Crown Audio 1200 Test 13 Reactive Loads, Test 14 Odep Limiting, Test 15 LF Protection

Micro-Tech 1200 Amplifier Service Manual

Electrical Checkout Procedures

Spec at 4 Ohm Stereo: >= 470W at 0.1% THD.

Spec at 2 Ohm Stereo: >= 600W at 0.1% THD.

International 8 Ohm Stereo: >=305W at 0.1% THD.

International 4 Ohm Stereo: >=430W at 0.1% THD.

International 2 Ohm Stereo: >=535W at 0.1% THD.

Initial Conditions: Controls per standard.

Procedure: Load each channel to 8 ohms. Inject a 1 kHz sine wave and measure at least 50.60 VAC at the output of each channel. Load each channel to 4 ohms. Inject a 1 kHz sine wave and measure at least 43.36 VAC. Load each channel to 2 ohms. Inject a 1 kHz sine wave and measure at least 34.64 VAC. All power measurements must be at less than 0.1% THD.

TEST 13: REACTIVE LOADS

Spec: No oscillations. Safe with all types of loads.

Initial Conditions: Controls per standard.

Procedure Capacitive: Load each channel to 8 ohms in parallel with 2 µF. Inject a 20 kHz sine wave with 33 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 20 VAC output for 10 seconds.

Procedure Torture: Load each channel with the primary (redandblackleads)ofaDC-300Atransformer(D5781- 6). Inject a 15 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 20 VAC output. After establishing signal, short the output for 10 seconds.

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 20 Vrms at the output. After a few minutes observe a wave form similar to Figure 5. 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 5. 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, or a 2 Hz 6VAC sine wave into each channel and verify that each channel cycles into mute.

TEST 16: SIGNAL TO NOISE RATIO

Spec: 100 dB below rated 8 ohm power 20 Hz to 20 kHz. 105 dB A-Weighted.

Initial Conditions: Controls per standard. Short inputs.

Procedure: Load each channel to 8 ohms. Measure less than 506 µV at the output of each channel (20 Hz-20 kHz bandpass filter).

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

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