Widescreen Review Interview #1 with Morris Kessler

$5.99 US $7.99 CanadaVolume 23, Number 3

Issue 185, March 2014www.WidescreenReview.com

WIDES

CREEN

REV

IEW®

WWW.W

IDES

CREENR

EVIEW

.COM

VOLU

ME23, N

UMBER

3, ISSUE185, M

ARCH2014

This is the second On Screen interviewwith the creative electronics designers atAudio Technologies Inc. (ATI), who alsodesign and manufacture Theta Digital prod-ucts. The first On Screen interview appearedin Issue 184, February 2014 with FounderMorris Kessler, Design Engineer DavidReich, and Marketing Director Jeff Hipps. Gary Reber, Widescreen Review: I’mhere at ATI, Amplifier Technologies, Inc. withMorris Kessler, who’s the founder, and DaveReich and Jeff Hipps, sitting together in thecompany’s intimate sound room. The subjectof this interview is the leading-edge designwork of founder Morris Kessler. What caughtmy eye recently is a communiqué I receivedfrom Jeff Hipps, and it had as part of the ATIlogo the phrase “American Muscle.” Ithought that was great description of ATI.Why did you choose that phrase? Jeff Hipps: I had just started with Morris.It was my third day working for him after hav-ing run a high-volume receiver company inthe U.S. for 15 years. I was in our suite atCES unpacking these mammoth things thathe builds. I finally get everything unpacked,and I open up the banner for ATI that we'regoing to use to talk about his company, andunder the picture of this huge, 130-pound,seven-channel amplifier, it said “TranslatingTechnology.” In my mind I said, “This isn'tabout technology, this is American Iron.”And as I thought about that phrase, I reallyliked the way it described what we did, but Ithought, “No, ‘American Iron’ is really toospecific. This is ‘American Muscle;’ this is theskill to build it; this is the know how to do it;this is the ability to design it; this is our ulti-mate product.” “American Muscle” perfectlycomplements what we do and is now ourmarketing slogan for Amplifier Technologies. WSR Reber: That's great. I like it. I thinkyou should stick with it. Morris, when youand I were growing up, it was an age of vac-uum tube amplification—mono amplifiersand the first stereo amplifiers. I built Eicoand Dynaco kits and I built Heath kits when Iwas a kid, so it's interesting to me that priorto founding ATI, your first amplifier was amodular solid-state design, and in 1967 youco-founded SAE. So, why solid-state?

Morris Kessler: Well, first of all, I didbuild tube amplifiers. In the old days allDynaco kits were tubes. Anyway, I've alwaysplayed with electronics, or electricity, if youwill, and I had a semi-relative who wanted toput one of those new-fangled stereo systemsin his house in 1959. So he grabbed me, Iwas 14 at the time, almost 15, and we wentdown to Melrose Avenue in LA, which wasHi-Fi row at the time. There were maybe fiveor six hi-fi stores within four or five blocks,and we ended up at Hi Fi Corner. He pur-chased this tremendous stereo system forabout $800, with a Fisher receiver, a Garrardturntable, and a bunch of JBL loudspeakersto be built into the walls and ceilings. Thenhe says to the owner of the store, “Mynephew here needs a summer job when hegraduates from Junior High.” And of coursethe owner said, “Sure, no problem.” I wasecstatic. This was in March of 1959, and Iwent and I put this stereo system in his newhouse. And the first day after graduation—Igraduated on Friday—and on Saturdaymorning I went down to Hi Fi Corner andwalked into the store and said, “Here I amready to go to work.” And the owner said,basically, “Who the hell are you? I don’tremember you.” “Don’t you remember? I washere three months ago with so and so, andyou said you'd give me a summer job.” He

said, “Oh, okay.” And my very first job in hi-fiwas bagging records. In those days most hi-fi stores had a little record department. Andthe records were not sealed. That wasbefore they figured out that they better sealthem because people would take them outand swap them around. Hi Fi Corner had their own hot-wire bag-ging machine. So my first day in audio wasputting records in plastic bags. I workedthere after school and summers for severalyears. Solid State was just starting to comearound and most solid-state designs usedgermanium transistors—the first Fisherreceivers, the first Scott receivers were allgermanium. They sounded terrible and theywere even less reliable than the way theysounded. Then a couple, three guys inMassachusetts from MIT led by Morley Kahnstarted a company called Acoustech. Do youremember Acoustech? I’m not sure you dobecause they lasted from 1960 throughmaybe ’63 or ’64. Acoustech was the firstcompany that I know of that actually madeamplifiers with silicon transistors. The firsthigh-quality, reasonable-cost silicon powertransistor was an RCA 3055. So they startedmaking amplifiers. They actually made a setof powered electrostatic loudspeakers, likethe KLH9's, except with the amplifier built in.

