PC Hi-Fi: Scythe's Kama Bay Amp

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March 24, 2008 by Devon Cooke

Scythe Kama Bay Amp SDA-1000
PWM Digital Power Amplifier
Market Price

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.

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