Source: http://www.muffwiggler.com/forum/viewtopic.php?t=98954&postdays=0&postorder=desc&start=100
The filter input is B.A.D. (Broken As Designed)
It has DC coupled inputs for the VCO outputs. And the pulse, square and saw waves have 5V DC offset.
There are no coupling caps inside the filter.
So it is *designed* to give a massive *THUMP* when the VCA opens.
If you trim the Filter offsets for minimal thump with these offsets still build in, the best setting depends on the patch...
So: have a look a the PCB, the TTSH has one single mod pre-thought: adding caps to the filter input. Thanks Jon 
(Speaking of "making the thing usable": this is one of the changes I would consider mandatory if you want to use an ARP2600 for more than fx sounds. )