“American Muscle”Amplifier Technologies IncorporatedGary Reber

Morris Kessler with first SAE amplifier and newest Series 6000 module under arm

Widescreen Review • Issue 185 • March 201446 1/7

Hi Fi Corner started selling Acoustech ampli-fiers and I just loved them. They were thefirst solid-state amplifier that actually couldgive a tube amplifier a run for its money. Butthey also weren't all that reliable. I was sell-ing audio at this point, and I would sell anAcoustech amplifier to someone, and I feltreally bad when the amp failed so I startedlearning how to fix them. I started seeing theweaknesses in the amplifier and beefedthem up so the fault wouldn't happen again.Pretty soon I knew how the amp ticked. Andby 1962 I decided, I'm going to build myown amplifier from scratch, and that's theunit you see up front. I basically said, I'm notgoing to build a kit, or someone else’sdesign, I'm going to design and build myown amplifier. After I built that amplifier, Ibuilt a few of the handmade, one-off kind ofthings and improved them slightly, extendingwhat Acoustech had done. So that firstamplifier you see there is built basically withmilitary surplus parts. It’s all hand-wired, withboards that actually plug in. WSR Reber: What a classic. Kessler: That amplifier is 50 years old, 51years old. It’s crazy when I think about itbecause I remember building it. WSR Reber: How many watts does thatput out? Kessler: It depends on what day of theweek it is. It's roughly about 20, 25, in that

range. It was a single power supply with out-put coupling capacitors, which is what yousee on the bottom. That was the main filter ontop and on the bottom were the two couplingcapacitors, a pair of 3055’s. Actually, this unitwas built before the 3055 existed, and it wasa computer—some of the transistors have beenreplaced because they've blown up over theyears, when I was actually using it. But that’sa silicon stereo power amplifier. Anyway, thisis the very first one, and then I started build-ing a few with hand-built circuit boardswhere I actually hand-taped and etched thecircuit boards—you know etch your own cir-cuit boards in a chemical bath and then drillthe holes for the pads...it's crazy. I worked at Hi Fi Corner till 1964—thatstore closed, the owner died and we starteda new store in Beverly Hills called The SoundCenter. Did you know The Sound Center inBeverly Hills? WSR Reber: I don’t remember that one. Iused to frequent Jonas Miller’s. Kessler: Jonas Miller on Wilshire. WSR Reber: Yeah. Dave Reich: That's where Neil Sinclair[Theta Digital] got his start, by the way. WSR Reber: Yeah, it was, that's right.And Ken Kreisel. Ken and Jonas foundedM&K. I became friends with Ken. Kessler: Well, the M in M&K was Miller.Sound Center was actually not far from

Jonas Miller on South Beverly Drive, and itwas there for 20 years, from 1965 to 1985. Ihad to make a living and making and sellinga handful of amplifiers wasn't a living so Iwent with both of the other guys from Hi FiCorner to The Sound Center. I worked thereselling and I started building amplifiers andselling them to a few of our customers on theside. Those customers went to differentstores and mentioned the amplifier. Thenone day I got calls from Henry Radio andHigh-Fidelity House. Did you know High-Fidelity House in Pasadena? WSR Reber: Yeah. Kessler: High-Fidelity House was the high-end audio store in Southern California, peri-od. They had heard about my amplifiers andwanted to offer them and I said, “Well, theydon’t really exist as a commercial product.” But there was a customer at The SoundCenter—I didn’t have the money to found acompany, I was barely paying my apartmentrent. Anyway, there was a customer at TheSound Center who said, “If I put in themoney and you put in the products and thedesigns, we could start a company.” And westarted SAE. We had three dealers: TheSound Center in Beverly Hills; Henry Radio,which actually had two stores; and High-Fidelity House. Soon we were selling ampli-fiers in some quantity, and we were gettingsomewhat of a name.

Morris Kessler's first solid-state amplifier featured modular design.

Widescreen Review • Issue 185 • March 201448 2/7

The next thing we had to do, of course,was create a preamp because you can't justhave an amplifier by itself. We started doingthat and then the financial partner startedfading away as far as participating. I wasable to borrow some money and buy himout. After that, SAE grew quite substantially,and by the late '70s, early '80s, it was one ofthe largest high-end brands in the world. Wewere consistently rated one, two, or three inthe hi-fi magazines’ product rankings. And Ihad a lot of interesting engineers whoworked for SAE over that period of time. The third product that we had to have, ofcourse, was an FM tuner. And I had all theseideas—the Marantz 10B had just come out,which was a beautiful machine––and was alltube. Obviously, I wanted to have a solid-state tuner. Our distributor at the time wasalso the distributor for Sherwood, andSherwood's chief engineer, Ed Miller, wasthe expert, in my opinion, of FM radio at thetime. Our international distributor recom-mended that I talk to him about doing an FMtuner. I had this great idea that I first saw inan elevator, I saw these things called Nixietubes, and they were reading out the eleva-tor floors as you went up and down. And Isaid, “Could we put these on the front of aradio and actually read the frequency?” AndI had a couple of conversations with EdMiller before he finally came back and saidthat he wasn’t interested in helping me withan FM tuner. That was 1969. So I sort of for-got about it for a while, and then I found outfrom our distributor that Ed Miller sold hisinterest in Sherwood and was moving to LA.And I said, “Oh, wow, I’ll call him again andsee if he's interested.” And I called himagain and said, “I have all these ideas thatwe've talked about in the tuner project”—lit-tle known to me, though, that Sherwood hadactually started designing a Nixie tube FMtuner, and I’m sure it was based on my origi-nal conversation with Ed. Be that what itmay, Ed Miller turned me down againbecause he was semi-retiring to SouthernCalifornia and had purchased a car wash, ofall things. Anyway, a few weeks later hechanged his mind and he decided to comework with me on an FM tuner and we createdthe SA Mark VI tuner, which really was thefirst digital read-out FM tuner in the world—even though Sherwood claims they werefirst, but their tuner came out later, sixmonths to a year later than the SAE. Weactually beat it. Ed Miller had figured outhow to make a frequency counter read theactual frequency. It's actually pretty simple,but it took someone like him to figure it out. So we had the VI and the VI B FM tunerand we had a preamp and we had an ampli-fier. And from there SAE really started to takeoff and created quite a name for itself. Ed

Miller worked for me. He actually was thehead engineer for several years. And then in1973 he came to me and said he was get-ting older, “I’m going to retire again, but I’mnot going to leave you in the lurch. I’ve foundan engineer to replace me.” “Okay, who isit?” “It's James Bongiorno.” Do you knowJames? So in 1973 I hired Jim Bongiorno tobe our head engineer and Ed Miller, ofcourse, changed his mind again and decid-ed to stay, so I had two head engineers,which actually worked out pretty well at thetime because Jim was mostly an amplifierperson and Ed was more of an RF-type per-son, although Ed knew a lot about amplifiersalso. Between the two of them and what Ithrew into the mix, we created a lot of niceequipment. Jim broke off and started his own compa-ny called Great American Sound and wenton his way and I went on my way. SAE grew,and in the late ’70s, early ’80s, had quite a highmarket share. We built a new factory on a pieceof property we owned in downtown LA thatthe city of Los Angeles later forced us to sellvia “eminent domain” for the subway. Thatkind of turned the whole company upsidedown and I decided to sell the company toGiorgio Moroder. Do you know who he is? WSR Reber: Yep. Kessler: Giorgio Moroder at that timewas flying high with disco music and DonnaSummer and making 30, 40, 50-million dol-lars a year and was using SAE equipment. Ihad a lawyer friend who had done somework for him and he said, “Moroder wouldlove to buy your company.” And I said, “Well,he doesn’t know anything about it but he'swelcome to buy it if he wants it.” It was kindof ironic because the owner of Sherwood atthat time was a Korean company calledInkel. They also wanted to buy SAE but theywere doing it the typical Korean way, whichmeans dragging it out and wearing you

down, and Moroder just said, “Tell me howmuch and I’ll write a check.” So we told himhow much and he wrote a check and Inkelsaid, “What happened?” But anyway,Moroder bought the company really on awhim and owned it for about 10 months andthen he sold it to Drew Kaplan at DAK. Doyou remember the DAK catalog company? WSR Reber: Yeah. Kessler: DAK could have beenAmazon.com if they hadn't screwed up. DAKowned about 25 different brands but wastaken over by their bank. Nine years later Iwas able to buy the SAE name back. It’skind of ironic. It's not often you get a chanceto buy your own company back. And I waskind of retired during that period, after I soldSAE, which was 1989, till about 1993. A draftsman that worked for me at SAEcontacted me one day and he told me aboutthis new Apple computer system and howyou can design things on it. It even had arudimentary CAD program, and all this kindof stuff. I said, “That’s nice.” And I went outone Saturday to visit him and he showed methis big monitor that you couldn't even liftand a Mac 3C, or something like that, whichwas their higher-end Mac, and how versatileit was. Using it you could lay out circuitboards and do mechanical drawings all byyourself, you didn't need to sit there with apencil and paper. And I said, “Wow, that’spretty cool.” So I went out and I spent about$8,000 and bought a whole Mac system, andI really didn't have any real idea what I wasgoing to do with it, but I started playing withit, which obviously millions of people did,learning how to use a desktop computer. Icame to the realization that the only thing Iknow how to design are amplifiers. So Idecided to design an amplifier completely ona Mac computer, from one end to the other,the circuit boards, the artwork, everything.And I did this, and I built a two-channel

WidescreenReview.com • Issue 185 • March 20143/7 49

amplifier with bits and pieces, and I builtabout 10 of them in 1993. It was a nice amp with good specs and300 watts per channel. I took it to CES inJanuary of '93 actually. And I got a room atthe Hilton Hotel and sort of walked aroundthe show and basically said, “Come see myamplifier” to anybody that would listen to me.I even had a brand name—ATI—AmplifierTechnologies. I invited a few people up tothe hotel room to see this amplifier and soon, and one of the people was NewtonChanin, the head of Adcom. Did you knowNewt Chanin? WSR Reber: No. Kessler: Newt had been a well-knownsales rep on the east coast. His company,Audio Associates, still exists but with differ-ent ownership, and he owned Adcom. So Ishowed Newt and his Adcom associates theamplifier I had designed. Adcom was a goodbrand name but was never really a manufac-turer, everything they had was made forthem, and they looked at this amplifier andsaid, “Very nice, but if you want to makeamplifiers, why don’t you make an amplifierfor us? Then from the get-go you could bemaking hundreds or even thousands ofthem.” So they offered a way to hit theground running, as they say. Instead of try-ing to make five amplifiers and find five cus-tomers, which could take six months, I couldbe building hundreds, if not thousands ofamplifiers from the beginning. But they said to me, you know, you’vebeen gone from the audio industry aboutfour years, and something was just startingto happen. They said they didn’t want astereo amplifier, they wanted a five-channelamplifier for surround sound. I said,“Surround sound? What’s surround sound?You mean, there's more than two loudspeak-ers in a room and you need more than twochannels?” I guess up to that time therewere no five-channel amplifiers. There werea few three-channels that people were mak-ing to put with an existing two-channel ampto create a five-channel system. But peoplewanted it all in one box. One thing about amplifiers that's kind ofinteresting—it’s why people like monoblocks. When you start putting multiple chan-nels in one box, they start to talk to eachother. They start to interfere with each other.One channel can cause noise in anotherchannel. Obviously, crosstalk is an issue. Ina stereo amplifier it's not too bad. You putone channel way over on the left and theother way over on the right and you put aslarge a gap as possible between them. Sowhen they told me they wanted five chan-nels, I put five channels in an amplifier and itwas a disaster. They were all talking to eachother. They were all making noises to each

other. They were all buzzing differently, andif you turned one channel on, another onebuzzed. And if you turned that one off thenext one buzzed. I learned that you just can'ttake channels and put them right on top ofone another. The first amplifier I did for Adcom, whichas far as I know was the world's first five-channel, all-in-one chassis, was the GFA-6000. It was, by our standards, wildly suc-cessful. We made a couple of thousand ayear for several years. And it performedokay. I got the inter-channel chatter down soit was at least acceptable but I started tryingto figure out how can I make an amplifierchannel that wouldn't talk to, or at least mini-mize the amount of talk to other channels.And I basically came up with an all-in-onesolution, where the power supply and all ofthe amplifier circuitry is on a single circuitboard. Essentially there are no wires.,Everything is on one board so it's all pre-dictable. This (holding an amplifier channel),is an extreme version because this is a fullybalanced channel, but the original versionwas a simplified version of this. Once yougot it like this and you put one channel rightnext to it and you figured out the pattern ofthe circuitry so it wouldn't talk to, or at leastminimized the crosstalk and cross interfer-ence, I was able to start getting five andseven and all the way up to 16 channels inone box, which I did for Crestron, with virtu-ally little or no crosstalk or cross distortion orcross noise. And that was the trick of gettingmultiple-channel amplifiers built. WSR Reber: So the Adcom was the firstone. Kessler: The Adcom 6000 was the firstfive-channel amplifier and the first one thatATI as a company built before it built any ofits own amplifiers. WSR Reber: Did you build the Crestronnext? Kessler: Crestron was later. WSR Reber: After ATI had already intro-duced its own line. Kessler: Yes, what happened with myarrangement with Adcom was, okay, obvi-ously I want to do this amplifier for you butI’m not killing ATI. In other words, once weget that established. So the Adcom 6000was actually the first product that ATI built.And then, of course, they wanted me to doother amplifiers, with one caveat. They want-ed Nelson Pass to design them. And I said,“Okay.” Nelson Pass is into Mosfets and Fetsand very simple circuitry. That part was nice,very simple, straightforward circuitry, notover-designed. The problem with NelsonPass' designs, if you want to call it a prob-lem, first of all I got all the schematics on anapkin. It was very informal, number one.And the other thing is that his stuff, as good

as it is, it’s quite good, but it’s really notdesigned for mass manufacturing. You haveto sit there and tweak each one, not dissimi-larly from the Theta. One of the things, just backtracking a littlebit, when you're going to build multichannelamplifiers with five and seven and 16 chan-nels, you can't sit there and tweak them all.They all have to be basically put togetherwith minimal or zero adjustments and turnthem on and they're all perfect. You can turnour current designs on one after another, justadjust the bias real quickly and you're done,and everything else is stable, perfectly sta-ble. You have to resolve that because youjust can't make that many channels and sitthere and play with them, as we do withTheta. It doesn’t make it a better or worseamplifier, it just makes it more viable for pro-duction. For a simple number, we built over560,000 channels of the Crestron amplifier.At that volume, they can’t be hand-built. So the combination of resolving the inter-ference from channels and being able tocreate channels that are as close to perfectas possible without having to play with them,and that's gotten to a point of sophisticationwith this latest version. WSR Reber: I want to go back to what Iconsider a very important question, what youdidn't address. Why solid-state over tube? Kessler: Well that's a good question, Iguess. The obvious thing is you certainlycouldn't make a 16-channel tube amplifier. Jeff Hipps: It would be the size of thisroom, number one, and efficiency wise... WSR Reber: I was thinking in terms ofperformance quality and fidelity. Is there adifference? Kessler: Oh, there's a tremendous differ-ence. You can get much lower tested distor-tion—measured distortion—on a distortionanalyzer, out of a solid-state amplifier. Tubeshave reached their limit. They're not going toget any better. The interesting thing abouttubes is that their distortion is highly even-order harmonic distortion. That's why a lot ofpeople like tubes because they're very warmsounding. Well, warm sounding means thatthey have a lot of harmonics, even-order har-monics. Every instrument, every room, every-thing, a piano or a violin, the harmonics arepart of the instrument. The question is, doyou want to add more than the instrument?Some people like that and that's fine, wherea tube amplifier actually takes the instrumentand makes it even more melodic, if you will.So a lot of people didn't like solid-state ampli-fiers from the beginning because they sound-ed too real, which is kind of a weird state-ment. And of course, the solid-state ampli-fiers have come a long way, where they neednot have the harshness and distortion thatyou relate to early transistors and amplifiers.

Widescreen Review • Issue 185 • March 201450 4/7

I mean that thing (pointing to his firstamplifier) played music, the old one sittingthere, but it certainly wasn't a great-soundingamplifier. It took awhile for solid-state ampli-fiers to really surpass tubes; there was anoverlap. A good tube amplifier sounded bet-ter than a bad solid-state amplifier.Amplifiers were actually pretty bad throughabout the mid ’70s, when we discovered howto use feedback properly, and also that feed-back could cause sonic distortions that peo-ple didn't like if used improperly. Then someengineers came up with this great idea that iffeedback can cause a distortion that peopledon't like, we’ll just get rid of feedback, sothey created a new distortion. That’s a wholelong... WSR Reber: Before we go in that direc-tion I want to come back to one other thingto close the loop. So we have Adcom andwe have Crestron, but ATI has built numer-ous amplifiers for other OEM clients. Whatare some of those clients? Kessler: Well, some I can mention, somethat I shouldn’t mention. The latest one, ofcourse, is Datasat. We build their amplifiers.They were built to be the cream of the crop,they're very, very good. We have built a lot ofamplifiers for Crestron, their whole audio linewas developed by us for about 12 or 13years. WSR Reber: Morris, are these amplifierdesigns your designs or collaborativedesigns, or designs by other people? Kessler: Going back to ’73, JimBongiorno, when he started working for me,introduced me to complimentary power tran-sistors from Motorola, dual differential inputs,all kinds of circuitry ideas. He was very cre-ative from that standpoint, no question. A lotof those ideas, if not most of his ideas, weredeveloped at SAE. And when he left... Hipps: If he developed it while he workedfor you, then by law they were yours. Kessler: Well, they were more than oursbecause we were building his designs, basi-cally, at that time. After he left I spent a lot oftime evolving those designs and provingthem and making them better. Transistorswere changing. To this day, semi-conductorschange. That's a whole other story too. Sothe basic modern...when we went from thatkind of single-ended amplifier to the fully bal-anced, the fully differential that was done inthe early ’70s, to the mid ’70s, at SAE. Andthen it's just evolved from there. Circuitryimproves with components that becomeavailable. The protection circuits are somuch better than they were. You have tohave protection circuitry, otherwise you canblow the amplifier up. The ones we use noware all optically coupled so the protectioncannot interfere with the sound. WSR Reber: A basic question; what is an

amplifier and its function in audio reproduction. Kessler: Well, simply, the amplifier is theengine. It drives the loudspeaker. Everythingbefore the amplifiers is all low-level, low-sig-nal, very weak voltages. To drive a loud-speaker, which is essentially an electricmotor, you need, depending on the size ofthe loudspeaker, you need a certain amountof high current and high voltage and combi-nations of the two. The amplifier takes thatweak signal, a power amplifier we're talkingabout, takes the very weak signal from thepreamp and it amplifies it both in gain tosome extent. It doesn't have to, but you needsome gain, usually around 20 to 30 dB, andalso has a zero-gain power stage, and that'sthe key to driving a loudspeaker because aloudspeaker's the one thing that's totally dif-ferent from an electric motor. In an electricmotor you turn it on and it runs at one speedand it just sort of stays there. A loudspeakeris running at, from a slow speed to a highspeed, at 20 to 20,000 different frequenciesinstead of just a 60-cycle electric motor. Soit's a lot harder to drive a loudspeaker than anormal motor, if you will. So the amplifieraffects that tremendously based on its capa-bilities to drive that loudspeaker. I’ve workedvery hard to have an output stage and powersupply that can deliver the current deliveredinto low impedances, delivered continuously,and I think the ATI amplifiers that we buildfor ourselves and obviously other customersdo that better than any other amplifieraround, as far as driving difficult loads. Sothat’s the key and that's what an amplifierdoes. WSR Reber: One of the major things thatseparate the many power amplifier designsis the class type. What are your views on themost accurate class type? There's A, there'sAB, there’s D. Kessler: And then there are a few made-up ones.

WSR Reber: Yeah, H or... Kessler: Yeah, Class H and Class G. WSR Reber: What are all these differ-ences? What does that all mean? Kessler: What it means, first of all, mytheory about classes of amplifiers, all of themare valuable. Pretty much all of them. Thequestion is application—meaning that there’sreally applications for almost all of these dif-ferent classes. Where you get into a problemwith amplifiers is trying to use a topology ora class of amplifier where it shouldn’t reallybe used, or it's overlapping where othertypes of amplifiers could do better. A ClassA amplifier is the purest form of amplification,no question about it. And if you only need a5- or 10-watt amplifier and don't care aboutburning 50 or 60 watts of electricity to do it,or more, a Class A amplifier is going to giveyou the purest sound, bar none. But forpractical purposes, where you need 100 or200 watts, or 300 watts, a Class A amplifierquickly loses its ability to be practical, sothat's what Class B... A Class A amplifiermeans that one device and one voltage isamplifying both halves of the signal, mean-ing that an audio signal is a positive wave-form and a negative waveform. So to do it inClass A you have to bias the amplifier tubeor transistor normally to half of its voltage,which means it's running at dissipating halfits capable power even if it’s not even play-ing. And then the signal, basically, to get thenegative half is still in the positive form. Soyou're not crossing through anything. Thesignal never switches. So Class B was invented. Class B basi-cally said, why don't we use one device foramplifying the positive half and one devicefor amplifying the negative half and that wayit would be a lot more efficient. It goes from10 or 12 percent efficiency to at least 50 to60, mid 60s, and that's a huge improvement.But Class B had a problem. You're switching

