by Sergey Romanov
04/08/2009 | 01:50 PM
Long time ago, when multimedia speakers were at the primeval stage of development – low-power and low-sound-quality plastic boxes – I would often check out the price of their more serious counterparts from the hi-fi audio world. Entry-level hi-fi speaker systems looked impressive and promised acceptable sound quality but every time my shopping was cut short by the necessity to buy a power amplifier. This indispensable component cost as much as a couple of speakers, so the total cost of the purchase grew twofold. If I could only plug those speakers into something so as to produce any sound at all and buy a good amplifier later on…
I should confess I recalled all that when I learned about the new product from Scythe, the well-known developer of computer parts. This company has already earned worldwide recognition as a maker of coolers and modding accessories, but it goes on turning out more and more original products. Some time ago it released an active speaker system for a 5-inch bay of the system case. And at CeBIT 2008 it showcased another original solution, a compact power amplifier for passive speakers and headphones called Scythe KamaBay Amp SDA-1000. It can be installed inside a computer case, too. Besides, it can be used as a standalone device for various applications. This makes me wonder if this small box can do big deeds.
The designers have done a good job on this amplifier. It looks perfect with its brushed-aluminum front panel. Its large black volume control has a shiny rim and turns around with nice soft clicks while the large Power button that just asks you to press it. The Mute button is neat and there is a little of chrome around the case as a finishing touch.
Just as you can expect from a noble power amplifier, the back panel offers four gold-plated screw clamps for bare wires to connect your speakers and two RCA connectors for audio sources. It would be just ideal if the clamps for speaker cables were spring-loaded as in the C.E.C. HD53R.
Three small rubberized feet can be screwed into the bottom panel to put the amplifier down on polished and other scratchable surfaces. If you want to install it into your computer case, you have to unfasten the four screws holding the plastic side panels. Depending on your personal preferences, the front panel can be either matte black or shiny silver.
Notwithstanding the small dimensions of the amplifier proper, its box is not small. It contains an external power adapter and a lot of accessories each of which is depicted on the back of the box.
There you can also find a visual description of all of the amplifier’s connectors and controls and read its specifications. The package design and the accessories are good – I can’t find any fault with them.
The amplifier is powered by a unipolar power source that can be a computer’s PSU (via an adapter for a Molex connector) or the included 12V/3A power adapter.
But how can this tiny box be a power amplifier? It has little resemblance to grownup models in size, weight, connectors and electrical parameters. Every owner of hi-fi equipment knows that an amplifier is a large and very heavy unit!
The fact is the Scythe SDA-1000 is not a simple analogue, but a digital amplifier (Class D) which heart is a Yamaha YDA138 chip.
Digital amplifiers differ from ordinary ones with high efficiency in the first place. Widespread amplifiers from the combined amplification class AB have an efficiency of 50% and higher only when the output power is close to maximum. It means that under ordinary conditions over half of the power received from the mains is dissipated by such amplifiers uselessly as heat. Class B amplifiers can achieve an efficiency of 75% but produce significant distortions at low output power. Class D amplifiers amplify not the sound proper but a modulated pure tone whose frequency is many times higher than the top of the audio range. This helps reduce the half-open period of the transistors and minimize useless heat dissipation without compromising the quality of the input signal. The YDA138’s efficiency is lower than 75% only at an output power of 1W or less. Such a high efficiency is achieved by using the output transistors in switching mode – they are either open (letting the current pass almost without loss) or shut.
You can learn more about the specifics of various amplification classes in Analog Devices’ material and by the following link: http://sound.westhost.com/articles/pwm.htm. Right now let’s make out what the main chip of the Scythe KamaBay Amp can do.
The Yamaha YDA138 is an integrated Class D amplifier with pulse-width modulation of the carrier frequency of 500MHz whose special feature is the ability to operate without low-pass output filters. The manufacturer calls this a “Pure Pulse Direct Speaker Drive Circuit”.
