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PC Hi-Fi: Scythe’s Kama Bay Amp

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Most SPCR reviews are about eliminating noise, but Scythe’s Kama Bay Amp is all about making noise — as accurately as possible. A stereo amp in an optical bay may not be for everyone, but for those frustrated with trying to get high quality computer audio, it may be a godsend. Why limit yourself to computer speakers when you can choose from a vast selection of superior quality hi-fi speakers for the low cost of this amp?

March 24, 2008 by Devon
Cooke

Product
Scythe Kama Bay Amp SDA-1000
PWM Digital Power Amplifier
Manufacturer
Market Price
US$40~55

OK, so it’s a little unusual for Silent PC Review to be reviewing a component
whose sole reason for being is to produce noise, but that’s no reason
to write it off altogether. In this case, the noise in question is desirable:
It’s music, soundtracks or whatever else you want coming out of your speakers.
What component is it? It’s a simple stereo amplifier shrunk down enough to fit
into a standard optical drive bay.

A little background is in order. Why would you want an amplifier hooked up
to your system in the first place? You’ve never needed one before — right?
Right … and wrong. The truth is, if you’ve played audio on your PC before,
you’re already got an amplifier somewhere in the loop. It’s just that, like
so many other components in the computer industry, it’s integrated into another
component, in this case, your existing computer speakers.

The purpose of an amplifier is very simple: To boost the line-level audio signal
coming out of your sound card up to a level that is audible when played through
your speakers. Typically, an amplifier will include a volume knob as well, though
this function is technically part of the pre-amp, not the amplifier itself.
Basic computer speakers (or "powered speakers") achieve this by including
an amplification circuit built into the speaker housing or subwoofer, and they
accept a regular 1/8" input rather than bare speaker wire like the conventional
speakers in your home theater.

This arrangement works well enough so long as you are content with the rather
limited range of computer speakers that are commonly available. The trouble
is, virtually all computer speakers are designed to sit on a desk aside a computer
monitor, so they are typically quite small and sound best at close range. They
are not intended to fill a room with music, and they don’t cater to the high
end market. As well, building the amplifier into the speaker comes with compromises.
Speakers are sound boxes: They depend on the the shape of their resonant internal
space to maintain as flat a frequency response as possible — a task that
gets harder when that space is full of electronic components. In addition, any
noise produced by the electronics will be amplified simply by being inside the
speaker. Many a humming subwoofer can be traced to a vibrating coil in the amplification
circuitry.


The box for the Kama Bay Amp is about the size of a no-name DVD player.

Scythe’s Kama Bay Amp is suitable for the growing number of hi-fi enthusiasts
who use a PC as their primary source of audio but want the wider selection and
better quality of regular unpowered speakers. It fills a niche between regular
computer speakers and a full-blown home theater or hi-fi setup fed by a S/PDIF
audio signal. It is the equivalent of a home theater receiver stripped down
to two channels and without any video capability. However, unlike a home theater
receiver, the Kama Bay Amp weighs less than half a kilogram and fits easily
into a regular PC housing.

This incredible reduction in size is possible because the amplification circuit
in the Kama Bay Amp is fundamentally much more efficient that that type of circuit
used in home home theater equipment, and thus requires smaller components, less
heatsinking, and less space. It is also rated for 10W per channel, while home
theater equipment is often rated for 100W or more.

Although it is called a digital amp, it is digital only in name — the
analogue signal is never quantified to a single number as it would be in a properly
digital system. It does bear one thing in common with digital audio, however:
The amplification process divides the signal into sections — approximately
one every 500,000th of a second — and amplifies each section independently.
This is similar to the 44.1 kHz sampling used in audio CDs (digital!) —
and also to the high frequency switching used in computer power supplies and
the PWM switching used to control fan speed. This is why Scythe refers to the
product as a "PWM Digital Power Amplifier".

This type of amplifier is known as a "Class D" amplifier. In the
past, Class D amplifiers have been considered inferior to the Class AB amps
typically found in home theater receivers, but recent Class D designs have improved
greatly. The Kama Bay Amp is based on a Class D chip from Yamaha, a fact that
Scythe proudly advertises on the front of the box. It is this chip that makes
such a small, low-cost amplifier possible.

