Living Room System

Friday, November 25, 2016

Carver TFM amplifiers

I have my last chance to measure the Carver TFM-224 amplifier that I have been borrowing.

Just how does it sound like a tube amplifier?  (In my sighted testing, it sounded more like the Krell than a Parasound HCA-1500A.  In DBX testing, I couldn't reliably tell the difference.  Anyway, I believe Bob Carver was doing some trick here that I might be able to reliably tell in DBT eventually.)

Well, for one thing it appears to have rather low damping factor.  I'm seeing close to 9 across the audio spectrum.  Tube amplifiers often have a damping factor of about 8, and sometimes less.

Meanwhile, I'm not seeing significant variation in output vs frequency (and, actually, my I didn't re-measure the input, it's a long story but the impedance of the input matters a lot, and I chose the "high z" output mode of my Keithley 2015 analyzer, since the amplifier input is fairly high z.  So, you can't necessarily even believe the measured rolloff  (around 0.1dB at 20kHz, about 0.3dB at 20Hz, relative to 1kHz) since those could be generator errors, to some degree, but the generator errors would not likely be making the response look better.

BTW, Damping Factor is surprisingly easy to calculate, measure output voltage under load and then unloaded, and then: Df = Vl / (Vu - Vl).

20kHz
8 ohms: 2.6858v
unl.: 2.9806v
df: 9.1

1kHz
8 ohms: 2.7307v
unl.: 3.0343v
df: 9.0

20Hz
8ohms: 2.6608v
unl.: 2.9530v
df: 9.1

The damping factor is remarkably low for a transistor amplifier, and it is remarkably constant across the audio spectrum for any amplifier.  Usually amplifiers have lower damping factor at 20kHz, not slightly more.  But the low and constant damping factor is not the real limits of the amplifying circuitry, it is the dialed in characteristic, "fake" damping factor if you will, so it can be as constant as anything so long as it doesn't go higher than the "actual" damping factor the amplifying circuitry is capable of.



Thursday, November 17, 2016

Silver Cables, and Zobels

Here's a company that sells interesting silver wire, teflon jackets.

According to subjectivists, silver wire may sound bright, etc.  (or everything else dull, if you're a silver favoring subjectivists).

The objective truth is that silver is better (though, most objectivists would say not so much as to be important).  Copper is worse because copper oxide is a very nasty conductor (a semi-conductor actually) and it forms readily wherever there is exposure to air.  And even if this is just a thin film, that thin film is specially important because of skin effect.  But there is further oxidation even below the film.

However I wouldn't jump to weird geometries.  Well shielded coax is hard to beat for rejection of interference in interconnects.  It is way better than loose twisted pairs, even if those twisted pairs are shielded.  Given high RF nowadays, and notably in my own house, I would not use anything but the most well shielded coax.  And all my equipment is high bandwidth, making ultrasonic interference rejection especially important.

Tinned copper, silver plated copper, gold plated copper or vacuum annealed copper (what Cardas does, for example) are three ways of addressing the oxidation problem in wires.  While audiophiles may think they love bare copper, bare copper should never be used, including in wire assemblies.

My own practice doesn't approach this yet, I used to think bare copper was the way to go.

Back to the geometry, speaker cable can be twisted pair.  Actually it turns out, that RF rejection and RF impedance are issues, just going for the least inductance might not be the correct answer.  I'm beginning to think it isn't the answer for my Aragon 8008BB.  I'm planning to switch back to zip from star cross, I think the extra inductance may be good for this amp (which has no zobel at the output).

I've been reading about that too...some say zobel is always necessary and you can't hear the choke, while John Curl, and Naim Audio, say you can hear the choke and they don't use one.  An interesting take may be that if you don't use the zobel on the output, you are achieving the same effect by overcompensating the amplifier, which is worse.  Iverson seems to have always used the zobel, and I think it becomes extra critical in high feedback amplifiers.

Anyway, Naim assumed they didn't need the zobel because they were assuming people were using zip wire, as they universally were in the 70's, or wire with sufficient inductance to provide the zobel effect.  Later, when specialty cables didn't, Naim stepped in to make their own "audiophile grade" medium impedance wire.

Here "zobel" is actually being applied to other named type networks, such as Thiele (sp?).  But it's the same idea.

Likewise MIT cables put their zobel networks at the load end, which is suitable for correcting the cable itself.  Perhaps the zobel should be built-in to the speaker itself, or something plugged into the speaker.

Some people say the MIT networks aren't just zobels, they are effectively tone controls.

It's not clear how much tone control you can actually do...and that is very amplifier dependent too.

A month ago the John Curl debating thread ("Blowtorch Preamp" topic) was discussing current mode amplifiers.  Mainly this was driven by Richard Marsh, whose been deep into the topic.  John Curl and others were quite interested.  Some objectophiles say it's a nonsense idea, not real electrical engineering.  Amps, volts, and impedances are real things, but "current mode" is just a marketing term.  Such as used by Krell (not mentioned in the Blowtorch room).  But seeing Marsh and other pretty serious guys considering it seriously, I think it's more than just a marketing term, it has some kind of effects, for example high bandwidth becomes not a problem generally.




Friday, November 4, 2016

Amplifier Voicing

I've been beginning to think that there is indeed a basic subjective difference among amplifiers which was aptly described as Yin and Yang by Harry Pearson.