WidescreenReview.com • Issue 185 • March 20145/7 51

from the positive to the negative half cycle,and you're going through zero, and any kindof amplification device, whether it be a tubeor a semi-conductor, when it gets near zeroit distorts. It’s kind of like starting your carfrom a red light. If you want to get from zeroto 50, it’s going to take a curve, and onceyou get to 50, then it's linear because you'restaying at 50. Well, every time the transistorsor tubes went through zero, you’ve got apoint where it’s switching off and then theother one's switching on and you get this lit-tle “whoop dee doo.” Hipps: That's the technical term for it,right? Kessler: A “whoop dee doo.” Crossoverdistortion is the technical term for it. Thesolution to that, of course, was to mix in a lit-tle Class A with the Class B, and you getClass AB. And Class AB was a big improve-ment because you could get through thecrossover distortion area and improve it 90+percent. You couldn't quite get rid of it, butyou could get it so close that it was indistin-guishable. Another thing that's happened,especially in solid state, is that transistorshave improved greatly, where the crossoverpoints have gotten smaller and smaller andsmaller. The crossover distortion, andbecause of that the biasing that's required ofClass A, has gotten smaller, which has madethe amplifier more efficient—a little bit, butmore efficient. Class AB amplifiers havebeen pretty much the ruling amplifier for thelast 50 years because of their performance,because it's still a lot smaller than, of course,a tube amplifier, it still puts out a lot less heatthan a tube amplifier, and so on. And now you’ve got Class C, which isbasically a radio transmitter amplifier. That'snot considered part of the audio world. Whatelse? A Class D. Class D doesn’t stand fordigital, it just happened to be the next letter. Hipps: I think it stands for Denmark,that's where they all come from. Kessler: Yeah, you're probably right. WSR Reber: There are a lot of Class D’sspec'd into subwoofers. Kessler: Yes, well, because switchingamplifiers work better at low frequencies. WSR Reber: So it's a switching amplifier? Kessler: Yes. The word “digital” appliedto a power amplifier is an oxymoron, they'renot digital. There are no ones and zeros inany of these amplifiers. All they’re doing isbasically modulating a switching power sup-ply. Efficiency of electronics increases withfrequency. What that means is that we'restuck with 60-cycle lights. If they would makeour power supply operate at 400 Hz, all theelectric motors would get smaller, all thetransformers would get smaller, everythingwould get better, but when they inventedalternating current they decided 60 Hz was

just enough, the flickering stopped, or atleast looked like it stopped, and they saidthat was enough. They weren’t thinkingabout transformers and motors and all thatkind of stuff. The switching amplifier, basical-ly is an analog amplifier, where you'reswitching the output transistors, in mostcases MOSFETs, because they're very highfrequency, at a very high frequency, andyou're modulating the signal in one form,there are different ways of modulating it, ontop of this high frequency. The major prob-lem with switching amplifiers is when youconvert it back to an analog signal theyhaven't yet figured that out. It kind of makesme laugh because they talk about the analogsunset, well, if there's an analog sunset, webetter learn to talk in ones and zeros andhear in ones and zeros because we're notgoing to be able to hear or talk or anything ifanalog goes away completely. You still haveto convert the signal back to an analog sig-nal at the end. No matter what, the loud-speaker doesn’t play ones and zeros. Andwhen they do that, you have to filter out thehigh frequencies. That's why I said, the earli-er, slower switching amplifiers were not badfor subwoofers. You can get a lot of powerout at a high efficiency, at least in the 80s,80 percent, some claim even into the 90s,although the sound quality gets worse withthe higher frequency. You have to get rid ofthis carrier frequency, which could be 200,300, 400 kilohertz, and it's not easy to do. Tofilter it out completely requires a passivecomponent that could be as large as a ClassAB amplifier, to do it properly, or at least todo it to a competitive state. I personally think that switching amplifiershave their place. If you need an amplifier totake to a rock concert and you want toschlep them around or hang them fromrafters, there's an advantage of having a 20-or 30-pound amplifier compared to a 100-pound amplifier, and you’re willing to give upsome sound quality, and so on. But for ahigh-end audiophile system with really good-quality loudspeakers, and all the rest of it, aswitching amplifier is going to be hardpressed to beat a well-designed Class ABamplifier. I don’t think it's possible. Correctme if you disagree. WSR Reber: But isn’t your company,Theta Digital, introducing a switching amplifi-er? Kessler: Yes. The answer is yes. It is alsothe closest thing to a Class AB amplifier thatwe were able to find. It's actually what'scalled a free-running switching amplifier. Itdoesn't have a modulator. It still does have acarrier frequency that has to be filtered out,and it has some value in that sense. It doesstill use a linear power supply, it's just aswitching output stage, and it's analog all the

