Crown 460CSL TEST 14 ODEP LIMITING, TEST 15 LF PROTECTION, TEST 16 SIGNAL TO NOISE RATIO

Power Base-1 & 460CSL Amplifier Service Manual

Checkout Procedures

Procedure Capacitive: Load each channel to 8 ohms in parallel with 2 µF. Inject a 20 kHz sine wave with 30 VAC output for 10 seconds.

Procedure Inductive: Load each channel to 8 ohms in parallel with 159 µHenries. Inject a 1 kHz sine wave with 15 VAC output for 10 seconds.

Procedure Torture: Load each channel with the primary (red and black leads) of a DC-300A transformer (D 5781-6). Inject a 10 Hz sine wave at sufficient output level to cause 3 to 5 flyback pulses, for 10 seconds. Procedure Short: Inject a 60 Hz sine wave at 5 VAC. After establishing signal, short the output for 10 sec- onds.

TEST 14: ODEP LIMITING

Spec: No oscillation on ODEP Limiting wave form; either channel controls limiting in Parallel Mono Mode. Initial Conditions: Controls per standard; rag or other obstruction blocking fan so that it does not turn.

Procedure: Load the amplifier to 2 ohms on each channel. Inject a 60 Hz sine wave and adjust for 15 Vrms at the output. After a few minutes observe a wave form similar to Figure 4. Remove the input signal from both channels and allow the amplifier to cool for a few minutes. Switch the amplifier to Parallel Mono and remove the load from Channel 1. Inject the signal into Channel 1 and observe that ODEP limiting occurs at the output of both channels. Remove the load from Channel 2, and install the load on Channel 1. Again, observe that both channels limit. Return all amplifier controls to standard initial conditions. Remove the fan obstruction.

Figure 4. ODEP Limiting Wave Form

TEST 15: LF PROTECTION

Spec: Amplifier mutes for low frequency.

Initial Conditions: Controls per standard.

Procedure: No load. Inject a 0.5 Hz 6 volt peak-to-peak square wave into each channel and verify that each channel cycles into mute.

TEST 16: SIGNAL TO NOISE RATIO

Spec: 100 dB (105 dB A-weighted) below rated 8 ohm power.

Initial Conditions: Controls per standard. Short inputs.

Procedure: Load each channel to 8 ohms. Measure less than 400 µV at the output of each channel (or –100 dB from reference of +34.25 dBu).

TEST 17: TURN ON TRANSIENTS

Spec: No dangerous transients.

Initial Conditions: Controls per standard.

Procedure: From an off condition, turn on the amplifier and monitor the output noise at the time of turn on. Note: Turn on noise may increase significantly if the amplifier is cycled off and on.

TEST 18: TURN OFF TRANSIENTS

Spec: No dangerous transients.

Initial Conditions: Controls per standard.

Procedure: From an on condition, turn off the amplifier and monitor the output noise at the time of turn off. Note: Turn off noise may increase significantly if the amplifier is cycled off and on.

TEST 19: INTERMODULATION DISTORTION

Spec at 0 dB Output: 0.01%.

Spec at –35 dB Output: 0.05%.

Initial Conditions: Controls per standard.

Procedure: Load each channel to 8 ohms. Inject a SMPTE standard IM signal (60 Hz and 7 kHz sine wave mixed at 4:1 ratio) at 200 Watts (32.4 VAC). With an IM analyzer measure less than 0.01% IMD. Repeat test at –35 dB (reference 200 Watts or 32.4 VAC) and mea- sure less than 0.05% IMD.

TEST 20: CLIPPING

Spec: No protective action during test.

Initial Conditions: Controls per standard.

Procedure: Load each channel to 8 ohms. Inject a 1 kHz sine wave at each input and drive output 6 dB into clip for 10 seconds. The amplifier should not activate any protective circuits (ODEP, Fault, or LF Protection).

POST TESTING

After completion of testing, if all tests are satisfactory,

the amplifier controls should be returned to the posi- 15 tions required by customer. If conditions are unknown

or unspecified, factory settings are as follows: