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High CMRR Instrumentation Amplifier (Schematic and Layout) design for biomedical applications

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Instrumentation amplifiers are intended to be used whenever acquisition of a useful signal is difficult. IA’s must have extremely high input impedances because source impedances may be high and/or unbalanced. bias and offset currents are low and relatively stable so that the source impedance need not be constant. Balanced differential inputs are provided so that the signal source may be referenced to any reasonable level independent of the IA output load reference. Common mode rejection, a measure of input balance, is very high so that noise pickup and ground drops, characteristic of remote sensor applications, are minimized.Care is taken to provide high, well characterized stability of critical parameters under varying conditions, such as changing temperatures and supply voltages. Finally, all components that are critical to the performance of the IA are internal to the device. The precision of an IA is provided at the expense of flexibility. By committing to the one specific task of
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Phono Preamplifier

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Simple circuitry suitable for moving-magnet cartridges


Passive high-frequency equalization

Parts:

R1_________47K   1/4W Resistor
R2________100R   1/4W Resistor
R3__________6K8  1/4W Resistor
R4_________68K   1/4W Resistor
R5,R6_______2K7  1/4W Resistor
R7__________2K2  1/4W Resistor
R8_________39K   1/4W Resistor

C1-C3_____100µF  25V Electrolytic Capacitors
C4,C5______47nF  63V Polyester Capacitors 5% tolerance

D1,D2__BZX79C18  18V 500mW Zener Diodes

IC1_______LM833  Low noise Dual Op-amp

Q1________BC337  45V 800mA NPN Transistor
Q2________BC327  45V 800mA PNP Transistor
 
 J1__________RCA  audio input socket
 

Comments:

In recent years, following CD's introduction, vinyl recordings are almost disappeared. Nevertheless, a phono preamplifier is still useful for listening old vinyl discs from a well preserved collection. This simple but efficient circuit devised for cheap moving-magnet cartridges, can be used in connection with the audio power amplifiers shown in these webpages, featuring low noise, good RIAA frequency response curve, low distortion and good high frequency transients behavior due to passive equalization in the 1 to 20KHz range. Transistors and associated components provide ±18V supply to the op-amp, improving headroom and maximum output voltage.

Notes:

  • R2, R3, R4, R7, R8, C4 & C5 should be low tolerance types.
  • Schematic shows left channel and power supply.
  • For stereo operation R1, R2, R3, R4, R7, R8; J1; C1, C4 & C5 must be doubled.
  • Numbers in parentheses show IC1 right channel pin connections.

Technical data:

Sensitivity @ 1KHz: 2.5mV RMS input for 200mV RMS output
Max. input voltage @ 1KHz: 120mV RMS
Max. input voltage @ 10KHz: 141mV RMS
Max. input voltage @ 20KHz: 127mV RMS
Frequency response @ 1V RMS output: 100Hz to 20KHz ±0.5dB; -0.75dB @ 30Hz
Total harmonic distortion @ 1KHz and 6V RMS output: 0.006%
Total harmonic distortion @10KHz and 1V RMS output: 0.02%