madbeanpedals Zygote, Manual

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There are a few key differences in building either the positive ground PNP and negative ground
NPN. If building the PNP, you should follow the layout diagram on pg.2. You will need to connect
your battery supply so that the black (negative) wire goes to the 9v pad on the board, and the red
wire (positive) goes to ground (typically this is done by connecting it to the ring of a TRS input
jack). Even though this setup uses only a battery to power the effect, the battery will only be in
use when a jack is plugged into the input jack. Once the jack is unplugged the battery
disconnects.
If you have never used PNP germanium transistors before, I HIGHLY recommend you by a
matched set from Small Bear. These are already tested for leakage and have the appropriate
gains for Q1 and Q2. Steve offers several sets to choose from.
If you want to use a power supply, you can do the following
· Use a PS like the VoodooLabs Pedal Power which can supply negative and positive
ground. It can do this because each 9v output is isolated. You can purchase a 2.1mm
cable which has the neg/pos wires flipped or make your own. If you are using a different
supply, make sure that the outputs are isolated or you will kill your board and possibly
your power supply.
· By a dedicated wall wart that has a 2.1mm positive tip plug. You can get these off
Mouser, although they are generally unregulated and put out closer to 13v.
·
Use a Road Rage board. This is probably the best solution because you can set it up like
a negative ground power supply, but the RR board flips the power to ­9v internally. This
means you can use the same PS/plugs as your regular negative ground effects, provided
you wire everything properly, and it will cost about the same as buying a dedicated wall
wart. I do not recommend using a battery in this situation. See the wiring diagram below
which illustrates how to do this properly.
To convert this layout to use NPN and negative ground, do the following
· Reverse the direction of all electrolytic caps
·
Reverse the direction of D1
·
Hook +9v to the 9v pad on the board. The GND pad hooks to ground, as you would any
other negative ground effect.
For the NPN version, there are many types of transistors you can use. I suggest either the
2SC1815 or BC108. Both of these were used in the “70” pedal at different times. Again, check
Small Bear to see what Steve has to offer. You can also use NPN germanium transistors,
although these a lot more expensive. Plain old silicon works really well here, so I wouldn’t worry
too much about that.
NOTE : PNP transistors, the little metal tabs that stick out from the housing almost always indicate
the Emitter of the transistor. Some transistors may have a red dot, and these can indicate
Collector in a few cases. While you probably will not damage the transistor by putting it in
backwards (I’ve never had this happen), try to figure out which is which before plugging it in.
Also note that the pinout of 2SC1815 is most likely different than the typical E­B­C (typical is E­C­
B). Consult a datasheet before using this type, as it may require you to twist the leads around to
plug into the correct spots on your transistor sockets (yes…use sockets).