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In Reply to: RE: Nobody here ever said tubes don't need break in. (nt) posted by gusser on August 25, 2015 at 12:08:01
But you don't find them in professional applications
Well, actually there is a strong return to the use of microphones with tube preamps and those are often single ended circuits.
There was an interesting article from the mid 70s where they went hunting for what went wrong with studio sound and they found the main culprit was the switch from tubes to transistors in those studios.
So faced with that the SET fans now claim that's the wrong type of distortion to measure?
Not SET fans at all...and starting way back at the dawn of the use of negative feedback from the likes of D.E.L. Shorter from the BBC, Norman Crowhurst and a few others crying the alarm but an industry not taking heed.
You keep misunderstanding the nature of the problem. It is not the level of distortion (Geddes demonstrates that there is no significant correlation between sound quality and THD and IMD...however, his graphs show a slight NEGATIVE correlation!) but the pattern of that distortion as a function of SPL level.
We have had "perfect" measuring amps for a long time now and many of them simply sound like shit. Otala found a part of the problem but not all and amps designed to minimize slewing often still sound bad.
"SET amplifiers are a cult."
I disagree with this stupid statement wholeheartedly. They are owned people who were drawn to how the things SOUND in an appropriate setup. THat are sensitive to things you are apparently not sensitive to. They probably would have stayed with their SS amps with 0.0001% THD (most probably started there and got dissatisfied...I know I did) if they thought they sounded better...but they didn't because they don't. I especially hate it when people try to put some kind of religious mantle onto what are nothing more than luxury objects to bring people joy when listening to music. No one is being forced to drink the poison coolaid here or to tithe over their bank accounts to serve a demagogue.
With the specific systems they work in they work better than anything else.
"but hardly the mainstream studios that mix 99% of what is available to the public."
I'm sorry, i thought we were listening to high quality recordings and talking highend audio here but apparently you are not. Like I give a crap what the latest Eminem or Beyonce records sound like or how they were mixed. Yes, some good rock music is also poorly recorded but I don't dumb down my system to make it tolerable...I would much rather have a good recording of Beethoven's 9th symphony sound like I am in the middle Zuerich Tonhalle.
Follow Ups:
The problem with early transistor preamps was lack of dynamic range which tubes are superior by default. Better silicon technology has greatly improved this however I will agree a tube mic preamp is still superior. It's the old question of if modern transistor preamps are good enough. For most pro applications, they are.As for single ended amplification, I was referring strictly to SET power amps. Look at any OPAMP circuit. Sure they are push pull output but the VAS stage is most always single ended. I am not denouncing single ended amplifier stages at all. I am denouncing $10,000 plus SET amplifiers with greater then 10% THD at a few watts of power and poor PSRR to boot! They are only made commercially by very small manufactures and sold in very unique stereo shops - often on special "made to order" policies. Not to many people buy them hence the cult status. Outside of table radios and low cost TV output stages, the audio industry abandoned SET since the 1940s and there is no evidence of it ever coming back en masse.
The Otala feedback theory is a farce and has been denounced many times since it's publication.
The physics and electronic theory is dead on. You cannot correct a fast rise time signal by measuring it after the distortion is applied. TIM can be demonstrated in most any feedback amplifier using a cheap square wave generator. And many audio magazines have shown the scope shots. But for all the electronics genius of Otala, many have overlooked the 800 pound gorilla in the room.
Show me a musical instrument or any natural or man made sound that can produce a fast acoustic rise time at over 10khz in our 15psi atmosphere? Beyond that show me a mechanical microphone that can respond that fast if such a pressure wave was even possible.
While TIM is real and can easily be simulated, no audio amplifier will ever be called upon to reproduce such a signal in sound reproduction. TIM in audio amplifiers is an academic exercise, nothing more.
The real issue with early transistor power amps was crossover distortion caused by early semiconductor limitations. This is no longer a problem for at least the past 20 years.
Otala's work did however bring to our attention stability issues. His work led us to superior feedback compensation design. This is why HF square wave testing is still very important in audio amplifier design, especially with today's commodity wide bandwidth power transistors.
Read Morgan Jones, Douglass Self, Rod Elliot, Randy Sloan for power amp design expertise. I have and my power maps, a 9.2.4 HT system are all DIY. I built some tube ampssp over the years as well.
Edits: 08/25/15 08/25/15 08/25/15
"It's the old question of if modern transistor preamps are good enough."
If the tube pre amp is still better for sound quality (of which we both agree) then how can a transistor preamp be "good enough" when sound quality should be the most important factor in making a recording??
"They are only made commercially by very small manufactures and sold in very unique stereo shops - often on special "made to order" policies. Not to many people buy them hence the cult status"
yes, the are handmade and therefore more expensive...priced a handmade car these days?? Craftsmanship costs...always has, always will. I agree with you though that it is not a guarantee of great sound...they can screw stuff up just like everyone else. The best ones though have been designed by inspired individuals with a deep understanding about the interactions of parts to make a whole.
A bigger problem that is not much discussed, IMO, is what happens with the back EMF pulse from a speaker. If the amp has a feedback loop some of that distorted back EMF pulse will re-enter the amplifier and be amplified along with the signal. It could well explain why some amps are very speaker dependent despite on paper being very load invariant. An amp without negative feedback cannot be impacted this way and might actually be more tolerant of certain types of speakers...especially those with highly reactive behavior like electrostats.
Apogee ribbons behave almost like a pure resistor (at least as close as you are likely to see in a real loudspeaker) and they are actually pretty tolerant of all kinds of amps. Amps seem to give their best with Apogees and I think lack of reactance is part of the reason why. SETs even work well because of the even impedance curve (my friend's Studio Grands are 5 ohms and only vary between about 4 and 6 ohms.).
"The real issue with early transistor power amps was crossover distortion caused by early semiconductor limitations. This is no longer a problem for at least the past 20 years.
"
I disagree, you can routinely see crossover effects in Class A/B amps in stereophile measurements. It is not really any better, or worse than it was for an amp like the Hafler DH500 or Crown Macro Reference (a horrible sounding amp according to several reviewers but measured nearly perfect). Again, the crossover distortion in those older amps was not at a very high level (inaudible most engineers would say...as if they had a clue) and yet it was highly audible because it produced a VERY unnatural pattern of distortion harmonics.
"Read Morgan Jones, Douglass Self, Rod Elliot, Randy Sloan for power amp design expertise."
Been there done that and it all reads very convincing...except where the proof is in the pudding as they say. The amps designed using the best engineering practice don't sound as good as those "antiques". Ever hear a Halcro amp? What about Soulution? Forget the price for the moment, which is ridiculous. Both of these brands measure about as good as I have ever seen for commercial amps. Halcro SOUNDS dead and sterile, Soulution sounds better but still "soulless" and clinical. It doesn't matter which recording and this tells me that it is an amplification artifact and not a source material choice. If you can show me better measuring amps I would love to see them but probably not to hear them.
So, why should this be the case...they are as Douglas Self would say "blameless". And yet I have heard Soulution on about 5 different pairs of speakers and rooms and still come away with the same damning conclusion. I am not the only one. I took my wife with me to the Munich show this year and we went first to the uber-expensive Magico/Soulution room. At first she was impressed with the clarity...it is definitely clear but then with wide dynamic material she noted that the dynamics seemed constricted and that the tone was rather "gray". She is not an audiophile and I said nothing to her about the room in advance because I wanted to run a little "experiment" with her to see which rooms she found natural and those she did not (she is a big fan of live classical and Jazz concerts though).
We went to the Silbatone room and listened to 1930s theater speakers with modern Silbatone electronics (SETs and vinyl of course). On came an opera singer signing in Russian and my wife started to cry! The sound was beautiful and lifelike and utterly moving. For sure the absolute distortion was an order or two in magnitude higher but for delivery of MUSIC it was no contest...Magico/Soulution lose big time.
I could go on but suffice to say the rest of the experiment mirrored this one. On other interesting thing. The room with the Tune Audio Anima horn speaker was very promising except for some sharpness in the lower treble that bothered both of us. When we looked at the system it was all tube except the amp, which was a Modwright SS amp. No other horn system at the show had this kind of sharpness that used a tube amplifier.
I like to do these kinds of experiments with music lovers who are non-audiophiles because there are not the pre-conceived notions. Then you really see when they realize something sounds realistic or not. My ex-girlfriend is a professional violinist (first violinist in a number of euorpean orchestras) and she could tell in about 10 seconds if a room was worth listening to or not. I used to record her and take some of my own recordings as reference material. That usually sorts things out rather quickly.
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