Triplett 630 - Measuring Output Volts (Decibels); Decibel Measurement Procedure

MEASURING OUTPUT VOLTS
(Decibels) |
Amplifier output is usually expressed in decibels (ОВ). The
decibel is a standard unit of measure used in sound, recording,
radio and telephone work to express gain, loss and power levels.
Gain or loss is usually expressed as a number of DB above or be-
low a reference level. This instrument is calibrated for a 0 DB refer-
епсе leve! when | milliwatt of power is developed іп а 600 ойт
load (0.775 АСУ into 600 ohms).
А 0.1 mfd, 400 volt capacitor is connected in series with the
OUTPUT jack io block the DC often present in output circuits (DC
in the circuit will cause an erroneous AC reading). Caution: do not
use the OUTPUT range in circuits where the sum of the peak AC
voltage and DC voltage is greater than the 400 volt rating of the
blocking capacitor. The impedance of the 0.1 mfd capacitor is
usually ignored at audio frequencies, however, it may have an effect
at low frequencies.
—20 to +51 DB:
|. Insert test leads into COM and OUTPUT—jacks.
2. Place selector switch in appropriate АСУ position.
3. Connect test probes across voltage to be measured as
shown in Fig. 5.
4. Read DB on black "ОВ" scale.
А 5. Add (ог subtract) DB value read from value indicated on
DB chart on meter dial (ie: if —2 DB is read on the 12
VAC range, add -- 12 DB, thus the actual value will be
+10 DB).
Do not confuse the DB with Не VU (Volume Unit) which is also
based on | milliwatt into 600 ohms, but is measured with a VU meter
having special ballistic characteristics. The DB reading will be only
relative if the load or line impedance is not 600 ohms.
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