|Q:||How should I configure my browser to best view the Marantz Classics site?|
Your display should be set for high-color. 24-bit is best, 16 bit is ok if that's
the best your machine can do for you. 256 color looks awful (we tested it!).
The pages were designed with an 800 x 600 display in mind; smaller will make things
look a bit compressed and weird, but it should work. You may have to scroll to see
some of the images. Larger should work just fine.
|Q:||What criteria are used to classify items as Rare, Scarce, etc.?|
These ratings reflect current and recent availability. The estimates are a
compendium of what shows up on the online auction systems, in the .audio
newsgroups for sale, and so on. The ratings are not related to the number
made, or if they are, it is only through the current apparent scarcity of an
item, meaning that if there were few made, we (naturally) see few for sale
If something begins showing up, the rating can be changed.
For instance, the 2210 receiver, a low end Marantz piece if there ever was one, has never shown up for auction, or sale. Perhaps that is simply because it is not, in the eyes of the owners, worth trying to sell. However, what it means is that its very hard to come by one, so it gets the X-Rare rating.
|Q:||Where do the images on the site come from?|
For the most part, from EBay auctions and web sites around the net.
We've gotten a few from contributors, some from scanning brochures,
and I own several "stacks" of Marantz separates and have
used images of those units as well. All images since March 17th, 1999
now have an attribution line under them that describes the image source.
NOTE: If you run into an image here on the Classics site that is also contained in an auction on EBay, do not assume that the auction is misrepresenting what they have.
First of all, I may have just pulled the image from that exact auction (although in that case, it should have a "caption" under it that says so... if not, it's been on the site since before March 17th, 1999.)
Secondly, many people don't have access to digital cameras and/or scanners, or they may simply not have an image of any kind. There's nothing wrong with posting a general image of the correct unit in a sale or an auction. Remember, you don't get the unit you see in the audio catalog, either!
If you're in any doubt and you truly think you have a reason to be concerned, e-mail me first to ask where the image came from. I can also check the date of the image and tell you when it was put into the database's file system (or when I last edited it.) Then, knowing the answer, you can make an intelligent decision about what to say to whom.
Whatever you do, do not hassle the seller in any way until you ask me if I got the image from them. That's just mean and thoughtless.
|Q:||Hey! That's my image! Can I get credit?|
You bet. Again, absolutely. The only reason that not all images have credits in the first place is
that some of the images came from contributors, some from EBay auctions, and were collected prior
to the database being actually implemented - at the time, there wasn't any reason to note where
they came from, because I hadn't thought of creating the site yet... they were just copyright free
images on my hard drive.
If you spot an image you know was yours, just let me know, and you'll get credit. Nothing would please me more than to acknowledge your photo(s). No harm was intended, and only images that (a) had no copyright claimed on them and (b) had no digital watermark I could find have made it into the database.
If I have a conflict - two people claiming credit for the same image - I'll give both credit and you can fight among yourselves. I have no interest in conflict, only in increasing the accuracy and detail of the site.
If you want your image removed, I probably will do so without much ado, though I wouldn't think very highly of such a request. It benefits no one, and hurts users of the site until a replacement can be found, which in some cases may be quite some time. Then again, I might not - as I said, all images were collected from non-copyrighted venues and were free of watermarks as far as I can tell.
|Q:||Can I link to the pages that describe an item or items I have for sale or auction?|
Yes. Absolutely. Please do. All images came from the web and were
without statements of copyright when they were collected, or else
came directly from a contributor to me. If you can, since you physically have
one of the units on the page(s), check what you see there to make sure
I have it right. We both want the pages to be as accurate as they
possibly can be. If you find an error, use the link on the unit's
page to send the corrections to me and I'll have them up there ASAP.
|Q:||Can I use the images here on the site in my sales and auctions directly?|
Yes - but make sure you copy the image onto your own image server in order to do so, and if
there is a credit to a source, make note of that credit in an obvious and easily noticed manner.
