Amplifiers....

[tysontom]

This is definitely somewhat off-subject regarding AR speakers, but since I drive my AR speakers with pro-style amps now, I thought this would be of interest to those searching for high-powered, safe-operating effortless power amplifier for their speakers. I've used Crown and QSC pro amps now for some time, and I've never had a failure. I have run parallel AR-LSTs (read 1.5-2.0 ohms) to high peak-power levels with a QSC RMX2450 and also with my old Crown Studio Ref I, with zero issues. These amps are in the 1000+ watt/ch category; with smaller 300-350 watt/ch amplifiers, typically less inexpensive and unfazed by quirky reactive-capacitive and low-Z loads, amps like the QSC GX3 amps are great. With regard to low distortion, stability and low noise, these amps will easily meet or exceed the specs of any consumer amp. They are designed to be durable and reliable for bands, rock groups, and other rigourous audio needs. They also have to have low distortion and high power. Check out this strife-testing; it looks like something HP used to do with their measurement equipment to assure proof-of-performance:

http://www.crownaudio.com/amp_htm/itechdroptestvideo.htm

The one drawback: a relatively quiet-running variable-speed fan is always on, and bumps up when you start approaching 100% power levels, so it is best to have the amp somewhat remote from the direct listening area.

--Tom Tyson

[frankmarsi]

This is definitely somewhat off-subject regarding AR speakers, but since I drive my AR speakers with pro-style amps now, I thought this would be of interest to those searching for high-powered, safe-operating effortless power amplifier for their speakers. I've used Crown and QSC pro amps now for some time, and I've never had a failure. I have run parallel AR-LSTs (read 1.5-2.0 ohms) to high peak-power levels with a QSC RMX2450 and also with my old Crown Studio Ref I, with zero issues. These amps are in the 1000+ watt/ch category; with smaller 300-350 watt/ch amplifiers, typically less inexpensive and unfazed by quirky reactive-capacitive and low-Z loads, amps like the QSC GX3 amps are great. With regard to low distortion, stability and low noise, these amps will easily meet or exceed the specs of any consumer amp. They are designed to be durable and reliable for bands, rock groups, and other rigourous audio needs. They also have to have low distortion and high power. Check out this strife-testing; it looks like something HP used to do with their measurement equipment to assure proof-of-performance:

http://www.crownaudio.com/amp_htm/itechdroptestvideo.htm

The one drawback: a relatively quiet-running variable-speed fan is always on, and bumps up when you start approaching 100% power levels, so it is best to have the amp somewhat remote from the direct listening area.

--Tom Tyson

2-27-09 10:45 P.M. E.S.T.

Tom, everyone’ seems to be afraid to speak up…

What’s that about?

Anyway, I’ve read extensively about those amps a few years ago and I feel that at the time I was considering them as the ‘next- logical-step’ for me and that I should sell and get what I could for my 6 in number PL-400’s. Well I didn’t, and I ‘waited-out-the-storm’.

I sit here today and listen to one of my PL400’s power the ‘upper-half’ of my system (four stacked AR-LST’s), whilst a ‘completely-rebuilt’ PL700 Series Two powers my lower two AR-LST’s.

I can tell you that as I wait-out the finding and rebuilding of another PL-700, I will be very happy when I have all the ‘amp-power’ I would ever want!.

I will realize that my ‘New’ --- ‘Same-Old-Same-Old’ LST’s will be powered by the same, albeit better ‘re-constructed’ old amps and I still will have the glory of knowing they were (the AR-LST’s) actually tested with by Julian H. , and that I listen to things that I always wanted to listen to as far as ‘electronics-and speakers-go'.

Hey, isn’t that what is implied here, AR speakers sounding their best?

Respectfully, Frank Marsi

frankmarsi@verizon.net

[Mexicomike]

2-27-09 10:45 P.M. E.S.T.

Tom, everyone’ seems to be afraid to speak up…

What’s that about?

Afraid to speak up? What was there to "Speak up" about? Tom posted about an amp he likes. I didn't see a question or controversy raised that would generate a "need" to reply. And Tom didn't ask for anybody's help or input. So where's the reason to "speak up?"

