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Hi JR,
There is nothing obsolete about Class A, it totally eliminates crossover distortion and is used where ever possible. The only time you use other classes of operation (A/B, B, etc) is in power amps where the quiescent power consumption of Class A operation limits how much power you can get out of the amp. Op-amps used for audio operate in Class A. However bragging about Class A operation in this case is bogus because virtually all small signal gear operates in class A. This is a case of marketing using an audiophile term inappropriately (class A power amps are special and very expensive) to try and make the ordinary and standard way of doing things sound special.
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Huh.... If you look at the internal topology of opamps they look very much like tiny Class AB power amps. Otherwise the typical console would require multiple cooling fans to deal with the heat load. For a little esoterica, I do recall some audiophiles experimenting with hanging a resistor to the negative rail from the outputs of conventional opamps to force them into Class A operation. This never caught on as even 20 years ago you could get adequately fast opamps at moderate cost.
Class A topology was common before large scale integration, but these days it costs more even for a machine to pick and place most parts than they cost. Perhaps my casual characterization of such circuitry as obsolete is incorrect as there are blocks of Class A within all linear integrated circuits. While I don't recall ever seeing a Class A opamp I do recall seeing a mic preamp chip many years ago that was designed for low voltage battery operation and may have been Class A or open collector output.
We're on the same page regarding Class A being a marketing conceit. I am unconvinced that Krell and the like are much more than a conversation piece but that just may be a personal problem
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The reason I mentioned phantom power is due to the DC coupled outputs. DI's normally either use a transformer or DC blocking capacitors in the outputs to protect themselves from phantom power (amplifiers break down when you put higher voltages than the supply voltages on their inputs or outputs). Unless Avalon is using supply voltages greater than 48V (which I seriously doubt) they are risking dead boxes in order to be able to claim DC performance (which nobody in their right mind needs for audio).
Phil[/quote]
As I previously stated, it is no big deal to tolerate phantom power as long as you anticipate it. For that matter, I can't imagine designing a DI and not (I did when I did). Depending upon the polarity of the Class A output stage used, connecting to an active phantom powered input will either increase or decrease the Class A operating current all of 7 milli-amps. In a clever design using PNP or P-channel outputs the current density and linearity would actually be increased by phantom power.
re: DC response, agreed again. Any imagined benefit from DC response will be forfeit upon interfacing with any mic preamp which in my experience are 99.99% capacitor coupled, or any microphone which AFAIK 100% don't pass DC. Of course offering DC response means never having to say you're sorry about where you set the LF pole, and will "sound" good on paper to the folks who like to brag on their equipment's spec sheets.
JR