Definition Of Terms; Input & Output Characteristics - Yamaha PM-1000 Manual

ТО 2
DEFINITION OF TERMS:
UNBALANCED, BALANCED & FLOATING
Unbalanced, balanced and floating circuits may all be
transformer-isolated. The distinction between them lies
in the way the circuits are referenced to ground (audio
common). A FLOATING circuit has no ground refer-
ence, as illustrated by the primary of the РМ-1000%
Sub In, PB In, and Talkback Mic input transformers and
by the secondary windings of the Line Out, Monitor
Out, Echo Out and Talkback Out transformers.
The PM-1000's input channel transformer primaries
are BALANCED by virtue of their center taps. A bal-
anced circuit requires either a center tapped transformer,
or resistors from each side of the transformer to ground;
either condition places both sides of the transformer at
an equal difference from ground potential. іп other
words, the transformer is balanced with respect ground.
Any circuit which causes one side of an input or out-
put to be grounded is considered an unbalanced circuit,
unbalanced in that both sides of the circuit are at dif-
ferent potentials with respect to ground. Most non-
transformer connections, including the PM-1000's
Master In and Master Out jacks, are unbalanced (there
are exceptions, but they are rare).
Typical unbalanced audio sources are: direct feeds
from electric instruments, from power amplifiers, and
from high fidelity tape machines. In order to obtain
best results when using these devices with the PM-1000's
channel inputs, a matching transformer should be
inserted at the remote device. The transformer prevents
the console's input transformer from becoming un-
balanced, which may induce noise and crosstalk. Also,
the matching transformer provides the best impedance
match for high impedance sources.
Typical floating sources (which maintain a balanced
condition in the PM-1000 channel inputs) are: micro-
phones, transformer-isolated submixers, and virtually
any transformer-isolated output from auxiliary pro-
fessional equipment.
DEFINITION OF TERMS:
dB, dBV, dBm and dB SPL
The term dB, which means decibel (1/10th of a Bel)
expresses a ratio. More precisely, dB is 10 times the
logarithm of a power ratio and 20 times the logarithm
of a voltage or sound pressure ratio.
dBV expresses a voltage ratio. It is not directly related
to current or circuit impedance. The 0 dBV refer-
ence is usually 1V rms.
dBm expresses a power ratio. It is related to the voltage
or current across a low impedance. The 0 dBm
reference is 0.775Vrms in a 600-ohm circuit, which
is equal to 1 milliwatt at 600 ohms.
dB SPL expresses an acoustic pressure (not power) ratio.
The O dB SPL reference is approximately the
threshold of human hearing at 1kHz, which is
equal to 0.0002 dynes/cm2.
dB expresses the difference between two levels (power,
voltage etc.) and is a relative term. The difference
between +10dBm and +4dBm is 6dB. The difference
between -20dBV and -10dBV is 10dB.
dBV and dBm are not numerically equal when dealing
with 600-ohm circuits, although they are close (OdBV is
2.2dBm at 600 ohms). As the impedance is changed to
other than 600-ohms (given a constant voltage), the value
of dBV remains constant while the value of dBm changes.
Consider а +4dBm output terminated by 600 ohms; the
voltage level is +1.8dBV. This circuit has a voltage drop
of 1.23V rms, and a power dissipation of 2.5 milliwatts.
If the voltage now remains constant, but the termination
is changed to 1200-ohms, the power dissipation drops
to 1.23mW, +1dBm.
Since the power dissipation in high impedance cir-
cuitry is negligible, "dBV"' is sometimes used to express
signal levels in high impedance lines. "dBm" is com-
monly used to express signal (power) levels in low
impedance lines, roughly between 4 and 1200-ohms.
To avoid confusion, we use the term "dB" to represent
a specific voltage, whether it is applied to a low or a high
impedance. OdB is referenced to 0.775V, and OdBm is
referenced to 1mW (0.775V driving a 600-ohm termina-
tion). For example, when 12.3V is fed to a high
impedance, the level is designated "+24dB." When +24
dB (12.3 volts) drives a 600-ohm termination, the level
is designated "*24dBm."
An increase of 3dB is equivalent to 2 X the power.
An increase of 10dB is equivalent to 10 X the power.
A decrease of 3dB is equivalent to 1/2 the power.
A decrease of 10dB is equivalent to 1/10 the power.
An increase of 6dB is equivalent to 2 X the voltage or SPL.
An increase of 20dB is equivalent to 10 X the voltage or SPL.
A decrease of 6dB is equivalent to 1/2 the voltage or SPL.
A decrease of 20dB is equivalent to 1/10 the voltage or SPL.
The open circuit voltage output of a low-Z micro-
phone (in dBV), given a 94dB SPL sound field, is approx-
imately equal to the microphone's rated EIA sensitivity.
If the sound level at the mic is higher than 94dB SPL,
add the difference to the EIA rating, and if the level is
below 94dB SPL, subtract the difference from the EIA
rating. Thus, a mic rated at -bOdB EIA sensitivity,
placed in a 104dB SPL environment, will yield about
-40dBV (-37.8dB, or 10mV) output.
INPUT & OUTPUT CHARACTERISTICS
INPUT SPECIFICATIONS
IMPEDANCE
Connection Actual Nominal Source
SENSITIVITY* INPUT LEVEL Connector
(At Max. Gain) Nominal* Max.before Clip. In Console
Inputs (1-16)
PB & Sub In (1-4)
Master In (1-4)
1700 О, balanced
2300 Q, floating
9000 О, unbal.
150 О Mics & 600 N Lines
600 О Lines & Instruments
5k О Lines & Instruments
0.25mV (-70dB) 0.8mV (-60dB) 12.3V (*24dB) XLR-3-31
40mV (-26dB) 80mV (-20dB) 3.2V (*12dB) XLR-3-31
З1тУ (-28dB) 62mV (-22dB) 12.3V (+24dB) Phone Jack
Talkback Mic 2300 Q, floating 150 Q Mics 8mV (-40dB) 2.5mV (-50dB) 1.23V (*4dB) XL R-3-31
OUTPUT SPECIFICATIONS
IMPEDANCE POWER OUTPUT LEVEL Connector
Connection Actual Nominal Load Nominal Max. before Clipping In Console m
Line A (1-4)
Line B (1-4)
Monitor (1-4) 100 О, floating 600 0. 1.23V (+4dBm) 10.8У (ғ2212аВт) XLR-3-32
Echol &2
Talkback
Master Out (1-4) 200 О, unbal. 5,000 Q 62mV (-22dB) 2.1V (+9dB) Phone Jack
Headphones 3.2 О, unbal. 8 О or greater 80mV (-20dB) 1.23V (*4dB) Stereo Phone Jack (x 2)
* This is the level required to produce an output of *4dBm (1.23V).