[dick]

There's been a few threads lately on amplifiers and ARs. I wish I could say that I learned definitive information from them.... Perhaps it started with the thread "Optimum amplifier wattage for 3a" -- which informed me a bit, although not as much as a talk with a local hi-fi shop owner who knew my speakers (3a's) from days of old. One thing I notice is that all 3 contributors to this thread have LST speakers. Could it be that the LST with multitudes of speakers really needs all those WPC to get on with it? Or is it that all 3 like to have your socks blown off, hair flung back, when you listen to driving bass lines...or?

In any event, I'm aware that amplifier choice does make a huge difference in what I hear coming from the 3a speakers. Testing amplifiers in my home environment allowed comparisons and a selection. I'm not sure, however, what it is about my new (admittedly humble yet loved) amp (NAD C372) that made my 3a's get the urge to sing fantastic: WPC? Flexible impedance? New electronic sophistication? All of these? More? I do know that I like what I hearing!

[Mexicomike]

" One thing I notice is that all 3 contributors to this thread have LST speakers"

I'm only a recent LST owner. But as I posted before, back "in the day" (early 70's) I had AR3as and their sound was dramatically improved with my Phase Linear 400 power amp at 200WPC as opposed to my previous amps which were in the 40-60WPC range. Fast forward to now...

Until I finished refurbing my Ebay LSTs in late '08, I was using 3As as my main speakers primarily with either my 270WPC McIntosh amp or my 300WPC Moscode 600. I also used them with my AR amp (60WPC) and they sounded quite good but NOT as clean and "tight" as they did with the other two amps. I do not listen at "hair blown back" levels and pop music, even played fairly loud, doesn't take more than around 50 WPC. But classical music, at a normal concert hall volume, which doesn't seem "too loud" to most people, can take a lot more power. Some organ stuff will definitely tax an amplifier!

It is true that if you only listen at background music levels, any amp will sound OK. Even on the LSTs, my McIntosh typically does not exceed 1WPC when I'm in the room and they are just providing casual listening. BUt as I posted in another thread, you might be surprised at how much power it takes, depending on the music, to reproduce sound when it's not even "all that loud." And remember, if there is a lot of low bass, it takes a lot of power; if the amp is producing a lot of power to reproduce that bass, then clipping is a real possibility and unless the amp has clipping protection, clipping is what damages tweeters. I had to replace several tweeters on my original AR3As until I installed the PL400. From that point on, no more blown tweeters. I was happy and I'm sure AR was happy since they completely covered all costs associated with replacing the tweeters each time.

I know it sounds odd but a high power amp is much "safer" than a low powered amp as far as your speakers are concerned.

I guess we're "speaking up" now, huh?

[dick]

MejicoMiguel,

I'm guessing you've got a device to measure WPC needed, which would be sort of neat. None here except the ears which only have a "pleasure meter." Your comments are chiseling at my thick skull; am starting to get it re: WPC & bass, etc. My new amp has an anti-clipping switch. But it was suggested to only use it when leaving the amp in the hands of others (an unlikely event). It apparently degrades the quality of normal-volume sound, but protects the speakers when someone decides to turn the volume up full blast.

Do you prefer your LST to the 3a, or vice versa? How much "+" would you rate the LST if, as I suspect, it garners a higher rating from you? In other words, tell me I'm not missing much....

Cheers to churros y chocolate late at night, Garibaldi Square at midnight -- Aiiiiiiii.

[Guest nathanso]

I've long puzzled over why more audiophiles don't use pro audio amps. From what I've read, the fan noise issue can often be mitigated or fixed outright with either a low-noise replacement fan and/or a slowed fan speed. The specs on most of these amps are certainly impressive enough, but the prevailing attitude in our market seems to be that they somehow lack refinement, or are brutish PA systems that can't possibly deliver finesse. I can't claim to have heard one in a home 2-ch setting but I've come close to pulling the trigger on a purchase or two.

[genek]

I've long puzzled over why more audiophiles don't use pro audio amps.

I think it's probably mostly due to a lack of marketing effort on the part of the companies. Crown used to make audiophile products, but hasn't in years. Maybe there isn't a customer base, or maybe the companies just prefer to deal their products to pros who don't require as much hand-holding now that full service audiophile salons have gone the way of the dinosaurs.

