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Thus, a safe ru1e to follow is:
Do not ground either side of
external circuits.
GGn8rally, the shields of the cables should
ground at thG console only.
They may be connected to the ground
terminals in the; consolD.
TheI'e may be exceptions to this ru18
esp8cially on microphone input circuits, so the shield grounds'
should be wirGdin such a manner that they can be lifted in the
console and grounded at the other end.
Again, this is part of
the test procedure to obtain lowest noise.
If patch panel facilities are used, special consideration of
circuit grounding is necessary.
.Look in the section marked
MODIFICATION
FOR
EXrpRA FACI.Ll'1'Iji;3 for instructions.
BAL"NCED AND UHBALANCED LINES
- - - , - - - - - - - - , - - - -
If a circuit is unground.ed, it is considered balanced to ground.
If one sicle is grounded it is unbalanced.
If the circuit is
center,,·tap grounded 'v1..th a pad or coil it is balanced to ground.
Refer to the third paragraph under GHOUNDING CIRCUITS for deter-
mining proper classification.
THisted shielded pairs should be
used for all circuits whether they are ba]anced or unbalanced,
Cancellation of noise and crosstalk pickup is app:coximately the
same for either "Ihen the one point ground system is used.
If it i.s necessary to connect a balanced line to an
unbalancea~
line, or the opposite, an isolation transformer should be used
betvieen them.
The transformer must have good balance, an electro-·
static shield, and magnetic shi.eldillg sClffic..ient to reduce the
hum pickup at least 65 DB below the signal level.
Impedance
t;:lPS
on pri.mary and secondary are important to properly match both
circui ts.
The Gates Radio Company
I
s
general catalog lists tllGse
transformers.
Balanced lines requiTe balanced pads and attenua--
tors, unbalanced li.nes requiro unbalanced ones.
Mixing them
generally resul.ts in poor noi.se, frequency response or other
.poor operation.
CIRCUIT HlP.2DANCBS
The mi.crophone inputs are factory connected for 150 ohms.
These
are balanced inputs.
The impedance can be changed to 50 ohms
balanced by changing the co=ections of the input transformer on
the preamp board.
See the preamp instruction book included at
the back of this book for more informati.on on this change.
The turntables and tape inputs are 600 ohms unbalanced.
These
impedances cannot be changed in the console and if other iill-'
pedances are desired, a matching pad or an isolation transformer
must be used.
If a matching pad is used it should be unbalanced
and its common side connec ted to the CO';11Ilon or grounded side of
the inputs.
The Executive
6/26/62
-,5-
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