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).

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

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

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.)