Vermes
Advanced Member level 4
This amplifier was prepared as a supplement to speakers removed from a dead Panasonic SA-AK45. You can use LM3886T, but TDA7294 would also be okay for this purpose.
Housing of that device was removed from an old PC. Then it was painted with 2 layers of black matt paint and a layer of transparent varnish. Back was made of aluminum plate wrapped in veneer, while the front was made of thick laminate also wrapped in veneer in gold color with silver lines.
There are two small fans which cool the heat sink and one large fan blows warm air from the device. All the fans operate in two modes, which can be selected using a lever switch:
- passive mode – continuous operation at voltage 12V fed to the fans
- active mode – the fan is turned on at 65 degrees Celsius, and off at 50 degrees (5 to 10V)
Active mode was implemented on voltage stabilizer LM317, thermistor NTC and voltage comparator (to determine the reference voltage at which the fans are to be turned on).
Two transformers TS80/8/668 connected in parallel are used in this construction:
Selector, diodes and the system of fans have a separate pair of windings on one of the transformers.
The preamplifier is equipped with control of bass, treble and sound intensity. Electrolytes used are Nichicon.
The final stage based on LM3886 can be easily found on the Internet – it can be for example AVT2180.
Power supply consists of a battery of capacitors (4x4700uF 50V, 25A bridge, resistors protecting the bridge in the moment of charging the capacitors – 0,1ohm 10W, fuses 3,15A).
Elements on the front panel of the amplifier:
- supply switch – implemented on primary windings of the transformers
- three lever switches:
- fans operation mode switch
- output switch (selector)
- MUTE LM3886T
- two control LEDs – blue (supply on) and red (fans on – active or passive)
- three knobs for regulation
Pictures:
Link to original thread - Wzmacniacz akustyczny "Diana" (LM 3886)
