Review: ART SLA-1 Amplifier

Category: Amplifiers

What do you get for two hundred bucks nowadays? Let’s see: I grudgingly spent $220 to feed my family at an upscale restaurant last Sunday, I spent nearly that on my electric bill last month, and I spent thrice that to get a couple of dings pounded out of my ‘96 Subaru. Don’t get me wrong, I’m not cheap—I actually enjoy spending money on the stuff that counts: namely, hi fi components. And since I don’t smoke or drink, or play golf, or drive flashy wheels, or take expensive vacations (unless my wife threatens) I figure I’m practically licensed to shoot maybe 10 to 20 grand per annum at said stuff that counts, and to drag it down into my basement lair for experimental purposes. To that end I’ve applied myself with stealthy determination over the past 15 or so hi fi seasons (January through Thanksgiving, whereupon I resign myself to spend the rest of the year above ground, nodding off to Christmas tunes alongside my well-fed family).

Where was I? Oh yah (as we say in Minnesota), two hundred bucks can get you a mini-mite amp called the ART SLA-1, made by a pro-audio company in Rochester, NY called Applied Research and Technology. But we don’t care about that, right? I myself, international hi fi trophy hunter these many years, never actually formed a single thought about pro audio until I read a now-cancelled thread in the Forum last week called “What’s the best amp you ever heard?” started by a guy who was actually selling mods for the unit (nameless in this review, although I’m not sure he’s been abused enough) who was making some pretty reckless-sounding “best amp” claims for the humble ART SLA-1. Since names like Krell and Lamm were being brushed aside like carp guts on “Iron Chef,” my next experimental assignment quickly formed itself. I pulled a credit card down from the rack and Googled (sorry) my way to a mail-order dealer. Two days later the tiny piece was in my hands.

So what did I get for my two hundred bucks? With dual volume controls on its rack-mount face the thing looks like a solid state preamp circa 1980: two inches high, nine deep and sixteen from fin to fin. The fins are coarse-edge sharp, by the way—I soon learned to lift the little bugger by grabbing from the front and back. Rear panel sports a set of balanced inputs in addition to ¼” inputs (what the hell are these?). No RCA’s. Ground lift switch, bridge mode switch. The cheap plastic binding posts are closely spaced and difficult to use with spades, but work all right for bananas or bare wire. A small external housing contains the AC input and a cooling fan. The whole thing weighs in at 13 pounds, and in stereo mode delivers 100 wpc into 8 ohms, 130 into 4. Lack of RCA inputs could have been a problem for me, since I don’t own a balanced out preamp, but I used the XLR/RCA adapters from my RM-200.

I slipped the SLA-1 into today’s system—TNT IV, JMW 12, Shelter 901, Lindemann SACD, Groove, Vibe/Pulse, Groove Tube cables, Piega P10s—flipped the switch, and lowered the needle into Brahms. I’d like to report that some kind of magic happened, but the first thing I noticed was the noisy fan (a problem that diminished during my ears’ recommended 100-hour break-in period. It also helps to keep the little beast at least 8 feet away). The amp’s dominant characteristic engaged me soon after, however: the orchestra (in this case, Bruno Walter’s) seemed faster, lighter on its feet, more effectively placed than I was used to hearing it. This speed and transparency really surprised me, and continued to surprise me over the next few days—everything I played, from gigantic Mahler to intimate Patricia Barber, seemed to have acquired a snap and drive that floated it out of the grunge and actually opened for me a new sense of musical priority. That’s a big deal for me, folks. I had pegged myself as too experienced (read: jaded and cynical) by now to allow my long-time preference for weight and tonal richness to be pushed around by a midget like this. But when I put my other amps into the picture the focus softened, things slowed a bit, voices and instruments thickened and somehow seemed “hotter” in an unnatural way: less revealing of time and space. These amps (RM-200, Dreadnaught, Innersound ESL) are all highly regarded, and I like them a lot, but I don’t fool myself that they are at the cutting edge. What they are, at least in the case of the Dreadnaught and ESL, is Big—big watts, lots of current—big enough to unroll a deep, black bass carpet out of the Piegas for the music to rest upon. That carpet is diminished using the SLA-1, although my newly minted musical priorities argue that fast bass may be preferable to more bass. For now, the kid stays in the picture.

So what’s the downside to this little boat-floater? Let’s face it; the Slay One (think...) is a cheap amp with cheap parts, so it can sound a bit lean and at times even threadbare (my ears are still breaking in, remember). Sometimes its pinpoint focus is just too intense through the Piegas’ highly sensitive ribbon tweeters, making me leap to the Vibe’s volume control for relief. Inserting my tubed cj16 adds body, but at the expense of some transparency (on balance, though, a nice match). And at 100 wpc it can’t drive the P10s with black-bottom authority; for my soon-to-arrive Sound Lab M-1s, fuhgeddaboudit.

A few notes: I left the dual volume controls wide open while using preamps, but I found them to be very effective in a direct run from the source. The arrangement posed the usual dilemma, of course—purity of signal versus dynamic punch. But maybe a good choice for a one-source ‘phile who’s really on a budget. If I had a budget of, say, $1000 to build a system, I’d start here. Also: I love turning this thing off and on for switching cables. Not a peep of protest, or lingering death. Flip the switch and yank the cable with impunity.

It would be nice to be able to draw a helpful conclusion here, based on some wide experience with good little amps, but I don’t have that experience. For all I know, any smaller amp might have displayed this kind of agility and transparency—but I seriously doubt it could sound this good at $200 plus change. I’ll leave it for others to debate whether a mod to this amp, or some other budget amp altogether, would be a more righteous investment. I had my fun; soon I’ll be dragging heavier stuff downstairs to feed the M-1s. What I got for my two hundred bucks was a pleasing glimpse of what I’ve been missing—and maybe a smaller electric bill next month.

Associated gear
JMW 12
Shelter 901
Origin Live Resolution
Origin Live Illustrious
Van den Hul Grasshopper III
Lindemann D680
Tom Evans Vibe
Tom Evans Pulse
Tom Evans Groove
conrad johnson 16LS series 2
Supratek Syrah
Supratek Cortese
Theta Dreadnaught
Music Reference RM-200
Innersound ESL
Piega P10
Groove Tube interconnects
Innersound speaker cables
Cool. Thanks for your initial thoughts. One question though. Your description of the AC inlet and fan have me confused. It sounds like there is a separate box for the transformer ( possibly entire power supply ) and the fan is on the power supply box. Is this correct ? If so, i can think of some very instant modifications that would really help this unit out.

As it is, I would recommend leaving it turned on 24/7 and playing music through it as much as possible. The lack of bottom end should fill out a little bit as it ages and the top end should get slightly smoother. The fact that you can turn it off and fiddle with connections with no problems signifies either a congested signal path ( various delayed switching & relays ), a very small power supply ( no doubt ) or a combo of the two. Given the "Pro" nature of this amp and since it was designed for studio use, i would not doubt the possibility of both aspects that i described coming into play. Please keep us up to date. It would be nice if others that have purchased one of these also chimed in with their experiences. Sean

PS... A lack of bass weight can tend to make things sound "more agile". Then again, with the level of gear that you have, i'm sure that you are aware of this.
I can take the abuse. The fact is the amp is as good as I said it was. Abuse away, I'm a big boy, I know good sound when I hear it.
D911, I owe you an apology for taking that cheap shot in my review--I was only anxious to distance myself from you so I wouldn't appear to be just some suspect shill. I can see that kind of sideswipe remark had no place in an equipment review. And now it appears it has confounded my purpose in writing the review in the first place, which was to initiate a discussion of the amp itself, instead of your behavior in promoting it. Yet here you are, ready once again to take on all comers, so I'm afraid we'll probably all get sidetracked again, too.

Truth is, the SLA-1 can in no way live up to the wild claims you made for it. I would never permanently pick it over any of my amps mentioned in the review--they are wonderful, consistent music makers--let alone a Lamm or Krell or the "95 percent of what's out there" you claimed in a previous post to be inferior to your mod candidate. I hope I made it clear in my review that I find the SLA-1 a worthy, special little amp that can enliven the listening experience with its speed and transparency. But it's tonally thin, upwardly balanced, and can sound harsh unless carefully matched both up and downstream. That's the reality. The magic is that it costs $200 and can bring a fresh perspective to my big-amp conditioned ears.

Sean, the housing is 1x2x5 and only holds the tiny fan and the AC inlet. I have photos which I wasn't able to upload for some reason. I can email them to you if you're really interested. I've got about 160 hours on the little bugger now, and I believe it's about done cookin'.

I think that was an apology. Forget the sidetracking, I agree that the discussion should remain topic related. I respect your view of the amp. I don't agree with your second posting which seems very different from the first posting (to me), but then my ears are not your ears. I never found the unit to sound harsh or thin. I am aware of your speaker, but I have not heard it thus I certainly can't comment on it.
Best regards
Dls: I'd love to see any pictures of the SLA-1 that you'd like to forward. Drop me a line and i'll shoot you my email address. Sean

You can see pics (including innards) of the SLA-1 at the PeAK's website -
Wonderfully written review, dlshifi. Thanks for your thoughtfulness and taking the time to post it for others' benefit.

A few questions:
How much burn-in time did you give it before reviewing it?
Did you use any power conditioning (transformers or filters) with it?
Can this unit be switched to mono operation to double the power supply and output to one channel?
Thanks, Audiojerry. I formed my opinions right out of the box, but didn't begin writing until it had been burning in for 96 hours. I ran it with a 10-ft basic Vans Evers pc right out of the wall, which is my usual amp MO. Yes, the amp can be bridged to double the power, but I imagine vertical or horizontal bi-amping (when speaker terminals permit) would be a better choice sonically. I want make it clear that I'm not a tech guy, I just listen to this stuff (and buy too much of it), so I hope somebody way more qualified than me shows up with good answers.

Meanwhile, go to the site recommended by Pmkap above for a truly comprehensive look at the SLA-1. Now, that's a guy who does his homework!

D911: I'll try to post another windy epistle in a few days, when I have more time, to address any seeming contradictions in my opinions of the amp. The apology is sincere.

Audiojerry: according to the website that Pmkap listed above, the unit can be bridged at the flip of a switch. Given the low power output / lack of power supply reserve that this amp has at 4 ohms, bridging it might actually agravate the "lean sound" of this amp to an even greater extent. This has to do with the fact that bridged amps effectively see half the impedance that is connected to it. As such, an 8 ohm load would look like a 4 ohm load to a bridged amp. If the speaker dropped to 4 or 6 ohms, the bridged circuit would effectively be looking at appr 2 - 3 ohms. Judging by the very small power increase when going from 8 to 4 ohms on this unit, jumping down to what the amp might see as a 2 ohm nominal load might actually give you LESS power than what you have at 4 ohms.

My previous suggestion was to tie the power supply for each channel together in parallel, not bridge the amp. What this does is keep the voltage potential the same, but doubles the amount of current available to the one channel that remains in operation. Judging by the pictures that i've seen, it looks as if this unit uses a common power supply for both channels, so my suggestion is probably a moot point.

Others may think that an increase in current may not be noticeable under most conditions, but the resultant decrease in voltage sag along various low level stages can produce a more consistent & harmonically correct presentation. The fact that the driver stages are fed from the same "under-nourished" power supply as the output stages on this amp doesn't help matters. As such, when one starts to increase the intensity of signal applied to the amp, the driver stages push the output stages harder. As the output stages pull more current to keep up with the greater signal demands, they begin to pull current away from the earlier gain stages. The earlier gain stages are now in a state of reduced linearity due to power supply restriction. The signal degradation that takes place in that situation is now passed onto the output stages, which in turn amplify those non-linearities. As such, it is kind of a "Catch 22" situation i.e. the circuit is chasing its' tail and can only feel pain once it catches up with itself.

The other thing that i noticed was that this amp has little to no power supply reserve ( filter capacitance ) available to it. Given that the amp shares a common supply between both channels ( from what i can tell ) this becomes even more critical. From what i can see in those pictures, it uses two 4700 uF 63 volt caps. If one could get this up to ( at least ) ten times that level, i would think that bass would be much firmer with greater punch. Then again, almost ANY increase in capacitance would probably be beneficial with the low level of reserve that this amp has in it from the factory.

Given the phenomenally small chassis size, one may have to do some creative wiring to achieve something of this nature. Having the caps wired to the point where the power supply actually feeds into each channel rather than at one common point of resevior would also help bass impact. This is due to the reduced amount of delivery time as needed on high level, short duration peaks.

One should be able to do something like this by installing two 10,000 uF caps ( or greater if size permits ) in the two front corners of the chassis and using them to feed the channel closest to them. This would allow one to leave the factory caps where they are or one could replace these with larger caps if they felt the need. Running bypass caps on the larger caps might also help get rid of some of the "shrillness" ( for lack of better word ) that Dls somewhat hints at on various recordings.

I could further into tips / tricks on this amp, but not having one handy to look at or a schematic makes that difficult. Suffice it to say that "beggars can't be choosers" at this price point and the amp is surely lacking in some specific areas. Given that one has very limited work space and heat dissipation with such a design, one might be better off finding an equivalent used amp of larger dimensions and modifying it. This is not to say that the SLA-1 doesn't have potential ( i'm sure it does, just as all stock circuits can be improved upon ), but that one could run into limitations with such a design faster than another design that was less "cramped" for space.

As a side note, the ART Dio ran into the same problem as it is "ten pounds of parts in a 2 pound box", etc... Same company, same design / construction principles, same limitations. Sean
Dlshifi: Thank you and I fully accept the apology.
Dls, great review...although this little amp is not a giant slayer, it is a fantastic little amp, and not just for the $$.
By any chance if you missed them[i did]there are four little rubber feet that come in the box.
Adding these litte buggers,seems to eliminate a lot of the percieved[at times] leaness.
Does anyone have experience modding this thing DIY? I'm interested in cheap low-power amps, but I can't deal with shrillness in my setup.
Email me if you have on-line reference material.
I have a page detaling some of the DIY details for the SLA-1: