What kinds of ideas have been used in the past to make so called "hi quality"
sounding amplifiers in stereo systems?
I'm thinking of things like the Carver amplifiers of the 80s. Are there any
odd ideas that people have tried in the past?
**You're kidding, right? The list is very long. **Carver actually used two separate and equally bad technologies to build
his lightweight products. They were: * TRIAC controlled power supplies. This system controls the amount of energy
applied to the primary of a transformer in response to the demands of the
musical signal applied. Kinda like a light dimmer. The problem with this
technology is pretty obvious to everyone. Except Carver, apparently. Mains
energy is supplied at a 100Hz (120Hz for the US) rate. Musical transient can
occur at rates of up to 20,000Hz.
* Rail switching technology. Rail switching amps (aka: Class H, Power
Envelope, etc) have been tried and dismissed by quite a number of
manufacturers. Marantz, Yamaha, Hitachi, NAD, et al, have all tried it. All
have dismissed the technology, because the result is a poorer sound quality
than regular, non-rail switching amplifiers. The problem relates to the
enormous characteristic changes inherent to ALL active devices, as the rail
Voltage is altered. IOW: Such amplifiers perform extremely well under steady
state, sine wave conditions, but poorly under actual, real life music.
As for your question, yes. The list of odd ideas is simply enormous.
One of the strangest was called "tubes". Something about
electron flow through a vacuum.
In the category of tubes there is a really odd one called
"SET" or Single-Ended Triode. Back in the late 1920s it was
found that using push-pull output stages provided a large
number of worthwhile benefits, but that apparently hasn't
stopped some people from trying to roll the clock back to
the days of Prohibition.
How about SS amps with no loop feedback? This creates a
number of problems including a near-total lack of power
supply ripple rejection.
Lots of them. Another oddity involved attempts to implement
SET using FETs.
Like a tube amp of multi-parallel triodes and no OPT?
Or multi-sectional cross-wound transformers?
Or bad ideas like:
The 'ear shaped speaker'... talk about convoluted logic...
The 'reflected Bose' speakers.
There is a long list..
If you download the circuit diagram and you know a bit about electronics you
will scratch your head even more. It's a class A design with bare minimal
components, EXTREMELY power hungry and inefficient, has a very high
distortion statistic (which is disclosed in a graph but not ever mentioned
in the text) but all in all if it gets people into electronics, I like it.
Looks like a lot of hobbyists have made it. Some of the box designs are out
of this world. One guy has made two monoblocks. Each as big as a floor
standing subwoofer. Due to the inefficient design of the amp, his listening
room would be similar to a room with a 2000W electric heater while running
them. Not just at full volume, but all the time!!
That must be why you see so many Marantz, Yamaha, Hitachi & NAD powered
theatre & stadium concert PA rigs, wheras the minnows of the PA world
Crown, QSC, BSS,LabGruppen etc have no problem with rail switching and
riding technology :-)
**Utter, banal nonsense. NAD, Marantz, Yamaha, Carver, Hitachi and many
others have used rail switchers in home audio products, because it allows
them to inflate transient power abilities, at very low cost. The first,
highly successful, amp I saw was the NAD 2200 power amp. It was rated at 100
Watts continuous, with 400 Watt transient ability. So successful was it,
that it spawned a line of smaller and larger amps from NAD. Of course, it
sounded like crap and had a bad reputation for destroying speakers, but it
looked great on paper and the reviewers fell over themselves to rave about
it. Consequently, customers fell over themselves to buy them. NAD later
dispensed with the technology, after losing significant sales to competitive
products (which didn't use rail switching technology).
The feedthrough from the rail switching into the audio path is actually minute.
I've designed several rail switching amps for SR use. As Arny says though, there
is considerable extra complexity in the bits so I wouldn't use the method much
below the 400-500 wpc category.
**Perhaps. That is not the major part of the problem. Examine the curves of
the output devices. Look at the difference in characteristics with different
VCE applied. **You may not. All the companies I quoted did use them in lower powered
amps. NAD have used rail switchers in amps with continuous power outputs as
low as 30 Watts.
