Pages upon pages could be written about these. Here’s my take on opamps and their relationship to audio.

 

I still remember thinking opamps were “sonic evil” and looked for ways to avoid them at any cost. (My old fanatic tube days)

In the late ‘80, it’s true that they weren’t very good, and not always reliable. However, they’ve improved since.

 

Like a 1990 “top of the line” Sony Trinitron TV is now obsolete, by today’s viewing standards. There’s no point in saying it’s anything special today and, nobody with a working brain, will ever believe you’d actually try buying this vintage TV, because it had “fantastic reviews”.

 

Yet, in the audio world, some people still claim that an obsolete Philips TDA1541 DAC chipset, operating in non-oversampling mode, is something very special. And then, trying to convince you to buy the pricey “double crown” version (the premium model) as a guaranteed ticket to your very own audio nirvana.

The Philips TDA1541 was indeed very advanced in 1982, when compared to the competition, but not so much against advances made by the current DAC crop.

What a shame… (I know very well. I built a TDA1541 DAC reading such ancient idiocy)

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Old museum pieces, like Western Electric electronics, command ridiculous prices, pushing this fallacy to the extreme.

They knew how-to-do-good sounding stuff back then. People today are just selling "crap". An old WE 555 compression driver driven by WE 91A single ended amplifier can't be beaten at any price. LOL

 

Following this total lack of understanding, some people try to cultivate the fear of yesterday’s opamp sound and even design to completely avoid them. This often requires making big compromises in their products. The average marketing department grabs the opportunity, with their brochures usually proudly stating “no opamp used inside” (insert your favorite superlative to complete the sentence)

Buyers often believe this BS as a “superior” product offering. A similar story could be said about the “evil negative feedback”.

 

In an audio product, opamps normally work based on negative feedback to achieve a linear output. An opamp contains several solid-state components inside, such as a minimum of 50 transistors/diodes/resistors. Opamps are much more than a little black box with a few pins. They’re little complex amplifier circuits!

 

Due to physical constraints and manufacturing processes, opamps do not contain capacitors and have severely limited value for internal resistor (because of heat). The engineer must design the opamp’s internal circuitry to avoid capacitor need. This requires some design “imagination” and often results in a more complex circuit.

Some opamps require external compensation (external capacitor) to be added on the circuit, for the opamp to work properly and achieve stability.

 

You probably already know that every audio amplifier sounds different.

And since opamps are amplifiers, and like audio amplifiers, sound different as well.

 

A quick look at the Digikey website, shows their current offering of 37,361 different models of opamps!

Why so many choices?

Well, there’s no simple answer, as some opamps are designed for audio, some for instrumentation and others for control. Some use transistor inputs, others use FET inputs for less DC offset. Some are optimized for low power draw (battery powered eqpt) while others are optimized to work at low voltages (i.e. cellphone). You can select low-cost options that are less elaborate, and flagship models that display superb specifications. There are many types to choose from, and all are optimized for certain design priorities. Application is the key.

 

Knowing this, means that ABC opamp is not necessarily better than XYZ.

The “overall system” matters as much as the opamp itself.

What the system “needs”, calls for different opamps, which is often overlooked.

 

A super-fast opamp might oscillate in certain conditions. The designer of XYZ originally used a low cost opamp that worked well in the “stock” application. One opamp roller swapping the popular low cost NE5534 for the THS3201, will likely encounter oscillation, as the THS3201 requires special care and extra design considerations. The NE5534 has limited speed and can achieve 13v/uS while the THS3201 can do 9800v/uS (9800/13= 753. Yes, 753 times faster!)

No wonder the THS3201 would likely sound bad and the average neophyte opamp swapper will review it as “bad sounding”. He’ll fulfill his duty to the community and immediately report his findings. Then he spends few lines describing, the best he can, all of the harshness he heard. (while the opamp was oscillating, this important aspect won't make it in the review, as the user had no oscilloscope or even knowledge of the problem)

 

Follower “blog readers” will not even try the THS3201, as somebody else judged it “bad” and nothing else could be done. THS3201 will never be popular in the HiFi world.

 

The same incorrect conclusion is often drawn with opamps designed to work optimally at 15Vdc to 18Vdc power supply rails, while the “tester” tries it in a portable headphone amplifier, working on a single 9-volt battery. Good intent, but unreliable conclusion.

 

With this “sheep following sheep” effect, you often get opamps sounding quite average, but working virtually anywhere (ie: general purpose) being constantly praised, and getting much un-needed publicity. (Also true with capacitors)

 

The LM4562 is a great example of “sheep following sheep”. It’s merely a mediocre sounding opamp, but works universally fine just about anywhere you plug it in. Online positive reviews are abundant, and people just keep buying the LM4562, pushing its popularity even higher. I certainly don’t agree, but what can you do? The flock is moving.

 

Power supply, system speed, compensation and physical layout are of paramount importance. Unfortunately, the average HiFi gear just can’t support exotic, better designed opamps without a few changes. Most HiFi product PCB’s don’t have a ground plane, thus restricting the super high speed opamp compatibility.

 

Just Google “opamp sound”, “ne5532 upgrade”, “opamp review” and you’ll get flooded with mostly useless opinions.

 

While I have no doubt they’re honest opinions, by genuine enthusiasts, the reality is that most are deeply flawed, due to incorrect testing conditions, and are about as good as a horoscope. Interesting read though.