[Occam]

I've started this thread as a forum for technical discussion of this amp. The 'buzz' is that it is the greatest thing since sliced bread. If it is anything like the Art D/IO, there is certainly potential, both as a stock unit, and modified to various degrees.
I will state that I do not own a SLA-1, nor do I plan to aquire one, until I hear some corroboration of its potential from a source that I trust.
What is needed is a schematic of the amp. The schematic of the DIO is available on the Yahoo DIO board..... And I assume, that the availability of the SLA schematic would be OK with ART, as it would only increase the sales of their product.

PeAK has generously established a site where he has posted pictures of the innards (and outards) of the amp, and from this and his descriptions of various components, some generalizations can be made.
http://www.angelfire.com/ca/rchau/audio/sla-1.html

Let the games begin.....

[Occam]

Input, single ended and balanced, are routed to a Matsushita AN6554 Quad opamp. This is a descendant of the classic 5534, but lower drive current due to there being four of them suckers on the chip. These are fine op amps, but there are better available, both in techincal specs and by consensus, subjectively. As  consumer 'pro'  piece of gear, I'll assume that this first stage is capacitively couped for both input and output. As I don't see any 'greenies', low cost but quite good in the appropriate application capacitors, I'll assume this coupling is via some of the small electrolytics surrounding the chip. The signal  is then routed to the front of the amp where the dual mono volume pots are positioned. While the amp accepts balanced signals, its is 'prima face' a non-balaced amp, as each channels volume control is single gang. It might be possible that it is truly balanced, using the attenuators as a shunt between the phases, but I doubt it. After leaving the mono attenuator(s) the signal is returned to the IC chip where the second pair of opamps on the chip, buffer/amplify, and, in the case of mono operation, a switch causes one of the opamps to invert the signal from the 'master' for bridged operation. These signals are then routed to Amplfier proper. Again, due to the bipolar nature of this chip, its output(s) is cap coupled (or the power amp's input is cap coupled). There might be substantial improvement with judicious, cost effective upgrades of coupling caps, as well as improvement from improved decoupling caps. The trick is maximizing bang for the buck.  I'm not sure how this chip is powered. I seen no voltage regulators, and I assume its power is provided by zener shunts, if that.

This circutry is essentially a preamp (+ bridging, but without source selection) and might offer substantial room for improvement, or outright elimination. If the power amp section has sufficient sensitivity and impedance, it might be possible to directly rout the input signals to the poweramp section, but one would forego the bridging capability. The attenuatiors might still be useable as a passive pre, but its efficacy would depend upon the inpedence of the attenuators themselves, the power sections input and source component's characteristics as well as all the all the baggage associated with the subjective evaluation of passive  pre, albeit with a known, fixed connection between pre and poweramp sections...

Alternatively, one could consider improving that opamps performance. The existing opamp is rather slow, but high speed opamps might tend to oscillate without a better power supply (what power supply?) An OPA2604 or LT1359 are obvious 'safe' choices. Higher speed chips, OPA2134, LT1365,... would require far better power supply decoupling than (I think) exists.  While I've my own preferences as to opamps, without actual hands on experience and subjective evaluation, my opinion is worth exactly what I'm being paid for this post, nada. The most feasable approach might be the implementation of a daughter card that mounts in a dip socket that would povide enhanced ps regulation and decoupling, and the potential to use multiple opamps and/or smt mount chips. The addition of a socket, although providing increased flexibility.,without improved decoupling very close to the chip, would only serve to exacerbate any tendency for oscillation.

If this opamp is in reality part of the poweramp proper (feedback from the amp output going to this 'preamp' chip's post volume control amps) causing a ridiculous feedback path from the left channel, all bets would be off, and I wouldn't touch this amp with a 10 foot pole....

Apologies for flying blind, and the probable errors, as I'm not working from a schematic or the actual amp.

[Occam]

Can't glean much from PeAK's photos, so I'll hazard a guess based upon standard practice.

First, what I do know -
The circut uses the UPC1237HA for protection circutry, offset limitation, short circut, power availabillity... to drive a speaker relay. The relays are far more substantial than I was expecting. As this chip's manufacturer  wasn't able to provide the overvoltage or overcurrent protection due to a patent dispute, I also assume there is some anciliary circutry that feed a 'trigger' on the UPC, Pin 1. Iff'n implemented properly, (very high impedance) this chips impact on the subjective sound should hopefully be minimal, save for whatever contribution from the relay itself.

