MOTM

>>   c.. You can build a similar effect that uses 20-pole all pass filters
>> instead of BBDs, using three PCBs, the "Dim T".
>
>How similar is this to your 20pole phaser board from a few months back?


It's the same PCB.
You need the Main Board and two Tau boards for the Dim T effect.
You don't need to solder in all components on the Tau boards, though.
I've also been thinking about a making dedicated board with the two all pass 
filters on one PCB, but I'll probably offer a bundle of two Tau boards 
(together with the main board) at a somehow reduced price instead.

A sound sample can be found here:
http://electro-music.com/forum/viewtopic.php?t=24529
(Short wav file. First, CS-80 dry. Then, CS-80 thru Dim T.)
Longer demo (18MB):
http://www.lulu.com/content/2136864

The effect is less "subtle" than a Dimension D, but IMO very pleasant on its 
own.
(With the BBD board, you'll get the exact Dim D sound, of course.)

JH.