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National Semiconductor's LM833: a new dual low noise operational amplifier National Semiconductor describe the LM833 as a "dual general purpose operational amplifier with particular emphasis on performance in audio systems". It is largely responsible for the outstanding performance of our Studio 200 stereo control unit. By LEO SIMPSON Although not strictly new, the LM833 is a new device to most audio enthusiasts and the latest available data (1988 edition) on it from National Semiconductor is still classed as preliminary; so it is new. However, it is already being used in large numbers, in the audio output stages of several compact disc players sourced from Japan. National Semiconductor claim that the IC uses new circuit and processing techniques to deliver low noise, high speed and wide bandwidth, without increasing external components or decreasing stability. It is therefore ideal for use in the preamplifier and high level audio stages of hifi equipment. As shown in the schematic diagram, the LM833 is a bipolar input op amp (as shown by the PNP bipolar differential input stage). Its input bias currents are actually higher than with run-of-the-mill op amps (such as the 741), being 500 nanoamps (typical) and lmA (maximum). It has low input offset voltage (0.3mV) and low input offset current (20nA). Its open-loop voltage gain is typically 11 0dB and it is intended for operation from the usual ± 15V supplies. The internal 15pF capacitor compensates it for all closed loop gains (presumably down to unity gain) but it has a relatively high slew rate of 7 volts per microsecond which is more than ten times that of the 741. Its gain bandwidth product is +Vcc-----1-------------8 Fig.1: the schematic diagram, showing one op amp in the LM833 package. 50 SILICON CHIP Fig.2: the pinout diagram for the LM833 dual op amp package. typically 15MHz (10MHz minimum) while its power bandwidth is 120kHz. Its outstanding parameter is its low input noise voltage which is typically 4.5nV/root Hz. This compares very favourably with the familiar Signetics 5534 low noise op amp with an input noise voltage of 4nV/root Hz (the 5534A input noise voltage is typically 3.5nV/root Hz). As a further comparison of specs, the LM833 is slightly better than the Signetics 5532 dual low noise op amp and slightly inferior to the 5534 single op amp. Just in case we seem to be making unfair comparisons with the 5534 and its kin, the LM833 does not have the 5534's ability to drive a 6000 load. Instead, its performance is characterised for the more usual minimum load of 2k0. Other parameters which are significant in making the LM833 an important newcomer to audio equipment are its high power supply rejection ratio (PSRR) of 100dB and also its common-mode rejection ratio (CMRR) of to0dB. Again, these are typical figures. Crosstalk between the two op amps in the package is quoted as - 120dB from 20 to 20kHz, which is excellent. Harmonic distortion is quoted as .002 % , from 20Hz to 20kHz. Our DC Electrical Characteristics (TA= Symbol 25•c. vs = ±15vJ Parameter Conditions Min Vos Input Offset Voltage los Input Offset Current Is Input Bias Current Av Voltage Gain RL = 2 kn, Vo = ± 10V VoM Output Voltage Swing RL = 10kD. RL = 2 kD. Typ Rs = 10D. Max Units 0.3 5 mV 10 200 nA 500 1000 nA 90 110 dB ±12 ±10 ±13.5 ± 13.4 V V VcM Input Common-Mode Range ±12 ±14.0 V CMRR Common-Mode Rejection Ratio V1N = ±12V 80 100 dB PSRR Power Supply Rejection Ratio Vs = 15-5V, -15- -5V 80 100 dB la Supply Current Vo = 0V, Both Amps AC Electrical Characteristics (TA = Symbol 8 mA 25•c, vs = ± 15v, RL = 2 kn) Conditions Parameter 5 Min Typ Max Units SR Slew Rate RL = 2 kD. 5 7 V/µs GBW Gain Bandwidth Product f = 100kHz 10 15 MHz Design Electrical Characteristics (TA = 25•c, vs = ± 15VJ The following parameters are not tested or guaranteed. Conditions Symbol Parameter t:.Vos/t:.T Average Temperature Coefficient of Input Offset Voltage THD Distortion RL = 2 kD., f = 20 - 20 kHz VouT = 3 Vrms, Av = 1 en Input Referred Noise Voltage Rs = 100n, f = 1 kHz Typ Units 2 µVl°C 0.002 % 4.5 nV/,/Hz pA/,/Hz in Input Referred Noise Current f = 1 kHz 0.7 PBW Power Bandwidth Vo= 27Vpp, RL = 2kD., THD,;; 1% 120 kHz fu Unity Gain Frequency Open Loop 9 MHz 60 deg -120 dB </>M Phase Margin Open Loop Input Referred Cross Talk f = 20-20 kHz Note 1: If supply voltage is less than ± 1SV, it is equal to supply voltage. Note 2: This is the permissible value at TA experience with the Studio 200 indicates that typical devices easily meet these specs and we would not be surprised to find that, when National Semiconductor finalises its data on the device, it will be effectively upgraded. Fig.3 shows National Semiconductor's RIAA preamp application circuit for the LM833 and it is very close to that used in the Studio 200. Our performance results were also very close to those claimed by National. The main difference in the Studio 200 circuit (presented last month) is in the RF suppression components at the input and the manner of provision of the 50k0 load for the cartridge (using a 100k0 resistor either side of the bipolar input capacitor). National's LM833 is not the s:: 85°C. 10 µF ·i1 1"100µF Fig.3: National Semiconductor's suggested circuit for a phono preamplifier with standard RIAA equalisation. Voltage gain is 35dB at 1kHz and claimed signal-to-noise ratio is 90dB A-weighted with respect ot 10mV input at 1kHz. quietest, fastest, lowest distortion or most stable op amp released in recent times but considering its overall performance, it must stack up as one of the best value op amp packages available. We predict that it will become extremely popular. ~ JULY 1988 51