Wheatstone SP-8, Technical Manual

Page: 124 / 128

Appendix Page - 3 SP-8 / Dec 95
A
PPENDIX
CS-08 MODULE OUTPUT CONNECTIONS
The SP-8 console's monitor module has electronically balanced output
circuits on its main output channels. Care should be taken when installing
or testing these circuits to avoid connecting the "low" side of these outputs
to ground or to an input circuit that has a low impedance to ground. While
such a connection will not cause damage to the console, levels will be
incorrect and distortion figures will rise. If an unbalanced connection must
be made to these outputs, let the "low" side float unconnected or else build
it out with a 620
Ω
or higher resistor.
NOTES ON LEVEL MEASUREMENT
Audio levels today are commonly referred to as voltage equivalents of
power levels in 600 ohm circuits. One milliwatt (0 dBm) in 600 ohms is a
voltage of .775 V. The corresponding unit for use in circuits where the exact
impedance is unknown or irrelevant is the dBu (the "u" stands for "unloaded").
Thus, 0 dBu is .775 V regardless of the impedance of the circuit where it is
measured. (Note the dBu should not be confused with the dBV; 0 dBV = 1
volt.)
For your convenience, here are some commonly encountered values:
0 dBm in 600 ohms = .775 V = 0 dBu in any impedance
+4 dBu = 1.23 V
+8 dBu = 1.95 V
-10 dBu = .245 V
-20 dBu = 77.4 mV
-50 dBu = 2.45 mV
When checking out a system, remember to measure the input voltage at the
connector, as variations in input impedance and generator source impedance
can invalidate your results.
TROUBLESHOOTING
BASIC PROCEDURES
If you have encountered difficulty in testing your installation, check the
items listed below before opening the console. Note that some items may seem
very obvious; it is often the most obvious things that we overlook.
1) Check that the AC power source for the console is live, and that the
console power cable is connected to the AC source.
2) Make sure that the sources you are using to test the console installation
are producing normal, line level signals. For example, if a cart machine is the
source, is the cart playing? Is the output of it connected to the console?
3) When checking for sound from the control room speakers, is the
amplifier on? Is the amplifier volume turned up to a normal level? Are the
speakers connected to the amplifier outputs?
Note these output connection
details differ from the SP-8's oth-
er modules (called out on the
previous page).
!