Equipment Class Confusion

[Frodo]

Okay-- another quest for geek data here.

Any answers in English will be greatly appreciated!

I confess that the little I know about equipment type and/or class has been very confusing and want to nail this down once and for all.

When buying mics, amps, compressors, or other types of equipment, discussions tend to be limited to price and sound preferences. But how do equipment types and class factor into all of this?

Are these classes universal with other types of equipment, or is it that when Class or Type A is used for a compressor it means something different from that used for a mic or preamp?

There are some classes of amps:

Class A: input and output voltages operate continuously (?)
--- good for cross-over points
--- less good for efficiency

Class B: input and output voltages operate alternately (?)
--- good for efficiency
--- less good for smooth freq cross-over

Class C: restricted to broadcast industry (I have no idea about this)

Beyond that, there are:

Class A/B
Class A/B1
Class A/B2
Class A/B plus B
Class D
Class B/D
Class E
Class F
Class G
Class H
Class I
Class J
Class S

signed,
stupid hobbit

[BradLyons]

Class A A type of amplifier design. When an amplifier's stage devices are passing current at all times, including when the amplifier is at idle (no music playing), whether the amplifier is single ended or push-pull, the amplifier is said to be biased in Class A. Because the current is flowing at all times, an input signal causes the current to be immediately diverted to the speakers, and therefore, the sound is very "fast". In the case of a push-pull amplifier, there is also less crossover distortion when the signal passes from the positive to the negative or negative to positive, since each side of the push-pull section is already "on". If all stages of the amplifier are biased in Class A, and the amplifier operates in Class A to full output (enough current flowing at idle that could be required for full output), it is said to be a "Pure Class A" amplifier. Pure Class A designs are understandably expensive to build and are usually only found in high-end audiophile equipment.

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Class AB A class of amplifier output design. As its name implies, it is sort of a combination of Class A and Class B operation. If an amplifier operates in Class A for only a portion of its output, and has to turn on additional current in the devices for the remainder of its output, it is said to operate in Class AB. Most amplifiers are in this category, and are said to be Class A/B amplifiers, since they operate in two classes. In class AB and B, the amplifier is slower than in Class A because there is a finite time between the application of the input signal and when the devices are turned on to produce a flow of current to the speakers. However, Class AB and Class B are more efficient than Class A and do not require such large power supplies.

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Class B A type of amplifier design. Class B differs from Class A in that there is no current flowing when the output devices are at idle, and as a result, they have to turn on from a zero current state when signal is present. In a push pull Class B design the output devices would each produce half of the audio waveform (one set for the positive half, and another for the negative half) and would not have any current flow when the other half is operating. Class B designs tend to have a slower slew rate and more crossover distortion but are less expensive and require less robust power supplies.

[Frodo]

Thanks, Brad. That takes my guesses to a whole other level.

Thanks, also, for the English version!!

So, how much consideration *should* be given-- or how much consideration do people give when matching mics, amps, preamps, compressors, etc?

I mean, are there any rules such as "never put a class x thingy with a class y doo-hickey unless you have a class z watcha-hoozits"?

And-- to add to the confusion, I'll assume we're talking only about Class 1 equiupment... (I do know what that means..)

[BradLyons]

Here's the consideration you should give...... IF WHAT YOU FIRST TRY DOESN'T SOUND GOOD, GET SOMETHING ELSE, TRY SOMETHING ELSE, ETC. If that doesn't work, take up under-water basket-weaving Specs don't mean anything, all that matters is how it sounds.

Those that know me know I swear on ADAM monitors, mine are 25Hz to 35khz. But this spec means nothing if it's not flat in between, doesn't have high quality components, and doesn't translate my mixes. This spec is important to a monitor, but it means nothing for a microphone. For example, the Soundelux E49 is 30Hz to 16kHz and an SM58 is 50Hz to 15kHz. HOWEVER, these mics are absolutely NOTHING alike. In other words, the specs don't tell you what it's really doing or how it sounds.

[Frodo]

Well, there you go!

As one who does more pre-production than post, I've always taken the visceral approach.

Thanks again, Brad. Ears are the answer once again!

