elwood@wam.umd.edu (Jim Bogard) (01/08/91)
Ok, a pair of questions:
1. What exactly _is_ 'line level' defined to be?
2. What's the lowest noise op amp?
(Don't read too much into this; nothing esoteric, just whatis
the quietest general purpose op amp. eg, 741,386, etc.)
Thanks.
J-.
--
Jim Bogard oper014@umuc.umd.edu jimbo@socrates.umd.edu
elwood@cscwam.umd.edu
disclaimer? I think UM has bigger things to worry about than my opinions.mcovingt@athena.cs.uga.edu (Michael A. Covington) (01/09/91)
In article <1991Jan8.072135.15225@wam.umd.edu> elwood@wam.umd.edu (Jim Bogard) writes: >Ok, a pair of questions: > >1. What exactly _is_ 'line level' defined to be? > I think it's about 1 V peak-to-peak, delivered into a high impedance. >2. What's the lowest noise op amp? > (Don't read too much into this; nothing esoteric, just whatis > the quietest general purpose op amp. eg, 741,386, etc.) Try a TL081/TL082/TL084. These are readily available and are much better than 741s. > >Thanks. > >J-. > >-- >Jim Bogard oper014@umuc.umd.edu jimbo@socrates.umd.edu > elwood@cscwam.umd.edu > >disclaimer? I think UM has bigger things to worry about than my opinions.
km3t@jjmhome.UUCP (Dave Pascoe KM3T) (01/09/91)
In article <1991Jan8.072135.15225@wam.umd.edu>, elwood@wam.umd.edu (Jim Bogard) writes: > Ok, a pair of questions: other stuff deleted > > 2. What's the lowest noise op amp? > (Don't read too much into this; nothing esoteric, just whatis > the quietest general purpose op amp. eg, 741,386, etc.) For audio work one of the quietest op-amps I've seen is the LT1115 manufactured by Linear Technology (Milpitas, CA). The LT1115 has a voltage noise on the order of 1.2nV/root Hz at 1kHz (0.9nV typical). Here are some other specs: Gain-Bandwidth Product: 40MHz Min. Slew Rate: 10V/us Min. Voltage Gain: 2 Million Min. .002% Total Harmonic Distortion @ 10kHz, Av=-10, R(load)=600 ohms Vo=7Vrms .0002% Intermodulation Distortion (IMD), CCIF Method, Av=+10, R(load)=600 ohms Vo=7Vrms It's a great amp for high quality audio work , like for preamps and any other type of low noise application (frequency synthesizer). -- Dave Pascoe | Internet: km3t@jjmhome.m2c.org KM3T/ZF2PT | UUCP: km3t@jjmhome.UUCP or ...!{harvard}!m2c!jjmhome!km3t
bill@videovax.tv.tek.com (William K. McFadden) (01/09/91)
In article <1991Jan8.072135.15225@wam.umd.edu> elwood@wam.umd.edu (Jim Bogard) writes: >1. What exactly _is_ 'line level' defined to be? For consumer products, it is usually somewhere in the neighborhood of -10dBu=0VU, which is about 250 mV RMS. Source impedances are generally less than 10K, and load impedances are generally greater than 10K For professional gear, it varies. The most common level I've seen on tape decks is +4dBm=0VU. +4dBm is about 1.2 V RMS and requires 600 ohm source and load impedances. >2. What's the lowest noise op amp? The king of the heap still seems to be the 5534 (single) / 5532 (dual). It has a bipolar input stage that requires a lot of bias current, and the supply current's kind of high, but it's very low noise, low distortion, and can directly drive 600 ohm loads. It's also fairly old and hence fairly cheap. There are some newer amps by places like Linear Technology that have lower noise, but most applications have too high an impedance to take advantage of it (most resistors generate more thermal noise than some of these new amps). Plus, they have either more distortion or less output drive and cost more. -- Bill McFadden Tektronix, Inc. P.O. Box 500 MS 58-639 Beaverton, OR 97077 bill@videovax.tv.tek.com, {hplabs,uw-beaver,decvax}!tektronix!videovax!bill Phone: (503) 627-6920 "The biggest difference between developing a missle component and a toy is the 'cost constraint.'" -- John Anderson, Engineer, TI
whit@milton.u.washington.edu (John Whitmore) (01/10/91)
In article <1991Jan8.072135.15225@wam.umd.edu> elwood@wam.umd.edu (Jim Bogard) writes: >2. What's the lowest noise op amp? > (Don't read too much into this; nothing esoteric, just whatis > the quietest general purpose op amp. eg, 741,386, etc.) Op amps have at least four kinds of noise, and it matters a LOT which is most important to you. There is broadband voltage noise, broadband current noise, low-frequency voltage noise (a combination of 'excess noise' and drift), and low-frequency current noise (bias current and bias current drift). Most op amps are not tested extensively for noise, but rather are spot-checked; as a result, many manufacturers don't guarantee noise performance, but only give typical values. Most applications don't need high input impedances on op amps, and as a result the current noise (especially the bias current) is relatively unimportant. For input impedances of 1k ohms or less, where DC offsets are important, typical low noise op amps would be uA725, OP-07, OP-27, LM308A, NE5532, RC4136. For input impedances of 1k ohms, where DC offsets are NOT important, one can add some JFET input op amps: LM356 is adequate, and the TL071 is the low-noise version of the TL081. For input impedances of higher than 100 k ohms, generally one considers ONLY the JFET input op amps. Additionally, one can get pre-trimmed op amps (from PMI and Burr-Brown and Analog Devices, mainly) at higher cost with some pretty fantastic characteristics. Unless the source is terribly low in noise to begin with, though, there's no real point in scrutinizing the poor op amp. A 16-bit D/A converter, for instance, has quantization error of a dozen microvolts relative to a 1V output; any op amp with less than 100 nV/root Hertz noise will have negligible noise by comparison (over the audio frequency range). In fact, good CD players have to add noise generators to mask the low-output 'blurble' of digitized sound, 'cuz the op amps don't add in ENOUGH noise to do it. John Whitmore whit@milton.u.washington.edu