[Mexicomike]

The most obvious difference between the LST and the 3a to me is the soundstaging and "airiness." The speakers do seem to "disappear" quite regularly. The LSTs ability in that regard is well beyond the AR3a, as would be expected based on the speaker design. It also seems to have a wide "sweet spot," which again makes sense based on the design. I also found that for reasons I don't understand, my LSTs have a bit more bass extension compared to my 3as. I have run test tones through both and the LSTs will produce a good solid 30HZ while the 3A loses authority at around 35Hz. This is with both in the same room, in the same position. I don't understand why there should be any difference since they use the same woofer. Both sets of speakers have all original drivers/controls and new caps. The LSTs' selector switch are set on number "2" which is the "flat" setting. The 3A's controls only affect the mid/tweeter but the LSTs controls affect the woofer. According to AR, the LST can play louder than the 3a based on its compliment of 4 mids and 4 tweets. I'm sure it's true but with a limit of 300WPC on my largest amp, there is no practical difference since the amp is the limiting factor and in either case, they will play much louder on pop/rock/jazz music than I would ever want to listen. Not necessarily true on classical though, depending on the music.

One sound that really impressed me was when the bass comes in on Neil Diamond's "Forever in blue jeans" (OK, keep the musical taste comments to yourself!). The first time I played it with the LSTs my mouth dropped open on the POP of the bass. I never heard it on the 3As. Again, I'm not sure why since both speakers use the same woofer. I suspect it's the upper freq content of the attack and the multiple drivers that gives it that presence. Heck, maybe it's not even accurate but it sure sounds real and I have a good friend that plays in a jazz group so I've heard plenty of live bass. Don't get me wrong, I love my 3As and would never part with them but I'd have to say that AR's reasoning for making an LST and calling it the top of the line at the time is certainly justified.

The device to measure WPC is simply my McIntosh amp's power meters which have a peak-hold function to allow you to see the max wattage the amp supplied or to see it edge upward as the music gets louder. Of course, they can also be left in the constant mode so the needles swing with the music.

[genek]

The most obvious difference between the LST and the 3a to me is the soundstaging and "airiness."

I had a conversation with my local AR dealer back when the LSTs first came out, and he told me that the LST's advantages over the 3a seemed to him highly dependent on the listening room. In a large enough room with space for the side mids and tweets to bounce their output off walls, the LSTs bloomed in a way the 3a's never could. In a smaller room with insufficient space between the speakers and the nearest side walls, nothing (though I doubt that he had done frequency testing that would have shown that under-35Hz response you note). It wasn't that the 3a's sounded better than the LSTs in the smaller room, just that the LSTs were additional expense with no noticeable sonic return on the investment (at that time, collector value was years away from becoming a factor).

[soundminded]

Not afraid to speak up Frank, afraid once I get started I won't stop. Like about most things, I have strong opinions. Not a good idea to express them after a bottle of wine but....

An amplifier is a purely electrical device. The only way to rationally judge one as I see it is by measured performance. Its input is an electrical signal, its output is an electrical signal, it perfoms an electrical function. Sadly for tyros, like many other things in life, it cannot be explained in one simple number alone. There are many facets to one and comparing amplifiers is complex, meaning comparing different facets of their performance and based on knowledge knowing which ones are important and which ones aren't. For example, an amplifier which has a frequency resonse out to 1 Mhz will not perform its functon in a sound system any better than one which only extends to say 50 khz. In fact, it may be worse since it is more prone to pick up stray RF fields.

I cannot agree with Ken Kantor that all solid state amplifiers sound exactly alike within their power capabilities if they are functioning normally...but the importance of their differences should not be overestimated either. In fact most differences among them are attributable to minor differences in frequency response with real world loads which can be corrected or compensated for with an equalizer, an extremely powerful tool many audiophiles but few professionals reject.

If a superior amplifier based on measurements causes a sound system to perform worse than an inferior amplifier, the correct decision IMO is not to try to mitigate one shortcoming, say a shrill sounding loudspeaker with another complimentary shortcoming like an amplifier or any other device like a wire which has a high end roll off that muffles the result and reduces the shrillness. The correct answer is to attack the problem at its source, the speaker.

If I have one gripe, and it's a minor one, I don't think the method for measuring amplifiers is particularly helpful today in discerning what their differences will be. Amplifiers that measure the same with an 8 ohm resistive load may perform very differently with a highly reactive loudspeaker load that may not even be a passive load. Also, low input impedence may load down the output of some preamplifiers. So called "passive preamplifiers" are the worst IMO, they don't amplifiy anything and their output impedence will vary with the volume control setting which can have a real audible effect.

Actually there are no audio "power amplifiers" per se. They are all cascaded voltage amplifiers where the output stage has sufficient voltage swing and can deliver enough current to drive a loudspeaker. Don't believe it? Watch output meters on any amplifier that has them. With speakers disconnected, you will see them swing back and forth even though no power is being delivered to a load. Those meters are volt meters calibrated for the power that would be delivered to an 8 ohm resistive load if one were connected. In the real world, they are usually not at all accurate because loudspeaker loads are so variable with frequency and are not usually resistive but reactive. A true power or current amplifier without a load but an input signal would generate an output at the highest voltage available to try to drive power or current into an infinite load.

Today's professional audio amplifers like Crown and QSC are by far the best amplifier values on the market. They are nearly textbook perfect, very reliable, and dirt cheap by historic standards. My only complaint, some don't have unbalanced inputs or enough gain for a consumer audio preamplifier. I'd love to have been a fly on the wall if and when Sidney Harmon put his top amplifier engineers from Crown and Mark Levinson in the same room and asked the Levinson designers why it cost five to ten times as much for them to build an amplifier of equal or lesser performance than Crown. Oh how the fireworks must have flown. Of course, Sidney couldn't care less if people want to shell out ten times as much profit to him for no more amplifier. (Sorry all you ML owners, I don't think that equipment is good value for money but it does carry prestige.)

BTW Tom, it is not surprising that Crown amplifiers are designed to take enormous abuse. Their tape decks, the original product they made were designed to survive a parchute drop in their own cases. Crown equipment is built to last a lifetime...and then some.

[Mexicomike]

Well, I've been an audiophile for a LOT of years and I apologize but I have to "Speak OUT!" re Crown, one of my favorite companies though I never owned any of their stuff.

Crown equipment used to be quite expensive and I really wanted one of their DC300 amps and tape machines. I never could afford either back then but now I see that a new Crown CDI 1000 (500WPC) is $599. I'm not sure that would have purchased the DC300 40 years ago though it may have, for some reason $499 pops up in my head but that could be wrong. So I can't help but get the impression that the Crown of today, like the AR of today, has very little to do with what they were "back in the days." When I read the specs and saw that a CDI 1000 only weighs 20 lbs, I really have to wonder...where's the beef? The current McIntosh Amp in that power range (1.2KW) weighs 147 lbs!

[tysontom]

I've long puzzled over why more audiophiles don't use pro audio amps. From what I've read, the fan noise issue can often be mitigated or fixed outright with either a low-noise replacement fan and/or a slowed fan speed. The specs on most of these amps are certainly impressive enough, but the prevailing attitude in our market seems to be that they somehow lack refinement, or are brutish PA systems that can't possibly deliver finesse. I can't claim to have heard one in a home 2-ch setting but I've come close to pulling the trigger on a purchase or two.

