MEGALITH DUAL DRIVE
5
BUILD NOTES
C7 capacitor
C7 is an 820n capacitor in the original. While these are still produced, they are only available from
a small number of manufacturers and may be hard to find. Presumably ZVEX chose this value after
experimentation since 1uF is a lot more common.
The Megalith PCB adds footprints for three capacitors in parallel (C7, C8 and C9) so you can mix and
match values to add up to 820n. The easiest combination is 470n/330n/22n (822n total), and this is
what is used in the parts list as the default. However, you could also use other combinations such as
three 270n capacitors or 470n/220n/120n, both of which add up to 810n.
2-pole filter values
Between the tone control and drive level, there is 2-pole filter formed by R16/C12 and R17/C13. In the
original Box of Rock, the two resistors are 10k and the two capacitors are 2n.
2n is no longer a standard value of capacitor, typically only available in green mylar “chiclet” types. If 2n2
capacitors are used for C12 and C13, then the resistors need to be 9k1 to preserve the same frequency
response. This is the default arrangement in the parts list.
If 2n capacitors are used for C12/C13, then R16/17 should instead be the original 10k.
MOSFET substitution
The BS170 and 2N7000 are nearly identical in specifications, but the pinout is reversed between the
two. If you have 2N7000 handy, they’ll sound the same in this circuit, but they need to be rotated 180
degrees from the silkscreen which assumes BS170.