FEATURE OVERVIEW

Although designed to fit in a standard optical bay, the Kama Bay Amp doesn’t
actually require a computer to work. It’s entirely self contained: It accepts
a stereo RCA connection as input, and has a pair of five-way binding posts that
mates with almost any speaker connection. It also has a standard headphone jack
that mutes the speaker output when in use. A Molex power adapter and a 1/8"
to stereo RCA cable are included as standard equipment for connecting to your
existing power supply and sound card, but it also includes a 12V power brick
and a regular RCA to RCA cable, allowing just about any audio component to be
connected to it with or without a computer.

Several other accessories are also included: A silver faceplate that can be
swapped for the existing black one, a PCI-slot cover with a hole for routing
cables into the case, and two thin-gauge lengths of speaker cable. All of the
cables are thin and poor quality, but none is long enough to warrant a need
for higher quality except in unusual, high interference situations.


There’s a lot of bits and bobs here.

Scythe Kama Bay Amp Feature Highlights (from
Scythe’s web site)
FEATURE & BRIEF COMMENT
Quality High Performance YAMAHA IC Chip
In order to create a high quality sound and not to compromise in the sound
quality, YAMAHA YDA138 chip is built into this amplifier!
It’s more than just built
in — this chip is the amplifier.
External or Internal Usage
Built into your PC case to create a high quality sound or use it as external
usage for your home theater system!
Amplifies any signal
— no PC required. Just use any standard RCA cable.
Luxury Appearance
Not only the sound yet front panel and entire material in high quality to
create luxurious appearance! Gold plated RCA jack and speaker terminals
to further enhance the appearance!
Hi-Fi in your PC. At
least they aren’t falsely advertising gold-plated connectors as giving better
audio quality.
All Cables Included
Cable for audio, speaker, and AC adapter are all included for ready-to-use!
A nice kit.
Scythe Kama Bay Amp Specifications (from Scythe’s web site)
Model Name
Kama Bay Amplifier
Model Number
SDA-1000
Manufacturer Scythe Co., Ltd. Japan
Dimensions (W x D x H) 152 x 113 x 41 mm
59.84 x 44.49 x 16.14 inch
Output

Speaker x 2 Channel
Headphone x 1 Channel

Input RCA Connector x 2 Channel
Power IC YAMAHA YDA138 (D-3) Digital Power Amplifier
Number of Channels 2 Channels
Continuous Max. Output 10W x 2 Channel
Max. Efficiency 88% (8Ω/10W)
SN Ratio 103 dB
Total Harmonic Distortion Rate 0.02% (1KHz/8Ω)
Headphone Amplifier 50mW x 2 Channel, SN Ratio: 95dB
Power Source DC 12V (4-Pin from PC Power Supply)
or AC Adapter
Weight 480 g / 1.06 lb

EXTERNAL OVERVIEW

With the exception of the sleek black faceplate, the Kama Bay Amp looks decidedly
unimpressive on its own. It’s a small metal box about the size of a paperback,
and it does a poor job of hiding the cable spaghetti that sprouts from the back
of it. In fact, the weight of the cables has a habit of pulling it out of whatever
position it is put in. It’s dwarfed by virtually every other home theater component
— game consoles, DVD players, HTPC enclosures etc.

An amplifier is a simple device, and Scythe has wisely avoided fancying it
up with unnecessary buttons and displays. It has a power button, a large, centrally
located volume knob, and a small mute button off to the side. There is also
a headphone jack next to the mute button. This is all an amplifier should ever
need.

The volume knob has some tension to it, and it clicks when turned like a mouse
wheel. Volume is adjusted in discrete steps with each click, not continuously
as you might expect of a volume knob. The range of adjustment goes from fully
off at approximately seven o’clock to a comfortable listening volume at twelve
o’clock (at least with our test speakers). The remaining half turn (twelve o’clock
to five o’clock) nudged up the volume relatively little, going from comfortable
to slightly-louder-than-comfortable. This suggests that the knob is aligned
linearly with the amp’s wattage output, not the subjective volume as you might
expect..


Good things come in small packages.