Without a credit, you may run into an irate photo-source/owner... most don't react that way, but some do, and they are within their rights if they have taken the time to make sure there is such a credit.
Regarding the placement on your own server, this is very important, otherwise, my poor little web server has to struggle to produce the image every time someone looks at your sale or auction. And I thank you for the courtesy.
You'd be well advised to link to the specific page for the unit, as well - there are tons of specs and feature details that are often not clear from an image, or the description you had time to write between eating dinner and watching the evening news...
No matter if the image is credited or not, you probably want to note in your sale or auction that this is an image of the correct model, but it's not your particular unit. This prevents any questions (appropriate or not) from being raised about the quality of your sales and auctions. Everyone will appreciate your candor.
|Q:||Can I use the database entries here on the site in my sales and auctions directly?|
Yes - but you must provide attribution to the classic-audio site
in this form:
Marantz information copied from
Place this line after the copied information.
It is also acceptable to create the link such that it points directly to the page where the data was taken; for instance, if you're auctioning off a 2120 tuner, then you can point directly to the 2120 tuner page instead of the root of the site.
That's all I require, but I do require it! If the data from the site is quoted and this attribution is not included, I will either contact the seller, or site hosting the sale or auction, and request that this attribution be added or the offending item be removed.
It is not acceptable to take the information on site here and use it in any manner that would give any viewer the impression that this is your own data, either directly or by omission of attribution.
All database formatting, indexing and textual content of this site is copyrighted, and any use of same must comply with the description here.
|Q:||Why are there no SRxxxx / PMxxxx / STxxxx units on the site?|
The site presently carries units up to, and including, the year
1980. This was the year that Philips of the Netherlands bought
the Marantz name. These units can be distinguished by model
numbers that generally begin with numbers rather than letters.
The general consensus is that units produced after 1980 aren't exactly "Marantz units", but rather "Philips units", as they were generally designed by others, using an entirely different philosophy, and finally produced under different quality guidelines. Even when some portions of the process remained stable, as they did in the United States for about the next ten years or so, the changes proceeded apace, much to the dismay of Marantz fans everywhere.
This is actually pretty obvious visually (starting with dial pointers, later the tuning knobs, finally the rest of the knobs and switches) as the model years advance from 1980.
Changes such as these had not occurred since the 60's. The reason why is that people loved the very particular Marantz look. And they still do! The extent of these changes become even more obvious if you examine the specifications of the units, or put them through some tests on the workbench. They're just not the same level of quality as the 1980 and earlier units, sad to say.
At some point, I may expand the site to include the Philips-era units, if I can get some additional web space without blowing my wallet out of my pocket. I rather enjoy the controversy it all engenders... :)
|Q:||Where can I get service and/or owners manuals for my Marantz?|
Service manuals for many Marantz units can be had from A. G. Tannenbaum's.
There is a link to Tannenbaum's, among other useful things,
on the Links Page.
Owner's manuals are extremely rare. In most cases, owners learned how to run the gear and then discarded or misplaced the owners manuals. There are no dependable sources for owners manuals, however, you can sometimes find them on EBay:
|Q:||What is the origin of the Marantz brand?|
Saul B. Marantz, born in 1911 in New York City, started the company. His interests
included photography, playing classical guitar, and collecting oriental artwork.
Prior to his audio undertakings, he worked as a graphic artist and also
spent some time in the military. He grew up in Brooklyn, New York, where his
interest in electronics first blossomed as a young boy.
He was working as a freelance advertising graphic artist in 1947, but his love of music led him to design the Model 1 Preamplifier in his basement, drawing upon his military electronics background for the requisite skills. The model 1 was completed in 1949, and was received very well by the music listening community.
The model 1 was originally sold in New York at Harvey Radio, now a well known and broad-spectrum high fidelity vendor.
