Here's another good octave down - the Colorsound Octivider (verified!)
I made a few mods to it to make it better. I built a layout of the original circuit first, but I didn't like it much. The original has a good octave down that tracks well, but the clean signal sounded dull and lifeless and had a low drop in volume, even in bypass (buffered). So this version is true bypass without the output buffer, insted I added a JFET buffer/splitter at the input to split the signal and preserve the original clean tone.
A blend pot replaces the old "Bass volume" (octave volume) and "Bass switch" (octave only), since it basically does the same things. A low volume drop for the clean part of the signal still occurs at 50/50 ratio (blend at middle position), but at least now it's not constant. The original circuit blended the clean and octave at 50/50 ratio before the output buffer with fixed resistors and therefor had a constant volume drop. Note: If you still want a octave only switch you could just put the BLEND 1 output on a SPST before the blend knob.
I also made the layout for standard CBE pinout transistors. It doesn't seem to be that picky about transistors. I tried a few different ones with the same result.
I build it today and it works great and sounds good. Very different from the Synthbox I posted earlier. This one sounds much more "natural" with a very bassy clean octave sound.
check out my building blog at www.parasitstudio.se
I just finished building it today but all i'm getting is a very low frequency oscillation with no clean or octave notes. i'm troubleshooting it for build errors now but I haven't found a single one yet. (damn!)
and BTW, I did correct the updated orientation of Q11 & Q12.
EDIT: Found it. I had a microscopic short between two rows, even though previously I ran a jeweler's triangle file between all of the rows multiple times before.
Thought I might share my layout for the Shin-Ei Octave Box that I did a while ago, since you mention it.
I have not built and verified it yet, but will soon.
I will also try the one above, and compare them. I can never get enough octave boxes, always great fun!
Be aware that my layout skills are quite fresh, so I guess there are many who will be able to make it a bit smaller. This is my biggest layout so far, so I would suspect that there might be some mistakes that I have not spotted yet, even though I have gone over it quite a few times...