The silver-gray body and the default black faceplate do not match and look
a little odd, especially in combination with the bright gold-plated connectors
sticking out the back. At first, it seemed that Scythe had left the exterior
unfinished because of the expectation that it would be installed in a PC, but
we were surprised to notice that the two sides are actually pieces of silver-colored
plastic which must be removed before it will fit in a drive bay. Clearly, the
silver-and-black color scheme is deliberate.


Gold-plated connectors for "luxury appearance".


Rubber feet must be removed when installed in a PC.

LONG TERM TESTING

SPCR does not have a standard test procedure for such an unusual
product, so we tested the Kama Bay Amp slowly over the course of two months
so we could really get to know its ins and outs. Initially, it replaced a cheap
Sony mini-system amplifier (I know, I know) that was feeding a pair of Pro-Linear
PL3.5B bookshelf speakers. This arrangement required heavy EQ in Realtek’s
driver software to sound even close to normal — but that’s what you get
when you use a mini-system with mismatched speakers. We’d have been very disappointed
if the Kama Bay Amp did not outperform the Sony amp. In both cases, the source
was the integrated audio on a Soltek SL-K8T Pro-939, powered by Realtek’s ALC850
audio chipset.

When powered by the included power brick, the Kama Bay Amp sounded
terrific — a night-and-day improvement over the crappy Sony mini-system.
The bookshelf speakers still sounded a bit boomy and cramped, but that had more
to do with the speaker itself and their position too close to my ears than any
fault of the amp (we do recommend taking care when positioning your speakers
— regular bookshelf speakers aren’t designed to be listened to from three
feet away). A little EQ quickly smoothed out the low end.

For the most part, the audio in this setup sounded crisp and pristine;
the relatively full-range Pro-Linear speakers proved their worth by delivering
clearer, more dynamic audio than I have heard from almost any powered computer
speaker. Some might lament the lack of subwoofer support, but for listening
to music this was a blessing; I’ve never yet encountered a well-balanced 2.1,
4.1 or 5.1 speaker setup for computers, and the relatively large bookshelf speakers
provided a richer low-end than most computer speakers are capable of.

Although the Pro-Linear speakers are not particularly inefficient
or hard to drive, I did notice occasional clipping when the volume knob was
above halfway. The clipping was most noticeable in tracks with heavy, synthesized
bass — the Portal soundtrack was particularly bad. This is no surprise
— sustained bass notes require the most power to amplify, and, at times,
the 10W per channel rating didn’t quite seem to be enough.

Unfortunately, we discovered one major drawback. While the audio
quality was excellent, we noticed that our wireless keyboard and mouse stopped
working whenever the amp was on. Some experimentation revealed that the effective
range between the peripherals and the wireless receivers dropped to about a
foot or less from six feet or more. A second, more robust wireless keyboard
and mouse dropped to about three feet from twenty. The range dropped even further
when the volume was cranked up high.

Clearly, the Kama Bay Amp has EMI shielding issues, and not small
ones either. According to Yamaha’s
spec sheet
, the switching frequency of the amp is in the realm of ~500 kHz,
and this is where you would expect the worst interference to occur. This is
two orders of magnitude lower than the 27 MHz band used by wireless peripherals,
so obviously the interference is not restricted to the 500 kHz band.

This interference was a rather serious problem, so we attempted
to solve it by wrapping the power brick in several layers of aluminum foil.
While this helped a little, it was nowhere near enough to allow ordinary operation
for our keyboard and mouse.

Next, we sought to eliminate the power brick entirely by using
the Molex adapter to power the amp from the system power supply. Unfortunately,
not only did this not solve the problem, it also revealed a truism about amplifier
design: an amplifier is only as good as the power supply that feeds it. With
the amp sharing the same power supply as the rest of the system, every drive
seek, every mouse click, and every spin of the scroll wheel was amplified audibly
as the electrical effect of each action propagated through the system. Using
a power supply with lower ripple and better voltage regulation might have helped,
but we’re hard pressed to recommend the Molex adapter to anyone who wants clean
audio. To top things off, eliminating the power brick from the equation still
did not solve our interference issues.

Our testing concluded by throwing the Amp into the deep end: It
was substituted into our lab home theater system, replacing Panasonic SA-HE200
receiver and driving a pair of transmission-line speakers built and tuned by
SPCR’s editor-in-chief, Mike Chin. The source? A Chaintech AV-710 sound card.

