Tended to be about noise rather than distortion. Entire mixers were built with no other active devices, and what complaints there were
Horrific as it may now appear, audio paths full of LM741s were quite common in the earlyġ970s. It would be quite unusable, as its very limited 0.5 V/μs slew rate allows a full output swing The OP27 (2.8 V/μs) you are sailing rather close to the wind. Most opamps can do much better than this, though with To reproduce this level cleanly at 20 kHz requires a ☑8 V, then the maximum possible signal amplitude is 12.7 Vrms, ignoring the If the rails are set at the usual maximum To assume that slew-limiting will never occur, even with aggressive material full of highĪrranging this is not too much of a problem. Users whack up the gain until the signal is within a hair of clipping, they should still be able While this is essentially an overload condition, it is wholly the designer's responsibility. May be instability in one of the intermediate gain stages. HF oscillation is visible on the output with a general-purpose oscilloscope, so the problem TheĬlassic example of the latter effect is the 5532, which shows high distortion if there is not aĬapacitor across the supply rails close to the package 100 nF is usually adequate. Putting a capacitative load directly on the output, or neglecting the supply decoupling. If the distortion is higher than expected, the cause may be internal instability provoked by Wholly internal and there is nothing to be done about it except pick a better opamp. If distortion appears when the opamp is run with shunt feedback, to preventĬommon-mode voltages on the inputs, and with very light output loading, then it is probably This is what might be called the basic distortion produced by the opamp you have selected.Įven if you scrupulously avoid clipping, slew-limiting, and common-mode issues, opampsĪre not distortion free, though some types such as the 5532 and the LM4562 have very There are several different causes of distortion in opamps. Quantization error arising from the use of a given number of bits has become more popular.įigure 4.2 hopefully provides a way of keeping perspective when dealing with these different With the rise of digital processing, treating distortion as the Accuracy here is often specified in terms of bits, so ‘20-bitĪccuracy’ means errors not exceeding one part in 2 to the 20, which is -120 dB or 0.0001%.Īudio signal distortion is of course a dynamic phenomenon, very sensitive to frequency, andĭC specs are of no use at all in estimating it.ĭistortion is always expressed as a ratio, and can be quoted as a percentage, as number ofĭecibels, or in parts per million. Opamp ‘accuracy’ is closely related, but the term is oftenĪpplied only to DC operation. Relatively few discussions of opamp behaviour deal with non-linear distortion, perhapsīecause it is a complex business. There are however other opamps, some of which can be useful, and a selected range is The package containing one, simply because it is more popular. Opamps are used almost universally, as the package containing two is usually cheaper than The TL072 and the 5532 are dual opamps the single equivalents are TL0. Reason to choose any other type of opamp for audio work. Took many years, the price of the 5534 is now down to the point where you need a very good Was reserved for critical parts of the circuitry.
Latter was used wherever feasible in an audio system, despite its inferior noise, distortion, and For a long time the 5534/5532 was much more expensive than the TL072, so the
The TL072, with its JFET inputs, was used wherever its negligible input bias currents and low cost were DS (font: 'Times New Roman',serif 12.Choosing of best sounding OP AMPs for the lowest possible THD+N - really the best Approach ?įirst some extracts from the rubric "Integrated Opamps and their Properties" (From page 109-165 in the book "Small Signal Audio Design" - go toĪudio design has for many years relied on a very small number of integrated opamp types the TL072Īnd the 5532 dominated the audio small-signal scene for many years.