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Summary of ART DI/O Mods

Here's a summary of ART DI/O mods as far as I know, NOT in any order of priority. I don't know if I've missed any. Some may not make a difference you can hear, and many people are happy with the stock unit.


1. Getting the unit dis-assembled: There are two screws that need to be removed to take out the boards, one is on the bottom and the other is on the back panel. After they are removed, you need to take the nuts off the phone jacks in back and on the front remove the knobs, nuts, and washers from the pots. Then you need to lift the main and connector board at the same time in a kind of "jack knife" fashion to get everything to slide out. Once the main board is out the DAC board has to be separated from the mother board to get at U1 and U2. Pull it off carefully, and make sure to follow anti-static precautions doing all of this work.

2. The analog output caps are on the connector board, they are C17 and C18. Some people have removed them and replaced them with jumpers. Some have replaced them with higher-quality caps of various values. There's really a lot of opinions on this one. The stock caps on my unit were Nichicon 22uf, 50V. Good sources for quality caps are welbornelabs.com and percyaudio.com. Black Gate caps have been getting some pretty good press. I removed mine and added shorting wires.

3. There are nine 1N4003 rectifier diodes, they are on the right hand side of the board in a row (when looking from the front) and they are black with a silver band. Replace them with 1 amp 90V IR schottky diodes from Digi-Key (Digi-Key item 11DQ09-ND, 38 cents each). Some people have only replaced the diodes associated with the D/A section, but I decided to replace all nine, they are cheap and once you crack the case you might as well.

4. If you are not going to use the A/D section, remove the tube and U2.

5. U1 and U2 are quad op amps, 14 pin DIPs. They are TL074's in the stock units. I removed U1 and U2 and added sockets, Digi-Key AE7302-ND. This is also controversial. There are those who feel that sockets could affect performance, so they solder the IC's directly to the board. I socketed mine because I plan to do "op amp rolling" and the board traces seem delicate to me, so I don't want to solder too many times.

6. Most people feel the stock op amps are not adequate. I replaced U1 with a a Linear LT1365 op amp. This is a quad amp with 70 Mhz BW and 1000V slew factor. It is also unity-gain stable and can drive loads with high capacitance. I don't know if the socket is detracting from the ultimate performance of this chip. This part is available from Digi-Key, LT1365CN-ND, $12.13 each. Once again, if you are only using D/A, then replace U1 (which is used by the D/A circuit) and remove U2 (A/D circuit). Other people have installed AD825 op amps with are mounted on little boards. These op amps are only available in SMT and are not available in a quad package. The boards are sold by audiocom-uk.com and lcaudio.com. If you go this way you'll have to do some pin mapping since there's not a 1:1 correspondence, and the sub board will "fly" beneath the DAC board. Both these companies are in Europe. Op amps are very subjective, and there may be other answers. I'm using the LT1365 for U1, it's a direct replacement and am happy so far.

7. The consensus is to replace the 100 ohm input resistor at the digital input (R10 on the connector board) with a 75 ohm metal film resistor. I used a Yageo from Digi-Key, 75.0XBK-ND. Other people like other mfgrs so pick your favorite brand.

8. Some people see improvements by grounding the case. I grounded the unit by replacing the bottom screw with a bare brass one, wrapping some wire around it, and screwing it down. I connected the other end to the cover plate screw on the wall outlet, which in my case is unpainted. It's important to use unpainted screws to ensure good contact, brass or copper(best).

9. The DI/O puts out over 7V at the analog outputs. This may cause a problem with some systems by overloading the preamp inputs. The "standard" value is 2-3 volts. My system doesn't have this problem. If you need to pad the signal, you can buy cables from boldercables.com or roll your own. See this post:

http://www.audioasylum.com/audio/digital/messages/30858.html

10. Most people replace the stock power supply. It puts out 9VAC at 800 ma. Most people use a Stancor STA-5790, 9VAC at 3.4 amps, alliedelec.com stock #928-9919, $18.29.

11. Some people are replacing the digital input connector with a Canare 75 ohm connector, and the analog output 1/4" phono connectors with quality RCA jacks like Cardas or Vampire. Once again, too many opinions on which parts are best, I'm still running stock right now. Welborne and Percy have many choices.

That's all I can think of.



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