|I am guessing that a large improvement could be gained from current monolithic opamps by adding some small and simple heat dissipating solution, allowing the opamp to go much further up on the output scale before resorting to class AB. Am I crazy?
not entirely crazy but that statement is.
The "guessing" has zero to do with actual fact and the "fact" is no chip opamp can drive a headphone directly in pure class-A period no matter how big of a heat sink you try to weasle on the plastic
|From all of this class A etc. discussion, have I correctly understood that it is is technically possible to bias a monolithic opamp into class A through all of it's output range, however the issue is heat dissipation in such a small package? Has anyone actually tried taking for example an OPA627, some appropriate cooling solution (thermal past -> heat sink -> maybe a fan) and fully biased it into class A?
Again not possible at these current levels and no amount of wishing it were not so will change the facts
.Power is heat and the higher the power the higher the heat and is WHY methods other than class-a of amplifictaion were invented in the first place !
Even A/B has proven too costly and generates too much heat for modern electronic devices and is the sole reason for the other newer formats.Not better sound but cheaper to build and easier to cool.
|I suggested this earlier and he said something about taking the plastic off and finding transistors; frankly, I was so baffled by his suggestion that a monolithic op amp is a plastic covering with a few transistors inside that I didn't bother following it up.
It was a joke for those who know that a chip is an etched silicon substrate and to illustrate how ridiculous some of this conversation has become where "experts" chime in with "feelings" while being too lazy to actually read some background.arguing to do it just because it feels good.
Look at any class of integrated circuits and you find what ? Different packaging for different power levels.There is not much doubt when you have a "small signal transistor" along side of a "power transistor" which is which but has anyone given any thought to what the actual difference is ?The Package the substrate is wrapped in and no more
A package meant for high power must
disperse heat so you will find exposed metal on the plastic which allows the designer to add enough heat sinking to draw the heat away from the actual silicon which would rapidly burn up without it.even the lowly three-terminal-regulator I.C. comes in different packages depending on output current levels.
TO-18 up to 100mA (with a heat sink)
TO-220 up to 1.5 amps (with heat sink )
TO-3 up to 5 amps (with a heat sink)
same part,same function,different package for different levels of power which means different levels of heat
look at your central processor chip,your RAM,your sound card,all with big mamma heat sinks with itty bitty fans and for what reason ? So they do not detonate as soon as you turn on your computer.
Heat is the enemy of solid state and is why small electronic devices use switching power supplies (on or off rapidly but NEVER on all the time) and opamps run in class-B for any appreciable output and also
why you will never see an opamp drive a mechanical device like a relay directly but only through a transistor buffer for the additional current.
Size and area of heat dispersal equates directly to power delivery and no way around it.
|Early opamps had limited bandwidth and speed, high noise floor, inadequate output drive capability, or other characteristics that made them sonically inferior to fully-discrete amplifiers.
Actually the earliest "Op-Amps" used 12AX7 tubes in a differential input stage mated to a cathode follower output stage and low bandwidth or noisy they were not.Even today the 12AX7 is used in some very highly regarded extremely low noise phono and microphone stages stages.The "crappy" opamps most often referrred to were the 741 series because they were considered the first "universal" be all end all gain stage in a box but never were they considered an audio device even if used for such by lazy designers trying to save a buck.
It wasn't until PMI showed the way that the opamp arrived as a device useable in high quality audio but those parts were extremely expensive then so again did noyt see much use.I actually have a mic preamp I built years ago using PMI OP27's which is identical to the modern Analog Devices OP27 because in fact ADI IS
PMI but even they are have moved away from serving a tiny niche market and into serving the bread and butter market of the portable device-cell phones,MP3 payer,etc and that means low heat which means high efficiency which in the end means as far from class -A as you can get and still be considered an analog chip.
Opamps are moving into the digital domain as is most all things audio and again it is ALL about the heat and class-a is a furnace so off the list of new devices
|Things have changed dramatically as technology advances. Today there are a number of very high performance opamps that are quite appropriate for high performance audio.
actually yes but this also depends on your standard of "high performance".Is it the multichip low noise recording console ? The portable headphone amp where you MUST have a low battery drain so efficiency of operation is a must ? A computer sound card ?
How many would pay $5,000 for a preamp that used an Op-Amp as its main circuit ? My money says not too many so the opamp has its place but the ultimate hardly and i don't care what you hang off the output in the way of a gain stage.Price points and value is what it is all about but the truth is a $1,200 amp rarely sounds as good as a $10,000 amp and this goes beyond a pretty face or fancy parts and directly to circuit topology.
All else being equal and assuming a competant design low level gain stages are on a scale from worst to best
2-Op-Amp class-A biased to around 2mA with a discrete or chip buffer stage
3-All discrete Class-a
4-All Class-a Triode
5-All Class-A DHT Triode
Stepping up to power amps it is just about the same but here the speaker becomes the main variable.
2-all the rest depending on your drive requirements so for instance a solid state behemoth of 200WPC may be what you need if you have a large multidriver low efficiency system but maybe a 45 SET amp if your speakers are a simple zero crossover single driver high efficiency type with pentodes/tetrodes/PP Triode all having a place depending on the speaker.
Headphone amps ?
Just a gain stage with a driver stage on the output and no more so it is "group-1" that has the most in common with the headphone amp
Do a search people instead of using conjecture on what "might be".The truth is out there and being the truth does not vary no matter who it is with the opinion.Simple physics says you can not have a true Op-Amp drive a headphone directly in pure Class-a and why I initially made the statement at the beginning of this thread that head-to-head a discrete Op-Amp will whip a monolithic chip Op-amp in sonics
because class-a operation is superior for music and no opamp can drive a headphone in class-a operation