class A amplifier topology -- all the current all the time.
a certain amount of distortion is actually caused by thermal variation as the transistors in an amplifier circuit do their thing. biasing a transistorized circuit into "class A" means configuring it to draw a maximal amount of current whenever it is connected to its voltage source. whenever the current isn't being used to amplify a signal/drive a mechanical actuator (eg, a speaker driver), the current is dissipated as heat, and hence there is a minimal amount of thermal variance over time.
ps, one thing about the opa627, other than that it is a bit of a power hog when biased into class A (like, it gets seriously hot, even when not oscillating), is that opa627s are only available as single channel chips. what this means is that each 627 chip contains takes as input one signal and outputs the gain multiplied clone of that signal (modulo distortion). this is actually because one of the other major causes of distortion in opamps is what's known as "crosstalk". remember in E+M when you learned that current is accompanied by perpendicular B and E fields? at VLSI scales, the B and E fields of one on-chip wire have very non-zero effects on the signals of other nearby on-chip wires (ie, all of them). in practice, you measure one specific effect of this, by measuring how much of the input signal of one on-chip channel is present in the signal output on the other on-chip channel (hint: it's very non-zero for dual-channel opas).
hence, the opa627, meant to be an opamp designs and produced for audio afficionados, is not available in a multi-channel design.
also, older big box integrated amplifiers like tipo's are typically class AB designs using discrete transistors (usually power mosfets. as this was all that existed before the age of everyman's VLSI) and high quality components (because that was literally all that was available at the time). their headphone ports are the amplifier output brought down to headphone voltages by a resistor network. they are exceptional values, and have a certain characteristic distortion that a lot of people love; it's the same distortion, coincidentally, that's present in most _recordings_ of that time. hence, to each his own.
if you want an inexpensive new integrated amplfiier with these same qualities, my favorite is the severely hidden and underrated onkyo a-5vl. it's cheap, has two beefy class AB channels, has a powered pentiometer that actually sounds good, a nice toroidal coming from mains, and if that weren't enough, they threw in a PCM1796 (one of my favorite dacs) with both toslink and spdif receivers. basically, it's a no-fuss way to power a couple of nicer-but-not-too-nice MTMs (i like the axiom m22 v3 -- ok ok it's a TMM -- but the sound is genuine). all of this together shouldn't cost you more than about 800 bucks, and it will sound fantastic (on-axis, of course) with nearly any source you pair it with at everything up to 20x20' room volumes.
