today as I found the A500K pot gave a lack of fine control, plus I did not like have the control working in reverse compared to the others.
Mouser has some models of C1M pot (anti-log taper 1M) and I used one of them. Both dialing in some amount of bass cut is now far easier (better fine control) plus knob turn direction were much more intuitive.
I auditioned a couple of different caps and chose the 3.3nF (.0033uF) in the end but the 4.7nf (.0047uF) was fine too, but with a little less bass cut. A value in the middle might be even better than what I chose.

Here is the revision: