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Amp/Preamp Asylum: REVIEW: Class D Audio SDS-258 Amplifier (SS) by Feanor

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REVIEW: Class D Audio SDS-258 Amplifier (SS)

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Model: SDS-258
Category: Amplifier (SS)
Suggested Retail Price: $360 for kit
Description: Class 'D' stereo amplifier
Manufacturer URL: Class D Audio
Model Picture: View

Review by Feanor on August 15, 2010 at 13:23:22
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for the SDS-258

Let me premise my review by saying that I am poor, a cheapskate, and like classical music. Now let me begin with a conclusion: this component handily exceeds my expectations for an amp that cost me $450, furthermore it is highly competitive with amps I've owned costing 5x as much.

The SDS-258 amp description can be found HERE . This is a class 'D' amplifier based on a commercially available chip, however implementation is proprietary to Class D Audio (CDA); the amp is made in the USA. The amp and kit can be purchased only online direct from CDA.

The Kit. I constructed the case myself though CDA does offer a metal case as a separate option. Case construction was most of the work, follow by the wiring; the amp and power supply modules themselves are plug & play. Unfortunately at this time there is no user manual specific to the SDS models, however basic instructions were adequate for me who is certainly an electronics neophyte. HERE 's a picture of my handy work; note that I opted for balanced XLR connectors since my preamp is balanced.

Associated Equipment. You see the rest of my system HERE , including my primarily reference, Monarchy SM-70 Pro amps. In recent years I have also owned the following amps, (latest to earliest): Bel Canto eVo2i (integrated); Adcom GFA-555II; NAD C270; Phase Linear 400.

Music for the review. For this review I relied mostly on classical music, especially large-scale choral music which offers, in my opinion, the best overall test of any component on account of its complexity. I did listen to orchestral and chamber works too, and some jazz.


Solid-state or class D "Nasties". Basically NONE! No grain, no etching, no glare, no dryness or "greyness". Personally I heard no "peculiar sounding highs" as some pundits have reported in case of class D, but I'll admit that I'm quite deaf above 10 kHz.

Hum & noise. No hum, no power-up or down transients, and no noise floor that I noticed.

Soundstage & imaging. Of course, these aspects are highly dependant on the recording, and this is where, IMO, quality, classical choral recordings are most revealing. I found that the SDS-258 delivers a very wide and reasonably deep soundstage; imaging was pin-point. However I'd say the SDS doesn't deliver the sort of artificial depth you get with tube equipment.

Transparency. Excellent! Not only exceeding anything I've heard near the price but also equalling or exceeding any of the aforementioned amps I've recently owned. By the the way transparency is not merely "detail": I equate transparency with "air", that is, the ability to separate instruments and voices from each other within the soundstage.

Tonal Balance ...

Solid and punchy as any of my mentioned reference amps; a bit more so than my current Monarchy SM-70 Pros, though probably the 2x-3x power helps in this regard. Perhaps the 50-100 Hz range is just a tad warm but just pleasingly so, (unlike the wooly NAD C270 for example).

Mid & Treble. CDA says its SDS amps have "beautiful smooth tube-like sound". Well it is free of the "nasties" mentioned above and I suppose tube-like as far as that goes, but if tube-like means "warm" to you, then you might be disappointed. Rather, in the mids and highs the SDS is quite neutral except for a narrow region of prominence in the lower treble. This is especially true versus the Monarchys which are a bit reticent or "polite" in that region, and also against the Adcom and the NAD. This prominence is slight but, to my ear, delivers a truer presentation of the harmonics of instruments including strings, brass, and percussion such as bell and cymbals. In fact, the SDS' reproduction of steel-brushed cymbals is the best that I heard -- no spray can "pssst" in this case.

On the subject of the true harmonics of instruments, I often feed that people who rarely listen classical strings think that they should always sound silky smooth -- well it isn't so! Depending on how and where they are played and, of course, how they are recorded, strings can sound quite strident. Brass too, and more obviously, can sound naturally strident. If a amp or any component unnaturally smoothes the natural stridency then it isn't delivering accurate reproduction. Whether the byproduct of its slight low treble prominence or for some other reason, the SDS-258 is as good or better at reproducing the full harmonic spectrum of instruments than any of my reference amps. But note I'm not saying that the SDS has the sort of "harmonic richness" attributed to a lot of tube equipment which is an artifact in my opinion.

I have always respected the Monarchys' sound but I now realize that it is really too polite in the upper midrange/lower treble. On the other hand the Monarchys are a forgiving amp versus the SDS-258. That is, depending on your associated equipment and taste, the SDS just might not be the right amp for you.

Product Weakness: There is a slight lower treble prominence which might make it problematic in combination up- or downstream components that have the same trait, or that are harsh or not well resolved. And Hey! this is a kit: you've got to find your own cabinet and wire in the modules.
Product Strengths: A cheap, powerful, transparent, harmonically accurate amp to compete with amps costing several times its price. As a kit it is extremely easy to assemble.

Associated Equipment for this Review:

Amplifier: Class D Audio SDS-258 (under review)
Preamplifier (or None if Integrated): Sonic Frontiers LINE 1
Sources (CDP/Turntable): Assemblage DAC 1.5
Speakers: Magneplanar MG 1.6QR
Cables/Interconnects: Blue Jeans Cable
Music Used (Genre/Selections): Mainly classical
Room Size (LxWxH): 20 x 12 x 7.5
Room Comments/Treatments: n/a
Time Period/Length of Audition: 6 hours
Other (Power Conditioner etc.): n/a
Type of Audition/Review: Product Owner
Your System (if other than home audition): n/a

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Topic - REVIEW: Class D Audio SDS-258 Amplifier (SS) - Feanor 13:23:22 08/15/10 ( 30)