Each of the amplifier’s two channels is responsible for two bridged outputs providing high output power at low voltage. However, the bridge design increases the minimum permissible load impedance (it equals 8 Ohms for this chip). Oddly enough, this fact is not mentioned in the end product documentation. When I perused the chip documentation more, I found out that it could work at a load impedance of 4 Ohms but the outputs of the left and right channels must be connected in parallel for that, transforming the amplifier into a monophonic one.
The chip also incorporates an analog headphone amplifier (2x50mW, class AB). Its wattage rating is more than enough for most headphones with an impedance of 32 Ohms and higher. Unfortunately, the amplifier does not use a bridge circuit and does not incorporate internal voltage converters. Therefore it requires blocking electrolytic capacitors at the output.
I also want to note that the chip allows setting one of four gain settings for both the integrated amplifiers.
I never had to turn the volume control by more than half-way, so the manufacturer seems to have chosen the maximum gain setting. This is hardly a reasonable solution because the output signal of most sources is higher than 0.5V and as high as 2V with modern sound cards.
More apprehensions arise when you look inside the amplifier. On one hand, everything is assembled neatly, but the input cables are not screened. They are connected to the PCB via connectors while the other cables are soldered in. A number of electrolytic capacitors from obscure firms are employed – even where Yamaha recommends using multilayer ceramic capacitors and where film capacitors might even be used to achieve higher sound quality. The chip is located on the reverse side of the PCB and has no contact with the casing. In other words, it dissipates its heat through the PCB itself.
Summing up this section of the review I want to show you the specifications of the YDA138 chip that are absolutely the same as the specifications of the end product called Scythe KamaBay Amp SDA-1000.
Before I begin my long tale about my listening to the KamaBay Amp and measuring its characteristics, I want to tell you first what you should not do with this amplifier. When I took the device out of its box I really wanted to install it into a 5-inch bay of my system case and forget about the included power adapter. But I soon had to give up that idea. When the computer had booted Windows up, I bravely pressed the Power button on the amplifier and the whole computer just shut down instantly. A sudden surge in the current consumed for loading the amplifier’s capacitors triggered protection in my Rosewill Turbo Series RT550-135-BK, which is quite a sturdy 550W power supply. Of course, there are no problems if you turn the amplifier on beforehand, but I don’t think it reasonable to risk shutting down your computer by pressing a single button. Therefore I used the amplifier only with its external power adapter. Moreover, when the amplifier was connected to the PC’s power supply, there was too much extra noise in the headphones among which I could easily identify the moments of activity of my hard drives and other devices populating my system case.
So I began my tests by listening to the amplifier in headphones. Like in my previous reviews, I used Grado SR 325i headphones and a C.E.C. HD53R-80 amplifier. This amplifier is a good choice for making a comparison with the KamaBay Amp because it allows connecting both headphones and speakers, too. Of course, these two devices come from different categories, the KamaBay being more than 10 times cheaper, yet it is better to compare sound quality with an etalon, and the C.E.C. amplifier can serve as such well enough. The sound source was an ASUS Xonar D2 sound card that had proved its overall superiority over the Creative X-Fi Elite Pro and Auzen X-Fi Prelude 7.1 in our comparative tests. I used various test materials that had one common property: every recording was ripped from a CD and saved either in uncompressed WAV format or in compressed lossless format (Monkey’s Audio). I reproduced them with foobar2000 version 0.9 with 24-bit precision Kernel Streaming output.
Quite expectedly, the Scythe KamaBay Amp lost the first round of the comparison. It was considerably inferior to the more expensive opponent (from amplification class A). The most notable difference was that it reproduced dry and muddy high frequencies, resembling the notorious “digital” sound compact-discs had been criticized for. I could also note it to have a worse attack, less rich timbres of vocals and instruments. It lacked the minor details of live recordings that created the effect of your being present in the concert hall. This can be characterized as the reduction of transparency and resolution. The sound stage is flat and the sound is unexciting overall. Connecting the headphones directly to the line output of the sound card (which has an additional buffer with dual general-purpose opamps) proved to be preferable. I even could not decide what sound I liked better: with the C.E.C. amplifier or without any amplifier at all.
