transformer une devi ever rocket pour avoir
Citation:
Adding a chaos switch has been covered over at Devi's DIY forum. If you look at the PCB and find the capacitor in question, you'll see that it straddles a little pad with two holes in it. Reposition one leg of the cap to that pad then wire an spst between the pad and where the leg was and you have a chaos switch.
As you can see on Devi's schematic for the SM/VFM (linked below), the only difference between the two is the orientation of the 2n2907a in the last stage. Likewise, the GZ and ZG are the same but using a 2n2222a in that position. Devi is terribly clever in getting the most out of a single layout so that shouldn't come as much of a surprise.
The schematic thread:
http://forum.deviever.com/view(...)=4191
There are two ways to do the SM/VFM/GZ/ZG switch with standard cheap Alpha rotary switches. The parts required would be:
Approach 1:
6pdt (last two positions will not be used)
Two 2n2222a
Two 2n2907a
Approach 2:
3p4t (all positions used)
One 2n2222a
One 2n2907a
I used the first approach the first time I built it and it was clumsy to assemble and on an old switch from Rat Shack with a couple bad contacts so it didn't work well all the time. Using that approach, the two poles of the switch switch the base and the leg connected to the collector of the MPSA18. You need four transistors in this version because you'll be hard wiring the leg that goes to ground because you only have two poles to work with on the switch. You can ground these to the body of the switch so you don't have to run a ground wire from the board. After that, you just wire the base and other leg to the appropriate positions for each circuit. You need to remove the 2n2907a from the board and run two wires for the base and other switched leg to the two poles on the switch and hope that your cluster of transistors don't have any legs touching.
The second approach is cleaner because it only uses two transistors. In this version, the three poles of the switch are base, leg to MPSA18 collector, and leg to ground. It's wired like a double version of de.engineered's image here (http://forum.deviever.com/viewtopic.php?f=153&t=8809) but with a third pole for the base so the base pole in positions 1 and 2 go to the base of the 2n2907a and to the 2n2222a in positions 3 and 4. It requires the same removal of the 2n2907a from the board and two wires and you can again link the ground-going leg to the body of the switch to avoid running a third wire. I'd attach a picture of my wired switch to give you a visual idea but photobucket's not cooperating with me right now.
There's kind of a jumble of information here and I think I tend to confuse as much as help when it comes to writing this sort of thing out so I hope you get at least some value out of it.
-Ken