 I'll also assume that when the protection circut is triggered, via an unseen chip mounted on the front panel board, a ULNsumth'n darlington array driver, drives the status LEDs.
I've not seen any trimpots for bias control, and won't hazard a guess, but probably that offset control is handled by one of the opamps  in the JRC 4558  dual opamp on each channel's board, functioning as a servo. The other opamp on each of those 2 chips (R & L) might (or not) handle the overcurrent/overvoltage support circutry, or it might be the input of the poweramp itself.
This opamp is essentially a dual 741, not a particularly 'good' audio amp.. While not thought of as being in the audio circut, servo controls can alter sound with poor choice of filter charateristics. Without more specific knowledge of what the chip does, I couldn't suggest any changes.

As to the rest of the actual poweramp circutry, I assume it is a straightforward, 'standard' implementation, but have no other basis other than economic realities. I'm not able to comment without a better understanding....

[JohnR]

Cool! All that from the photos?! How do you go about getting a schematic?

Unfortunately, in Australia the *discount* price on this amp is $550 -- ie $US360. Which doesn't make it quite the screaming bargain it appears to be in the US.

[Occam]

One poster has stated that this l'l amp sounds like a 700watt amplifier. To that, I can only respond - Exactly who's ass was he blowing what kind of smoke, up?

If that little pancake torroid transformer is 300va, I'd be truly amazed. Not unreasonable for the price, and overall, this amp is an impressive material value. But if you compare it other value products, Norh for example, you'll find substantially more core/watt output. My own (not a Norh) 100watt monoblocks each contain a 330va torroid transformer. My 50watt Llanno monoblocs (cool running low bias), have 350va torroids, each. This is not a criticism of the SLA, simply an acknowledgement of economic realities. Made in the PRC or no, the economics of capitalism is a constraint. A powersupply, shared beween both channels is to be expected. And the marketing driven 1U rack size, and its shallow depth, constrains both the transformer and capacitors. From the power output, I assume the rails are approaching 50v, too close for 50v electrolytics, so you're constrained to 63v, or higher, caps on the rails. Its not that bad, in that 63v electros are generally at the sweet spot in dissapation factor.
One 4,700mf per ps rail is all they can fit in these cramped quarters. Where would you put the minimal 30-40,000mf one might expect in a 'world beater' 100w/channel stereo amp? Well, you could replace them with Panasonic TS-HAs, leaving the total capacitance alone, they'd probably fit and sound better. But if you disable the fan, due to its reported negative sonic impact, and leave those unperforated covers on, those caps are going to degrade quite rapidly, regardless of the fact that they're longer life and higher temp rated than the generic 85*C provided. Because if you run the amp hard, that little transformer is gonna heat up.... and without the fan, the heat has got nowhere to go.

Then again, maybe the compliant nature of the ps configuration is ideally tuned to this specific amp. I doubt it. Rather, I think is the obvious result of size and economic constraints. For lack of specifics, I can't comment on the state of its local ps decoupling, the IC power supplies, etc...

So whats a fella to do? We could go upwards, placing the caps vertically, as opposed to the present lying down orientation, possibly getting double  the capacitance(or more), at the cost of having to obtain a new top.  But unless both the bottom and the new top covers are perforated, providing convection airflow, you really haven't accomplished much, other than temporarily provide an improvement, that will rapidly dissapate.

The only thing I can think of is either -

Remove the transformer from the amp, putting it in a seperate chassis (a BudBox for economy?) which would give room for additional and/or better quality (low impedence at relevent frequencies), and possibly local decoupling and bypassing.... You would remove a major? source of heat within the amp, while providing additional room for different/larger capacitors. I'd still perforate top and bottom if I found the fan detremental to the sound.

or

Buy 2 of the amps and run them as monoblocs, disabling one channel on each. This would give each channel it own powersupply, transformer, rectifier bridge, and capacitance. If anyone gets 2 stock units, I'd be interested in a comparison between a stereo unit and the 2 amps used as monoblocs. If you're willing to give up the ability to return to stereo/unit operation, you could gain more space by trashing one of the channel (being careful as the inputs are all on the right channel, and the outputs on the left channel, i.e. each channel of the stereo amps are not stand alone)

And the rectifier bridge, many expouse the benefits of Schottkey or fast/soft recovery diodes, snubbers optional. If a dropin replacement of such types wouldn't fit, one could obviously put the bridge (along with some capacitance, in the same that chassis that you're putting the transformer in. Or if you're running as monoblocs, put the new diodes on the heat sink you're not using.

And those numerous other little electrolytics not used in the signal chain, obviously,  there would be various levels of incremental benefit by upgrading them. I'm not talking high priced exotics, nor am I advocating mass replacement, but where appropriate, things like Nichicon KGs, or the numerous brands of low esr (and low impedence at relevant frequencies) brought to you courtesy of the switching ps demand.


Any part upgrade, or architectural change, whether in the signal chain or power supply, must be  evaluated not only for its absolute benefit, but in comparison to its next best and cheaper competitor.  If our metrics were straightforward, and individual changes were orthogonal, optimizing performance for cost would simply be solving a system as a  lp problem. But they aren't , they aren't, and it isn't.....

As to powercords, I/O connectors, circut breakers.... Knock yourself out if thats where you think that will maximally float your boat / $. Certainly, the Volex 17604 @$5ea., are the ultimate, next-best, cheaper powercord. Spend <$5 on a resettable circutbreaker that fits exactly in the existing fuse holder hole? As long as you can compentently work with AC, it won't hurt, and these breakers offer less resistance under high current draw, and you're not screwed when the fuse blows, and inevitably you can't find a replacement.  As far as beautifully machined input sockets and binding posts, if it give you pleasure, either sonically or from an 'audio jewelry' perspective, and you can justify the cost, enjoy!  Given the innards, that would not be the first place I would put my money, as you can buy a whole passle of OPA2604s for the price of one machined phono socket.

[Occam]

Cool! All that from the photos?! How do you go about getting a schematic?

Of course not, PeAK has been gracious enough to answer my nattering questions of "Whats this? Whats that?", combined with the kind, patient  tutelege of my betters.

As to the cost of the SLA-1 in Australia, its 'bargainometric' rating would depend upon what else is available and at what price. Our steadfast ally, Australia, always seems to get the short end of the stick, whether dealing with companies in the States or with our government. If you think you're getting screwed as a consumer, consider your own countries agriculture. We preach free trade, but we put up unconsionable barriers while subsiding our own agribusiness with unneeded, defacto corporate welfare.
[end rant]

I've got a call into ART, left a message, and they haven't called back.

As you can see from my follow up posts, I do have concerns with the PS and associated volumetric constraints. This is not to say that as is, and/or with judicious cost concious upgrades the SLA is not a tremendous bargain.  But ultimatlely, to surpass some arbitrary level of performance, one incurs the cost of additional volume. The chassis is just too dang small! Similarly, one ultimately muses, gosh the output transistors (or whatever) are really great for the price, but the xxx are objectively and subjectively better in these ways.... At some point, depending on how you value your own time and efforts, its simply more effective to belly up to the bar.

[peakrchau]

  ...
As you can see from my follow up posts, I do have concerns with the PS and associated volumetric constraints. This is not to say that as is, and/or with judicious cost concious upgrades the SLA is not a tremendous bargain. But ultimatlely, to surpass some arbitrary level of performance, one incurs the cost of additional volume. The chassis is just too dang small! Similarly, one ultimately muses, gosh the output transistors (or whatever) are really great for the price, but the xxx are objectively and subjectively better in these ways.... At some point, depending on how you value your own time and efforts, its simply more effective to belly up to the bar.

Thanks Occam for creating this thread and putting down such detailed  thought down...it should be a useful interim spot (what do we do when we get schematics ?)  to capture thoughts on SLA-1 mods.  I have added a link from my SLA-1 Page to steer traffic here.

I agree with most of what you said above about heat and venting. Most modders I know of with grown up kids are constantly at work on their units that the tops on often left unattach...as in my case. It partially solves the venting/space issues. Yep, the WAF is low.

