Sunday, July 2, 2017

Flying with the Eagle

After running for a week on the left channel only with no issues, using either speaker, I unplugged the FPB 300 for awhile, connected the right channel, and let it run on the easier left speaker.  It ran for about 20 minutes and shut down.  OK, I've got the RMA, and it's getting packed and going back to Krell for service.  It's been my audio pride and joy for 8 years, far more neutral and dimensional sounding than any other amplifier I'd listened to.

But what to play next?  The Aragon has proven itself to be Acoustat capable, as much as any amp, after all, it's run the Acoustats for about 50% of the time since I got them.  I was almost inclined to do that, but finally I decided to hook up the Eagle 2 I had bought last year, and done some technical testing (it worked, basically, I didn't do much except for quick power testing), and then it sat, since I was a bit afraid of how it would deal with the Acoustats.

But now I have the 3 amp fuses in place, the Eagle was explicitly sold to me as 'working' (the seller said to have been using it for a month), it tested OK, so why not.

WOW!!!

This has changed the presentation entirely.  No longer am I listening to the "Lacking in Transparency(tm)" Acoustats!  My speakers are now ceiling high line source ESL-63's, if there were such a thing!

Allowing a bit of break in, and for the fact it is far more voltage sensitive than the Krell (though having the same 100,000K input impedance--something I now consider a very important factor), before I knew it, I could measure peaks as high as I do with the Krell, yet, it didn't seem to be playing hard at all.

Moxie Power!  As Montcrief describe the Robertson 4010 amplifier (an Iverson design, but made after Iverson bailed from the company Electro Research, selling everything to Robertson to pay for their costs in tooling the EK-1 phono system), I'm sure this would apply even moreso to Iverson's own amp, made under his direction in USA.

(The Robertson was a small 60W amp that Montcrief described as having 10,000W moxie power.  Meanwhile, some big enormous high power amp was described as having a mere 10W moxie power. Montcrief even described a moxie power methodology.  I personally would not get a Robertson because they were into using potted modules to hide their actual parts, potted modules which have been known to crack.  Despite Montcrief's glowing review, the company was not around long.  Iverson's own amp is far more powerful and robustly built.  I consider the Eagle 2 his ultimate masterwork and I believe he did too.  It got the glowing review and personal ownership by J Gordon Holt.  It's simpler than the higher power models.  Iverson and Munro tried to sell me one at an audio meeting in 1988, and I've been very sad I didn't buy it, but now, the magic is in the house.)

This disproves audiophile nonsense about feedback.  This amplifier breathes feedback to the max, that was the idea.  Iverson understand how to do that, stability and linearity and low propagation delay.  Then you can crank up the feedback way beyond what others dare, and get a virtually perfect voltage source.  This amplifier is rated as 800 damping factor and I wouldn't be surprised if it delivers more.  Power supply stability is important too.

Along with that, distortion down to 0.0025%, that's like CD quality, frequency response DC to 100kHz, noise at 90dB (when other amps are quite often down in the 60's).  These specs matter, contrary to audiphile nonsense that 1% distortion is fine as long as it's the 'right distortion.'  No--you want zero distortion.

But still I think the outstanding magic here is the perfect voltage source operation, as illustrated by the super high damping factor.

So here it is, so transparent I could not imagine my speakers sounding like this.  Not only transparent, but smooth and incredibly dynamic.  I don't need those Linkwitz speakers now, my line source electrostats have caught up, thanks to improved amplification.

Objectophiles couldn't believe it, but nothing has proven to me the important of amplifier choice like this.

And just like EKSC says, it's clear, smooth, dynamic.  It's more listenable as well as fun to listen to.  There more there there, and it's popping right out you in more 3D than ever (and intense separation, because there's more there there) but not clobbering you or making you want to cover your ears.

Even the slight warpage of low power college radio is rendered so nicely I can just listen and listen.  The instruments, everything, sounds more real than ever, even in the most sketchy reproduction like this.  You do hear the music, not the source problems somehow.

