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Description:
When I set out to design this amplifier, my aim was to create a product
most suitable for the reproduction of complex music and speech signals.
Although I placed high emphasis on electrical characteristics, the
single most important requirement is achieving an audibly superior
sound, vivid spatial imaging and superb tonal clarity.
Although the average listening level is normally less than 10 watts,
my design approach was to create an amplifier with ample reserve power,
but biasing it for class A at average listening levels reducing
cross-over distortion to extremely low levels.
There is not one capacitor in the signal path, improved the accuracy
of the tonal characteristics of instruments and voices significantly.
The RAS 300 has almost zero phase distortion far beyond the audio range
resulting in perfect resolution and totally un-coloured sound.
Amplifier Specification:
Maximum Output: 240 watts rms into 8 Ohms, 380 watts rms into 4 Ohms
Audio Frequency Linearity: 20 Hz - 20 kHz (+0, -0.2 dB)
Closed Loop Gain: 32 dB
Hum and Noise: -90 dB (input short circuit)
Output Offset Voltage: Less than 13 mV (input short circuit)
Phase Linearity: Less than 13 0 (10 Hz - 20 kHz)
Harmonic Distortion: Less than 0.007% at rated power
IM Distortion: Less than .009% at maximum power
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Description:
This project is based on ISD2560P IC which allows us to record 60 seconds voice record and playback it with very high quality. As shown in the schematic, we input the voice by using an electret microphone. If a dynamic microphone is used, R2,R3,R4 resistors and C3,C5,C7 capacitors will be omitted and microphone will be connected to 17 and 18 numbered pins directly. Since it has better frequency response, we choose electret microphone in this project.
Controlling the circuit is
very simple. Sw1 switches between record and playback modes. Push
button B1 is used for start and pause functions. B2 stops the process.
To
record voice, first move Sw1 to record position and push B1 once. IC
will start recording and during this process red LED will bright. One
push to B1 pauses and second push continues recording. You can record
60 seconds by this way. To stop recording push B2.
To listen the voice recorded before, move Sw1 to playback position then
push B1. During the playback process red LED will bright again. One
push to B1 pauses and second push continues playing. To stop playback
push B2...
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Description:
Tr1 and Tr2 transistors functions as direct
coupled voltage amplifiers. R6 resistor, D1 and D2 diodes determine the
standby current of complement driver stage (Tr3/Tr4) and output stage
(Tr5/Tr6). C3, C5, C6 and R3 help keeping stability. Amplifier's input
sensitivity is 400mA at 4 ohm load and 12V supply and 600mV at 8 ohm
load and 17V supply.
Gain can be increased by decreasing R4 value but it is not recommended because of increasing distortion.
Notes:
Speaker's ground must be connected directly to the ground of supply stage and must be kept away from the circuit.
Separate supply connections must be applied to the supply connection points.
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