GAIA PREAMP DRIVE MK. I
6
BUILD NOTES
Using SMD JFETs
The 2N5457 JFET is no longer available in through-hole format. This PCB uses a hybrid through-hole/
SMD outline for each JFET. An extra “G” (gate) pad is included to accommodate surface-mount devices
without the need for adapters.
SMD JFETs should be oriented as follows:
All surface-mount JFETs use the same pinout, so this configuration will fit any type that we’re aware
of. However, always check the datasheet if you’re uncertain—they’re difficult to desolder if you make a
mistake.
Using through-hole adapters
If you’re not confident in your ability to work with surface-mount parts, Aion FX offers
that come pre-soldered to adapters for use in through-hole designs. These are from
the same manufacturer as those used in the original Catalinbread pedals and will perform identically.
Using old-stock JFETs
JFETs are an odd category of component because their manufacturing process is highly inconsistent.
The datasheet for a given part number will usually show an enormous range for crucial specifications
such as V
GS(off)
and I
DSS
.
However, in practice, parts from the same manufacturer are usually much tighter in specification. So
while the 2N5457 has a V
GS(off)
range of -0.5V to -6.0V, devices from ON Semiconductor (Fairchild) will
usually be between -1V and -2V. This is the brand of JFETs used by Catalinbread in this pedal.
This means that the part number itself is not usually enough to go by if you’re trying to replicate a circuit
that uses JFETs in certain types of applications, notably when they’re used for overdrive.
So while the 2N5457 is sometimes available from manufacturers such as Central Semiconductor or
InterFET, the ones we’ve tested have been very far outside the ON Semi range and will perform very
differently in this circuit. Therefore,
it is not recommended to use 5457 JFETs from any manufacturer
except ON Semiconductor
—although it makes no difference whether it’s an old-stock through-hole
type or the current-production MMBF5457 SMD type.
Conversely, if you find a different type of JFET that measures in the -1V to -2V range for V
GS(off)
, it
should work just as well as the 2N5457.
