First of all, let's pinpoint two the functions of the control board in a good amplifier:
- Soft-start and shutdown of the amplifier;
- Protection of the amplifier and the speakers;
- Amplifier status indication;
- Flexible (firmware defined) setup parameters.
Our digital control boards equipped with the following key components:
- Standby transformer - a low-power transformer, always connected to the mains, powering the control board. The control board runs constantly, regardless if an amplifier is on or off.
- At least two power relays for controlling the main amplifier PSU(s) - one relay is responsible for inrush, the other one takes over at the end of the soft-start sequence, being engaged in the normal operation of the amplifier.
- Microcontroller (ATMega328) with our firmware running in it, responsible for all the logic of control board operation and indication features.
- i2c ports for interacting with the Solid State (SS) relays - controlling the power rails and the speakers - and with the sensors - providing information on DC offset at the outputs and temperature of the main heatsinks.
- Connectors for the power button and the LED indicator, placed on the front panel.
- Optional connector for remote control trigger socket, placed on the rear panel.
Soft-start, and shutdown of the amplifier
Amplifiers, designed for accurate music reproduction, are normally equipped with high-power PSU (or a number of them, depending on particular configuration), involving a lot of capacitance in the main rails filters. Connecting such PSU(s) to the mains requires special attention because of a high inrush current peak taking place if you do it directly.
In order to soften that peak, we use a so-called soft-start sequence for connecting the PSU(s):
- The 1-st power relay connects the PSU(s) to the mains via a thermistor. Thermistors are very good for the purpose, as their resistance is high in the beginning, then, as they warm up, the resistance decreases.
- As soon as the inrush delay is over (normally set to 5 seconds), the 2-nd power relay connects the PSU(s) directly to the mains. Half a second later, the 1-st power relay goes off for better energy efficiency.
- The LED on the front panel goes 100% bright, indicating the amplifier is in normal operation.
As soon as the power off signal comes from the power button, or in case of emergency, the 2-nd relay disconnects the PSU(s) from the mains, and the LED on the front panel indicates the reason of the last shutdown.
Protection of the amplifier and the speakers
In case of emergency (something goes wrong with an amplifier), the first thing we'd like to do is to disconnect the speakers from the amplifier's output, ensuring we don't do any harm to the speakers. We also want to preserve the amplifier components as much as possible, so we disconnect the OPS from the rails (if the PSU is equipped with controlled rails feature) and perform the amplifier shutdown.
Our amplifiers are equipped with the sensors, watching the following kinds of emergency:
- DC offset at the output;
- OPS over-current;
- OPS over-temperature;
- AC failure (mains blackout or clutter).
In case the control board detects any of these emergency conditions, it disconnects the speakers and shuts down the amplifier.
The DC offset emergency channel has got an analog acceleration circuit - the speakers disconnect immediately even before the control board notices the emergency condition, followed by the emergency shutdown, performed by the control board the normal way.
The DC offset and OPS over-current emergency signals utilize the hardware interrupts of the microcontroller, providing very fast reaction of the system.
Amplifier status indication
The LED on the front panel, shining bright in normal operation, indicates one of the following statuses after shutdown:
- Constantly dimmed - normal power-off;
- Intense blinking (every 0.2 sec) - DC offset emergency;
- 1 blink every 2 seconds – AC failure;
- 2 blinks every 2 seconds – overheat;
- 3 blinks every 2 seconds – OPS over-current.
In case of the emergency shutdown, you will not be able to power on the amplifier, until you disconnect the power cord from the mains, identify the issue, eliminate the cause and reconnect the power cord. It doesn't make sense trying to just reconnect the cord and switch the amplifier on - if the control board indicates the issue, the issue is there. Thanks to the status indication - it shows what caused the shutdown.
Flexible (firmware defined) setup parameters
All the setup parameters are set in the header section of the firmware code - that makes our Amp Control Boards extremely versatile, applicable to any kind of amplifier. Here is an illustration of the header section:
A selection of our excellent Amp Control Board bundles and their supplementary components are available here:
AMP CONTROL BOARDS
You may be also interested in the PSU boards, equipped with the controlled rails and front-end regulators:
PSU & REGULATORS