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A review of the SDS-254L (an SDS-470 with a 254L amplifier/power supply). Let’s start with this basic statement; I’m an extremely frugal person. Whether this is due to my Scottish ancestry, I'm not sure (or my ex-wife, or my student loans...). I have never paid full price for anything. If I can barter for something, I do. If I can haggle between two sellers peddling the same item, I will. If there is a way I can DIY it, I’m up for the challenge. With that sufficiently out of the way, let me tell you about the Class D Audio SDS-254 power amplifier kit. Class D Audio, the company, has been around for a while. Tom Ross, who started things and runs the place, is an extremely good-natured guy and easily accommodates just about any request (via email) you can throw at him! He’ll answer just about any question you might have, like specs and such, and divulge just enough technical stuff without giving away the farm (after all, the guy is trying to make a living with this stuff!). He offers this amplifier as a kit, or as a fully assembled and tested product for an additional $125. That still keeps this particular product around $600; something that a died-in-the-wool, frugal individual can probably live with. If you are handy and know electronics (read/warning; college trained tech or better!) like me, you can save the assembly fee of $125 and get the whole thing delivered to your door for a hair over $500. If you aren’t so tech-savvy, get the assembled version- either way, you get an amp that will EASILY compete with pretty much ANY $600 amp on the market, make some $1 to $2K tremble in their proverbial boots, and even take some serious shots at amps in the $2-3K range. Yes, it has that much potential! It’s not perfect; but for a $600 amplifier, it is a lot of bang for the buck! Initially, I had a LOT of questions to throw at Tom before I took the plunge and bought the kit, and he took my questions in stride and did his best to answer them. I say that he “did his best”, as there is one sore spot I have with this kit- specifically the instruction manual (or lack thereof). The lack of concise instructions is the only real sore point of this kit; they are almost non-existent! There is some material on his current website, but it doesn’t nearly address any of the major assembly issues. What he did well was accommodate my request for blue rather than the traditional red LEDs for the front panel, but there was a small rub with that as well. Read on! With regards to the (lack of) manual (and my LED color request), one is left to puzzle out the following- 1. Because there is no wiring diagram whatsoever, how to wire the back panel were a bit of a mystery. Sure, the positions of the input/output connects , RCA/XLR input switch, IEC power jack and level control pots are labeled, but there is no guide as to HOW to wire any of this to the circuitry. Okay, before you think I’m a complete idiot, let’s look at this clearly- First, if one doesn’t know that the left and right speaker connections hook up to the appropriate left and right speaker +/- connections on the amplifier board, they should probably go for an assembled unit. Second, HOW the wiring of the XLR and RCA connects together isn’t revealed to us at all. The amplifier board proper does have +, - and ground connections. But since the back panel has both RCA and Balanced connections AND a switch to select either, there are a few ways to do this. Therefore I had to email Tom about this. He sent me some “assembly photos” of what I assume is what the finished amp looks like if the people at Class D Audio do it for you. But there was still no solid instruction on how to wire this section. He also included a paper which gives some clues, but not a lot of detail regarding the rear panel wiring (the paper looks hastily written and has some grammatical errors). If you aren’t going to use the balanced connections, then just wire the + from the RCA to the + on the amp board, and the ground tab to (you guessed!) the ground. I was warned NOT to connect the RCA + to the amp’s – terminal (for phase inversion) - Tom goes so far as to say you could damage the amp. That is okay, I still haven’t bothered connecting the balanced jacks, or the switch, for that matter… 2. Transformer wiring. The website DOES furnish a diagram for both 115 and 240VAC transformer detailing the connection of the secondary windings to the power supply board. Here is where another (and potentially disastrous) issue can occur. The 115VAC transformer I received had two pairs of secondary windings- two blue wires and two green wires. No problem there. The instructions (again, found on the website after a good amount of searching, and not in the box!) says to connect the blue wire of one secondary coil to the green wire from the other secondary coil. This will give you the center tap, which becomes the ground for the power supply board. The other green and blue wires are attached to the AC input terminals. What wasn’t marked out on my transformer was which blue and green wires belonged to their respective secondary coils! If I were to attach the blue and green wires of the same coil together thinking that now had the center tap, and then powered things up, Blamo! I might be in for a seriously scary smoking transformer show before the fuse kicked in (a 6.3amp slo-blow is included with the 254 kit, and the rear panel has printing for 6.3, 8 and 10 fuses- you simply check the appropriate box). Is Tom is willing to replace a smoked toroid? I mentioned this to him in one of many back and forth emails. His reply was that each set of secondary leads should be marked with red tape. No red tape to be found anywhere on my transformer! I had to wire up the fuse block, the power switch, and then connect the primary leads of the transformer to my DMM and measure voltages of the individual wires to find the proper blue/green pairs. Only once I got that figured out, did I power down, unplug everything and wire up the transformer secondary to the power supply board. That worked the first time I powered it up (again, the board is easily marked, but disaster could have struck at any moment with incorrect wiring!). I verified + and – 50VDC at the supply board’s output. Rock and roll! 3. The one “creature comfort” request I made of Tom was the inclusion of blue front panel status LEDs over the stock red ones, just to match my existing pre-amp’s power indicator. He was more than accommodating, and told me he’d have to change a pair of resistors on the amp board to allow for this. Once I had the kit and was ready to install and wire up the LEDs, I ran into another inconvenience- The newly wired up front panel LEDs refused to light up, even though the amp board LEDs indicated that the amp was operational. I puzzled over this; even checking that the enclosed LEDs weren’t blown by running them off my bench test PSU. They came to life at 2.9VDC and were plenty bright at 3.5VDC. I measured the voltage across the LEDs on the amp board; I got 2.5VDC. As examined the traces of the PCB, I realized that the only way that I would be able to get the front panel LEDs to work would be to unsolder the LEDs from the PCB. They were causing enough voltage drop (they are wired in parallel with the LED connectors on the PCB ) so that the front panel ones would not light when attached- removing the PCB LEDs appears to be the only way to provide just enough voltage for the front panel one to operate (again, being handy with a soldering iron and steady enough to unsolder 0204 SMT LEDs…)- the front panel LEDs glow a soft blue, without being too bright. I don’t like extremely bright blue, just enough to let you know the amp is on and operating. Excellent cosmetics! In a recent email to me, Tom explained that Class D Audio was in the process of revamping its website. That will probably be for the best, as there is a lot of information that I initially wanted, as well as specs that just aren’t there yet. Between maintaining the fulfilling of orders, selling as an OEM to other manufacturers, and updating the webpages, he’s a very busy guy! He’s trying, and I’ll concede that to him! I hope he gets the instructions and the web-page together sooner rather than later. What’s that about first impressions? Now that I am done with the quibbles, on with the Sound Quality… Warm Up-One “Inmate” over at audioasylum.com (who owns the EXACT same amp kit) suggested that this amp takes about 15-20 minutes to warm up. A few others who own class D amps have said similar things- these amps need anywhere from 10 minutes to an hour to “come on song” as it were. Indeed, I have to concur; in my case, for the first 10-15 minutes (and as a first impression after powering this thing up for the first time), the amp sounds rather dimensionless, with little image extending beyond the speakers. It also sounds rather unfocused. Dynamics are still pretty awesome. I initially thought I had made a BIG mistake purchasing this amp. I was tempted to send Tom another email (after a great many previous to my purchase), but held off. I am a believer in burn in, and reasoned that it wouldn’t be fair to slam this product right out of the box. I let it play for about a half hour, and went away to do something else. When I came back, I was thoroughly surprised. It didn’t sound like the same amp! Each time I power this thing up, it initially sounds as I have described- it needs a short warm up. It’s not until the amp seems to reach its equilibrium after 10-15 minutes that you suddenly notice things like voices and their proximity to the microphone, or the fact that the acoustics in Dick Schory’s “Music For Bang Barroom and Harp” (RCA LSP-1866) now extends beyond the boundaries of the speakers and behind you. Overall- Tonal balance reminds me of the good qualities of a Bryston 4B (yes, those amps do have some good qualities, IMHO) or Audio Research D76a amp. Or the Linn Klout. Or Naim gear. PRaT (Pace Rythem and Timing) reminds me very much of better Linn or Naim amps. Dynamic swings are scary good; both micro and macro. VERY FAST. Very tight sounding. I want to say “lightning fast” or “Zero to 60” sound. Sound emerges from a totally black background as well- the “jump factor” of this amp can actually scare you! Drums have the crack and slam you’d expect from a live (meaning; real) drummer. It is very easy to follow individual lines in a recording. Multi-tracked recordings are easy to aurally rip apart (in my case, I find it very easy to focus on what the bass player is doing, or the conga player or the second violins, etc…). Tracks played included the following- Various selections from my band's DVD-Audio disc (“Silmica”, 2006, Scrumpy Records). Since I was there for everything from the recording right through to DVD-A authoring, I really have an intimate knowledge of this music. The intended 3-D rendering of reverb, on better systems can sound like you’ve installed surround speakers in your listening space. That holds true when played through this amp. As well, the back to front depth of the instruments came across just as I had heard in during the studio playbacks and mixing. Stunning! “Relax! 3-D New York Mix”, by Frankie Goes to Hollywood 12” 45RPM EP (12 ZTAS1 A-4U). I like to play this record for two reasons- the first reason is the amount of bottom end; not too much and not too little, but deep in spots. It is not overblown and thuddy, like most 80’s pop can be. A good amp (and sub/speaker combo) will render the bottom with a taut-sounding drum machine kick-drum, bass-synth melodies that go deep without boom. If it sounds bloomy, bloated or out of control, it’s not right. Period! The SDS-254 does this very well. The second reason I love this record is for the dynamic swings, or as I call it, “jump factor”. This re-mix has a LOT of dynamic layers to it. There are some serious micro-dynamics between drum machine, sampled and real percussion, as well as some plaster-peeling processed vocals and synth screams that can make one dive for the volume control (or at least wake them up lest they be falling asleep listening to this!). This is a rare exception in pop recording when certain sounds jump out at you and are, as I like to say, “scary-good”. Another phrase I might use is that this amp goes from zero to 60 (or in this case, maybe 250Watts) blisteringly fast! Serious PRaT here. “Ascent”, by Donald Dorsey, from Time Warp, Telarc (CD80106). Telarc always warns its listeners on its CDs (and on some of its early vinyl) that the dynamics on their recordings are not compressed or limited, and that no equalization has been applied. One should be careful not to advance the volume too high, unless they like popping fuses and speakers (my words in italics). The SDS-254 is a bit of daredevil- it’s almost like the amp is daring you, “Come on! Turn that darned volume control up some more! I can take it!” It seems like it has limitless power. The amp never seemed to break a sweat. It never got even moderately warm to the touch. I never heard it clip, and I never even triggered its protection circuitry, even driving my (supposedly) 80db sensitive Adire Audio DDRs! It simply got too loud for me to take. Believe me, that is a good sign around here! “Exodus”, by Bob Marley and The Wailers (Mobile Fidelity Sound Lab, MFSL1-221, pressing #2811). I only intended to listen to a few tracks on this masterpiece, but I ended up playing the whole thing- both sides! Top to bottom, this amp has control! I'm hearing reverb tails and little things in the mix of this amp (like Familyman Barrett's bass amp speaker cones buzzing slightly on the opening track, “Natural Mystic”, or the subtle punch ins on the lead vocals on “Waiting in Vain”). This is another case where if the amp is not up to the task, the bottom end (and resulting overall focus) suffers greatly. The title track has Marley and the Wailers almost screaming “Exodus!” and “Move!”; these dynamic swings in the vocal are not overshadowed by the bottom end thump. Amazing that an amp in this price range can cope with and (effectively) sort all of this out while still pushing the speakers like an olympic weightlifter!!! To sum it up, here is an overview of the amp’s characteristics- Bottom end- full and tight. No overhang or muddiness. There is a warmth there that doesn’t mean slow, muddy or fuzzy, like some (but not all, obviously) tube amps are prone to do. Whether running the amp full range, or with a subwoofer (the SDS-254 running with a crossover point of 50hz, with a 3rd order high pass), there is authority and a base for the sound. Midrange- Very tuneful. Holographic with a great sense of depth, width and height, like a good tube amp. Vocal presentation is incredibly lifelike- resolution in this range is so good that even when watching television shows with decent (read; not compressed to crap) dynamics, you can hear head/body movements of the actors in proximity to the microphones. ADR (dialog in movies that is replaced in a studio during post production) is easier to hear when it is added to a live scene. The sound is reminiscent of some of the better class A amps I've heard (tube or solid state). Treble- grain free and extended, with just a hint of forwardness. A slight edginess to mid-treble register right around the tip of the “t” and “sss” vocal sounds. But in all honesty, this has all but vanished over the 20+ hours I’ve put on it so far. It just seems to get better with age. As time progresses, the amp has mellowed. The top end has become clean, clear and VERY focused. Sources or components that have ANY sort of edge or “fizzle” will be unashamedly revealed. Is it the best thing in the world? No. You would have to spend a LOT more to get better. But this amp does so many things well for its price point, one would honestly be STUPID to not try this (or any of the SDS variants) in their system. After all the fuss I've had with a great many amps, I think I've finally found a reasonably priced keeper! David Johnstone
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Placed on July 3, 2015
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very great products and service! Tom
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Placed on February 18, 2015