[quote author="buttachunk"]TK@
yes-- "oldschool" resistor biasing can lead to problems in this case because of the opamp output's sensitivity to DC. the constant current source is far more linear and far more accurate than say a 1% 6k resistor from the VE- to opamp out. from my reference materials, the ccs should be set to 3-5 ma for class a bias without nasty side effects. :wink: (getting too hot or sounding nasty)
having said that, i like resistor biasing for some less critical-current transistor stages-- sometimes the "slop" factor makes it sound vintage.. the "warmth" of 20% tolerances!!! :green:[/quote]
I have to respectfully disagree. The switch from single ended to symmetrical output creates a spray of odd harmonics regardless of the biasing method used (resistor vs. CCS). It never sounded like "warmth" to me, but you may be after high frequency distortion so I will not argue about the sound . A thirty foot cable can cause enough capacitive load for all the current (5ma) to be sinked to charge the transmision line. At that point the output switches from single ended Class-A to symmetrical Class-B. Actually a single ended Class-A output with constant current source cannot be more efficient than 25% so most of the power ends up as heat and even less power is available to drive the load. That is the reason why this sort of opamp biasing is never used without a subsequent buffer (even in the Audiophool world). However, if you give it 5ma and make absolutely sure that you will never draw more than a mA from the output it will work just fine.
Cheers,
Tamas