[mhschmieder]

I'll try to remember to post something about Class D soon. We've been moving in that direction recently, so I need to learn more about it anyway for my job. Send me a reminder if I forget -- things are pretty hectic with lots of training sessions atop preparations for the AES Show in SF next week.

[Frodo]

I'll try to remember to post something about Class D soon. We've been moving in that direction recently, so I need to learn more about it anyway for my job. Send me a reminder if I forget -- things are pretty hectic with lots of training sessions atop preparations for the AES Show in SF next week.

Thanks, MH.

Ooo--- AES.

To quote from Close Encounters-- "Toys!!! Toys!!"

Just for reference, this is the best (if partially explicable) definition I've come across:

Class D operation is switching, hence the term switching power amplifier. Here the output devices are rapidly switched on and off at least twice for each cycle (Sampling Theorem). Theoretically since the output devices are either completely on or completely off they do not dissipate any power. If a device is on there is a large amount of current flowing through it, but all the voltage is across the load, so the power dissipated by the device is zero (found by multiplying the voltage across the device [zero] times the current flowing through the device [big], so 0 x big = 0); and when the device is off, the voltage is large, but the current is zero so you get the same answer. Consequently class D operation is theoretically 100% efficient, but this requires zero on-impedance switches with infinitely fast switching times -- a product we're still waiting for; meanwhile designs do exist with true efficiencies approaching 90%.

[Historical note: the original use of the term "Class D" referred to switching amplifiers that employed a resonant circuit at the output to remove the harmonics of the switching frequency. Today's use is much closer to the original "Class S" designs.]

[GRS Historical Note: "Class D is a subset of all possible switch-mode amplifier topologies that is typified by use of the half-bridge (totem-pole) output stage that has two interconnected switches operating in time alternation. The paradigm is that of Loy Barton's class B, but uses the statistics of conduction angle to produce amplification (PWM). There are many subclasses within class D that describe the origins of the modulation. Class D is at least as old as 1954 when Bright patented a solid-state full-bridge servo amplifier U.S. 2,821,639."]

No hurry on a reply-- but anything in the way of real world practical advantages would be appreciated.

[baanes]

As far as I know, a class D amp switches on and off rapidly at a certain frequency (usually in the mhz range, I believe). If you were to "zoom out" from this back to the audio range the little ons and offs would combine into the waveform you're looking for. Its a little like how PWM works if you are familiar with that. I know that some of Sharp's consumer electronics use 1-bit class D DACs. The advantage I believe is that it uses very little power and can sound okay. The wikipedia article also says that Class D was originally used for applications other than audio, such as driving dc motors, but is now being used for audio systems that do not require extremely high quality.

I'm not an engineer or anything, so please correct me if I'm wrong.

[mhschmieder]

Here are some brief contextual descriptions of Class D from some paper presentations that I will be attending at AES tomorrow in SF:

"Simple amplifier topologies are not the norm for integrated circuit (IC) class D amplifiers. A simple self-oscillating topology is mapped into a standard CMOS technology and fabricated in a 0.5 micron process. The output stage is optimized for a range of modulation indices, simultaneously increasing average efficiency and reducing chip area."

"Digital class-D amplifiers are cost-effective solutions for a wide range of digital audio applications because of their high power efficiency and ease of integration. A real-time cost-effective power supply correction algorithm increases the power supply rejection of an open-loop digital class-D amplifier substantially. It enables open-loop digital class-D amplifiers with inexpensive power supplies with less decoupling."

"Automotive applications using class D digital PWM switching amplifiers have long been limited by the approach••™s perceived higher cost, the potential for radiated electromagnetic interference affecting in-vehicle electronics, and the difficulties of designing this type of amplifier using discrete components. An integrated circuit built on a high performance analog mixed signal plus power silicon process coupled with innovative circuit design now allows the deployment of high power class D amplifiers in vehicles that had previously been confined to only class AB amplifier designs. Class D PWM amplifiers, switching to 400 kHz or more, can achieve an unweighted dynamic range in exceeding 100 dB, linearity in excess of 80 dB, and PSRR greater than 80 dB with a full scale audio signal."

"There are compelling arguments as to why it is advantageous to use class D, even for output powers as low as 40 mW, such as for heaphone amplifiers. Significant savings in power can be achieved at typical listening levels when compared with a conventional class AB amplifier."