Quiescent Power Draw; Voltage Gain; Current Sense Calibration; Common Mode Rejection - Crown Com-Tech CT-1610 Service Manual

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6.2.6 Quiescent Power Draw

Spec: 60 watts maximum
Procedure: With no input signal the amplifier should
draw no more than 60 watts from the power source.
Slightly high readings may be due to out of tolerance
Output Bias Adjustment.

6.2.7 Voltage Gain

Spec CT-810 : 26 dB – Gain of 20 ±3%
.775V for 8/4 Ohm – Gain of 64 ±12%
.775V for 70V – Gain of 90 ±12%
Spec CT-1610 : 26 dB – Gain of 20 ±3%
.775V for 8/4 Ohm – Gain of 64 ±12%
.775V for 70V – Gain of 90 ±12%
Procedure: With the switch in the 26 dB position, inject
a 0.775 VAC 1 kHz sine wave into the input. Measure
15.5 VAC ±0.5 VAC at the output. With the switch in
the .775V 8/4 Ohm position, inject a 0.775 VAC 1 kHz
sine wave into the input. Measure 29.45 VAC ±3.5 VAC
at the output. With the switch in the .775V 70V posi-
tion, inject a 0.775 VAC 1 kHz sine wave into the input.
Measure 70 VAC ±8.4 VAC at the output. Return the
Input Sensitivity Switch to 26 dB.

6.2.8 Current Sense Calibration

Spec: 2 amps = .665V at sense point.
Procedure: Load each channel to 8 ohms. Inject a 1
kHz sine wave into each input and adjust the level
such that 16.0 Vrms appears on the outputs. For chan-
nel 1 measure Vrms at pin 9 of TP100 and adjust R361
until voltage at pin 9 is between 0.66 and 0.67 Vrms.
For channel 2 measure pin 9 of TP200 and adjust R461.
In
.047 uF
Figure 6.1 Differentiator Circuit
6-2
Com-Tech 810 and 1610 Amplifier Service Manual
Out
1K Ohm

6.2.9 Common Mode Rejection

Spec: >70 dB @ 1 kHz.
Procedure: Using a cable with the inverting and non-
inverting inputs shorted together inject a 0 dBu (0.775
Vrms) 1 kHz sine wave into each channel, one channel
at a time. At the output measure less than 4.9 mVrms.
For channel 1 adjust R103 for the greatest rejection.
For channel 2 adjust R203 for the greatest rejection.

6.2.10 Current Limit

Spec CT-810: 39 ±6 Amps
Spec CT-1610: 39 ±6 Amps
Procedure: Load the channel under test to 1 ohm. In-
ject a 1 kHz differentiated (10% duty cycle) square
wave. See Figure 6.1 for differentiator circuit. Increase
output level until current limit occurs. Current limit should
occur at 39 ±6 amps (39 Vpk) on CT-810 s and CT-
1610 s. Observe clean (no oscillations) current clipping.
See Figure 6.2 for differentiated wave form at current
limit.

6.2.11 10 kHz Square Wave Response

Spec: No overshoot, ringing, or oscillations. Slew rate
17 - 25 V/µS into 8 ohm load.
Procedure: Load the channel under test to 8 ohms.
Inject a 10 kHz square wave to obtain 35 volts zero-to-
peak at the output. Observe the wave form. It must not
include overshoot, ringing, or any type of oscillation.
Rise time should be between 17 and 25 volts per mi-
crosecond. See Figure 6.3 for typical 10 kHz square
wave response.

6.2.12 20 kHz Crosstalk

Spec: 60 dB below 8 ohm 20-20kHz power.
Figure 6.2 Differentiated wave form at current limit
Rev. 0