INTRODUCTION
Thanks for purchasing a Diamond J-Drive MK3 combination clean boost / overdrive. The
MK3 evolution of the J-Drive family incorporates the liquid drive of the limited edition J-
Drive TR with the transparency of a new low noise JFET / BJT clean boost.
Remember to protect your hearing and wear appropriate hearing protection when play-
ing loud…
DESIGN BACKGROUND
The original concept of the J-Drive
began as the happy marriage of an
overdrive with a separately
switchable clean boost - a clean
boost that could be used either on
its own or as a means to ‘overdrive
the overdrive’ as a solo boost. The
limited edition J-Drive TR ex-
panded on this idea by adding the
ability to transform the clean boost
circuit into a higher gain ‘treble
boost’. Unfortunately, the availabil-
ity of NOS 2N388 JAN mil spec
germanium transistors and careful
gain selection for those transistors limited the TR’s long term production. The TR did in-
troduce a new, more liquid drive section that we really liked - and one that was not reliant
on limited availability components. The MK3 has been designed to incorporate that same
TR overdrive circuit, including Schottky diode clipping, bright shelf EQ and transformer
output smoothing, along with a new two-transistor clean boost section that incorporates
concepts from both the original J-Drive and the TR.
FEATURES
•
independently switchable clean/treble boost and overdrive, each true bypass
•new discrete clean boost circuit with JFET input buffering and bipolar drive
•post-volume control overdrive transformer output stage that smooths upper mids and highs
•premium audio components, including 2% polypropylene capacitors, 1% metal film resistors,
Vishay transistors, and a Burr Brown OPA2134 opamp
•'Close Asymmetry' Schottky diode clipping circuit
•warmth control – replaces the traditional fixed frequency cut/boost circuit with a variable high-
frequency cutoff filter coupled with variable low-frequency gain.
•switchable highpass shelf filter for additional 'bite', implemented without additional active
components
•battery or standard negative tip regulated 9V DC adapter operation
•
genuine Hammond cast aluminum 4.7 x 3.7 x 1.1 inch case
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J-Drive MK3 user manual v1.02
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