The Aria amplifiers designed by Michael Elliot (best known as the founder of Counterpoint who made many innovative tube audio products in the 1980's) are available in a upgraded XL version with custom voicing.  When you get the custom voicing option (which adds $1499 to the price) Michael Elliot comes to your home to do the voicing himself, by making small changes to 4 resistors which are initially matched to 0.1%.  He says:

By making subtle shifts in the operating points of devices in the amps, I can shift the "tonal center" of the sound upwards, to emphasize upper harmonics, speed, and transient impact, or downwards, to provide a rich, pure midrange with velvety soft highs. 

 I find this idea to be very interesting.  I do seem to be able to categorize my amplifiers as Yin (the dark, the receptive, the mother womb) and yang (the bright, the fire, the rising white light).

But while most (including Elliot) claim to make their default "neutral," I am thinking there may be no neutral, just a possibly smaller tilt one way or the other.  Neutral is a point so small you never land on it.

Another thing I agree with Michael, high input impedance is essential a line level (and good amplifiers).
On this page he says higher is always better, never accept a line input stage with impedance less than 50k.  He chooses 100k for his line stage, and a mind boggling 470k for the Whole Tone power amplifiers.  My intuition would be to go for 75k on both.  Power amp inputs are not in most cases higher than line preamp inputs.  In most cases, preamps are actually buffered attenuators, reducing level somewhat.  Thus the power amp should not have a higher impedance corresponding to higher input levels.  But his super high impedance on the power amp probably helps move the effective voicing from slightly dark (typical of tube amps) to neutral.

Here's a discussion of OTL amps, which features the designer of Atma Sphere amps describing many things.  Most of the alleged downsides of OTL are prejudice which followed just a few bad apples.  Just a few of the dozens of "totem pole" designs by Julius Futterman and others were unstable.  Most have been rock solid, and other manufacturers using the Circlotron circuit, like Atma Sphere, have no stability problems at all.  And with Atma Sphere there is no loop feedback at all, total "class a2" operation--with a tad of sliding bias. I'd be very interested in how well those work with my Acoustats.  The only downside for me is rather high price.  If I had the time, the optimal approach would be a direct drive tube amp like the one designed by a friend of mine.  I don't think the direct drive amp originally made by Acoustat was very good.

Wednesday, November 2, 2016

Marantz in the 1970's

Here's the finally updated AudioKarma thread on the giant Marantz factory in Chatsworth.  The background story is that after Superscope/Marantz opened this around 1976, they had spent so much money building it, and the market had fallen off since construction began, and costs in Japan had gone so far up, that they were broke and sold out to their foreign partners (a typical story in business, the Taj Mahal Building story).

Add to that my first personal story.  I had lusted after Marantz equipment ever since seeing a 20 in a store in 1970.  But I did ponder many alternatives before deciding what to get to replace my lousy and ill-functioning Dynaco SCA35.  I tried to have the SCA-35 repaired at a repair center on 30th Street in San Diego California in 1973.  The repair person did a bunch of things, but when I got back to my dorm room in Los Angeles, I had the same original problem--a frying noise.

I had talked to that erudite repair person about my choice in getting something new.  He wasn't inclined to see anything wrong with the SCA 35.  But anyway I proposed a Dynaco 120 plus a PAT-5, and a Marantz 2270.  His answer was that there "was no comparison."  I found this answer unilluminating and maddening.  Did he mean the Marantz was so much better?  Or that I shouldn't even be considering such choices?  He seemed to know more but be unwilling to say.  Maddening!

I though the Dynaco more reasonable for the money, but the Marantz seemed nicer somehow.  So when Pacific Stereo in Pomona dropped the price of 2270 to $399 in the summer of 1974, I couldn't resist any longer.  The frying-sound amp had one more chance at repair before becoming my sister's amplifier, but it failed that and was virtually donated when she got a nice reliable Kenwood amplifier that served her for 20 years and perhaps still.

At first, for a few weeks, I hated the 2270.  Among other things I found some of the controls a bit scratchy.  I took it back to pacific stereo for repair.  I got it back a week later identical.  Oh, well, I found after a few days the problem went away.  But also, all along, I was noticing a thin-ness compared to my SCA 35.  The SCA35 tube amplifier was giving me nice rounded out bass, whereas on the transistorized reciever the bass was all dried up.

By a couple months later, I had as much as forgotten that initial impression, and now it seemed, and decidedly so, the transistorized receiver had much tighter and more accurate bass.  Anyway, I was fine with the sound of the Marantz and the whole system I had (Dual 1209 turntable, large Advent speakers, Shure V15 III cartridge) for about 3 years before nagging doubts set in.  And for the first year, I felt like Big Man On Campus as people came and wanted to hear my system, I weirdly brought it all to the girlfriends house over christmas vacation, and so on.  By the second year, I was in the second tier, and so on.

Anyways, it was in the mid 1970's that I was hanging out with some friends of mine back in the San Fernando Valley, and one of them worked at G.A.S, which was located in Chatsworth (as was Electro Research, Quatre, and perhaps other small high end audio companies).  The first time we were driving past the Marantz building on Nordhoff (a street whose name is still familiar from my childhood in the Valley), it blew my mind there was such a big building which I had not remembered from my high school days.  I think I may have been told it was Marantz/Superscope, but that was so unbelievable to me then it didn't sink in.

A few years later when we drove by, I was told only that it was "nothing, anymore."  "What was it?"  "Nevermind."

I think only in 2009 or so I learned and it really stuck that the giant building we had been driving past was the Marantz/Superscope building from reading the beginning of this AudioKarma thread.  Although I knew Marantz had an "A line," whatever that was, and my 2270 was in the "B line", I just never imagined Marantz having such a large factory building in the USA.  Anyway, I was back in LA, and I wanted to drive past the building, but the photos on the AudioKarma thread had gone.  So I went driving around a bit, and saw nothing.  I did find the now mostly re-purposed Harman International campus.  It seemed only JBL had their original offices, other divisions had left and were replaced with marketing firms and the like, and available space.

Anyway, now the thread has been renewed, and the photographs restored later, and now we can see that the address is 20525 Nordhoff Avenue, which is also Nordhoff and Mason (another familiar sounding name), and the address is strangely close to my childhood street address in nearby Woodland Hills.  (Mason was the street at the western end of my childhood subdivision, I recall, the street that ran by the junior high I went to.)

Up until the Millenium, I had just not imagined Marantz being in my own back yard (or, actually, former back yard by then).  They were always in my imagination far away, and I still imagined Long Island City being central, though it hadn't been since 1964, the year Saul Marantz sold out to Superscope after the excess cost of developing and manufacturing the Model 10b tuner (and, also the newer manufacturing plant in Woodside?  I think there may have been a Taj Mahal factor rarely mentioned.).  Marantz headquarters and operations quickly moved out areas around Los Angeles, famously Sun Valley where Superscope was based, with the mass manufacturing moving to Japan, Standard Radio, the later owner of the Marantz name in Japan, until they changed their name to Marantz Japan in 1975.

OK, I did know enough by 1973 that Marantz was now Sun Valley but I figured that was just a distribution hub since manufacturing had moved to Japan.

Still it had seemed to me that Marantz was respectable right up to the time I bought one, by the summer of 1974, and by late 1975 they were possibly behind Sansui and Pioneer.  Real hifi was G.A.S. or Audio Research.  In fact, when I worked at a high end shop in San Diego in 1978-79, current production Marantz was lumped in with all the asian brands into something derogatorily called "mid fi."  No one mentioned (or even seemed to know about) the A line Marantz components made in USA (until the ending of Superscope, when the SM-1000 was actually built in Japan instead of back at the Superscope factory).

But I had sort of heard about the A line briefly, not enough to know anything about it really, and in a backhanded way, in the fall of 1975.

Hearing that I had bought a Marantz receiver, my then G.A.S. employed friend wanted to have an amplifier comparison.  This was in the fall of 1975.  So I brought my 2270 receiver, he brought his SAE clone, and there may have been something else, to somebody elses apartment.  I can't remember much about this except that I myself couldn't hear much, if any, differences between my 2270 and my friend's clone of the SAE Mk XXXI, designed by James Bongiorno.  But others didn't seem to find my receiver very acceptable.  Sonically I recall they criticized the bass, and the dynamics.  This was attributed to damping factor.  Then afterwards, the main thing I remember amazingly clearly (though I didn't understand most of it at the time) is a little bit of conversation:

Friend: "Do you mind if we take the cover off?"

Me: "No, go right ahead.  I did that the first day."

Friend takes the cover off of the Marantz, and some other guy takes a careful look.  (Was this other guy Andy Hefley?  That's likely, he was a good friend of my friend, though it could have been someone else from G.A.S.)

Friend: "Castor?"

Andy: "No, B Line."

Me: "What's a bee lion?"

Friend: "You wouldn't understand."

And so it went.  I didn't really understand the A and B lines until I read about it on The Vintage Knob or some other website decades later.  The A line was the Superscope-era Marantz line built in the USA, and the most famous designer of A line amplifiers during the 1970's was Mike Castor.  These were the likes of the 250 and 500 amplifiers.  The B line were the Japanese made products at lower prices, like the 22xx series receivers (at least most of them).

I didn't understand, but this was the beginning of the end of my honeymoon with my Marantz.  From then on, it wasn't the shining light, it was the slime I had mistakenly fallen for in my ignorance.  Audiophilia nervosa had started setting in.

Now I look on this whole situation a bit differently.  The then-infamous "B-Line" components were actually pretty good.  They were robustly built (as Marantz ads of the time liked to show) but not indestructable: I burned through one set of output transistors around 1979 and got them replaced.  But generally speaking these units were solidly built, with good transformers and decent circuits mostly.  I felt the phone preamp decent, the line preamp only adequate, and the tuner and power amplifier very good for an inexpensive receiver.  For quite awhile now the B Line components have enjoyed highly collectible status and often sell at prices higher than "high end" components from the same era.  People seem to feel better about them now than they did then.

Also I think what my friend and Andy and others were on to at the time was bogus.  There was this feeling that fully complementary circuitry as laid out by James Bongiorno was fundamentally way better.  Now many people have dumped the fully complimentary approach and have gone back to the quasi-complementary amplifier outputs used in the earliest B Line components.  Why?  Well with the wisdom of much time, it appears the quasi complementary outputs might actually work and sound better.  Or if not better, perhaps not enough different to worry about much.  And that was what I myself though I had heard in 1975.