All that and it's running pretty cool.  One channel got up to 118F at the end of my most intense listening so far, with peaks at 88dBC, which is about my peak on the Krell.  The Krell would have been showing 165F left and 155 right (due to airflow patterns).  And the Eagle 2 cooled down fairly rapidly to  a mere 108F only at a slightly lower level.

It's like it doesn't have to exert itself to handle the highly reactive but non-absorptive load of the Acoustat.  The Eagle just wiggles it's shoulders and it's moxie power does the rest.

Monday: The flying continues.  This is the most transparent sound I've ever heard, there is more there in everything.  I listed to Emerson Lake and Palmer and now Another Green World, and both classical and indie rock radio.

I see now lots of amplifiers have high damping factor, and I'm thinking there's more than one way to achieve that.  I continue to believe the magic of the Iverson designs is pushing feedback to the maximum.  That's how he gets distortion (THD) down to 0.0025% at rated power, which is basically the same as the 90 dB S/N level.  According to Baxandal, feedback is only useful in very small or very large amounts...in the middle it doesn't help (but that's where most amplifier designs are).  Most modern amplifier go after the small and medium amounts of feedback.  Iverson took the feedback thing as far as it could reliably go.

So what I imagine is happening here is that distortion is effectively being 'eliminated' by pushing it back into the noise floor, which is the ultimate limit--can't get THD to go below that.

My Krell FPB 300 is fairly low distortion as modern designs go, but 0.02% at 1kHz is ten times what the Eagle 2 has, and the FPB rises up to 0.15% at 20kHz, despite the fact that power response actually goes to 300 kHz.  So there is rising HF distortion that goes 40 dB above the noise floor at the highest frequencies.

The Parasound JC1 has even higher damping factor than the Eagle 2, but distortion also rises to 0.15%.

Thanks to misunderstandings, audio engineering for high end audio not only downplays the importance of low distortion it seems to bring on more distortion, because it can (according to audiophile mythology, going for too low distortion is bad).

So actually you could say the Eagle 2 isn't magic, it's just one of the few that does things the correct way.  But I still consider that to require a fair bit of magic.  And there may be other magic involved too.

When you go to the upper amount of 'good' feedback (above 35dB) you begin to actually suppress the high order harmonics which are actually reinforced by middling amounds of feedback (5-35dB).  Once you know those high and odd order harmonics down, you get smooth rather than brittle sound, and the Eagle 2 is incredibly smooth as well as being incredibly clear.

Stereophile reviews of the Eagle 2 do indeed rank the sound quality higher than Eagle 7.  I can see why you could imagine needing more power, so that's the reason for the Eagle 7 and other models.  I remember at the time Iverson was showing off the Eagle 2 (and it was indeed a magic show, including arc welding and lots of other tricks) he disagreed that the Eagle 2 could be improved with higher bias.  The higher bias in the Eagle 7 was there because that amplifier needs it...to be almost as good within its rated power as the Eagle 2 is within its power ratings.

But possibly I can crank it up well beyond the 1v input on peaks.  I've been holding back a bit, though sound levels are still reaching 87dB peaks.  This is an old amplifier...far older than the Krell actually, and it probably badly needs a refurb, but still sounding great.  This is not just magic, it's a miracle.

Later I shut the amp down, with Tact gain set to +2dB, playing The Doors album on my table.  Digital output peak of -6dB peak was showing, that would correspond to about 1.25V.  I suspect the amplifier was shut down by current limiter, possibly that monitors regulated voltage as on the Eagle 7, which I have an unofficial schematic for.  There is a LOT of high frequency grundge on this album.  I had played Dylan Blood on the Tracks at +4dB without issue.

Playing with Fire

My thinking that Iverson was going after the high end of feedback, above 35dB, was entirely a guess simply based on the low distortion numbers.

But taking a look at the Eagle 7 unofficial schematic I found, it looks like my guess is correct.  This amplifier has at least 2 more gain stages than usual, and they are triple darlingtons like the outputs.  This has open loop gain out the window and across town.