It is fair to say that this defines the start of the company, though Marantz as a corporate entity wasn't actually founded until 1952. The model 1 was launched as a formal product in 1953. Marantz embarked upon production of one wonderful piece of audio gear after another. Designs were initially all tube, with transistor units appearing in the sixties. Marantz tube gear is now the subject of collector enthusiasm that borders on the fanatical, and with good reason.
The Marantz company was sold to Superscope in 1964, though Saul Marantz remained with the company. This transition marked a number of definite changes in the company's approach to both design and manufacturing (and a very positive change in available funding). This provoked a great deal of worry among audiophiles about the consequences to the Marantz product lines. Those concerns, which persist to this day, (though only in the ranks of the uninformed) turned out to be quite groundless.
Marantz continued to put out incredibly high performance audio gear, constantly improving. This trend finally culminated in a superb line of audio separates that appeared in the years 1978 through 1980. The peak of the trend can be seen in units such as the 3600 preamp, which was hailed universally, and correctly, as so good that the test equipment of the time couldn't properly measure its faults.
Not inclined to rest on their laurels, Marantz produced the 3650 preamp next, a unit that outperformed the 3600 several times over. The 150 and 2130 tuners show a similar trend, and Marantz's flagship 300dc amplifier may be one of the best amplifiers produced by any company in those years, regardless of price. Not only did the products of these years have specifications that far exceeded anything Marantz had previously manufactured, but they still had "that sound".
In 1980 Marantz changed hands again. This time the new owner was Philips in the Netherlands. They bought the rights to use the name everywhere but in the USA. Eleven years later, in 1991, Philips gained control of the Marantz name in the USA as well. The designs and cosmetics of the brand changed radically as a result, and subsequently lost its luster to audiophiles.
Today, in 1999, the Marantz component of Philips appears to be struggling back towards a valid position in the high-fidelity marketplace. There is some road to travel yet. We're not seeing the kind of flexibility in controls today that we take for granted in the earlier units, nor do we see the same standards for performance. For instance, the company's high-end tuners of 1999 still don't quite meet some of the specifications of the units that were sold in 1979. Though to be fair to Marantz, the top of the line tuners of today are more sensitive than the older units. This is something we can reasonably expect given the advances in semiconductor technology and design.
Today, Marantz is clearly focused on broad spectrum consumer features such as Dolby surround and simplistic operating controls, as are most of the rest of audio manufacturers. Perhaps someday they will return to their roots, which I would describe as the provision of audio systems characterized by the highly flexible, configurable and connectable units of maximum fidelity of the late 70's. No better news could be had for the discriminating audiophile.
One very positive note is that Marantz has already brought more "friendly" cosmetic designs back. The current (1999) model year includes beautiful gold-finished models that you can (finally!) read the control legends on again. Finally we see a movement away from the hideous black effluvia that has plagued the audio component designs of virtually every manufacturer for years.
The best news for Marantz collectors is that 1980 and earlier Marantz gear was built so well that many of the classic units we can still find today continue to work better than just about any current audio gear you can buy "off the shelf". From anyone.
Saul Marantz died on January 16th, 1997, at age 85. He will long be remembered for the fine experiences he made possible.
In January of 2000, Saul Marantz was one of the first fifty individuals inducted into the Consumer Electronics Hall of Fame.
|Q:||What does the 'B' designation on some components mean?|
Not much, really. Sometimes, it means cosmetic changes. Sometimes, circuit changes. Sometimes both.
Nothing you can depend on, though. At the most, it means, "We're going to do this better,
There are cases where the model completely changed in the transition from non-B to B designation (like the 2285 and the 2285B; sometimes, there is little obvious about it at all, like the 1200 and the 1200b integrated amplifier.
You can also find models that have electronic changes internally only (the 10 and the 10b are good examples of this... after making about 100 model 10s, they reworked the IF strip on the 10b, for one thing, but my understanding is that it looks like the same tuner), and models that have new features and just the required cosmetic changes to accommodate the new features, such as the 3250 and the 3250b, which adds a moving coil amp for the phono input.
|Q:||Why does a 35 watt marantz sound better and louder than many 100 watt receivers?|
Because 35 watts as specified by Marantz in the 1970's meant...