After making a number of comparisons using various kinds of audio materials, I found out that when the headphones were connected to the ASUS Xonar D2’s line output, I could hear more of smaller details and the sound was livelier overall, but the sound card would lose its ground on intensive passages, not coping with the reproduction of all the nuances of the performance. The C.E.C. showed its best where maximum dynamics was needed. It maintained the purity of timbres and excellent resolution in any situation. With powerful bass and delicate drive, the C.E.C. did especially well with classic musical compositions. For example, the ASUS Xonar D2 would occasionally produce slack and clamorous sound even in calm places (those without much polyphony) of Rimsky-Korsakov’s Scheherazade.
The KamaBay Amp should be given credit for passing the Scheherazade test successfully. I was quite carried away with the composition when listening to it via that amplifier. The difference from the C.E.C. amplifier was in the lack of the concert hall feeling, poor echeloning, unexpressive medium frequencies and muddy high ones (like in the ringing of the triangle). This impaired my experience from the suite somewhat, but it was even less fun to listen to it without the amplifier.
After the main tests I noticed that I could make the sound more comfortable and increase the depth of the scene by lowering the sound card’s volume and increasing the volume on the amplifier. As a result, the KamaBay Amp delivered a confident, crisp bass, good dynamics, and a huge reserve of volume. Therefore I can recommend it for headphones with low sensitivity. The 32Ohm headphones squeeze rather too many distortions from that amplifier whereas high-sensitivity headphones don’t need such a high gain setting. Formally, the KamaBay Amp supports 16Ohm headphones, but you shouldn’t expect good sound then.
Next I tested the amplifier with a speaker system that had an impedance of 4 Ohms. To remind you, Scythe never mentions the allowable load impedance for the digital amplifier although the chip manufacturer says about the need to use speakers with a resistance of 7.5 Ohms or higher in stereo mode. This is half true. The KamaBay Amp could actually work with a 4-Ohm load until a certain level of output power as determined by its protection. The level was higher than what I could get from the C.E.C. HD53R-80 which is specified to deliver 2x10W with such load. So, it is quite possible that the KamaBay Amp was just limited by its power adapter’s capabilities. Anyway, the sound quality of both amplifiers was far from perfect, even though the C.E.C. produced a clearer sound. On the other hand, the Scythe was colder. Its case did not heat up even when working for long at the maximum volume.
To go on with my experiments I needed speakers with an impedance of 8 Ohms. After some deliberation I selected the popular multimedia speaker system Microlab Pro 3 with dedicated amplifier. It is with this system that the KamaBay Amp had the final battle. I installed the new Microlab Pro 3 in the part of the office room that was free from furniture and placed the speakers in such a way that they formed an equilateral triangle with the listener. Each side of the triangle was no shorter than 1.5 meters, and the distance from the nearest wall was over 1 meter. The speakers were set at a height of about 80 centimeters above the floor at the edges of two office desks. In other words, I had to achieve a more or less correct sound staging with what I had at my disposal since I had no special room to perform the test in. And I guess I achieved my goal well enough. The signal source and player remained the same, and I used a Dali Stereo Demonstration CD as the test material.
When I turned the KamaBay Amp on, I realized that it was not inferior to the Microlab Pro 3 amplifier in terms of output power. Both easily delivered sound volume above the comfortable listening level. Overload would show up on the KamaBay Amp as wheezes at low and medium frequencies whereas the Microlab amplifier cut the ear with high frequencies even at medium volume level and it was too much for me to bring the latter to obvious overload. The KamaBay Amp had stiff high frequencies (perhaps, it is a peculiarity of the Microlab speakers) but they were not that irritating. The KamaBay’s tonal balance seemed truer to me but the Microlab amplifier had less distortion in medium frequencies because even the most excellent vocals provoked no excitement on the KamaBay Amp. Both amplifiers coped so-so with the piano but I just could not listen to Deep Purple on either of them. There were differences in terms of sound staging: it was washed-out on the Microlab while the KamaBay lacked any echeloning.
Summing it up, the KamaBay shows nothing extraordinary as a speaker system amplifier, but its sound quality is on the same level with amplifiers of multimedia speaker systems. Since it delivered dry stiff sound with a flat scene in the headphones too, I can guess that this is not the digital amplifier’s fault. The problem is in the passive analog components accompanying the chip or the input cascade that is set for too high amplification.
As for the Microlab amplifier, it seems to be let down not by its LM4766 amplification chip but by its low-quality digital volume/timbre regulator because I have a similar amplifier with a passive volume control and a disabled timbre unit which does not produce such obscenities with high frequencies.
Of course, I was interested in measuring the parameters of the KamaBay Amp objectively, but it was problematic with the tools I had at hand (the RightMark Audio Analyzer software and a sound card for recording signal) because of the bridge design of the main amplifier’s output cascade. There is no “ground” in the outputs and I didn’t risk measuring the output signal relative to the “ground” of the input connectors. The headphone amplifier’s characteristics could be measured easily, however. Running a little ahead, I can say that they coincided with the specs of the employed chip well enough, so I will just show you the distortion graph of the digital amplifier from that document.
Digital Amplifier, Stereo Mode
Digital Amplifier, Mono Mode
So, the level of distortions corresponds to chips like the popular TDA7265. This quality is high enough for a good TV-set, but owners of more or less decent passive speaker systems will ask for more.
Now I invite you to the most interesting part of the test. I will test the Scythe KamaBay Amp’s headphones amplifier and compare it with the line outputs of two sound cards and of a C.E.C. HD53-R80 amplifier. The level of distortions was measured for a real load (a pair of Grado SR 325i headphones) thanks to a Y-shaped splitter connecting the amplifier’s output with the headphones as well as with the line input of a Creative X-Fi Elite Pro sound card. I preferred that card to an ASUS Xonar D2 due to a trivial reason: having almost the same recording quality, the Creative card allows to easily amplify the input signal. With the ASUS card, the signal would have had to be recorded into a file and processed in a sound editor. The signal has to be amplified because the sound of my headphones is just unbearably loud at the level required for RightMark Audio Analyzer. No one will listen to music at such a high volume, so there is no point in performing any tests in such mode.
So, my objective tests were limited to the following measurements:
These three variants will allow us to track changes in the distortions at different output power. I want to note that even the third variant is too loud for most of modern highly compressed musical recordings.
Before discussing the results, I have to note one peculiarity about them: poor separation of the channels. When making the splitter, I did not take into account that the rather high currents flowing through the low-impedance headphones created interference between the wires of the left and right channels that shared a common screen. Anyway, we still can get some useful information. So, let’s see.
When without load, the Scythe KamaBay Amp delivers excellent parameters for an amplifier: the frequency response deflects by less than 0.5dB from 22 to 50kHz. The signal-to-noise ratio is -100dB, even exceeding the specifications. Interestingly, this amplifier is absolutely free from ground loops that might have worsened its noise characteristics. The level of harmonic distortion is also impressive at 0.0005% whereas intermodulation is completely lost in the noise.
This idyllic situation was disrupted by the connection of 32Ohm headphones, yet the THD of 0.01% at both volume settings can be considered acceptable. The level of intermodulation is proportional to volume, but not excessive, either. Interestingly, the signal-to-noise ratio didn’t lower when I connected the headphones. It means that this amplifier has zero output resistance.
Let’s check out the individual characteristics in more detail. From here on, the first diagram shows the frequency response, the second diagram shows the harmonic distortion spectrum, and the third diagram shows the intermodulation distortion spectrum.