The main advantage I can see with pro-audio amplifiers is the durability issue. There are drawbacks, such as the fan noise and the commercial-utilitarian appearance, but that is a small tradeoff to pay for the performance. I have my equipment rack-mounted anyway, so that is another plus. As for sound quality and low noise, the professional crowd today demands very high quality, so the competition between Crown, QSC, Crest and many other pro units is pretty intense. There really is no existing "consumer" market for big stereo amplfiers anymore, but the pro market is very large and flourishes, and hence the technology in this segment continues to grow. A good example is the "Class H" design, basically moderate-sized Class A/B amplifiers with multiple-voltage rails somewhat akin to what NAD used to do with its power supplies. The Class H versions are vastly more sophisticated than the NAD units, however, and more seamless in operation. In most cases, these amps are stereo units, with a great deal of electronic flexibility, filtering, specialization and so forth. There is nothing grainy, harsh or brutish about the sound in any good professional amp I have heard (some of the old PA amps were definitely that way, of course). The performance is usually top-notch, any any of the good pro amps can deliver either a few milliwatts or sometimes up to megawatts of distortion-free, full-bandwidth amplifier power that is unconditionally stable. You are not ever likely to bring a big pro amplifier to its knees (as I managed to do with several Dynaco and Marantz solid-state amps over the years), and as Mexico Mike aptly points out, more power is much better than too little power, even if you play music at moderate levels. Only a few consumer amps can match that overall flexibility -- mainly those produced by McIntosh, Brysten, Krell, etc. Overall, however, if any of the good amps (consumer or pro) are operating well within their power rating, the sound differences between them are likely to never be noticed in a double-blind listening test.

So, the real point of my original message was to just throw out another option for driving the fairly difficult loads presented by some AR speakers.

--Tom Tyson

[Dave S.]

The main advantage I can see with pro-audio amplifiers is the durability issue. There are drawbacks, such as the fan noise and the commercial-utilitarian appearance, but that is a small tradeoff to pay for the performance. I have my equipment rack-mounted anyway, so that is another plus. As for sound quality and low noise, the professional crowd today demands very high quality, so the competition between Crown, QSC, Crest and many other pro units is pretty intense. There really is no existing "consumer" market for big stereo amplfiers anymore, but the pro market is very large and flourishes, and hence the technology in this segment continues to grow. A good example is the "Class H" design, basically moderate-sized Class A/B amplifiers with multiple-voltage rails somewhat akin to what NAD used to do with its power supplies. The Class H versions are vastly more sophisticated than the NAD units, however, and more seamless in operation. In most cases, these amps are stereo units, with a great deal of electronic flexibility, filtering, specialization and so forth. There is nothing grainy, harsh or brutish about the sound in any good professional amp I have heard (some of the old PA amps were definitely that way, of course). The performance is usually top-notch, any any of the good pro amps can deliver either a few milliwatts or sometimes up to megawatts of distortion-free, full-bandwidth amplifier power that is unconditionally stable. You are not ever likely to bring a big pro amplifier to its knees (as I managed to do with several Dynaco and Marantz solid-state amps over the years), and as Mexico Mike aptly points out, more power is much better than too little power, even if you play music at moderate levels. Only a few consumer amps can match that overall flexibility -- mainly those produced by McIntosh, Brysten, Krell, etc. Overall, however, if any of the good amps (consumer or pro) are operating well within their power rating, the sound differences between them are likely to never be noticed in a double-blind listening test.

So, the real point of my original message was to just throw out another option for driving the fairly difficult loads presented by some AR speakers.

--Tom Tyson

I've lately been a fan of the dicontinued Hafler Pro amps for price, power and reliability. I used to own a Hafler P505 that I drove AR9ls and Allison Ones with and it sounded fine and didn't break a sweat. I'm looking for a Hafler amp now for a pair of Allison Threes. I agree with the earlier statement about too much power being better than not enough.

[mluong303]

So, the real point of my original message was to just throw out another option for driving the fairly difficult loads presented by some AR speakers.

--Tom Tyson

Hi Tom

Thanks for bringing up the QSC amplifier brand. For the price and trouble free in the long run, it would make more sense for one to pick up the QSC GX5 than to keep on dreaming of getting the old Crown PSA2 or similar amp of decades ago...

Minh Luong

[tysontom]

Not afraid to speak up Frank, afraid once I get started I won't stop. Like about most things, I have strong opinions. Not a good idea to express them after a bottle of wine but....

>Today's professional audio amplifers like Crown and QSC are by far the best amplifier values on the market. They are nearly textbook perfect, very reliable, and dirt cheap by historic standards. My only complaint, some don't have unbalanced inputs or enough gain for a consumer audio preamplifier. I'd love to have been a fly on the wall if and when Sidney Harmon put his top amplifier engineers from Crown and Mark Levinson in the same room and asked the Levinson designers why it cost five to ten times as much for them to build an amplifier of equal or lesser performance than Crown. Oh how the fireworks must have flown. Of course, Sidney couldn't care less if people want to shell out ten times as much profit to him for no more amplifier. (Sorry all you ML owners, I don't think that equipment is good value for money but it does carry prestige.)