The other place to start would be start with a different unit with decent sonics and equivalent power. I have some links on the Samson Servo 260 (100W into 8 ohms, 2x130W into 4 ohms...hence the name). The unit was quite a bit more expensive than the SLA-1, but the lower powered Servo 170 was only $30 more.  It has no bridge mode (most will use it...so really a non-feature) and chintzy spring loaded speaker connnectos which will probably be easy enough to upgrade. Cheers.

[Occam]

PeAK,

The wonderful thing about the internet is the speed at which folks can share information. Without your help, I'd have had no basis for posting.

There is an informative and humorous review of the SLA over on Audiogon.
http://forum.audiogon.com/cgi-bin/fr.pl?ramps&1054774771&openfrom&1&4#1

To an inquiry on that thread, I've posted a link to your site. I'd be interested in your comments as to how that review correllates to your own impressions.

I've still not heard back from ART about the schematic. And I just realized that even if I do get it, I've no way of posting it until my scanner doesn't crash my system ( my son just 'upgraded' me to XP Pro). If someone else (hopefully, with a working scanner) wants to give ART a try, their contact link is-
http://www.artroch.com/default.asp?p1=6&p_id=42

With regards to the Samson Servo's price relative to the ART's,  I generally find its street price to be lower -
http://www.zzounds.com/prodsearch?q=samson+servo
But the situation in Canada might be different.

I'm not familiar with the Samsons other than their website's info and Todd Kreiger's enthusiatic commets...

Regards

[Brad]

JohnR,

Couldn't someone here buy one for $200 and then ship it to you?
Gotta be less than $160 to ship it there, right?

[peakrchau]

PeAK,

...I've posted a link to your site. I'd be interested in your comments as to how that review correllates to your own impressions.
 ...

I had a "Gggooooooooodd listen" last night and agree that it is a remarkable value ...make that just plain remarkable. In my system,  the SLA-1 forms a  mighty fine partnership based on  hearing it evaluated using some high quality reference recordings going through a friend's recently tweaked DI/O. Read my review of last night's 5 hour listening session .

Last night's experience convinced me that   I'm going to mod it very much in the short term. Despite it's simple and smallish capacitor bank (compared to a KRELL) it seems to work fine when the rubber hits the pavement. My problems are futher upstream...again. Some remarkable comments in a way for a modder like me...hmmmm?


For members of Yahoo Group's DIOMODS, various spec sheets on the components (4558, UPC1237) and the SLA-1 User's Guide have been uploaded to the file section of the Diomods group:

http://groups.yahoo.com/group/DIOmods/files/Art%20SLA-1%20Amp%20stuff/

Due to the low traffic with regard to new DI/O posts, I think it would be a good alternative to posting detailed mods about the SLA-1 in preference to the LAB section in this forum...it has far better  facilities. I've asked the moderators to see what they think and will upload more stuff pending further approval.

Enjoy,

[nature boy]

PeAK,

Thank you for you extended, objective listening impressions about the stock ART SLA-1.  They are greatly appreciated.


Regards,

NB

[eric the red]

I'm curious as to how reviews can ever really give an idea what a component sounds like. Besides the main point of everyone's hearing being different, how can anyone actually tell anyone what something SOUNDS like by reading about it, especially if you're not familar with the audio cliches used on audio boards and in audio rags?  No two systems are the same, rooms are different, set-up is different, and people like or dislike different recording that may vary wildly in their quality. When even a small change in speaker set-up can have a big difference in how someone's rig sounds, how can anyone possibly imagine that they can get an idea what something will sound like (especially something like an amplifier that needs a cdp and speakers in order for someone to describe its "sound") without hearing the component using their own rig in their own room using their own hearing? If someone described the ingredients of something they had eaten and tried to describe what it tasted like, would a review do it for you without actually tasting the food yourself? No offense, but most reviews for me are a lot of fluffy cheap entertainment and tell me nothing except that there is a new product out there that someone somehow is pushing and my eyes glaze over and I start nodding off when the reviewer inevitably gets to the part where he describes the sound of the piano on Bach's # IIX piano concerto in D minor. If you can't hear something in your own home with your own ears (besides pitching new products) what good are reviews anyway?

[Occam]

Eric,

You've raised an excellent point, "How is one to interpret someone's subjective review with what would be your own subjective evaluation if you could just hear the dang thing".

