|I'm going to build a class-a op-amp with a cooler from an ATX motherboard southbridge and thermal adhesive as a proof-of-concept, one of these days
well you better crack open the opamp plastric casing then figure out how you are going to use an etched substrate transistor with very little actual metal to bond to an external heat sink or you have no shot.No heat transfer and so pissing in the wind.
An audio output transistor is not a computer chip processing ones and zeros but a continiously active device,more so if full tilt boogie
class A.think analog and not digital logic
|It is relevant to note, as you did, that some opamps are designed for audio. I don't know if there are others, however the 627/637 were designed with a specific use in mind. Of course, they cannot be completely customised to the circuit in which they are placed, however they do have an intended use right back to the design stage.
yet you still have no access to the front end,any of the the bias points at any stage,the current mirrors,the driver stage or the output stage so a "box" that you can hang things on,change what happens OUTSIDE
the box but not a single internal parameter other than opening up one single output transistor of the output pair to class-a operation on a limited bassis.An improvent but by nature of the beast a limited one.
Is what it is and wishing does not make it any different
|My two above statements in no way contradict each other. Stating that you can build a bad sounding amp with either approach
Who has ? what examples ? Name a single "bad sounding" class-a discrete Op-Amp that is for sale anywhere,just one single example will do.
Theory is OK in its place and if it has any merit but argue some actuals.In "theory" anyrhing is possible but I live in the real world and use real world examples to illustrate points ( looks back to pet peeve rant)
|As for really cheap amps... I should have made that clarification I guess, but the vast majority of headphones sold are also well under $100, but I don't see much debate on the various merits of different $15 earbuds on head-fi.
Are they ? The vast majority of headphone amps from a legitimate outlet and with any kind of factory backing and from someone who actually did a design ? Or are we talking about DIYers stuffing boards on the kitchen table who could not put a LED in the chassis without asking in the DIY forum what size current limiting resistor to use.Obviously that person could not even do a single transistor stage without a road map but that does not mean it is better.
Anyway.At $65 per I would take one of these over any I.C. on the planet unless the target use is portable (30ma per is not very battery freindly but neither is class-a)http://www.forsselltech.com/JFET990-2a.PDF
Toss a serious output stage on to provide drive current,say another $25,and a power supply,box it up and the total amp cost comes in at around $250,maybe $300 depending on power supply and if the person doing the build is more interested in "pretty" parts or just good sonics.If commercial would be over $1K because we all know in order to sell it would need to "ooh look how pretty inside" pictures and that means all parts must follow the approved color scheme no matter if they sound best or not and thosae parts are expensive.
So in the $K class if commercial,the $250-$350 area if built for personal use and would be a pure class-A amp in the 2 Watt range able to drive anything out there except the difficult K-1000 and some of the 600 ohm AKG cans.
Toss another stage on after the 2W stage (which is now a class-A driver) and you can ramp the output up to whatever you want withing size and $$$$ limitations and you now have a true power amp stage capable of driving whatever it is you are looking to drive.Simple,elegant.reasonably priced and full class-a front to back which I defy any opamp to stand to up in a head to head contest even though this also
is an op-amp.that is me using an real world example and not "I feel" then ramble to no purpose
Here is another I would personally choose over any I.C. Op-Amp :http://www.welbornelabs.com/classa.htm
Again a pure class-A Op-amp at a price of $79 per channel,another $30 prebuilt and ready to drop into a box yet will blow the doors off any I.C. Op-amp as in the first example but with the difference neing this is ready to rock and needs no additional output stage.
Another example,this time a Hybrid :http://www.welbornelabs.com/hyb.htm
I have actually built a version of this years ago and I can say from my personal experience it blows the doors again off any I.C. Op-Amp I have ever heard.Again is a class-A Op-Amp and again at a good price of $75 per channel minus tubes (the 6GM8 is not real expensive),$30 per channel pre-built.Put it up against any opamp on the planet and hands down it will whip its a*s with only the stubborn few wanting to argue being able to deny it once heard head to head.
|1W is high for driving headphones.
for an opamp it is.Not
for a buffered opamp which most are capable of the 1W and others more when the buffers are stacked.My Szekeres is 2Watts,all my triode headphone amps 2-4 watts.
1W is NOT
high for a headphone AMP
at all and is very common
|Couldn't agree more with you, but then that's my preference and opinion and in the grand scope of things counts for little...
Most have no clue what it is they want and even less how things work but always the loudest dissenting voices.They like
to argue but have no credibility if they bring nothing to the table other than blowing smoke or calling names.Experts in their own mind because they hate to admit they have no clue and must attack those who do AND that stand by their guns instead of being intimidated into silence
Taste is valid but when that is strictly based on very limited experience or maybe second hand news only a closed mind sh*ts on the options or a new idea just because.
|The reason I mentioned about opamps that I have used in my design (and apparently rickcr42 missed my point) was that there are power opamps that can dissipate 10W
I did not miss the point at all.This is an audio discussion and those opamps suck for audio so why use them as a counter to what sounds better ? I can stick an ADSL driver in a batery operated box,call it a headphone amp and point to the close to 500ma output as its main feature yet as soon as someone used it for music I would get "WTF ?"
because it would sound like crap even though it looked good on paper
and i know this because I tried this and it did not work out
|So I don't know why he keeps using examples of opamps with max output current of 35mA to demonstrate the idea that at full Class A an opamp will go thermal runaway and be destroyed be heat. There are several opamps out there that can do several Amperes of output current and they are designed to dissipate several watts if not tens of watts
one more time then (exhales........)
the question was which is better.A discrete Op-amp or an I.C. Op-amp for driving headphones
Still with me ?
Headphones need power,power means heat,heat means either heat sinking or limited power drive or going out of class-A operation and into class AB operation to keep the heat down
Every single opamp on the planet would use class A operation if they could but since they can not comprimises are made to make it work within limitations.One method is to add an external buffer and is 90% of the headphone amps in use by head-fi members but it is still a comprimise.
NONE of the above pertains to a discrete op-amp circuit so why I initially said it is a better way and if you can not understand what I wrote then it is not my failing to explain but yours to understand since you keep referring to my statements.
|I dont think Rick has missed any point. He has explained the differences what .... three or four times. But then someone misunderstands and he ends up addressing something further and further away from his original points.
read back a few of my posts man.Where I stated it is my thought this is an intentional attempt to blow smoke on the topic so the crystal clear again
becomes cloudy and misinformation can rule the day as it mostly does at headfi.Why I rarely bother trying to clear up unclear topics anymore.Some folks just don't want to know and the ones who do must deal with the fact there are some who would rather they also have no clue.
Why ? I have my suspicians but will keep them to myself in the interest of peace and harmony (lalala lala lala laaaa )
|I appreciate your efforts and I learned some info that enhanced my understanding of the subject
You are welcome Earl.I really do try to shoot for balanced and clear and fully enjoy a discussion on the topic if it is one that interests me (most don't,boring and same old) but every time I do we end up at the same place.More confusion than clarity and 25 pages of crap fest personal baiting but being thick skinned,having a serious "kiss my behind" attitude and one of the baddest headiers on the planet I WILL
as always plow on and try to bash my way to clarity
"lead,follow or get the fk out of my way"
True words, hard to come by