BTW Tom, it is not surprising that Crown amplifiers are designed to take enormous abuse. Their tape decks, the original product they made were designed to survive a parchute drop in their own cases. Crown equipment is built to last a lifetime...and then some.

Soundminded, another eloquent rendering!

I agree about the value of pro amps. Until you get into the 5000-watt amplifier range, the prices are usually very reasonable, largely because there is competition, and lots are sold, etc. In other words, the "value-per-dollar" of pro stuff is much, much higher than consumer equipment. As for balanced-vs.-unbalanced inputs, some of the smaller QSC amps have all three: balanced phone jack, balanced XLR as well as unbalanced phono input jacks. In any event, it is quite easy to convert a balanced input to an unbalanced input, and the difference is practically nill unless the cable lengths are greater than ten feet or so. As for input gain, most have the 1.5 volt for full output, so I can't see much difference there, plus all pro amps have adjustable input levels for each channel. Any decent preamplifier ever made should be able to produce at least 1.5 volts at no distortion; some can deliver upwards of 10 volts before distortion sets in.

I agree about the Levinson vs. Crown thought you have! There is really no rational excuse for designing an amplifier such as the Levinson, (which is of course beautiful to look at) that cannot come even remotely close to matching a big Crown amplifier -- that cost 1/4th as much money to produce and sell. The Crown drop test looks very similar to what Hewlett-Packard did with virtually everything it made for industry back in the instrument days: extreme strife testing. HP went a lot further than Crown, of course, because everything was rated for salt spray, drop test, extreme altitude and RF interference. This is one reason HP rose to its prominence back then, and still to this day. One audio company did follow HP's lead in construction quality: McIntosh. Most of the better transistor-powered amplifiers made by McIntosh had electro-gold-plated circuit lands, which HP always used, and this assured very few circuit faults.

--Tom Tyson

[tysontom]

Hi Tom

Thanks for bringing up the QSC amplifier brand. For the price and trouble free in the long run, it would make more sense for one to pick up the QSC GX5 than to keep on dreaming of getting the old Crown PSA2 or similar amp of decades ago...

Minh Luong

Thanks, Minh! Even the GX3 should be able to power about anything AR made with ease, but especially the GX5.

--Tom Tyson

[Guest oldfart]

nice amps sure, but why load them with 2 ohm, ?? i dont see why that one does that, ok the amp can handle that with ease,

i was just wondering what happens to the THD with loading under the design resistance, ,that off ,or out of specs, for what the manufacturer guarantees,

currents will be higher, I

think that the THD will suffer from this under-loading, ok youve got headroom enough, you probably even wont notice anything, but fact is,

thd will go up if you load outside the 4 to 8 ohm window....

what say gentlemen (and woman)???

[Mexicomike]

nice amps sure, but why load them with 2 ohm, ?? i dont see why that one does that, ok the amp can handle that with ease,

Brings up a good point...some amps just have a speaker lead hookup with one hot terminal and a ground. Other amps, like McIntosh, have separate connections for 1, 2, 4, and 8 OHM speakers. The amp output specs, continuous RMS and freq response, are identical for all four impedance loads. Why does this exist on some amps but not on others?

[genek]

Brings up a good point...some amps just have a speaker lead hookup with one hot terminal and a ground. Other amps, like McIntosh, have separate connections for 1, 2, 4, and 8 OHM speakers. The amp output specs, continuous RMS and freq response, are identical for all four impedance loads. Why does this exist on some amps but not on others?

It used to be common for amps with output transformers to have multiple taps to match different impedance speakers. Amps without transformers were rated for a specific impedance, and the different wattages listed for different impedances were the result of not using transformers to "match" impedances, to better or worse effect. Do Macs have output transformers? I've never owned any.

[Mexicomike]

Do Macs have output transformers? I've never owned any.

Yes they do...very large HEAVY ones! My Mc 7270 has the 1,2,4,8 ohm output connectors, weighs 82lbs and the vast majority of that is transformers - 1 power, 2 output.

