I agree with the opinion that "performance levels of the TL072/82 and the 5534 to be sub standards when compared to the current generation of high performance OP AMPs. My top three devices for serious analog audio work are LME49990, OPA1611 and OPA211. LME49990 is the only one capable of true 24-bit analog performance when powered with +/- 15 V supply (S(N = 159 dB,THD = 146 dB). As the THD of LT1028 is 96 dB, it is "only" good for 16-bit systems. NE5534A is even less linear, THD = 93 dB.
I will never buy another book authored by Douglas Self. I have one of his books on audio circuits - they are simply reprints of his articles from a magazine and they contain no design details at all. Poor material for engineers.
I have found the performance levels of the TL072/82 and the 5534 to be sub standards when compared to the current generation of high performance OP AMPs like the AD797 and AD8597/AD8599. In addition, the uA739 was superior in performance to 741 and other early opamps designs, excluding the 5534.
The AD797 is a very low noise, low distortion operational amplifier ideal for use as a preamplifier. The low noise of 0.9 nV(root)Hz and low total harmonic distortion of -120 dB at audio bandwidths give the AD797 the wide dynamic range necessary for preamps in microphones and mixing consoles.
Furthermore, the AD797's excellent slew rate of 20 V/Ás and 110 MHz gain bandwidth make it highly suitable for low frequency ultrasound applications.
The AD8597/AD8599 are very low noise, low distortion operational amplifiers ideal for use as preamplifiers. The low noise of 1.1 nV/vHz and low harmonic distortion of -120 dB (or better) at audio bandwidths give the AD8597/AD8599 the wide dynamic range necessary for preamplifiers in audio, medical, and instru-mentation applications. The excellent slew rate of 14 V/Ás and 10 MHz gain bandwidth make them highly suitable for medical applications. The low distortion and fast settling time make them ideal for buffering of high resolution data converters.
I first saw this technique ("forced Class A") used in Walt Jung's "POOGE" modifications for the Philips DAC960 DAC unit in the early 90s. It has since become de rigueur in the DIY/audiophile community to "bias op amps into Class A", where it seems any op amp in a circuit is an excuse for an accompanying pull-up/down resistor or CCS - even op amps driving high-input-impedance buffers:
I have a tube of "GL358s" which are actually not unity-gain stable! A very good technician kept reporting that a very-low-frequency twin-t notch filter (with feedback to greatly increase the Q) was oscillating, and I assured him that he must have wired something up wrong! Nope!
The plain 358 (or as a quad, the 324) almost always has severe crossover distortion, except at very low output currents, and some companies actually treated that strategy of forced class A as a trade secret!
For years I never saw a voltage noise spec, but recently noticed that it is now listed as 40nV/rtHz.
Bcarso, right you are. The TL082 noise spec is 16 nV/SQR(Hz), and my resistor combinations at the + and - input terminals created 5.59 nV/SQR(Hz). But in my first attempt, where I used higher value resistors, the resistor noise was clearly audible when the circuit was idle. I lowered the value in two stages, and noticed the deminishing returns of lowering resistor values.
If I'd used very low noise opamps, with noise spec around 3 nV/SQR(Hz), it may not have been as easy to lower the resistors enough to make a negligible contribution. Because of interfacing issues with other components.
Just thought I'd mention those two items, load capacitance and theral noise, because I didn't think the article mentioned them explicitly.
Gasp. Reminds me of the pre-amp I made using a pair of 741's for my new Technics turntable to go into my ancient receiver that didn't have the phono inputs, only line inputs. Ok, this was 1981 vintage, freshman EE cobbling, but it worked just fine. I saw it in the basement piles of old "junque" a few weeks ago.
Really nice article with great details and information! Makes me want to read the book (BSEE - digital guy, but I like analog audiophile applications). Thanks!!! I always look forward to Doug Self's stuff..
I recall using LM1458's and LM358's extensively in telecom circuits (tone generators, filters, voice coupling, etc.). Not Hi-Fi, but low enough noise and distortion to meet telecom requirements of the time. We encountered significant performance variations between different manufacturer's devices of the same part number, as well as some date code dependencies. One trick that still sticks in my mind was having to add a "forced class A" modification (output pulldown or pullup resistor) in small signal stages to tame output crossover distortion from certain makers.