But thinking back, something else is pretty clear too.  My high end audio friends were a bunch of snobs.  That may have rubbed off on me also, but I think I wasn't really much of a snob until I myself worked at a high end store in San Diego and learned the terms "mid fi" and so on.

(As far as quality construction, the very top Sony equipment starting with the F line like the 3200F amplifier and 5000F tuner, then the top ES models up until the last super CD players, such as the X779, are models of superb construction and, I believe mostly, longevity, etc, far surpassing my Marantz receiver.  The two earliest SACD players, the SCD-1 and SCD-777ES were overbuilt to the max, but I believe certain design problems led to them not having the same reliability as earlier units.  Since then, Sony and Pioneer (Sansui sadly no longer exists) aren't what they used to be.  While perhaps the SCD-5400ES player (is that still sold new?) was the best performing SACD player if not CD also, and CD about as good as Sony has ever done (I have a peculiar like of the 1 bit interpretation as opposed to the sigma delta, so I don't believe this, and I think the final X779 and 707ES may have been better for CD's), but they are not overbuilt in the same way as that now golden era of Sony products, perhaps 1966-1996.  As far as Woodside, the 20B tuner was a marvel, though not always appreciated, but a friend of mine had a Model 23 (?) receiver, the smallest one, and the FM tuner it had was terrible compared with my 2270 being perfect--then.  It was then that I no longer regretted, though I should have, getting one of those...they looked fancier and were made in USA, but Woodside models weren't available for long.  I'm not sure that any were any were even as good as their Japanese counterparts, except perhaps, the Model 19...oh oh boy did I lust over that for a year before finally deciding only to buy the 2270.)

Friday, October 28, 2016

Wizard on the Hill

John Iverson was the greatest story teller of all, but I've got my little story to tell about him.

A very geeky friend of mine was building DIY transistor amps in the early 1970's, I think he had his first one in 1973, while we were still in high school.  This was cutting edge stuff at the time.  His first was modeled after the least powerful SAE amplifier, designed by James Bongiorno.  He bragged about the leading design principles.  Bongiorno did become well known soon as one of the top audio designers.

By 1975 or so that friend was actually working for James Bongiorno, in the original G.A.S. factory in Van Nuys, CA, middle of the San Fernando Valley.  I was no longer living in The Valley, but had come by from Pomona College near San Bernardino.  My friend introduced me to James at that factory, who was busy wrapping up some piece of work.  The great James made some joke, I think he had already thought of the name Charlie the Tuner.


James: "How do you like your Tuner, Charlie?"

Me: "What?"

Friend: "Oh he's making a new tuner, called Charlie.  It's some kind of joke."

Me: "Oh, sounds cool.  I like good tuners.  I liked those ones with scopes.  But also that have good sensitivity."

Almost three decades later James would be arguing at me about tuners on the FMTuners group.

Anyways, that same friend left G.A.S. and lived with me during his first year at Cal Poly (and my second-to-last year at Pomona College).  And by that time he didn't think James was necessarily the very smartest designer, though he had done some good things.  The very smartest designer was John Iverson.  And that was not only his view before long.  Iverson quickly became famous for the A-75 amplifier, and rumors of the unique massless Force Field speaker which some people got to see.  Then, later, well known for the EK-1 strain gauge phono system, which got rave reviews but was not easily found or purchased.

*****

During my high school and college years when I was living in Los Angeles I sometimes dropped into Mel Schilling's Music and Sound store, which was just on the side of my neighborhood in Woodland Hills.  Little did I know Mel was or would be a parnter with Iverson (he certainly was by the last time I visted M&S in their larger store further down on Ventura Blvd).  It seemed to me all the interesting people and things were on the East Coast.  That's where I thought Marantz was (though they had moved to the Valley before I entered High School...and before I finished High School had moved to Chatsworth, just a few miles from where I lived).

So while I thought all hi fi production and cool people were on the East Coast, such as Marantz (I believed them to be in Long Island City or Woodside New York) in actuality, they had started moving to my home city of Los Angeles while I was till in elementary school.  While I was in college they opened one of the largest manufacturing buildings ever in Chatsworth California, not far from my childhood home of Woodland Hills.  Also in Chatsworth later were G.A.S. and Iverson's Electro Research (I had no clue where that was, once again I figured far away).

Iverson was the mythical wizard, my friend spoke of (sometime later telling me about the truly magical force field speakers, sometime later after they had already been dismantled, but I was scared to go near them anyway), and before long I was reading brochures about things like the amazing EK-1 and A75, they looked and read so cool, and reading praise of these things by J Peter Montcrieff in the International Audio Review.  Mentions may also have early occured in Stereophile if not The Absolute Sound.  Most of these review rags had said barely anything about Bongiorno, for example, who himself often claimed he virtually invented the modern transistor amplifier complimentary ("symmetry") circuit.  (BTW, a friend of mine and I and other seem to be thinking quasi complementary is still better anyway, for various reasons, even transistors today decades later aren't really complementary enough.)  But Iverson seemed to get lots of buzz.  But perhaps it was all because I visited Music and Sound and Mel Schilling was Iverson's partner.  I had no clue about any connection between Mel Shilling and Iverson.  I though Iverson lived on the east coast, where all good hi fi came from, I thought then.

