User Guide

Model฀74/75฀User฀Guide฀ Issue฀3,฀November฀2016฀
Studio฀Technologies,฀Inc.฀ Page฀41
for Surround
Monitor฀Output฀Gain฀
Structure
The฀Model฀74฀Central฀Controller’s฀monitor฀
outputs฀are฀configured฀for฀unity฀gain.฀When฀
the฀rotary฀level฀control฀on฀the฀Model฀75฀
Control฀Console฀is฀set฀for฀maximum฀level฀
(fully฀clockwise)฀the฀output฀level฀is฀essen-
tially฀the฀same฀as฀the฀input฀level.฀The฀input฀
trim฀potentiometers฀allow฀precise฀adjust-
ment฀of฀the฀input฀circuitry.฀This฀was฀provid-
ed฀so฀that฀level฀variations฀in฀input฀sources,฀
the฀Model฀74’s฀circuitry,฀and฀the฀associated฀
power฀amplifiers฀can฀be฀“trimmed฀out.”
Definition฀of฀Levels
Whenever฀possible,฀when฀describing฀audio฀
signal฀levels฀Studio฀Technologies฀has฀opt-
ed฀to฀use฀the฀dBu฀designation฀as฀it฀seems฀
to฀be฀quite฀rational.฀The฀dBu฀designation฀
refers฀to฀dB฀referenced฀to฀0.775฀V,฀with฀no฀
reference฀to฀load฀impedance.฀This฀takes฀
into฀account฀today’s฀audio฀scene฀where฀
signals฀have฀a฀low฀source฀impedance฀and฀
a฀high฀input฀impedance.
The฀Model฀74฀is฀designed฀to฀interface฀฀
with฀audio฀signals฀that฀have฀nominal฀sig-
nal฀levels฀of฀–12฀dBV฀to฀+6฀dBu.฀You฀might฀
wonder฀why฀“dBV”฀came฀into฀the฀picture.฀
Most฀people฀don’t฀realize฀that฀equipment฀
that฀utilizes฀“–10”฀levels฀usually฀mean฀฀
–10฀dBV—substantially฀different฀from฀฀
–10฀dBu฀(–10฀dBV฀=฀–7.78฀dBu).฀The฀dBV฀
designation฀is฀simply฀a฀different฀way฀of฀
measuring฀signal฀level฀and฀is฀often฀used฀
when฀dealing฀with฀portable฀or฀consumer฀
audio฀equipment.฀The฀dBV฀designation฀฀
refers฀to฀dB฀referenced฀to฀1.0฀V,฀rather฀
than฀dBu฀which฀refers฀to฀0.775฀V.
“Hot”฀Disconnection฀of฀the฀
Model฀75฀Control฀Console
Should฀you฀need฀to฀relocate฀the฀Model฀75฀
while฀your฀StudioComm฀system฀is฀oper-
ating,฀there฀is฀no฀reason฀why฀you฀can’t฀
disconnect฀the฀cable,฀move฀the฀unit,฀and฀
then฀reconnect฀the฀cable.฀If฀the฀Model฀75฀
is฀disconnected฀while฀it฀is฀operating,฀the฀
active฀operating฀parameters฀are฀saved฀in฀
non-volatile฀memory฀and฀the฀Model฀74฀
Central฀Controller฀will฀continue฀to฀oper-
ate฀as฀before฀the฀connection฀was฀broken.฀
No฀clicks,฀pops,฀or฀other฀noises฀will฀occur฀
when฀the฀Model฀75฀is฀again฀connected.฀
The฀Model฀75฀will฀go฀through฀its฀standard฀
power-up฀sequence,฀send฀a฀message฀to฀
reset฀power-up฀defaults,฀then฀send฀the฀
operating฀parameters฀as฀are฀stored฀in฀its฀
memory.฀Depending฀on฀its฀configuration฀
settings฀vis-à-vis฀power-up,฀the฀Model฀74’s฀
monitor฀outputs฀may฀be฀placed฀in฀their฀
mute฀mode.
Monitor฀Output฀Transient฀
Protection
The฀Model฀74฀Central฀Controller฀contains฀
a฀power฀up/power฀down฀protection฀fea-
ture.฀This฀limits฀the฀chance฀of฀damage฀to฀
the฀monitor฀loudspeakers฀during฀the฀time฀
when฀AC฀mains฀voltage฀is฀connected,฀
disconnected,฀or฀has฀dropped฀significantly฀
from฀nominal.฀During฀testing฀it฀was฀found฀
that฀upon฀power฀up฀the฀monitor฀outputs฀
remained฀very฀quiet;฀during฀power฀down฀
a฀moderate฀“tick”฀was฀the฀worst฀that฀was฀
heard.฀A฀combination฀of฀hardware฀and฀
software฀is฀used฀to฀monitor฀one฀“rail”฀of฀฀
the฀internal฀power฀supply.฀Upon฀initial฀฀
connection฀of฀AC฀mains฀power฀electro-
mechanical฀relays฀maintain฀a฀short฀circuit฀
condition฀on฀the฀monitor฀outputs.฀If฀the฀
AC฀mains฀input฀voltage฀exceeds฀90%฀of฀