12-10-2012, 03:10 PM
A Low Distortion Audio Preamplifier
Distortion Audio.pdf (Size: 41.77 KB / Downloads: 35)
In an audio amplifier the quality of sound depends upon a number of factors, e.g.
quality of active and passive components, circuit configuration, and layout. To an
extent, the selection of components depends on the constructor’s budget. The
discrete active components like transistors have been increasingly replaced by
linear ICs, making the task of designer easier. With the passage of time, the
general-purpose op-amps like LM741, which were being used in audio/hi-fi
circuits, have become The preamplifier circuit presented here is based on a dual
precision op-amp for the construction of a low distortion, high quality audio
preamplifier.
A dual op-amp OPA2604 from Burr-Brown is used for all the stages. The FET
input stage op-amp was chosen in this context it is worthwile to mention another
popular bi-polar architecture op-amp, the NE5534A. It has, no doubt, an
exceptionally low noise figure of 4nV/Hz but rest of the specifications compared to
OPA2604 are virtually absent in this IC. Also This IC is also capable of operating
at higher voltage rails of ± 24V (max.). Also its input bias current (100 pA) is
many orders lower than its bipolar counterpart’s. This ensures a multifold
reduction in noise.
A channel separation of 142 dB exists between In the circuit, buffer is essential
for the proper working of the subsequent blocks. A nominal input impedance of
47k is offered by this stage which prevents overloading of the preamplifier. The
tone control is a baxandall type filter circuit. The bandwidth limiter is basically a
low-pass filter with an upper cut-off ceiling at the end of the useful audio spectrum. The gain at 10 kHz is approximately 17 dB. The design is essentially 3-
pole type and the upper frequency is set at 25 kHz. This Setting the unit is fairly
simple. Check the power leads feeding the IC for symmetrical voltages. High
quality audio output from the line output socket is to be fed as the input signal to
this preamplifier. Output of the preamplifier is fed to the power a The whole
circuit consumes about 10 mA when the above-mentioned ICs are used. Power
supply requirements are not critical as the circuit works on 7.5V to 15V DC.