My Moscode 600 has a single speaker connector and does NOT have output transformers and weighs 40 lbs, the vast majority of that being the power transformer.

So I assume, as you said, that the various outputs on the Mac are from the different taps on the output transformers.

[soundminded]

Brings up a good point...some amps just have a speaker lead hookup with one hot terminal and a ground. Other amps, like McIntosh, have separate connections for 1, 2, 4, and 8 OHM speakers. The amp output specs, continuous RMS and freq response, are identical for all four impedance loads. Why does this exist on some amps but not on others?

I'm not familiar with the current MacIntosh design but it sounds like they stuck with the concept of using an autotransformer to couple the output stage. IMO this is an unfortunate choice. The output transformer whether it is a primary/secondary type or an autotransformer which shares primary and secondary windings is a major source of distortion in the circuit topology (as opposed to the power supply which is another story altogether.) It is also very expensive, large, and heavy. It will however yield the same output power and performance at all load impedences when the correct taps for the connected load are used.

IMO, many "serious" audiophile amplifiers are designed by tinkerers, not electrical engineers. Someone once wrote that if you put a chimpanzee in front of a typewriter long enough, sooner or later he would type out the entire Encyclopedia Britanica and all of Shakespeare's plays. With enought trial and error, even the most inept circuit designer will stumble upon something he and someone else will like in a particular sound system and put up money to manufacture it for, advertising it as the greatest electronic wonder on earth. Some of these tinkerers even have credentials. One famous one whom I won't mention is a physicist. It helps if you can get someone to write a kludgey paper justifying yhour idea. One such paper is a thesis for a Masters of Electrical Engineering degree written by someone named Cheevers. You can google it. It is one of the weakest and most flawed technical papers I've ever read and if I were on the judging committee, I'd have questioned his bachelor's degree. But it has been the darling of people looking for justification of vacuum tube amplifiers.

What does it take to become a real electrical engineer and acquire the technical competence to design audio amplifiers? A four year electrical engineering program consisting in part of the following; Two years of Calculus and analytic geometry, one term of ordinary differential equations, a term of Systems Analysis where the concepts of Laplace and Fourier to system design are introduced, a term of circuit analysis where concepts like Kirkoff's laws, Thevenin's and Nortons theorems are introduced, a course in Electronic device analysis where various vacuum tubes and transistor models such as Beta, hybrid pi,and h parameter are presented, analyzed and problems solved, a year of advanced circuit design and analysis, and one of the toughest courses imaginable, feedback control theory. This is just part of a full engineering course of study,there's lots more. How do I know? I survived it forty years ago although looking back on it, I'm not quite sure how.

BTW, those who dismiss the importance of negative feedback in amplifier design don't know what they are talking about. When I took the course in 1968, the professor who taught it said it was the single most important advance in electrical engineering since World War II. That may still be true today. In fact our modern world would not be possible without it.

Anyway, the companies that sell to audio professionals will not play games because they cannot get away with it. But for audiophiles, a lot of very high priced equipment when viewed with a critical well informed eye is pure junk. Don't argue with them though, they are sold on their religion.

[ar_pro]

Over the years, Crown has occasionally sought to sell some of their amp & preamp products to non-professional users, but at no time did their standard of quality dip. In other words, ANY Crown product could be used in a professional capacity with confidence. Crown amplifiers were about as dependable and unflaky as could be.

And although McIntosh has a rich history of providing amplification for professional and scientific purposes, their focus was always on the consumer. That said, Mcintosh amplifiers will go forever, too - their cosmetic extravagance (that beautiful glass faceplate) and the transformer weight make them somewhat less practical for pro use, though - the Wall Of Sound, notwithstanding.

Obviously, there are other amplifiers that have had long life-spans, but among solid-state designs, I can't think of any manufacturers that are in the same league as these two.

And I'm a big fan of the McIntosh autoformer design, too - especially when used with difficult loads like the LST or 9, Mac amps really shine, with a solid, controlled LF.