"35 watts delivered into 8 ohms for one hour from all channels at one time with no significant change in distortion or other specifications at any time during or after the test hour."
...while 100 watts today (for instance, in my JVC surround system) means
"The unit can deliver 100 watts for about a second, in one channel only, if the other channels aren't running and nothing else high energy has happened to drain the power supply in the last few seconds."
In fact, my JVC claims 500 watts RMS, but the power consumption lable on the back panel tells the story:
320 watts drawn from the wall, at the most.
If the receiver was 100% efficient (which it isn't), that'd give you 64 watts a channel. But since it is (at best) 50% efficient, the system could perhaps generate 32 watts a channel continuously, which is pretty sorry compared to the rating. Less than a 2235. Shocking, eh?
Turning it around, because of the way that the units were rated in the 1970's, a classic Marantz rated at 35 watts a channel can dependably produce much more than 35 watts in both channels for a minute or two (far longer than the peaks in a modern receiver.) An honest rating for use with music for the power amplifiers of an older Marantz is generally in the range of 120% of rated power or even higher.
These ratings were instituted because of many false claims for power output that were being made using many different types of power measurement and general baloney at that time. IHF, RMS, Peak, Peak Music Power, Average, etc. RMS is what was settled on, and it's still widely used today, but the one hour rating was dropped some time back.
Interestingly, the situation that caused the RMS for one hour ratings to be made standard is now recurring - as I mentioned above, my JVC's ratings are pretty obviously designed to deceive the consumer, certainly they don't paint an accurate picture of what the receiver can actually deliver. My Sony car stereo suffers from the same kind of deceit: Right on the front it claims a very high wattage, but reading the manual, it turns out that the actual RMS power is far, far less than the front panel claims. I guess it's time for someone to step in again and slap these people around.
To the relatively straightforward power issue, you can add the fact that the design of the audio and RF circuitry in a Marantz is absolutely top-notch, and you can hear that in the character of what little distortion there is, in the way the bass, midrange and treble controls (and loudness contour and filters) affect the signals, in the way the FM signals come out sweet and clean, and so on. As an engineer, I really don't like to drop into using descriptive terms meant for food or lovemaking and so on for sound, but you know, when you A:B a Marantz against other units that are supposedly equivalent, the bottom line is it sounds better, and obviously so.
|Q:||What is a receiver or tuner "FM Quadradial Output" jack used for?|
Quadradial jacks are basically a direct take-off of the FM detector circuit prior to the
filters that remove the stereo subcarrier signal components at 19 and 38 kHz. The
idea at the time was that FM stations would begin broadcasting in a 4 channel
mode (some did, in fact, do so) and that Marantz (or a third party)
would develop a device that would extract the 4-channel information from
the "raw" FM signal available at the Quadradial jack in much the same manner that the stereo decoding
circuitry in tuners had been extracting stereo since the late 50's/early 60's.
There were a number of quad encoding schemes tried; but all in all, there are very few, if any, external FM decoding units out there now, and of course there are no quad FM signals to decode, either...
That direct take off can be used to decode other specially encoded signals, though. There are a number of things "stuffed" into the FM signal such as SCA audio ("Muzak"-type stuff, usually), the new character station ID's and station class information signals (country, rock, classical, news, etc.) Perhaps we'll be able to use those outputs to drive external decoders for those features someday. It'd be interesting, at any rate, and it's certainly technically feasible.
If anyone knows of such decoders, let me know, and I'll make note of them right here.
