Studio Technologies 80 1997 - Manual (Page 12)

Model 80 User Guide Issue 4, March 1997
Studio Technologies, Inc. Page 15
output” would be in dBu and the “–10
output” would be in dBV. We soon real-
ized that this would cause “cranium”
problems for many users. A user monitor-
ing one of the Model 80’s outputs would
expect to see a 14dB drop on their VU
meter when going from the +4 to the –10
DIP switch position on the Model 80’s front
panel. They actually would be switching
from a +4dBu output to a –10dBV output,
a difference of 11.78dB; confusion would
immediately reign! To avoid this situation
we took the liberty of keeping the –10
referenced to dBu. This should in no way
effect the ability of the Model 80 to inter-
face with other equipment, while making
life easier for everyone.
Circuit Description
This information will help you under-
stand how the Model 80 functions and,
if required, help you identify where a
failure may be located. Please refer to the
attached block and schematic diagrams
while reading this material.
Schematic Nomenclature
The schematics show the graphical repre-
sentation of all the electronic components,
along with their electrical value and con-
nections. Traditionally, a problem with
schematics has been the decimal point
marking. It either disappears due to bad
printing, or dust, dirt or other imperfec-
tions end up looking like decimal points.
For clarity, Studio Technologies has
adopted a more “European” component
marking scheme. Upon first review it may
seem quite confusing, but it can eliminate
problems. For resistors, the designation
“K” for kilo (1000) has been moved to the
decimal point position. A 4700 ohm resis-
tor is shown as 4K7, rather than 4.7K. An
example for a one percent value, a 49900
ohm resistor would be shown as 49K9.
For capacitors, the letter “r” is simply
substituted for the decimal point marking.
A 0.47uf capacitor is shown as r47uf.
Once you are accustomed to this system
you may well prefer it.
Power Supply
The Model 80 contains one linear power
supply circuit that generates filtered and
regulated ±15Vdc. The circuit uses a step
down transformer, with the primary side
containing two 115V windings. This allows
it to be configured for nominal AC mains
voltages of 100V, 120V, or 220/240V. For
100V and 120V operation the primaries
are connected in parallel; for 220/240V
operation they are connected in series.
The configuration is performed using
jumper straps on the circuit board. For
safety, a fuse is in series with the incoming
AC mains power.
Because the Model 80 is intended for
continuous operation, an AC mains power
switch is not included. This serves several
purposes: eliminating the chance of a
power switch being accidently turned off,
increasing the physical isolation between
the nasty 50/60Hz fields and the sensitive
analog circuitry, and eliminating the physi-
cal space required by a switch.
The step down transformer has dual 17V
secondaries for 120V and 220/240V op-
eration, and dual 20V secondaries for
100V operation. The secondaries are
connected in series, with the series con-
nection point providing circuit common,
as well as being strapped to the metal
chassis and the ground pin of the power
entry connector. The transformer’s sec-
ondary is fed to a full wave diode bridge.