I also knew a little bit of Iverson's life story.  His father was a TV repairman in the 1940's and 1950's, who was always tinkering with high voltage.  This was too much for the man's wife, who divorced him.  But he lived with his son, John E, who acquired his high voltage passion.  Later, among other things, John E devised the 'corona' speaker, based on high voltage ionization.

This is the story of someone who doesn't just flirt with danger, they live within it.  That's the kind of person who wouldn't feel uncomfortable tinkering with amplifiers with super high open loop gain.  One wrong move, and SNAP!  Not to say that there's necessarily any high voltage here...the Eagle 2 amplifiers operate with less voltage than many amplifiers today because they are lower power than many amps, rated at only 110W RMS into 8 ohms, which corresponds to about 29 volts.

Yin and Yang

But when you have loads and loads of bipolar open loop gain, something special is happening.  As bipolar transistors heat up, their gain increases, so they want to heat up more.  So the electrical force of the amplifier is constantly pushing outward, only to be held back by the feedback which forces it to act like a more perfected amplifier of normal gain.

That feedback however cannot act instantaneously.  In the very short interim, measured in nanoseconds or something like that, the amplifier does perhaps slightly exceed correctness, only to be held back by the propagation delay of the amplifier.  Until just now I had not understood why that was important in an amplifier like this, except for permitting the high feedback to work in the first place.  If the propagation delay is too long, you have to sacrifice bandwidth, and this amplifier retains closed loop bandwidth to 100kHz which is fine.

Anyway, what I've just described, the constantly pushing outwards only to be held back characteristic is exactly the defining quality of maleness, or yang.

The opposite yin quality is exemplified by Class A bipolar amplifiers, a fact which just struck me yesterday.

Class A bipolar amplifier are heating up to the maximum degree when carrying no signal.  When a signal is being amplified, the less-active devices on the negative side of any swing cool down ever so slightly while the signal becomes negative.  So rather than heating up with signal, they are cooling down, and therefore losing gain.  A Class A amplifier is, therefore, always falling slightly behind, and the feedback serves to give it the prod to keep it fully out there.

So now I'm thinking neither rendition is fully accurate, but the two different renditions, yin and yang, are complimentary.

Speakers, however, one might expect to be mostly yin, so a bit of extra yang from the amplifier makes it balance out.

AND that's what I think I hear, the Yang of the Eagle 2 is complementing the infamous Yin of the Acoustat 1+1 transformer coupled electrostatic speaker, together making the most musical sounds I have heard, perhaps not fully accurate, but very punchy, moreso than ever before, with rythm, pace, and transparency I never thought I'd hear without ribbon tweeting or direct coupled amplification.

Emergency Landing

With deep regrets, I decided to take down the Eagle 2 on Tuesday Night (4th of July).  It had shut down the first time on Monday night.  I had first played Bob Dylan's Blood on the Tracks LP at nearly maximum volume (Tact level 98.8) which was skating on thin ice because in principle some pop could come by (though this is a clean nearly new record and none did) and clip the DAC output at 2.5V, which is more than twice the rated power sensitivity of the Eagle (1.0V).  Because the Eagle has slightly more gain than the Krell FPB 300, I was actually playing this album more loudly than I ever had (it's hard to get vinyl cranked up on my system because the phono gain isn't quite high enough) and enjoying it immensely.  But lady luck shone brightly and the Eagle delivered a stirring performance, also with very well defined cymbals in roughly the same plane as Dylan (though, perhaps the drum kit should have been slightly more back, but it was already a bit behind the plane of the speakers.  A friend had asked me to make sure the cymbals didn't sound like white noise, and they didn't.  But on a few vocal and harmonica forte fortissimos, Dylan or his harmonica did come slightly in front of the plane of the speakers.  I am now thinking this was a distortion, possibly current limiting.