Anyways, despite living near the Wizard for years, and haunting a few of his haunts, knowing some people he knew, I never met the Wizard while I lived in LA in the 1970's.

I met him in the beginning of the years of his decline, we all know now, his desperate national tour after after giving up the big factory on Empire Blvd. in Lake Havasu (the desperate tour did pan out fairly well, actually, and his boat was beginning to rise again before his biggest fall a couple years later).  All seemed fine to me (not paying close enough attention).  Iverson had come to speak at a meeting of the San Diego Audio Society, of which I had been "President" for a decade.  (I didn't actually do much more than print and mail the meeting announcement, after being told by a friend that Stereo Unlimited had scheduled a speaker.  No, we didn't use email or the internet in the 1980's.  I never had to round up speakers...they just appeared largely through the efforts of Bruce at Stereo Ulimited, or a friend of mine,...and they included many of the greats.)

It was one of the most memorable meetings.  I was almost...almost sold on getting an Eagle 2A right on the spot.  I can't remember what discouraged me.  Perhaps I thought an Eagle 7A would be even better.  I couldn't make up my mind because I felt I didn't need the power of the 7A but I would have loved the higher bias.  Of course I also liked the lower price of the Eagle 2, and people seemed to praise it more.  Anyways, I didn't buy anything, but I found Iverson to be the most charming speaker, and especially when he invited everyone in the end to an after-meeting dinner.  That may have been the only time that ever happened.  And it was the most fun part of all, while Iverson continued to tell one far out story after another, of which I sadly can't remember anything.

I liked Iverson a lot, I thought.  He wasn't the scold I had imagined (Bongiorno, for example, I would describe as prickly, for as much as I respected Bongiorno I could hardly avoid setting him into a rage of some kind by showing the tiniest questioning of his authority), instead Iverson was just a really cool guy you could say anything to and he'd have a great answer.  And that's probably part of why my friend thought he was the smartest also. But despite both my friends (my high school era friend and the one at the audio meeting in 1988) being Jewish, neither mentioned any trace of anti-Semitism.   Only now in 2016 I read about Iverson and hear him described as flaming bigot, anti-semite, and so on.  I never saw that myself, though I did hear the some of the libertarian right wing anarchist side in 1988 (it seemed to me then he wasn't nearly as far out as many), and it may have been that part which was central to his undoing (as one who strongly avoided paying taxes, for example, leading to increasing avoidance of and encroachment by authorities, I think that he would not contact the police when perhaps he actually needed police protection, as might well have been necessary in his final predicament).

Another friend of mine who was actually at this 1988 meeting wasn't so impressed.  He pointed out that he was apparently living in a motorhome with his wife and business manager and selling product out the back door, and consumed two bottles of whiskey during the meeting and dinner, and was clearly lying about a number of things and worst of all didn't understand my friend's own wisdom.

Following Iverson's stories, one might have imagined Iverson on top of the world, with his own private jet and so on.  I figured that was exaggeration, but I never imagined him on hard times.

Anyway, I'll concede to the frequent consensus he was a technical genius, sadly never one who reached his potential, and a life-work sadly ended at least partly due to a dark side of himself, and the cruel world itself, but I also think of him as a kind of maniac, who toiled with an extreme manic intensity to produce highly polished and perfected designs.  He was a child prodigy at transistor circuit design, and could get complex arrangements working just right.  I think he highly polished the designs he came up with, but not to say he found the best possible designs necessarily, it seems there is always an even better design because the design space keeps expanding.  But he did some things right that others have had a hard time duplicating, and it seems nobody has really duplicated or bettered the Iverson thing in an Audio poweramp.  It was a special and so far unique magic, that required a particularly manic design and construction, and required a somewhat maniacal designer.

Comparing his 7A to Ampzilla I realize that the use of servo loops, for example, isn't entirely optimal, though I consider it far better than the usual capacitor coupling (or worse, transformer coupling).

While servo loops isolate the capacitor a lot, it's still sloshing around and messing with the low and other frequencies, and it's no way to get to a "null" of amplifier vs source, for example, which I suspect Iverson was interested in, as many were up until the 90's.  Much better simply to have correctly and thermally balanced push pull, which Iverson always achieved by design, careful matching, hand assembly, and fine tuning.  Of course the best of all is intelligent designs, and some believe the most intelligent design makes adjustment unnecessary,  but I think there is usually a performance price to be paid for that, and if your goal is to reach the very best performance--a true null not just an approximation--you cannot rely on slowly approximating solutions.  Then if something needs to be right on, to reach the very peak, this may require adjustment.  (Now it seems recent designers like Nelson Pass have created circuits that are inherently balanced and don't need any adjustments.  I think that's part the progress of cleverness--in particuar Nelson has been very clever, and part the giving up on the pursuit of the nth degree of nulling, and part the luxury of huge available chassis dissipation made possible by ten to eighty times pricing, most often for far less available power.  Even with amplifiers weighing 10 times more Nelson claimed (until the recent .5 upgrade, followed by even better .8 upgrade) not to be interested in creating "arc welding amps."  So you might not be able to arc weld with a 300 pound amplifier, but the 30 pound amplifier from Iverson will arc weld all you want, and still not sound "transistory" with a smooth and wide open top and a warm middle.  A classic "transistory" Class AB hard, steely, cold, clinical soudning amplifier would never become the choice of J Gordon Holt ever.  So you get both the arc welding, and the refined sound, in the original $895 30 pound amp from Iverson.  In 1985.  A miracle!