You know... if you'd really like to amuse yourself, you could hook up an old external stereo decoder (like a Scott tube de-multiplexor) and then feed the output of the stereo decoder to another amp... it should work fine. Hmmm.
|Q:||How does my tuner or receiver decode stereo broadcasts?|
The basic idea of encoding more than one channel into the essentially mono signal that FM
broadcasts were originally conceived with was to create a mono signal that would work for
receivers that didn't have stereo capability. This choice was made so that older mono-only
receivers would not become obsolete - useless - when stations began to broadcast in stereo.
With the compatible mono signal in place, the broadcasters would transmit other
information that could not be sensed by mono receivers, but could by stereo receivers. This new
information would be used by additional circuitry in an FM stereo tuner to create a stereo
signal from the mono signal.
The problem with creating a mono-compatible broadcast is that this information has to be added in such a way as to not be audible to the person listening to the original mono signal - it can't make the mono signal distort, lose volume or become more difficult to receive. That's was really tough to do if we wanted equal quality for the stereo signals.
The designers of the FM stereo system did a great job of approaching all these problems by choosing to put the mono signal in as (left+right), or the "sum" of the two signals. Addition, just like on paper. Then, they add a signal that contains the difference (left-right) between the two channels. Stations broadcast this signal as part of the normal audio signal, but encode it so that it is above the range of human hearing. The tuner carefully filters that signal out once it has been used, so not only was it above the normal direct range of hearing in the first place, it is completely removed from the audio by the time it reaches the amplifier.
This approach could work because FM signals are inherently wideband, that is, they were planned from the beginning to take up enough of the radio spectrum so that they could contain frequencies far above the range of human hearing.
Here's a simple example of how a stereo signal can be recovered from such an encoding, in essence:
|Q:||What do the Multiplex filter or Hi-Blend functions on my tuner or receiver do?|
FM broadcasts that are in stereo use the multiplexing system described in
the FAQ item just above. As described there, one of the restrictions on the
design of FM stereo broadcasts was that it could not affect the ability of
a monophonic receiver to receive the mono component of the signal. There
wasn't quite enough room to broadcast two complete channels in the spectrum
allotted to an FM channel, so the only choice left was to reduce the amount
of spectrum given to the stereo signal, instead.
What this does is reduces the amount of signal available for the FM Stereo encoding as compared to the mono (L+R) encoding; as a result, the tuner must have a stronger signal from an FM station to get the same amount of "quieting", or noise reduction, in stereo as the quieting it can achieve with the same signal in mono. If you'd like to try an experiment so you can see this happening, just tune to a moderately distant FM station. If you have a hi-blend or multiplex filter function, turn them off. Set the tuner or receiver to mono; and then pay attention to the amount of noise on the signal. Now set the tuner or receiver to stereo - notice how the noise level increases? That is the direct result of the FM stereo encoding being a less powerful portion of the broadcast signal.
When noise occurs in an FM signal, the way human hearing works ensures that it is most objectionable in the higher frequencies - to put it another way, we are more annoyed by a quiet "hiss" than by a quiet rumbling.
In order to allow weaker stations - in other words, the noisy ones - to be listened with the benefits of stereo, the FM multiplex filter (sometimes called "Hi-Blend") mixes the higher frequency portions of the mono signal (which is stronger, remember) with the midrange and lower frequency portions of the stereo signal.
As an example, one result of this would be that a struck triangle (a classical instrument that produces a very high and clear bell-like sound) that would have been mostly in the left channel will instead appear in the center of the stereo field. However, a guitar chord or kettle drum (these are mid- and low-frequency sounds, respectively) will appear properly positioned in the stereo field.
Because the high frequency component of the stereo signal is not fed to the output of the tuner at all, neither are the objectionable noise components. The end result is a better quality stereo signal from the weaker stations. When you switch the multiplex filter on, you should be able to readily hear higher-frequency components of the signal move to the "center stage", while mid- and low-frequency components remain normally separated.