A question, Trevor. If the reviewers praised the product, and
customers bought it en masse, how did NAD lose "significant sales to
competitive products"? It sounds as though you were the only one who
noticed it sounded like crap.
**You need to understand how the retail world operates. In reality, the
number of people who actually listen to products, before purchase, is
incredibly tiny. Almost all purchase based on the following: * A glitzy brochure.
* A well written and glowing review.
* A nice front panel.
* Fancy features.
* Word of mouth.
I would estimate that the number of people who actually do a good, hard
listen to a product, BEFORE purchase, at around 0.1%. Or less. Bribery in
the audio business is pretty much ingrained (though not in Australia,
AFAIK). Reviews are bought and sold in the US and the UK. Before you ask: I
have dealt with US, UK and Australian reviewers. No Australian reviewer has
asked for 'consideration' for a review. SOME US and UK based reviewers have
spelt out, in no uncertain terms, how much a good review will cost. I cannot
say if that is a function of the publication, or just corrupt reviewers.
Either way, I don't trust any of them. Except Scot Markwell. He seemed to be
honest and straightforward.
NAD had (justifiably) acquired an excellent reputation for budget, 'high
end' sound quality (my favourite was the brilliant 3120). Albeit, with
rather dodgy constrution and suspect component choice, thanks to the
manufacturing company - Fullet. Sometime around 1984-5 NAD moved production
away from Fullet and released the NAD 2200 power amp. As an NAD dealer, at
the time, I ordered them for my store. I was immediately struck by three
things, when I listened to the amp:
* It's spectacular amount of power, for such a modest price. It was a very
potent package. (A point which should not be underestimated)
* It's pretty decent build quality, compared to previous NAD products.
* It's extremely average sound quality, compared to earlier, less powerful
Based on the above, it is easy to see how, with a good review, the NAD 2200
would gather significant sales. After all, few people actually took the time
to listen to the thing. The market place is a funny thing. Like most things,
there is a time lag, between cause and effect. Yamaha, for instance, built
very good amplifiers, back in the 1970s. Quality plummetted in the 1980s,
but their sales continued rising, during the 1980s, due to the high quality
of their products produced a decade earlier. Marantz is another company
which built very good products in the 1960s and pretty decent products
during the 1970s. Late in the 1970s, my boss at Marantz called me into the
office. He explained that Marantz was about to embark on a new style of
constrution called 'value engineering'. This sounded exciting. The reality
was somewat different. Products produced by Marantz in the late 1970s were
very poorly constructed, using cheaper parts, than the equipment I was
accounstmed to. Nevertheless, sales increased. Largely due to the previously
excellent reputation and the more contemporary styled front panels. IOW:
Outside they looked great, inside was crap.
[ASIDE]: I sold a 2200 to a client who was using a pair of KEF 104.2
speakers. Although I had sold lots of KEF 104.2 speakers, I had only sold
one 2200/104.2 combination. Some time later, the customer brought back the
KEFs complaing that they had no HF. They didn't. Both (ferro-fluid cooled)
tweeters were fried. This was unheard of. The KEF 104.2 tweeters are very
tough. I sent them back to the distributors (Fred A Falk) for under warranty
repair. They rejected the warranty claim, suggesting that the amplifier was
at fault. I replied that the amplifier was an NAD 2200 (which Falk also
imported). Silence. "OK, we'll repair them free of charge." Apparently, the
NAD 2200 has/had an appalling reputation for destroying tweeters. Here's my
Customer turns amplifier up to the point of clipping (400 Watts). Then
allows the amp to run for a period of time at high levels. The Power
Envelope circuits have a time/energy circuit, which prevent damge (to the
amp), which shuts off the high Voltage supply, after a period of time. Thus,
instead of mild clipping, the amplifier reverts to massive clipping, thus
allowing huge levels of high order harmonics to destroy HF drivers. The
listener, whose ears are suffereing from continuous high level audio, cannot
hear the massive clipping and the tweeters are destroyed.
It sounds as though you were the only one who
**I very much doubt that. I am pretty certain other people actually listened
to the stuff too.