The lack of notable deflections in frequency response at the resonant frequency of the headphones’ dynamic heads and at high frequencies indicates again that the amplifier has zero output resistance. The slump of frequency response at low frequencies is proportional to sound volume and is due to the presence of DC-blocking capacitors at the amplifier’s output. I guess they have the right capacitance, and the 1-decibel difference at 30Hz won’t be perceptible. The nonlinear distortions – a very long and nearly not swooping spectrum of harmonics with prevailing odd-numbered ones – do not bode anything good. The reduction of sound volume doesn’t reduce the harmonics after the 20th one. The intermodulation distortions are reduced at lower volume, but the high intermodulation constituents near the higher-frequency tone (7kHz here) and its harmonics (14, 21kHz) remain unchanged.
Thus, the KamaBay Amp shows ambiguous results in my tests but I will make my final opinion after I discuss the results of the other devices.
Next goes the incomparably more expensive amplifier from C.E.C. The HD53R-80 differs from most devices of its class with having two stereo amplifiers that allow to connect up to four headphones simultaneously (thanks to some exclusive system called Load Effect Free) or a couple of high-resistance headphones and speakers. Thus, the amplifier’s left and right outputs, differing with the recommended load impedance, are equipped with two sockets for 3.5 and 6.3mm connectors. I found out that the connection of a second pair of 32Ohm speakers to the right amplifier’s outputs (rated for a load of 16 Ohms and higher) did not affect the sound of the first pair. The left amplifier, although rated for headphones with impedance of over 100 Ohms, copes with the Grado headphones but overloads at high volume.
The C.E.C. amplifier proved to be noisier than the Scythe but I could not normally notice that. This amplifier had a surprisingly low growth of harmonic distortions under load: the difference from the distortions at no load was less than 0.0005%! That’s Load Effect Free indeed. What about the shape of distortions introduced by the amplifier?
That’s just amazing! The left section of the amplifier, optimized for high-impedance headphones, does not introduce harmonics higher than the third one, and even this harmonic is missing in the right section. To be exact, the third harmonic is lost in the noise whose characteristic peak is indicative of a ground loop. The user manual strongly recommends using additional grounding (there is a special screw at the bottom of the case) but I hadn’t looked this piece of advice up before my tests. According to the manual, the grounding will help get rid of noises when you are turning the volume controls.
Practice suggests that the volume controls are the weakest spot of the C.E.C. HD53R-80. When the controls point at 1 o'clock or lower, they bring a considerable difference into the volume of the channels. When set above the middle, they begin to lower the level of low and high frequencies as can be seen in the frequency response diagrams for the right and left amplifiers recorded at different positions of the volume controls. There we can also see the distortion of the frequency response under load, which is due to the nonzero output impedance of both amplifiers. However, these deflections are too small to be taken seriously. The nonzero impedance worsens the electric dumping of the dynamic heads, increasing distortions in low frequencies that spoil the result of the intermodulation distortion test. But it should be noted that the right amplifier only has a high second 60Hz harmonic whereas the left amplifier, which is not actually meant for 32Ohm headphones, lowers the harmonics quickly – you can see them up to the fifth harmonic only. It is all right at the high frequencies with the C.E.C. HD53R-80: the slim column of the second 7kHz harmonic is the only indication that this amplifier is not perfect.
Well, the reason for the very clear sound of the C.E.C. amplifier is obvious enough. I will now check out how the sound cards cope with the headphones. First goes the Creative X-Fi Elite Pro which has only served as a registering instrument until now. The measurements were performed at two positions of the sound card’s main volume control corresponding to the two tests of the KamaBay Amp in signal level.
It is clear from the table that this sound card doesn’t like high volume: the distortions in the headphones are growing up like an avalanche. This might have been expected since the operation amplifier at the sound card’s line output cannot provide an alternating current with an amplitude of more than 1V at a load impedance of 32Ohm.
NJM2114 Load Driving
Even at a volume of 65% the X-Fi Elite Pro sound card is considerably inferior to the inexpensive Scythe KamaBay Amp in every parameter, save for signal-to-noise ratio. The difference in terms of channel crosstalk is especially impressive: the amplifier lost about 20dB when I connected the headphones but the sound card lost about 80dB! This is a very poor result since the crosstalk limits the stereo panorama and clarity of musical instruments.