What I do is try to calibrate the reviewer opinions, particular hotbuttons, monkeybones, likes and dislikes..., of products which I have also heard and formed an opinion of. Certainly, the anciliary equipment that is used will have a strong impact. But for example, I've followed Todd Kreiger's comments on various stages and types of modifications on the ART DIO over on AA. Luckily, I've personally heard many of those same mods to DIOs via my own minimal mods and those done by members of my local audio club. My conclusion is that he has-
1. A higher resolution system than I do, and is incredibly concerned over 'noise floor', that 'blackness' around the notes, microdynamics.
2. Like me, he demands a cohesive, full range, tonally consistent presentation.
3. Soundstaging, imaging... are not as high on his priority list as it is in mine. and the list goes on...

So when he comments on a poweramp that is unknown to me but makes a comparison to an amp which I have heard, like a Marsh, I do feel I can catch the gist of what he is trying to communicate. Luckily, I belong to a local audionerd club, and generally get to hear a new piece of gear each month. I'm very familiar with the host's own system, so when the auditioned product is dropped in, I think I can get the measure of the product. When a vendor comes by with a 'system', we attempt to listen in total, and additionally, with components swapped into the known system, one at a time, much to the consternation of some vendors.

After hearing many components in a known system, I attempt to calibrate my opinions against some arbitrary reviewer's own opinions of products of which we have both heard,  and hopefully can extend that normalized callibration to components which I've not heard. But your point about ancilliary equipment and component synergy is certainly valid. The president of the club is a good friend, he goes to most of the big shows, and knowing his particular metrics and exposure to far more equipment than me, I find him a tremendous resource.

Then again, WTFDIK?

Eric, this is a really good subject, but not really on point for this thread. I'm afraird that that the only viewers might be those interested in this threads actual topic (which doesn't seem to be many) and those who might be curious as to who I've antagonized most recently. If you start a thread over on Audio Circle, the discussion might be far more inclusive.

[eric the red]

Am also kind of curious as to whether you think using different names on audio boards is a kind of sockpuppeting and why you are so set on ripping on Don Nance on different audio boards when you could easily ask him the questions you're asking via email or by a phone call (Don is very easily contacted trust me as are most of the people who frequent audio boards), but you're right, that's not the subject of this discussion so maybe you could answer the same question on the Audiogon thread as I just posted this same question over there.

[Occam]

Eric, I post as Occam here and on Discord, all other boards I post a pmkap. As you can see on AudioGon, I freely acknowledged this prior to your enquiry here.  Discord and Circles are the last boards I joined, and the monicker is a reference to his rayzor, something I endeavor to weild properly. I've never used any other names and have certainly never engaged in pudpuppeting, that orchestrated 'call and response' between different aliases or between cronies. If you consider my consistent use of two different names, unique/board as sockpuppeting, that is your perrogotive. Although Mr. Nance's shenanigans have been exorcised by Audiogon, his exploits on AA are still there for anyone to judge for themselves.
http://db.audioasylum.com/scripts/t.pl?f=tweaks&m=83630

The 'menage a trois' between d911, audiodilbert and Jack Seaton was truly a marvel to behold.

As to why I asked questions on AudioGon, and not Circles, its simply because he was answering questions on AudioGon, here he was simply blowing smoke. As to why I posted my responses on both Circles and  AGon, it is because Mr. Nance had already been 'discussed' on AudioAsylum. I wanted a public record. I wanted a clear 'internet trail' so that the audiophile community could make their own judments of both the integrity to which he shows in his exchanges with the public, and the technical expertise and value which he provides in his products. You are free to judge the technical 'exchanges' between myself and Mr. Nance, as you so choose. I would think that some within our community might be interested in both in forming their judgements.

If you want to continue this question, please take new or more appropriate thread. Feel free to take it to the extant OvsD in the fightclub. Similarly, if you were serious about your 'evaluating the reviews', a really excellent discussion topic, it would potentially be far more inclusive in it own thread, rather than buried in this one. But obviously, you are free to do as you see fit.

[eric the red]

edit: you boys should start your own high-end rag. Here's a title suggestion: " High-End Boilerplate"

[Occam]

Eric,
What exactly about this thread, nominally devoted to technical discussion of the SLA-1, puts your knickers in such a twist?
Why do you feel a need to write such off topic posts?

I fail to see how my response to your query on evaluating reviews would elicit -

edit: you boys should start your own high-end rag. Here's a title suggestion: " High-End Boilerplate"

and when you make obscure references, please show the courtesy of letting others be privy to your latest credo.
http://www.mastersonvideo.com/features/20021101.htm

Nothing I wrote is in disagreement with what was said by Mr. Masters (or Floyd O'Toole) or Dan Banquer, but rather expanded on the point that vocabulary without context is meaningless, i.e. In order to  derive the meanings of adjectives from context, we really must know specifically 'What' the writer is making comparison to. This is how folks learn new vocabulary. If you missed the gist of what I said, I'm sorry, but really don't see how I can make it clearer to you. Normalized Metrics are really not that hard to understand.

This is the 3rd time I'm asking you to keep this thread on topic. Please exhibit your frustrations and insecurities elsewhere.

Regards,
Occam

[eric the red]

Actually I cited Floyd in my response to Peak's AA SLA1 review and didn't find it necessary to do so again. Plus I haven't seen many bibliographies attached to posts by the audio pseudo-scientists who frequent internet audio boards whose ideas are lifted directly from the vast amount of regugitated hi-fi claptrap that is everywhere on the web. I'd love to see made-up audio terms like "more air" and "blacker background" cited so as to see where those particular bad audio cliches originated, but it ain't going to happen. So yes, I was taking my own liberties here in citing Dr. Toole's words and it won't happen again. I'll also try and find the source of "Loose lips sink ships" if that bugs you plus I promise from now on to stick to the topic at hand. So maybe you could chime in here on this question to Peak regarding the stock SLA1.
     From Peak's AA review of the stock SLA1 amp: " Tried 83802 cable (his Belden power cable) with polarity reversed via cheater plug resulting in more air but diffused bass."  So I ran this by my EE student cousin (who works as a professional A/V installer) and his response was this:

     "Reversing the polarity on a unit that uses an AC plug is not going to change a thing due to how AC works. "Alternating current" (his quotes) alternates between each pole and should have no effect whatsoever on the sound. This gives me more evidence that some of these people are insane and hear things that aren't really there".

     Can you or Peak maybe set the record straight here for him and maybe enlighten a few of us on how putting a cheater plug on the end of a cord can actually improve and/or change the sonics of an amp in a little more detail?  Nothing too technical, just a plausible non-cliched explanation.
     And to answer your main question: My shorts aren't in much of a knot haha    as I think that most of the reviews and technical arguments out there in audioland on how something 'sounds' are a bunch of hooey and have no relevance whatsoever on how a component will sound to my ears. I'll bet 99% of internet audio reviewers couldn't get their cliche-ridden garbage prose reviews published anywhere else but on the net, and I'd rather read what Mike Piazza has to say about his Krell gear than read most of the horseshit that pawns itself off as audio journalism or audio reviews these days. Plugging in a cheater plug "resulted in more air but diffused bass" sounds like someone had a problem with their home heating or cooling system and fixed it to me.

[peakrchau]

...Can you or Peak maybe set the record straight here for him and maybe enlighten a few of us on how putting a cheater plug on the end of a cord can actually improve and/or change the sonics of an amp in a little more detail? Nothing too technical, just a plausible non-cliched explanation.  ...

Eric, I'll take the bait (along with the boilerplate ).

You could also use GOOGLE and type "chassis potential" and "polarity" for a better explanation. Cheers to student EE cousin's choice of vocation, I suggest he  wind his own transformer one day and report back on the difference between practice and theory... back to fish pond:

"The isolated/secondary side of the transformer can be viewed as floating at some potential in the world and common to the amp chassis.  Stray capacitance from one side of the primary widing can be different (assymetrical) to the other one used as return.  The result can be  differing amounts of power and RF  coupling from the line to the chassis when the hot side of the primary is interchanged with the return"

Easier if you just try it...might save you from spending $500 in modifying a perfectly good amp  ...to paraphrase Occam's life advice above...whatever you do, try to leave the world in a shape better than you found it...

P.S. Where I live, I could swear there is more air and a blacker background in the sky...it makes for great stargazing. PEACE BRO.

             |  /
            \|_
           .\\|

[eric the red]

haha point taken . It's...just...so...hard...not ...to...be...an...audio...cynic...somet imes...