I further speculate that Iverson may have been reaching for a particular possible design that gets you to null rather than just "good."  And that would be the upper end of the Baxandall optimal feedback.

Baxandall determined in 1960 that negative feedback doesn't actually reduce distortion overall unless applied in the correct amount.  Incorrect feedback actually increases distortion, though it often pushes distortion up to higher and higher harmonics, for example, so sometimes with limited bandwidth measurement miss this.

The correct feedback for the simplest transistor amplifier is either 4 db or less or very high, 30dB IIRC.  Most transistor amps err with feedback somewhere in between.  Some of the better ones use simple circuits and low feedback, but not necessarily low enough.  The 4 db would apply to a single transistor, with multiple transistors the optimal feedback would be even lower.  And on the high end, a more complicated amp might need even more feedback--if it could be applied.

Now you can go after the high end of optimal feedback.  But it's very hard because the open loop amplifier has to be very linear and very stable to handle such a high feedback level.  It takes very careful, even maniacal design.  And that's how I consider Iverson a kind of maniac over these details.  And stiff, probably regulated power supplies also.  And finally he obsessed over reducing propagation delay closer and closer to zero, which seems unnecessary to me, but certainly important in feedback amplifiers, and for achieving simple good nulling results.

The one thing I am sure about is that he obsessed over his design details.  And that's partly why his amplifiers are so widely regarded as best, to those who have spent some time with them.

A few other notable amplifiers are based on the high feedback method, including Halcro and Wolcott, very very expensive.  Even those wouldn't replace an Eagle 2 for many, since the Halcro lacked the low impedance drive (really doubling down to 2 ohms, and playing at even less) and the Wolcott was actually a tube amplifier, also certainly not a low impedance champ.

Iverson was creating his super high technical performance well regarded high end amplifiers, hand built in the USA, for peanuts, in the 1980's.  Earlier products under the Electro Research brand (originally started by Iverson and Schilling) were mind blowing expensive in their day, though by todays's standard extreme bargains as the high end icons they were and still are.

The Iverson Eagle 2 was highly praised in Stereophile mentions.  It was said to be much better sounding than nearly all transistor amplifiers, with excellent midrange, highs, and bass.  It had much cleaner and more enjoyable upper 3 octaves than the Eagle 7A.  It was the personal reference amplifier of the founder of Stereophile himself, the very respectable J Gordon Holt (curiously having the same middle name as Iverson)--a person who could have the best of transistors tubes or anything.

Enough!  I have finally bought an Eagle 2 this week, and will see how it compares.  If I like it, I will have it upgraded by Russel Sherwood.  My hope is that it doesn't have the usual Class AB transistor amplifier sound (though I've seen many offhand statements to that affect, always by non-owners, owners always describe it as far better than other transistor amps in midrange presence and high frequency smoothness).

One way or the other the wizard was lost, not long after I finally met him.  But the legend, and hopefully the amplifiers, live on.  (BTW, I wonder about the intended buyer for Iverson's special gun. If such a buyer was intending the gun for criminal activities anyway, why not one more?)

Class AB I believe has an inherent "bright" or "thin" sound once you get past the Class A portion.  Feedback, especially the low baxandall optimal feedback, can't entirely eliminate this.  But high feedback can, at least if you clean up the notch itself, and use reasonably high AB+ biasing, Class AB  with high feedback can duplicate Class A sound I believe.  But few designers push the feedback high enough.  I speculate that Iverson did, he pushed the open loop gain and feedback higher than anyone, and this gives his amp a peculiarly good sound.  He's not getting stuck in the middle feedback morass.

The Eagles also run pretty high bias.  The 7A has considerably more bias, but the 2A is better anyway I gather, and is simpler and more effective being non-bridged.  In fact I remember Iverson and company steering me to the Eagle 2, Iverson spent all his time demonstrating the 2, and then seemed to think that was the best for me.  I wanted a low power amp in the Eagle 7 case running higher bias, stubbornly, couldn't decide.

You can achieve very nice low distortion with low feedback with Class A, or at least Class AB+ in most cases, most of the time.

Here's interesting info on the EK-1.  I regret not snapping one up when I had the chance.  A friend wanted info on adjusting "phase compensator" controls.  According to this thread the Singapore factory did so with a square wave test record, according to one owner, who did the same and was happy with his.  This does not guarantee that this method was approved by Iverson.

What Iverson has designed in the EK-1 is clearly a pair of discrete op amps, with associated circuitry, to implement a strain gauge preamp.  Nothing all that magic, the question is how good are his discrete op amps?  One number I hear claimed was better than 125dB S/N with inputs shorted.

That's pretty good, and that was actually just a guestimate anyway, and I've heard the opposite claim that EK-1's are noisy, and that might be true in some circumstances.  It appears that the designers use of  a solid stainless case is not coincidental.  With the kind of power Iverson is running in those op amps, one might expect high RF succeptibility.  The stainless steel probably works in most cases, anyway, that's one explanation for claimed variability.  Another is states of misuse and disrepair.  And, of course there is always: people make stuff up.  So what to believe?  I'm pretty open to believing it works well for some, not so well for others.