I was not so lucky playing The Doors first vinyl album, which I had purchased for the first time ever a few days earlier.  It was mastered louder and so I dialed back the level to 95.5.  But I could see from my currently unused tweeter crossover that there were a lot of spurious high frequencies on this album, moreso than typical SACD's.  But it never seemed like it was going too loud or anything, until it just quit, the Eagle 2 shut down, turning off the power light.  (I turned it off, then was pleased the amplifier came back on again when I tried 45 minutes later.)  After the fact, I noticed that the Peak Peak (as opposed to peak rms) digital level had reached -6dB, which would correspond to 1.25V output into the amp, just above clipping.  But amplifier usually shut down because of overcurrent, not just overvoltage, especially for so small an overvoltage.  The Peak RMS level was less -10dB.

Hoping to avoid that situation, I continued playing the amplifer into the next day.  But then, playing some Tangerine Dream, another shutdown occurred.  This time I had only reached a Peak Peak level of -10dB, which should be well below any kind of clipping.  Though it could be that this amplifier isn't capable of handling the Acoustats, I am thinking it is because it is old and needs service.  The second shutdown having occurred at significantly lower level, it's possible that some part(s) are now failing more each time.  This is a good reason to pull something out of the system and get it repaired before a more drastic failure occurs.

I put the Aragon 8008 BB back online, which has served more time playing the Acoustats than any other amp primarily because it has never shut down at all, let alone shut down in a progressively deteriorating fashion indicating the need for repair.  I've long felt the Aragon may have been somewhat lackluster compared with other amps, even the Parasound amps designed by Curl may be more electronically sophisticated, especially signature products like JC1.  But if indeed the Aragon is lacking in design refinement (and to be fair, the big name designers aren't always perfect either, and some are clearly stupid or worse) which I'm beginning to reconsider seeing its impeccable bench performance of the 8008 when new, it makes up anyway for in incredibly high quality construction.  The relatively simple and proven design probably is itself also a factor in reliability.  When it was sounding positively bad, I had attained a serious underbias (though 'normal' by later specs) by putting on tall feet...it is equisitely sensitive to tweaking like that...which I now think was a design intent to some degree, and I re-adjusted the bias for the taller feet, and everything is great now.  Anyway, it sounds OK after being warmed up, though the deeply caffinated and liquored magic is gone, I'm back on the ground floor.

Speaking of which, I should add that I've also become a bit suspicious of what the Eagle 2 is doing (when it is working correctly).  Somehow, it may be making things sound better than they actually are.  I'm not sure how that could be done, but I'm thinking along the lines of cancelling earlier IM distortion by only creating the reverse polarity of IM distortion, at least what little there is (rated at 0.0035%, which is higher than the THD at 0.0025%, and it's unusual for the IM to be higher than the THD, but both numbers are very small compared with typical ratings nowadays, when people seem to believe that good specs mean bad sound.

Anyway, I really don't know if it uses many stages of darlingtons like the Eagle 7, but that other design is further evidence of Iverson's use of the high feedback amplifier design concept.  I think he must have done that here, and it gives him super low distortion, super high damping factor, and because it is done correctly, super smooth and wonderful sound.  If he is also positively improving the sound somehow, that would be interesting to understand.  But I think it's almost certain to be a product of the basic design of the circuit, if maybe done with some intentionality, rather than a bolted on sonic coloration.  IIRC, Iverson knew lots of tricks and he may have pulled a few ones here.  I don't think it will get tiresome, it continued to draw me into to music I had previously found hard to listen to.

And that's the kind of thing I want to understand more.

But meanwhile I believe I want to refurb my now 3x Eagle 2's and get two of them converted to higher current mono operation for the Acoustats.  I'm going to ask if that would do it.  Whether or not the Eagle 2 is slightly altering the picture, and I suspect it is, it makes everything sound better, more worth listening to.  It might not be the amp to listen to all the time, but it is so much fun, I want to use it mostly, I think.

And get the Krell fixed too, as the next best alternative sonically, when it isn't the best.




















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