ATI Audio BGD200-PPM-P - Manual (Page 2)

ATI Audio Inc. ■ Tel: 856-719-9900 ■ [email protected] audio.com
DESCRIPTION
ATI BGD200 and BGD400 Series bargraph audio displays are an effective and
economical means of displaying multiple audio signal levels. They can give you that
warm comfortable feeling that there really is audio going out with your video, audio is
feeding the switcher, and there definitely are outputs going to downstream equipment.
Along with providing a nice touch of color for your studio, the BGD200-VU and
BGD400-VU provide a good visual match to the ballistics of a standard ASA VU meter
in bright, three color, ten segment displays. The BGD200-PPM and BGD400-PPM
closely match the peak-following characteristics of a standard PPM meter in a more
conservative red and green color scheme. The BGD200 is a horizontal two-channel
display and the BGD400 is a four-channel unit with vertically oriented displays. Models
ending in “-P” are equipped with headphone jacks and phase indicators.
Two sections of a quad bi-fet IC, National LF347N, form a selectable gain,
instrumentation amplifier input stage. The instrumentation amplifier provides precisely
equal loading to each side of a balanced line with good common mode hum rejection yet
will easily bridge a high impedance IHF level audio line (typically found with RCA
connectors) from HI input to GND without the necessity of also grounding the LO input
terminal. Three position jumper plugs for each channel (JX02) select input stage gain for
nominal 0 VU or 0 dB displays at -10, +4 or +8dBu input (0dBu reference is .775Vrms).
Trimpots accessible through the front panel allow precise level adjustment.
The remaining two sections of the LF347N in each channel are used for the active full
wave signal rectifier and time constant networks. The VU network has a slightly
underdamped two-pole response, which reaches 99% of final reading in 300ms and
overshoots by not more than 1.5%, closely matching ANSI specification C165. The PPM
network matches the integration and return time specifications of DIN45406 by
indicating a response 1dB down from steady state for a 10ms tone burst and 4dB down
for a 3ms burst with an equivalent return time of 1.5s to -20dB.
The LED bargraphs are driven in a power conserving series mode by an LM3916 (VU) or
LM3915 (PPM) display driver IC. The VU display indicates from -20 to +3VU in ten
steps. The PPM display indicates levels from -15 to +12dB in 3dB increments around
0dB.
Swings of the external 24VDC supply are limited by zener regulator stage Q1 to protect
the display driver ICs. Several BGDs can share a single external WA100-1 or -2 external
power supply up to the limit of its rated current capacity. A BGD200 draws 70mA and a
BGD400 draws 130mA. An accessory DC power jumper cable P/N 20602-1 loops power
between units sharing a common power supply.
Up to three BGDs will mount side-by-side in only one 1-3/4” rack space using an
available rack mount shelf. They may also be neatly stacked or mounted side-by-side on
your desk with accessory desk mounting kits.