Anyway, nowadays one wouldn't do this sort of thing.  One would simply use the best available chip op amp, which is still the OPA 211, which has a hybrid silicon germanium process.  It can't be beat with silicon transistors in terms of low noise, distortion, etc.  And then an ordinary machined aluminum case would do, and if executed well, it would work for anyone.

And one would apply the best available EQ, well understood, the reverse of the RIAA, flat from 500 Hz down and flat from 2122 Hz up.  Fine tuned to each cart, that's what Iverson did and it's still good.

So many shortchange things, like saying you don't need EQ with strain gauge cartridges, and get away with none, or a highly uncompensated response, bass heavy and all.

It becomes so common, it takes unusual strength of character to stand out sometimes and do things the right way.  Iverson had a lot more moxie to do things to the nth degree than most at the time.

I liked Iverson so much...he had that charisma that some people do...I wanted to join his circus kind of feeling...I could so easily get an Eagle 2 to replace my stupid frying-sound Citation II.

I remember the moment of feeling like Iverson and Munro were family, after having talked about the two Eagle amplifiers and which would be better for me.  Having easily given up on the very kindly sale due to my indecision, Munro asks if I'm bothered by Iverson after he walks out.  No, I say.  I feel afraid for him.  "Tell that to John," she says huskily, smiling, turning away with a cough.

But the feeling to buy an Eagle amplifier, which few Americans realized they had the chance to, passed.  I think shortly thereafter a friend pointed me to the same of an Amiga 2000 computer with all accessories.  I jumped on it, which led to endless friends and clubs still going on, through my "exotic computers" club.  So with all that going on, I forgot about the Iverson amplifier, and when I had money again to consider buying somthing, I didn't much believe in amplifier differences, and besides the HCA-1000A got good reviews, seemed to be designed well by John Curl, so I got one of those.

Now I wonder if it isn't at least fool around with the hypothetical idea that amplifiers do sound different, and what special magic Iverson achieved, which I even vaguely remember to this day.  The HCA-1000A is still good, the HCA-1500A better, but I think I like the Krell FPB 300 still better, what else is there?

*****

I also specifically remember feeling a bit worried about Iverson hearing him describe some of his exploits and anti-government feelings and the Audio Society meeting and afterwards.  I remember being very worried that this wasn't going to end well for him primarily, though sometimes he made me fear from the government also, that didn't worry me as much.  At this point I find it very hard to believe that Iverson lived much beyond the disappearance.  I think he desperately wanted to make a likely illegal sale in order to raise funds to free himself from debt, or to make a new expansion, in one way or another most likely to save his company and his career, just like DeLorean famously tried.  But Iverson's buyer was too unsavory, and prepared to just ambush him and rub him out.  The buyer wanted the gun for personal reasons...as a doomday style weapon at their own residence or venue, where they could let loose and kill lots of people, but not worry about all the lead in the next days.  Almost certainly a mobster type, American or not.  I think the real military could find someone else to make the gun if they wanted it.  Mobsters have to go with what they can find and trust.  And really really don't want anyone else to know or be able to buy or duplicate it.  Iverson was good, but his unique genius at such things has been often oversold, I believe.  He was just willing to go farther out on his own for audio amplifiers than most others.  And a few other things.

Iverson was a shining light, I don't think he could hide for so many years.  And I don't think he really was the James Bond he portrayed himself as.  He was son of a reclusive but curious TV repairman in LA, and a great story teller, and a brave man but possibly too brave in one instance.



*A friend speculates that Bongiorno and Iverson simply copied circuits from the semiconductor manuals.  That is precisely what Nelson Pass said was his training, at ESS he read the semiconductor book and thought about all the circuits they showed, something for every occasion.  Nowadays the deepest design is still done by semiconductor designers, the ones who design integrated circuits.  But this is indeed a brand new world of powerful design tools and so on.  Not a world of wiggling leads.  Iverson was the man for and of his time of discrete circuitry, for doing his kind of thing, making miracles.  As always it wasn't individual circuits but a particular combination of them set just right which made Iverson's amplifiers great, and most ultimately in the Eagle 2 series because it wasn't an overreach but the simplest Iverson.  Likewise Bongiorno, there may well have been some cleverness in his combinations, but I do find his audio work prior to the 21st century to be not quite as good.  (I suspect he did far better in his post-millenial products than before.  The original Ampzilla and others were clear and dynamic amplifiers but lacking the smoothness and midrange transparency of Iverson's amplifiers, starting from the jaw dropping A-75 if not before.  It was no random thing that Mel Shilling co-founded Electro Research with him...he was clearly the best.

Iverson was the golden boy, and widely recognized as such at the time, and he probably could have had the world if things had worked out better.

I remember the praise J Peter Montcrieff of The International Audio Review heaped on the Robertson 4010.  They invented a whole new kind of power, and found that the 4010, a relatively low powered amplifier, had 1,000 (or perhaps 10,000) watts of Moxie Power.  In contrast, some other 300W amplifier was found to only have 3W of Moxie Power.  This is related to the increase or decrease of power into lower impedances, I believe.