The impedance of this sound card is much higher than that of the C.E.C. amplifier. The harmonics are even higher than with the Scythe amplifier and their spectrum is not much shorter. This result can only be considered acceptable with one reservation: at everyday use I almost never had to increase the sound volume above 45% which was the default value set by the sound card’s software when I selected the Headphones configuration.
Does the other sound card perform better thanks to its special cascade for headphones?
The ASUS Xonar D2 having an extremely high output resistance, the level of the measured signal for the 32Ohm headphones was reduced considerably which didn’t allow me to perform the measurement at two levels of volume. Therefore the results are rather ambiguous: the card has the lowest coefficient of harmonics but the highest coefficient of intermodulation. However, as I wrote above, it is important to view the signal spectrums rather than the totals to correctly evaluate an amplifier.
The frequency response diagram of the ASUS Xonar D2 sound card shows the dependence of the headphones’ impedance on frequency in detail. The first hump at 100Hz corresponds to the resonant frequency of the dynamic heads employed in the Grado SR 325i. You can also see two small resonant peaks in medium frequencies which are caused by the speakers’ acoustic enclosures. The smooth growth of impedance at high frequencies is due to the inductance of their chokes. As you see, this sound card can be successfully used for purposes other than just listening to music.
So, the extremely low THD delivered by the ASUS Xonar D2 at a load of 32 Ohms coupled with a very short spectrum of harmonics makes this sound card as good as the best headphones amplifiers. No wonder I could not easily decide in my subjective tests what sound I liked more – with or without the amplifier. The high intermodulation distortion coefficient shouldn’t mislead you – the intermodulation proper is not conspicuous in the spectrum of the recorded signal as is also confirmed by measurements made according to another method.
RightMark Audio Analyzer contains an alternative intermodulation distortion test that uses two “sliding” sinusoidal signals with a frequency difference of 1kHz.
Here we can see that the intermodulation distortions of the C.E.C. amplifier are almost always lower than the level of noise whereas the Scythe KamaBay Amp is but slightly inferior to it in comparison with the line output of a regular sound card.
To wind up this section, I will show you the results for all the four devices.
An attentive reader might have noticed that connecting headphones to the line output of the Creative X-Fi Elite Pro is not quite correct because this sound card is equipped with an external unit that has a dedicated headphones output. Theoretically, it should cope better with headphones load, but practice can be different. As a matter of fact, headphones with an impedance of 250 Ohms (Beyerdynamic DT 770 Pro) sounded less detailed when connected to the external unit’s output and my measurement showed that the external unit was far inferior to the line output in terms of SNR. Why? The external unit is powered by one of the standard PSU connectors that are used for powering HDDs besides other components. The increased noise is the consequence, just as when I tried not to use the external power adapter of the Scythe KamaBay Amp. Moreover, the digital-to-analog converter in the external unit is lower quality than the line outputs’ DAC, so the owner of high-quality headphones should not count on the external unit of the X-Fi Elite Pro. The X-Fi Extreme Gamer coupled with Scythe KamaBay Amp will sound no worse at a much lower total price. After all, the X-Fi Elite Pro performs in this test session just as an example of a regular sound card (without integrated amplifier) working with headphones.
The additional buffer in the line output of the ASUS Xonar D2 card coped with the headphones excellently save for the extremely high output resistance. This buffer consists of two RC4580 opamps whose outputs are usually connected with resistors of a few dozen Ohms. A similar solution can be seen in M-Audio Revolution 5.1 and Audiotrak Prodigy HD2 sound cards. For some reason the resistors in the front output of the ASUS Xonar D2 have a very high rating, which is the reason why the impedance is beyond reasonable limits. Perhaps this defect has long been corrected and could only be seen in a small batch of sound cards sent for hardware reviewers to test.
The higher noise of the C.E.C. HD53R-80 in comparison with the other three tested devices is due to a ground loop between the sound card and the amplifier. It is thus the result of certain circumstances. For comparison, you can read our ASUS Xonar D2 review and find that the noise was much better when the measurement was performed through the Xonar D2’s line output (a Creative X-Fi Elite Pro was the sound source then, too).
As you can see, at a certain position of the volume controls and the sensitivity switch at the back panel, this amplifier can yield a dynamic range of over 100dB and a channel separation of almost 90dB at the expense of a minor increase in harmonic distortions.
The table above gives you a notion of the quality of the interblock cable supplied with the Scythe amplifier. It is 50 centimeters long and its electric characteristics are in between the 50cm Monster Interlink 200 and the 1m-long cable included with the ASUS Xonar D2.
The Scythe KamaBay Amp SDA-1000 has confirmed its right for the title of amplifier as it copes with the headphones better than the regular sound cards. But when compared with special sound cards, it can only offer its zero impedance and better separation of the channels.
By the way, RightMark Audio Analyzer helped find out the exact gain setting selected by the KamaBay Amp developers out of the four values available for the YDA138. The headphones amplifier increases the amplitude of the input voltage by 12dB. So, the developers selected the third value with a sensitivity of 0.28V.
The Scythe KamaBay Amp SDA-1000 amplifier offers an appealing combination of price and capabilities, an attractive exterior design and small dimensions. It can make a nice addition to a notebook that cannot provide the desired volume in headphones or help organize sound in a room where there are speakers without an amplifier. Unfortunately, several design slips do not allow this device to show its full potential.
The main problem is that the amplifier is not meant for speakers with an impedance of 4 Ohms. Moreover, Scythe somehow forgot to tell the customer about that. As I found in my tests, the amplifier could work with such load, but the high level of distortions deprived music from all beauty. For the amplifier to work normally with a load of 4 Ohms, two YDA138 chips must be used in monophonic mode while the included power adapter must have a higher rating.
The second problem was encountered when I tried to use the KamaBay Amp in my system case. Turning the amplifier on triggered the PSU’s protection and all the power noise is perfectly audible in headphones. The primitive adapter from a Molex connector to a round plug that goes into the amplifier is not enough. A full-featured LC filter that might suppress noise and limit the surge of start-up current is required. This reminds me of the "wonder cables" from OCZ we tested in our labs a few years ago.
Now, what about the sound quality of the Scythe KamaBay Amp? Comparing it with the amplifier of the Microlab Pro 3 speaker system, I found the KamaBay Amp to cope well with 8Ohm load. The only thing I can find fault with is that the medium frequencies are not exactly clear and the sound stage is flat as a wall. The KamaBay Amp did better as a headphones amplifier, delivering good dynamics and tonal balance, but of course it is no match to hi-fi models priced at a few hundred dollars. The lack of echeloning is its main problem, again. There is one oddity here, though. When you set the amplifier’s volume control at its maximum and lower the sound card’s output signal level, the KamaBay Amp sounds much softer and you begin to feel the sound stage. This raises my apprehensions about the quality of passive components employed in the amplifier’s input circuitry, and the third slip of its developers shows up.
For some unclear reason the amplifier’s chip has a very high gain setting: 30dB for the digital and 12dB for the headphones amplifier. This reserve of volume was not called for with every sound source I had. So, I guess that the lowest of the four gain settings available for the YDA18 chip (18dB for speakers and 0dB for headphone) would be quite enough. The developer might have provided a sensitivity switch for very quiet sound sources.
Summing everything up, I want to acknowledge the developer’s courage, promising concept and sparkling product design. At the same time, I wish the amplifier’s electronics were revised to correct the above-mentioned drawbacks. I guess, a Scythe KamaBay Amp SDA-2000 with two Yamaha chips and high-quality passive components inside, a miniature sensitivity switch at the back panel, and a “wonder” wire for connecting the amplifier to the computer’s PSU would be a much more desired product for many potential buyers.