Generally, you would only want to use this function if you are hearing high frequency noise when listening to a station in FM stereo. Otherwise it should remain off, or you may be giving up high frequency stereo separation available on strong signals for no reason.
|Q:||What does the FM Multipath function on my tuner or receiver do?|
When an FM signal reaches your tuner or receiver, it is important that the signal
is received directly from the station - think of it as looking right down a flashlight
beam. FM signals can reflect, just like that flashlight, off of certain types of
surfaces such as metal buildings and even geological rock formations. When this
happens, the reflected portion of the signal has traveled a longer distance to reach your tuner
or receiver, and this causes the phase of the sine waves that make up the signal to
differ from that of the direct (non-reflected) signal.
Since the two types of signals are traveling over different paths, the term "multipath" was coined to describe this condition concisely.
The reflected signal mixes with the direct signal at the receiving antenna, and the combination of the two is what reaches your tuner or receiver. From basic algebra we know that when you add two identical waveforms that are out of phase with each other, you get a third, new signal with a new waveform shape - which, in the case of FM reception, means that you are receiving a signal that now contains a distorted representation of the audio component within it. That, of course, is not what we want to be listening to.
The FM Multipath options on tuners and receivers allow you to either hear, or see, the component of the signal that is out of phase. That, in turn, allows you to direct (turn or aim) your FM antenna so that the amount of reflected signal is as small as possible as compared to the direct signal. This results in the least possible distortion when your audio system presents the recovered FM audio to you.
In the case of a "listen-to" design, the button is usually a momentary push-button This means you have to hold it in... it will spring back immediately when you release it. That is because the designers felt that you would not want to listen to the distorted (reflected) portion of the FM signal. It may also have been done, I believe, so that they would not get calls about the "audio being distorted" from customers that had somehow accidentally left the button depressed. It would be more useful if it stayed depressed, because some users have to cross the room to reach the controls that turn their antenna rotators, if indeed they have such gear (highly recommended, by the way!)
In the case of a "see" design, either a meter of some sort or an oscilloscope display is used. With these, you simply adjust for the least amount of displayed signal. Usually the designers of the tuner have allowed you the option to leave the oscilloscope or meter in the multipath measuring position, because simply viewing the multipath component doesn't affect what you hear at all.
|Q:||What is "Dolby FM"?|
Note that this explanation is simplified, but fairly accurate. Here goes...
Dolby FM is a system where the broadcasting station modifies the transmitted signal to contain more of the treble frequencies - the higher pitches. These are the same pitches where the "noise" is most objectionable. So when the FM signal arrives at your FM receiver, it still contains the same amount of noise, but more of the treble signal components.
Then, when this signal is processed by a Dolby decoding system, the total amount of treble is reduced according to the limits and methods of the Dolby technique, and as the treble is reduced... so is the noise!
Since there was more treble in the first place, and in just the amount that it is now reduced, the signal now has the original, correct, amount of treble, and less noise - because the noise is high frequency and it gets reduced right along with the real treble information.
The 25 uS de-emphasis switch changes the receiver or tuner's method for receiving FM to allow more treble through, but that is only a portion of the Dolby noise reduction method. The rest of the job requires a Dolby Decoder module, which is a fairly complex device. If you turn on the 25 uS de-emphasis switch without the decoder, you just get more treble... and the signal is no longer correct. Worse, if the signal is even a little bit weak, it will have more noise than it should.
For Dolby noise reduction to work properly, you need these three things: the proper de-emphasis (25 uS),the Dolby decoder, and for the station to pre-emphasize the signal using the Dolby standards at the time it is transmitted.
As far as I know, there are very few, or no, stations using Dolby processing at this time. So this feature is generally not of use any longer. Unfortunate. It worked very well.
|Q:||What does the "Antenna Attenuator" switch do?|
It's there for people in environments that are very near a broadcast
station's antenna. If you're really close to a transmitter, it can affect
reception all across the dial in a negative way. This could be another FM station
or even a transmission from a utility service such as police or fire radios
that are very near to the receiving antenna for the FM tuner.
