Jumper maps, Ground lifts & isolates, Twin direct 2 – Millennia TD-1 Twin Topology Half Rack Recording Channel User Manual
Page 15: Input pcb, A word on isolation, Millennia
TD-
Twin Direct
2
JUMPER MAPS
INPUT PCB
For more on jumper options inside the TWIN DIRECT, please refer to the
Signal Flow Diagram and detail instruction pages. Remember, before
you remove TWIN DIRECT’s top cover, always assure that the IEC AC
power plug has been disconnected for at least five minutes. This will al-
low potentially lethal voltages inside the TWIN DIRECT to dissipate to a
safe level.
BUFFERED
BUFFERED
UNBUFF
UNBUFF
JP3
JP3
JP1
JP1
JUMPER WHICH SELECTS INTERNAL
PATH OF DIRECT OUTPUT.
JUMPERS AT TOP OF JP2 & JP3 GIVES
ACTIVE BUFFERED DIRECT OUTPUT,
BUT MAY REDUCE DI INPUT IMPEDANCE.
JUMPERS AT BOTTOM OF JP2 & JP3
GIVES HARD WIRED FEED FROM DI
INPUT TO DIRECT OUTPUT. DEFAULT.
JUMPER WHICH SELECTS INTERNAL
INPUT GROUND LIFTING PATH
JUMPER ON HEADER JP1
JUMPER OFF HEADER JP1 GIVES
CREATES
RESISTIVE + CAPACITIVE ISOLATION
WHEN INPUT GROUND LIFT SWITCH IS
SELECTED
TRUE
GROUND LIFT WHEN INPUT GROUND
LIFT SWITCH IS SELECTED. DEFAULT.
Direct Output Buffered / Non-Buffered Output Jumper
Input Ground Lift / Isolate Jumper — Input Board
GROUND LIFTS & ISOLATES
Grounding remains a subject of debate within the audio community, yet
standard grounding practices, such as outlined by Muncy, Atkinson, Gid-
dings, Windt, Fause, (et al) in their foundational AES Journal papers (J.
Audio Eng. Soc. Vol 43 No. 6 1995 June), define clearly the safest and
best performing grounding practices for both recording engineers and
product designers. Design inconsistencies among audio product manu-
facturers, along with the variables of real-world recording environments
(such as AC power irregularities in large auditoriums and old churches)
can present the recording engineer with “ground” far from zero volts po-
tential, or even multiple “AC power grounds” exhibiting varying potential
throughout a building or stage.
Because of these wide variations, a well-designed DI box must effectively
anticipate all manner of audio and electrical systems. To remedy most
interface problems, TWIN DIRECT provides five different methods of
ground alteration options, allowing an unusually high level of user control
over hums and potential mismatch.
A WORD ON ISOLATION
Inside TWIN DIRECT are jumpers which allow Input and Earth Ground
Lift switches to be converted to Ground Isolation paths. Ground Lift is
a complete removal of all internal ground paths (earth, power, or audio)
from the targeted audio connector(s). Ground Isolation is a technique
whereby the ground path of targeted connector(s) is delivered in se-
ries with certain passive components. Ground remains “sensed” at the
connector(s), yet it becomes “isolated” via series resistance. If pure
ground lifting does not cure a hum problem, isolation may be an effective
technique.
Ground lift and isolation options are presented in the Rear Panel, Front
Panel, and Jumper Map sections of this manual. When encountering
hums or buzzes, try altering TWIN DIRECT’s internal grounding, as fol-
lows: (1) Earth Ground Lift, (2) Input Ground Lift, (3) Using Transformer
Output, (4) Using Transformer Output with Ground Lift, (5) Input Ground
Isolate. By itself, the galvanically isolated DIT-01 transformer output will
provide an ideal source of ground isolation. For your personal safety and
the safety of others, never under any circumstance lift earth ground be-
fore it enters the TWIN DIRECT’s IEC power connector. When IEC earth
ground is secured, earth-to-chassis safety integrity is preserved under
all circumstances, regardless of TWIN DIRECT’s internal ground lift or
ground isolation selections.