What is Discrete Class-A?
As you peruse the web looking at gear you’ll often see this as a major bit of marketing.
“Discrete, Class-A”
It has nothing to do with keeping your mouth shut or your social position.
Lets break it down starting with Class-A.
“Class-A circuit design” refers to how an amplifier is designed and how it does it’s job of amplifying. Amplifying devices operating in class A conduct over the entire range of the input cycle.
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| Class A circuit, transistor is biased to conduct the full wave form |
You don't typically see the drawbacks of Class A mentioned, things like inefficiency of power usage and running hot. In spite of modern component manufacturing Class A transistor designs are still more prone to component failure. Heat kills gadgets. If you rack gear on top of each other without air flow you're going to have processors failing.
The word Discrete means: individually separate and distinct.
As applied to circuit design, “discrete” means an integrated component made from seperate and distinct parts rather than an Integrated Circuit produced on a single piece of silicon with multiple components etched or formed on it. A common application for discrete construction is operational amplifiers.
Why Op Amps?
An operational amplifier is often referred to as an op amp or opamp. In its purist interpretation an op amp is a DC-coupled high-gain electronic voltage amplifier with a differential input and usually a single-ended output. Op amps are sonic building blocks, when combined they produce bigger amplifying systems like microphone preamplifiers and mixing consoles.
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| An Op Amp built from discrete components |
An Op Amp can be constructed using individual, discrete components or it can be a monolithic Integrated Circuit (I.C.) produced on a single piece of silicon or a hybrid combination of these technologies.
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| An I.C. op amp |
Integrated Circuit Op Amps were brand new technology in the late 1960’s and they did not sound great for high quality audio. IC op amps have always strained driving low impedance loads such as transformers. Even today, in 2021, many professional users frown and look down on the lowly integrated circuit which is often at the heart of lower priced audio products.
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| Vintage API op amps, potted in black plastic to protect contents and provide thermal stability |
In 1970, serious high quality professional products relied on small plugin circuit board packages for amplification stages. API is one of the best known for their 2520 op amp. With this single amplifier stage API created a range of multiple products and their custom built mixing consoles became famous because they sounded great. These products relied on discrete op amps and audio coupling transformers.
Neve introduced the 1073 preamplifier stage in 1970. This preamp was itself a plugin device which could be quickly and easily replaced in case of a malfunction. Transistors were still a relatively new and developing technology in 1970, it was not uncommon for them to fail. Inside the 1073 preamplifier cartridge smaller plugin circuit boards helped facilitate quick repair and replacement.
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| Vintage Neve 1066, note plugin circuit boards inside module |
“The tyranny of numbers" was recognized in the 1940’s when complexity of circuits reached a level at which the losses from failures and downtime exceeded the expected benefits. If you look at the construction of 1970’s Neve and API mixing consoles you see a high degree of complexity from the integration of many components.
A large scale recording studio in 1970 (with an expensive new Neve or API console) could not afford to go offline due to equipment failure so replaceable channels with individually replaceable circuit components were the norm.
DOES “DISCRETE” SOUND BETTER?
I don’t care about hype. I do care and I’m quite passionate about recording and sound. I am only being critical of marketing rhetoric.
I use my ears and years of critical listening to guide me rather than marketing-speak. I own several pieces of gear which utilize “discrete” circuit topologies. They sound great or they would not be in our studio.
My Soundcraft mixers rely heavily on I.C. technology and they are some of my all time favorite studio purchases. The big Midas consoles from the 90’s relied on gobs of IC op amps. These mixers sounded great in spite using a lot of monolithic IC’s in the various signal paths.
Back in the 1980’s I owned a 32 channel mixing console which offered 16-track tape monitoring. It was a lovely looking piece of equipment but the longer I owned it and spent hours listening to audio passing through it I came to realize it was just a bad design. There was an irritating edge to audio passing through. It was subtle but the longer I used it the more I focused on that character I hated. I was highly suspicious of the power supply being under sized for the application but I grew to detest that mixer and in its eighth month it went to a new owner. I remind myself that it’s not I.C. op amps that make bad sound, it’s bad designs that make bad sounding gear.
EPILOGUE
As a bonafied tone-chaser it is your job to separate hype from truth.
The terminology “discrete class-A” is only telling you a small bit about a product.
I dislike when you get punched in the eyeballs with “discrete class-A” hype and then they don’t show you basic important product knowledge like signal path, distortion, maximum input level, frequency response and maximum output level. Wattage of power used, weight and physical dimensions are often not provided. These are basic specifications every piece of gear should make known but instead we’re given terms like “legendary” and “discrete class-A” to inform our purchase decision making process. Maybe it’s just my age but I find a lot of advertising insulting. I like manufacturer’s who are humble and over-deliver on performance.
In a sea of confusing marketing, hopefully you now have a little bit better understanding about “discrete Class-A” and what it really means.
Thanks for reading High on Technology, Good Music To You!
©July 2021 by Mark King, it’s not ok to copy or quote without written permission.
