CH and CL Series Power Amplifiers
5 Principles of Operation
normally runs at very low speed when the amplifier is idling or when it is being used for low to moderate duty work. If the amplifier is delivering large amounts of power into low impedance loads, the heatsinks or transformer may heat up enough to increase the speed of the fan to medium and possibly to high speed. If the temperature continues to increase, the TLC circuit uses the compressor to reduce the gain of the input stage and thus reduce the power dissipated by the amplifier. As a further protective measure, if the temperature contin- ues to rise (due to blocked airflow for example), the amplifier will stop running and keep the fan on high speed to quickly bring the temperature back to an operational level.
If a signal presented at the input of the amplifier will not be passed through to the output, the Fault LED will blink to get your attention. The
An RJ11 modular jack is mounted on the back panel. Pins 2 and 5 are connected to an opto- isolator that is always in a
The Signal Presence Indicators tap the signal chain just before the level controls and prior to the power amplifier chain. They are not ampli- fier output indicators and should only be used to indicate the presence of signal to the ampli- fier front end.
The Clip indicators are driven from the output of the compressor circuitry and light to indicate the onset of audible distortion. The Power indi- cator LED is driven from the
5.2.2 Power Supply Operation
AC power enters the amplifier through a power cord equipped with an IEC (unplugable) con- nector. It then is passed through the EMI filter. Circuits that use switching technology will nor- mally send a small amount of
The power then enters the Power Factor Cor- rection (PFC) Boost stage. This stage is what allows the CH4/CL4 to be plugged into any outlet in the world without any modifications to the amplifier. The PFC stage uses switching power supply technology to take whatever AC line voltage comes in, convert it to DC and boost it to 400 Volts. The circuit also uses intelligence to draw the current from the line sinusoidally and in phase with the line voltage. This reduces the load on the power companies and also allows the amplifier to pull more peak power from the power source (the outlet). The power is drawn in small amounts 62,500 times each second and is used to provide power to the isolation stage and to fill the large energy reservoir capacitors.
The power then goes to the “buck” isolation stage. This stage takes the 400 Volt PFC volt- age and, again using switching power supply technology, converts it down (“bucks” it down) to the level needed to power the audio output stage. The isolation stage also satisfies a safety requirement by providing isolation, using a transformer, between the AC mains power and the power that is delivered to the speakers. The isolation stage moves power 125,000 times each second from the primary to the secondary to power the audio output stage and keep its large energy reservoir capacitors full.
In order to keep the power supply controllers, protection circuits, and the audio signal path components powered, another switching power supply is used, this one also running at 125 kHz. This one is also a “buck” type supply in that it takes voltage from the 400 Volt PFC bus and converts it down to the low voltages needed. This circuit also uses a transformer to provide safety isolation.
Like the audio signal path parts of the amplifier, there are many ways that the power supply pro- tects itself. Part of the
Operation Manual | page 27 |