Differences between the Panasonic receiver and the Kama Bay Amp
were small but noticeable. The Kama Bay Amp sounded less cohesive and "focussed"
than the Panasonic; at times, the music sounded like a collection of instruments
playing at the same time rather than a band (or an orchestra) playing together.
On the other hand, bass-heavy drums and loud thumps were more dynamic and "impactful"
on the Kama Bay Amp — possibly because it lacks the subwoofer crossover
that is active (even in "Direct Mode") on the Panasonic, and therefore
allows the speakers to perform at their full frequency range as is desireable
in a setup with no subwoofer.

CONCLUSIONS

The Kama Bay Amp is not for everyone, but it does open up possibilities
for a new market segment. Gamers and avid movie fans will probably pass on it
because it is stereo only, and those used to the mandatory "subwoofer"
included in most computer speaker kits will be disappointed that a subwoofer
is not supported. Avid music listeners, however, should be thrilled: This small,
inexpensive amplifier allows a much wider range of speakers to be used —
without the hassle of hooking the system up to a large component-based audio
system. With such selection, it should be easy to find speakers that more than
make up for the loss of multiple channels and a subwoofer. And, if you really
can’t live without them, you can always use multiple Kama Bay Amps (three for
a 5.1 system).

The audio quality isn’t perfect, but it’s probably good enough
to satisfy the compact hi-fi market that it targets. 10W per channel doesn’t
go that far for pure volume, but with most speakers it should be enough. As
long as it’s fed clean power (the Molex adapter was hopeless), we had no issues
with the audio quality.

The interference issue was more serious. While not everyone uses
wireless peripherals, there are enough wireless devices around that nearly everybody
has at least one. Wireless phones, wireless networks, some remote controls,
and even cell phones are potential candidates for interference. Then there’s
radio, broadcast television, and even medical equipment that could be affected.
The obvious fix is better shielding, but our experiments with aluminum foil
showed that this isn’t as simple as it sounds, especially since both the power
brick and the amp itself appear to cause the radiation.

Like just about every other product we review, our opinion of
the Kama Bay Amp comes down to noise. Except, this time, the audible noise is
fine — it sounds as good as we ever thought a $50 amp could sound. The
problem this time is electrical noise. Electrical interference is an engineering
problem that should have been solved before the product ever shipped, but it’s
hard to say whether it’s a deal-breaker or just a minor inconvenience. Ultimately,
the answer is probably subjective: If your household is wireless-crazy, avoid
the Kama Bay Amp. If not — who knows? It might be worth buying just to
drive the neighbors crazy when their phone drops out…

Many thanks to Scythe
USA
for the sample.

COUNTERPOINTS


by Steve Hayashi
I would say that the Kama Bay is for an extremely niche market. It’s specifically for people who want a cheap higher quality amplifier with a small footprint. For the same amount of money, you can go on e-Bay, and get a used stereo amplifier/receiver that will blow this product away in terms of power and possibly sound quality (though it’ll take up more space). Receivers/amplifiers aren’t exactly new technology (excepting high quality class D) so it’s not unreasonable to suggest looking on the used market for quality. Those who want something new could spend around $100 for a new receiver or $200 for a higher quality receiver.

Even if it was fully functional without the interference, I would find it difficult to recommend this to anyone. Those that are happy with their current amp aren’t likely going to be spending money, and those who aren’t happy with their current amp are likely willing to spend the additional money (or go used) to purchase a superior amp. This is more of an in-between step for those who want to spend more of their money on nicer speakers.

by Russ Kinder
I think the real competitor to this is something like the Sonic Impact T-amp. Same concept, except for not being drive bay mountable and it being a class T instead of a D. Its cheaper too, like $35 at Amazon or Target. [Editor’s Note: The price seems to have climbed a lot since Russ last looked; BuyItNow prices at eBay are >$65.] The other big difference is that the Sonic T sounds amazingly good. I’ve been using one for a couple of years now in my workshop system, and it consistently impresses people. Jeff Day did a nice write-up of it over at 6moons a while back.

 



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SPCR Articles of Related Interest:
Squeezebox 3 Digital Music Box
Zalman ZM-RS6F Surround Sound Headphones

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