The Robertson audio products were made by the Singaporean firm named Robertson that had been signed up to build the EK-1.  At some point, Iverson and Shilling bailed, selling the firm to the Singaporeans.  (The TAS story lays much blame on Iverson's absolute insistence on a cast Stainless Steel chassis, and not being satisfied with the castings.  This dragged out the introduction of the product for a long spell and jacked up the cost.)

It is not clear to this day whether the Robertson 4010 was actually designed by Iverson and obtained legally in the sale of the company, ripped off from Iverson by Robertson (as some have suggested), or a similar amplifier created using only the ideas of Iverson, whatever they actually were, as told to or figured out by the Singaporeans in the course of their interactions with Iverson.  In one way or the other the 4010 is an Iverson-like amplifier, the Moxie Power being found in all the others, probably better in the real, fully credited Iverson amplifiers.  The Eagle amplifiers were made under Iverson's supervision in one of his USA factories, the largest and most famous one being the 10,000 sq foot facility at Empire Drive, the final one being just a small building near his house.

(I called Iverson the Wizard on the Hill because in the Lake Havasu subdivision where he lived, which wasn't necessarily over opulent, he nevertheless had a somewhat unusual lot that had a small hill that the house was perched atop.  Such goodness for an audio guy.  I have the similar fortune of having a large setback to my house, and no nearby house having facing windows.  This makes for being able to be playing music at reasonable levels without anyone nearby even noticing.  A hill would be even better, and Iverson would have needed that.  Back in The Valley days he may have lived on a hill as I did and as did many people.  And then also, it just sounded good.)

Friday, October 21, 2016

Aragon Preamp

Recently I've been using the Aragon preamp merely as a source selector, just using the unbuffered tape outputs, with no AC power being provided to the unit.  However, looking at the schematic, there are 2k output resistors to the tape outputs so it's not 100% transparent.  With my low cap cables that likely makes a negligible difference, but when convenient I'm going to bypass those resistors.

I prefer the Aragon preamp as source selector to the DB Systems selector simply because the Aragon is a big heavy box which doesn't move when you turn the knob.  It also looks very cool, is very heavy, and has wonderful chassis mounted jacks.  I wouldn't say that it sounds any better than the DB Systems selector though.  I thought them about the same, but the 2k resistors would darken it somewhat.

I'd always thought the Aragon 28k preamp to have a slightly "dark" sound through the main outputs also when I was using them--though they seemed to measure as perfectly as anything.  Well now I see that a darkened sound might compliment the Aragon 8008BB power amp, which I'm finding (now) to have a (somewhat excessive) brassy top end.  I'm going to be examining the Aragon and other amplifiers technically this weekend, following a week of A/B/X testing last week.  I did not reliably hear differences according to a simple ABX test, but I still strongly believe the differences I hear anyway.  The basic differences are that the Krell is the best sounding and has sweet and entirely unagressive highs, next the Carver TFM-24 which was designed to sound like a tube amp, next the Parasound HCA-1500A which was slightly brighter than the Krell but very transparent--perhaps the most transparent, and the Aragon which is sounding transparent but harsh at times.  Kudos to John Atkinson, still one of my favorite audio reviewers though I often criticize him, who admitted recently he hadn't heard a difference in an ABX test.

A great test disc is the Tchaikovsky Pathetique on RCA Living Stereo hybrid CD.  Just after 10 minutes into track one, there are some biting violin riffs that can be positively strident with some amplifiers.  It sounds more or less OK on Koss ESP-950 electrostatic headphones, which produce the most  transparent and accurate sound I have.

I'm not sure if I like the Aragon preamp circuit at all, but it's apparently the same as in Aurum preamps (in Aurum they use 2 per channel because it's a balanced preamp).  It looks like a miniature power amplifier all bipolar with feedback and adjusted bias.

Here's a discussion on modifying the Aragon Aurum preamp.  It includes a crucial section on how to do the bias adjustment on all Aragon preamps.

I've been thinking of modding mine in a few ways, adding balanced inputs and outputs and making the selector deal with that.  The balanced outputs would be pseudo-balanced with ground as the negative.

That would allow me to hook up balanced device(s) and run balanced to Lavry ADC, rather than doing an unbalanced conversion right at the Lavry input jacks with adapters.  Then I could insert the ABX test box and since it would have balanced inputs and outputs there would be minimal degradation.

It would also allow me to have a polarity reverse switch on the Aragon (or the ABX).

But it would have been better with the balanced already designed in.

I would use the line amplifier only when doing gain adjustments on devices for ABX comparison.  Otherwise I'd just use the unamplified tape selector.

But doing that kind of modification, I almost might just as well get a fresh chassis, and indeed I've been looking at the many interesting clone preamp chassis on ebay.


Thursday, October 20, 2016

Hacking I'd like to do

Here's a start to hacking the Sonos API.

I'd be more interested in hacking my Tact RCS 2.0 digital preamps.  Most of the "hacking Tact" groups are really about audiophile mods and don't sound interesting to me as I simply use digital inputs and outputs.  What I'd like to do is bypass the system so that I can set parametric EQ's without having to select a room correction (I don't actually use the room correction feature).  And more conveniently change system polarity with one button press.  And so on.  Making it more useful to me bit by bit.  Maybe add tone controls, something more like Cello Audio Pallete.  Mark Levinson's latest company has a software Pallete but it requires a computer.