The diagram will show a "snubber circuit" (resistor + capacitor in series) across the transformer primary. If this burns out, the power supply fails.
If an output transistor shorts out, dangerous DC voltage could pass straight to the speakers, burning out their voice coils. A DC detection circuit constantly monitors the output terminals. If DC is detected, the circuit opens the output protection relay (or mutes the audio) to isolate the speakers.
Connectivity includes balanced XLR and 1/4" TRS inputs for each channel. Outputs are provided via Speakon connectors, 1/4" jacks, and robust 4-way binding posts. Mode switches allow selecting Stereo, Parallel, or Bridge Mono operation.
: Safeguards speakers from DC offset and shuts down the unit if temperatures exceed safe limits.
When the audio signal is low, the amplifier runs on the lower voltage rails to reduce power wastage across the output transistors. When a massive audio peak occurs, the circuit seamlessly switches to the high-voltage rails to prevent clipping.
Weaknesses / Suggestions
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Thermistors mounted to the aluminum heatsinks change resistance as temperatures rise. This circuit first ramps up the variable-speed cooling fans. If temperatures exceed safe thresholds (usually around 90°C), the circuit mutes the audio channel until it cools down.
The VAS uses transistor pairs configured as current mirrors to ensure linear amplification and low distortion.
The power supply is working, but the audio signal is cut.
| Pin | Signal | Connection to Source | | :--- | :--- | :--- | | Pin 1 | Cable Shield / Ground | Connect to the ground/shield of your mixer or processor's XLR output. | | Pin 2 | Positive (+) / Hot | Connect to the positive (+) pin of the source XLR. | | Pin 3 | Negative (-) / Cold | Connect to the negative (-) pin of the source XLR. |
When a technician services an NX Audio RX 4000, the circuit diagram serves as a roadmap for tracing faults.
Bias is wrong, or output transistors are desoldered.
When you finally obtain a high-resolution scan of the PCB layout (often labeled "RX-4000 Rev 2.1" or similar), follow this practical repair workflow: