minor tweaks and some miscellaneous information regarding the ART SLA-1 amplifier

I have had an ART SLA-1 (aka the Unika MT1000) amplifier for nearly two years now.. I got it after Col showed me it was heaps better at driving my Alesis Monitor One speakers than my old faithful Rotel 30 watt amp. This is not that the Rotel was a bad amplifier, it just didn’t have the headroom to drive the relatively low efficiency Alesis speakers, they really do need a 100W power amp to get the best from them.

ART SLA-1 with no volume control

Here I’ll document some minor tweaks and random info on the ART SLA-1 amplifier for future reference..

ART SLA-1 info scattered around the net

Perhaps the most exhaustive  page is Peaks ART SLA-1 page. He obviously got hugely enthusiastic over the ART SLA-1 for a while and gathered a lot of information about it. Some of it very useful, some in the more “crystal gazer” magic power cable audiophile vein, but a useful resource.

As well as that googling will find lots of comments and postive reviews from Audiophile types showing this amp is considered a low cost “secret weapon” amp for audiophiles.. for a while even a tweaked upgraded version was being sold by an after market customiser.
Googling the Unika name mentioned on the PCB board of the ART SLA-1 it becomes apparent that the ART SLA-1 is also sold under the name Unika MT1000 in Asia, or at least Taiwan. Unika appear to make gear under license for Yorkville, who own ART – or perhaps Yorkville/ART rebadge Unika designs.. regardless it appears they are the same unit.

My semi-successful op amp upgrade idea came from these comments by John Lance, where he upgrades an ART SLA-2.

Minor Tweaks

Disable volume controls:

The volume controls are fiddly to use as they are dual mono, so easy to end up with mismatched volume levels, so to shorten the signal path I opened up the amp and solder short snippets of solid copper to short the across the edge connectors that lead up to the front panel PCB where the volume control lives. This cuts the volume controls out of the circuit, as well as about 25 cm of think hookup wire from the signal path.

left: edge connector going to master volume controls
Below: copper jumpers shorting out the volume lines (covered in solder).

After all this I’d like to think it sounds better but it’s hard to say. I don’t have the time or resources to do a full ABX test. I then removed the knobs and covered the holes with black tape.
Upgrading the op-amp:

I orded the LME49740 chip from ebay after reading about its stunningly low THD specs and other people having success upgrading other ART amplifiers with it. I desoldered the AN6554 chip and soldered in a 14 pin socket and plugged in the LME49740. Initially it sounded great, but a day later I noticed a very faint whine/buzz sound in the left channel. It was actually so faint I didnt pick it up over fan noise from the computers and amps in the rooms initially, but sticking my ear against the speaker it was definately there, while the right channel was dead quiet.

Opening up the amp and moving my fingers around the op and nearby capacitors changed the sound of the buzz… looks like the circuit layout caused some oscillations in such highly specced chip. Replacing the LME49740 chip with a TL074, a pin compatible op amp chip that is higher specced than the AN6554 but not as highly specced as the LME49740 eliminated the noise completely. So I’ll call the first stage of the tweak a partial success. Both chips “seem” to sound better with a few hours listening (remember the LME49740 sound was virtually inaudible in normal use, it was just annoying me that it was there at all in an otherwise very silent amp) – but again it could be perception bias from my excitement over the upgrade, I’ll give it a bit of a long term listen to see how it all pans out.

above: socketed op amp. moving fingers around the capacitors caused the left speaker interference to change, at one stage even picking up radio.

Conclusion: I think it sounds better. But I am aware of the biases of my own perception due to doing the tweaks so hard to say. But in theory all of the improvements will have cumulative benefits so will help get the best sound.

3 thoughts on “minor tweaks and some miscellaneous information regarding the ART SLA-1 amplifier

  1. Hello, I am currently trying to repair my Art SLA 2, I have been searching for a picture of the whole board. Mine is currently not functional and the guy I bought it from we think replaced some of the parts with wrong capacitors ect…. Would greatly appreciate it if you could email me a picture of the whole board, so that we can see the components needed.

  2. You say the TL074 is “higher speced” than this AN6554.

    Based on what?

    The data sheets for neither chip publish THD and noise figures!

    The TL0XX are known to be noisy pieces of crap with poor distortion performance and driving ability.

    The AN6554 is not widely known. I can’t google up any information about it (like independent tests).

    The data sheet claims that it is low noise. That is believable. I have a 31 band equalizer whose filter bank is based on eight of these IC’s, and the unit is super quiet (and has very decent sound). I don’t think it would be that way if it was loaded with TL074’s.

    The TL074 is simply not a good replacement for anything. Whatever it is replacing has to be very, very bad in order for there to be an improvement. In this case, I think that replacing the AN6554 is a crap shoot that is weighted heavily against the TL074.

    Sorry to read about your disappointment with that 49740 (which is a de facto quad version of the LM4562, IIRC). Maybe it just needed an external compensation cap soldered across the pins. It was certainly worth a shot!

    A very nice, yet inexpensive quad is the MC33079 from On Semiconductor (formerly Motorola). Distortion and noise figures are published in the datasheet. Give it a shot. It just might work great.

    The 33078/79 have BJT input stages, and all NPN output stages, rather than complementary: thus, no crossover distortion! You can easily get this in 14 DIP form to fit your socket (unlike the OPA2134 which is only in surface mount, unless you can get your hands on new-old stock). I’m thinking of replacing the 8 AN6554’s in my equalizer with MC33079’s. A concern there is current draw. The 33079 draws only 10-11 mA. Still, that is a bit more than the AN6554’s 8mA, but not by much.

    • OK, thanks for the suggestions! Good to get some informed and opinioned comments!
      I think I’d just read the comment re: TL074 googling about for forum opinions on the chip at the time.. also it being pretty much the only drop in replacement I could readily source at the time was a big factor 🙂
      The SLA1 amp has been on the shelf for a while as I play with Class D, but thanks for the suggestion of the MC33079, I may just give it a shot.