Analog current drive amplifier
user manual
Overview
Amplifier board is stereo with balanced inputs. Input sensitivity can be adjusted by soldering resistors.
This amplifier is made to be current drive amplifier to reduce distortion in loudspeaker driver. It is nothing new but almost not existing outside DIY world. But current drive is not optimal at drivers resonance. So this amplifier is mixed mode by design. Voltage drive at low frequency and current drive at high frequency. Actually board is universal and has 3 modes of operation: voltage amp, mixed mode 1, mixed mode 2. Modes are chosen by the jumper.
Current mode means voltage controls output current. So voltage output depends on the load. So for mixed mode to be relatively flat, amplifier has frontend which adjust gain and filter response for any given driver without the need of DSP. (adjusting done by soldering). This amp designed to work with the naked driver without passive filters, for active systems. Passive systems with multiple drivers and filters might not work as expected. Depends on the system. Current drive benefits can be reduced for such systems or DSP needed to flatten frequency response.
Amplifier has silent turn off/on feature. Amplifier turns on/off silently by supplying voltage from power supply or by controlling enable/disable input pin. This input pin is fully isolated, it doesn't add any ground loops or other noises. Silent turn on/off feature also will acts as power loss indicator in example due to fault in power supply or inadequate current . Sudden sag of power supply voltage will trigger it.
Amplifier has several protection features. One is clip protection. Because clipping is distorting signal a lot and should not happen anytime in high quality audio reproduction chain.
Second one is fast overcurrent protection. It also can act as oscillation protection.
Third is over temperature protection. All these three protections are controlled by onboard IC. Status of protection is outputted over onboard LED. Also there is fault output pin for external IC interface. It is also isolated.
The amp uses LM3886 chip as power driver in composite configuration, which itself has second layer of additional overcurrent and over temperature protections. The amp is safe to use. Some protection features can be disabled by soldering some jumpers. Amplifier is designed to work best with switching mode power supplies.
Pinout and layout
Powering on
Amplifier power on/off is controlled by onboard J2 or by external control over J4.
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If J2 is on, then external control is disabled and amplifier is always on. Power supply controls if amplifier is on or off.
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If J2 is off, then external control is controlling amplifier. Active hight signal. 3.3V to 12V control input. Galvanically isolated.
​​ If amplifier is powered and in ON state. Green LED will be on.
Fault output
There is fault output signal on J4 connector Control OUT pin. This pin can be used to inform external MCU about amp state. If no protection is active this signal is open collector output. If some protection is active fault signal pulls down to GND isolated pin. You have to limit current to be below 40mA max.
Any MCU input with pullup will work. This output is isolated over opto isolator.
Amplifier protections
Amplifier has protections:
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Overtemperature protection
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Clip protection
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Overcurrent protection
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All these protections will output state over green LED. If some protection is active LED will start blinking every second 500ms pulse followed by 2 seconds pause. Counting blink code tells which protection is active.
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If protection kicks in amplifier goes to off state. And stays there until reset. Reset is done by repowering amp by power supply or J2 or J4. Power suplly resets instantly and J2 with J4 resets after full error blinking code is blinked out.
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Clip protection is a little different. It is more a quality feature than a safety feature. So if clip is detected the amp mutes for 3 seconds only. But if it happens more than 5 times over 30s period, then the amp switches off and blink code appears. And reset needed. This feature is to inform the user that he is entering into clip zone, and input signal has to be reduced. Clip protection see which amp is clipping and which polarity it is happening at. Positive or negative.
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Power loss protection works as silent turn off/on feature and can detect if short voltage drop occurs on power rails. If it drops more than 4.5V but voltage stays above 20V the amp switches off and blinks out error code.
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Overcurrent protection kicks in if current >5.4A. Reaction time 30uS.
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Overtemperature protection uses thermistor mounted on power chips and are set at 70 deg C​. If heatsink is not adequate or has restricted airflow this protection will switch off the amp for safety reasons. The blink code will output.
Additionally second layer of protections is on power chip itself. Overcurrent and overtemperature protections just at higher current and temperature.
Speaker outputs
Speaker output terminals J3 and J17 has two + pins. They are internally connected. - pins are not grounded and cannot be grounded in any way ! Speaker both terminals should be left floating and cannot be paralleled or bridged left with right channel. - pin also has some voltage. So it is very tricky to measure amplifier performance if you want to do so.
Dimensions
Dimensions are in mm. Bottom picture shows four holes to mount amplifier to a heatsink. Amplifier comes with L shape brackets. M3 bolts should be used.
Specifications
Upcoming