With the switch on, the attenuator reduces the signal strength of every signal coming into the tuner, effectively moving all the stations further away.
In an urban environment, where most stations are close anyway, this usually eliminated the problem of the too-near transmitter(s) and left the other stations perfectly listenable.
In a more rural situation, where you're trying to receive stations that are further away in the first place, using the attenuator can make an otherwise listenable station unlistenable - but if you're suffering from severe interference, this may be your only option.
This kind of interference usually occurs in the receiver's front end and mixing stages, before the IF stages, so even tuners like the 10B that have outstanding adjacent channel rejection characteristics can suffer from this problem.
If your tuner doesn't have an attenuator, you can make one or buy one. A really good solution is to pick up a Magnum Signal Sleuth, which is a purely linear device that preselects signals before it gets to your receiver's mixing stages. Check out the review on the reviews page for more on the Signal Sleuth, including links to the manufacturer. I have no connection with them other than being a very satisfied owner of one I purchased from Antenna Specialties.
|Q:||My receiver has a "Custom Calibrated" plate on it. What's that?|
Basically, with these units, Marantz assembled and aligned the receiver and then
put it on the bench. They put a blank faceplate in the unit, and then
with a signal generator, located exactly where on the dial each
FM marking should go, and then had the dial hand-painted to match the
The result was a tuner dial that, for FM, had an extremely accurate dial scale, something that was not very common at that point in time. I have not heard that they did this for AM tuner sections, though certainly the same technique would work there as well.
|Q:||Where can I get the factory wooden cabinet for my Marantz unit?|
Factory cabinets are rare. In most cases, units were purchased without the
There are no dependable sources for cabinets, however, you can sometimes find them on EBay:
|Q:||What does the "DC" designation on some components mean?|
The "DC" designation refers to the fact that this preamp, amplifier or
integrated amplifier can amplify signals over a much wider range than non-DC
designs. Here is why that is useful:
The sounds that most people can hear from their stereo are created by speaker surfaces that are being forced to move back and forth by precisely controlled positive and negative surges of current driven through them by the audio amplifier. This occurs at rates of from twenty times a second, to as high as twenty thousand times a second.
For the slowest rates (20 times a second), the amplifier has to correctly amplify these slow signals; if it does not, the sound that comes out of the speaker will be different than the sound on the audio source. Many amplifiers do a fairly poor job of amplifying such slow signal changes - they are designed to cover a wide range of signals, but at the edges of that design, the amplifier's performance limitations begin to affect the signal adversely.
The reason that designs like this are marketed successfully is that most people cannot hear very well, or at all, at the outer limits of their hearing range (20 times a second, or 20 Hz, for instance.)
DC amplifiers, preamplifiers and integrated amplifiers are designed to be able to amplify signals that are much slower than the 20 changes per second that you can hear if your hearing is very discriminating. They can amplify signals at 10 changes per second; at five; at one, and even signals that don't change at all! That last type of signal is a special one called a "direct current" signal, or "DC" for short. That's precisely where the term "DC" comes from when you see "DC amplifier" or "DC Preamplifier".
This example should serve to explain the term DC a little further. If you connect a battery to a lamp, the battery steadily provides a current that does not change (until the battery runs down, of course.) A DC amplifier should be able to respond accurately when a battery is applied to an input - the current output to the speaker should then change until the amount of amplification set by the volume control is reached, and then stay there. Note that you would definitely not want to actually try this, as it is not good for the speaker at all!
The idea of a DC audio component is not to actually amplify a direct, steady current, but rather to extend the amplifier's ability to correctly reproduce a signal so far below the 20 changes per second it needs to that the 20 changes per second is no longer at the "design edge", and so benefits from the same benefits as the majority of the middle range of reproduction does.
It is interesting to note that most of the Marantz DC amplifiers have a switch on the back to actually prevent the user from applying a DC signal to the amplifier inputs, specifically because this can damage the speakers, as I described above - and no one wants that!