way through, up to the output stage. Andthat's for Theta. Theta lives in that world.How should I say this politically? I still don’tthink it’ll be the sound quality of the 6000,the ATI 6000, or the analog amplifiers thatwe do, but it’s close. Has close ever beengood enough in the high-end audio world, bythe way? Hipps: Of course. Kessler: Yes? Hipps: The reason close is good enoughis because you have people who make emo-tional investments in certain design camps.And they simply tune out any evidence to thecontrary. Kessler: Well, let's not go into other peo-ple's philosophy. WSR Reber: Well, let me give it from thisperspective. I have three reference systemsin my home, and my main reference systemis using ten channels of Classé, 300 watts, 8ohms. What's interesting about this is that myelectric bill, for a few years I just let themstay in standby mode, and my electric billwas humongous. My wife keeps complainingabout our electrical bills, so I finally decided,with my Equi=Tech balanced-power, 30-ampelectrical system, there's a power switch on it. Hipps: Yeah, you could turn it off. WSR Reber: So what I do now is I onlyturn my system on when I'm going to do areview. I actually turn the whole thing offfrom the source and everything is shut down.And my power bill just dropped, like morethan 50 percent, just by doing that simplething, turning off the juice to the system. Sodoes the Class D use as much electricity asthe Class A designs, which are always on,even in the standby mode? Kessler: That's an interesting question.Depending on the Class D, their standbypower when they’re on is not that muchlower than a standard amplifier, I don’t think. Hipps: But aren’t we now designingstandby stuff at a half-watt standby? Kessler: Well, there are different stand-bys. Leaving the amplifier fully on is differentthan turning an amplifier off but being readyto be turned on. Hipps: I think an AT3007 dissipates 150watts a channel when it's idling. And instandby we can get that below a half a watt. Kessler: There's no reason not, in spite ofwhat some people think, that it takes fourhours for the amplifier to stabilize and so on,especially newer amplifiers. This thing takesa few seconds, literally a few seconds. Wecan measure this amplifier within a minute,let's say, half a minute, of turning it on, andits specs are stabilized. They’re not going tochange. The bias isn’t going to get... Hipps: Is that partially because of thethermal trak transistors? Kessler: It's partially because of the ther-

Widescreen Review • Issue 185 • March 201452 6/7

mal traks, partially because of the wholedesign. This thing about warming up youramplifier, breaking in, electrolytic capacitorsare about the only thing that actually reallydoes break in. You don't break in semi-con-ductors. You don't break in resistors. Youdon't really break in any kind of capacitorexcept electrolytics. Correct me if I'm wrongor if you disagree with me. Breaking in amplifiers is kind of silly.Leaving them on is even more silly. You canturn this thing off, turn it on, and within,arguably, 30 seconds you're going to get asgood a sound as you're going to get out of it.Maybe you have a 20- or 30-second window. WSR Reber: I’m referring not to just turn-ing off the power switch on the power ampli-fier, I'm talking about turning off the electrici-ty that even gets to the power amplifier. Thatsaved a lot of money. Kessler: Okay, then, back to Jeff’s state-ment. When you turn our amplifier off fromthe front switch, it's drawing between, abouta half a watt continuously, and that's actuallya new, relatively new, mostly in Europe, safe-ty requirement. WSR Reber: Is that low by comparativestandards to other amplifiers? Hipps: Yes WSR Reber: Wait a minute, all theseamps on the market are what? Hipps: Maybe they're lowering the biassomewhat, but they're still drawing a lot ofpower out of the wall.

Kessler: You have different things thatare drawing power. You have the power sup-ply by itself draws some amount of power inthe conversion from AC to DC, and then inthe amplifier channels, depending on howmany amplifier channels you have, you havethe biasing, the Class A part of it. Eventhough it’s small, it's still there, and if you'retalking about seven-channel amplifiers you'retalking about seven times the bias, and inthe case of a balanced amplifier, you’re talk-ing about 14 times, because this has twooutput stages. When an ATI amplifier goes into standbyit reduces down to a half a watt. WSR Reber: So that's significant. Kessler: Oh, yeah. WSR Reber: That's a significant savingsin electricity for the customer. Kessler: Now that's one of the otherarguments that needs to be discussed.Class D amplifiers are always saying, “Oh,you’ll save all this money in your electricity,”which is really insignificant because whenyou're actually using the two amplifiers sideby side, the same amount of time, from thetime you turned it on to the time you turned itoff, and the duty cycle of an amplifier, whichis like 10 percent, 1/8th now is consideredthe average duty. An amplifier runs at 1/8thits power 99.9 percent of the time. If youactually compare the two from a powerstandpoint, its pennies, to run a switchingamplifier versus a Class AB. Your savings is

negligible. WSR Reber: Isn’t that partially becausethey rate Class D amplifiers as most efficientat full output? Kessler: Well that's true of both ampli-fiers. All amplifiers are more efficient at fulloutput, yes. But switching amplifiers candraw more power at lower levels than aClass AB, some of them. It depends on thedesign. They're all a little different. But you'llnever get the signal-to-noise ratio that we’regetting in our most advanced Class A/Bdesigns out of a switching amplifier. Our A/Bamplifiers may be 10 to 20 dB better. That'ssignificantly better. Many Class D amplifiers,if they can push 100 dB for signal-to-noise,they're really doing good. Our SignatureSeries ATI amplifier is almost 130 dB. Hipps: This may be the only amplifier inthe world capable of 130 dB. Kessler: But most Class AB amplifierswill be at least 10 dB quieter than a Class D,even the better ones. And noise is a distor-tion, by the way, pure and simple. WSR

To be continued in Issue 186, April/May 2014.