[soundminded]

Over the years, Crown has occasionally sought to sell some of their amp & preamp products to non-professional users, but at no time did their standard of quality dip. In other words, ANY Crown product could be used in a professional capacity with confidence. Crown amplifiers were about as dependable and unflaky as could be.

And although McIntosh has a rich history of providing amplification for professional and scientific purposes, their focus was always on the consumer. That said, Mcintosh amplifiers will go forever, too - their cosmetic extravagance (that beautiful glass faceplate) and the transformer weight make them somewhat less practical for pro use, though - the Wall Of Sound, notwithstanding.

Obviously, there are other amplifiers that have had long life-spans, but among solid-state designs, I can't think of any manufacturers that are in the same league as these two.

And I'm a big fan of the McIntosh autoformer design, too - especially when used with difficult loads like the LST or 9, Mac amps really shine, with a solid, controlled LF.

The main problem with a ferrous core magnetic device in an audio signal circuit whether it is an inductor, a transformer, or an autotransformer is core losses. These are principally of two types. One is eddy current losses. These are electrical currents circulating transversely within the core induced by the electric field. The goal of minimizing these losses is the reason magnetic cores are made of thin lamina that are electrically insulated from one another with shellac or varnish instead of a solid chunk of steel. The smaller the cross-section, the lower the losses. The other principal type of loss is hysteresis losses. This is the loss due to trying to magnetize the core. It is not 100% efficient and varies considerably with the type of core material used and the construction. The best transformer irons are aluminimum killed steel alloys called permalloy and supermalloy which have a magnetic saturation point of around 15,000 gauss. Their B-H curve which relates the coerced magnetic field to the coercive magnetizing field is the typical double Ess curve. In this type of steel, the two esses are long, close together, steep, and flatten at the top and bottom where they join (they all do the last.) Other less suitable steel alloys that are magnetically harder like mild cold rolled steel have their esses much further apart and are much shorter. The area bounded by the two curves is the work lost to turning the magnet domains around on each half cycle. What makes it especially bad is that it is frequency dependent. Even the best and most exotic cast core transformers are only about 97.5% efficient. Others range from around 92% to 95%. That being said, there are advantages to an autotransformer. The output transistors get an added measure of protection from damage. This may not sound critical today but in the early days of transistor amplifiers, blown output transistors were a very common source of failure. At one manufacturer, Pilot Radio, my inside sources told me that at one point console stereos with solid state amplifiers were coming back for repair with one channel blown after 8 hours of use, faster than new ones were being assembled and shipped. Crown like many of the better amplifiers of the late 1960s and later years found ways to make their solid state amplifiers nearly bulletproof. Perhaps some buyers of McIntosh amplifiers feel the type of disotrtion produced by having an autotransformer gives their sound system a characterisitic they are more familiar with and have come to like...or it may simply mitigate the shrillness of some loudspeakers. But they are very well built and fun to look at and touch. Some aspects of buying decisions for consumer audio equipment have nothing to do with performance.

[Mexicomike]

Well, I don't know a thing about audio circuits as far as design but I have never heard anyone note that the frequency response and distortion specs for McIntosh amps were in any way inferior to any amp made by anybody. Of course, like anything, there are folks who prefer the sound of one amp over another for various real and imagined reasons. Frankly, I prefer the sound of my Moscode 600 but the Mc is really bulletproof and the Moscode takes some care and feeding to keep it at its best, including occasional bias and offset adjustment. I also don't care for the noise of the Moscode cooling fan. The Moscode has a more lush, "musical" sound that is noticeable to almost anybody under serious listening conditions. I have done blind testing on the Moscode and other amps with a bunch of different people and the selection of "better sounding" and "noticeable difference" goes to the Moscode virtually every time by every listener. I'm sure that "musicality" is probably some sort of distortion but as Carl states in the bottom of his messages, it IS all about the sound.

If you told me I had to toss 2 of my three amps, I'd keep the Mc because I believe that when I die it will still be working as well as it did when I bought it new 20 years ago. The Moscode and AR...well, I'm happy if they work today as well as they did yesterday! Of course they are older yet...

Some of the new multi channel surround-sound Mcs do not use output transformers but all the high powered stereo amps do. The current most powerful Mc takes 3 chassis and weighs nearly 300 lbs total!