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© 2006 Wohler Technologies Inc. ALL rights reserved
AMP1A-4S/-10S/-LP4S/-LP10S
User Manual P/N
821527
Rev-
B
Section 3: Technical Information
The "PPM-1" version of the 919017 meter driver input is driven single-ended from the main circuit board. Gain selection via S1 and
S2 of the DIP switch module (page 17) allow the circuit to be configured for an input level of -6, 0, +4, or +8 dB to indicate '0' on the
actual display. The input attenuator network consists of R1-R4, R11, R17, R18, and R19. The buffered signal (and its inversion) are
coupled to half-wave rectifiers IC2a and b.
The two half-wave rectifiers provide full-wave rectification of the AC signal from the input amplifier. IC2a provides output on
negative excursions; IC2b is for positive excusions. C8 is charged via R14 (or R26); the time constant of this resistor-capacitor
combination determines the attack time of the meter. When the input level decreases, C8 discharges through R14, R16, and D1 (R27,
R28, D3); the resulting time constant determines the decay time of the meter. By switching in additional RC (R21, C10) with S3, the
attack time is increased and the decay decreased, to approximate VU characteristics. S4 is closed along with S3 to adjust the
reference voltage to compensate for the voltage dividing effects of R21.
The popular LM3916 10-segment LED bargraph driver has internal voltage comparator references at VU meter intervals. R25 sets
the current for the external reference network and the LED drive current, which is about 10 times the current taken from pin 7. The
top of the internal comparator resistor ladder is connected to pin 6, the bottom to pin 4. The voltage across R23, R24, and P1 is the
reference against which the rectifier output applied to pin 5 is compared. The meter is calibrated by adjusting P1 (PPM) or P2 (VU).
ZD1 sets the voltage at the bottom of the resistor ladder and the bias for the rectifier circuit with C11 as a bypass. NOTE: The driver
PCB connects the LEDs in the bargraph in a SERIES string. The anode of the LED corresponding to the LOWEST input level (-20) is
connected to V+, with the other 9 LEDs following, and the outputs of the 3916 connected to the node between each LED. Only ONE
output of the 3916 is active (LOW) at any one time ("dot" mode), so if the LED string is "broken" (open) at any point, the bargraph will
go OFF whenever the input level is AT OR ABOVE the level corresponding to the break.
Bargraph Driver Circuit Description (919017)
Level Meter Specifications
Level Calibration:
Frequency Response:
Level Meter Type:
LED Colors:
Metering Range:
Display Mode (Ballistics):
VU Characteristics:
Rise Time =
Decay Time =
PPM Characteristics:
Attack Time =
Decay Time =
Bargraph Length:
LED Segment Size:
LED Segment Pitch:
Segment Brightness, (I f = 20 mA):
Segment Brightness, Uniformity:
Adjacent Segment "Off" Brightness:
Peak Emission Wavelength:
-6, 0, +4, +8 dBv, Selectable
20 Hz to 18 kHz (±0.5 dB)
10-segment LED Bargraph Display
Tricolor (red, amber, green)
23 dB
VU or PPM, Selectable
300 millisecond to 99 % of full indication
300 millisecond
10 milliseconds
2 seconds, 0 to -20 dB
2.00" (50.8 mm)
0.152" x 0.305" (3.56 x 7.75 mm)
0.20" (5.08 mm)
5.5 mcd
<8% difference between segments
<1% of brightness of active segment
green: 570 nm red: 630 nm
