I dicovered the ART DI/O last year as I was looking for a external DAC/ADC to extend the number of I/O on my external soundcard using the two SPDIF input/output connectors.
What attracted me in the DI/O is it was a very good quality and cheap DAC and tube driven ADC, with plenty of room for mods/improvements. The DI/O uses 7V (+4dBu) analogue input & output levels which is fine in my case since I connect it to a Mackie mixtable… It wasn’t long before I got one from ebay…
The unit rapidly became a new reference for me. This DAC outputs tight bass, well defined mediums and realistic without being overwhelming highs. Just the sound I’ve been looking for!
A few weeks later I didn’t enjoy listening to the analogue output of my powerbook anymore and realised the Airport Express’ analogue output – although very descent – produced tiring muddy bass. In comparison to the Art DI/O, the analogue out of my Tascam soundcard at the time sounded very good, but lacked a bit of presence in the mediums.
The next logical step was to route every digital audio stream available through the ART DI/O’s DAC. On one hand, I could have spent loads on a descent coaxial S/PDIF switches (the expensive ones re-sync the streams and have transformers on all I/O to avoid ground loops), or go optical and use an inexpensive 3 way optical switch to switch from my CD Player, to the Airport Express, to another optical source!
The problem with the optical solution is that the ART DI/O doesn’t have any optical input, hence you have to use a converter to transform the optical signal into a ‘coaxial’ one…
I found an litle box at Maplin that just do what I wanted. It’s a TOS Link to coax digital converter (the picture of adaptor should appear on the right of this paragraph). The little box worked a charm but wasn’t very convenient since it requires a power adaptor (and my mains extensions are overcrowded).
I managed to resist the temptation to open the SPDIF converter for a week. I wasn’t surprised to find almost nothing inside: just a few ceramic capacitors, one electrolytic capacitor, a diode, a few carbon resistors and a small IC.
I sometime wonder if people don’t design stuff for other stuff unintentionally: the optical convertor board was just the perfect dimensions to fit vertically inside on the sides of the ART DI/O.
Components that can be removed form the TOS Link convertor board:
- The red LED (D3) and it’s resistor
- The diode (D1)
- The DC in socket
- The cinch socket (coaxial output)
- The 96 Ohms output resistor (R3) it’s important that you remove this one otherwise this resistor will be connected in parralel with the digital input terminator resistor of the ART DI/O and you will had a perturbed digital signal!
Bellow are a few pictures of the end result:
I’ve summarised the mods in a PDFs: ART DI/O optical TOSLINK input mod diagram.
As far as I read across web, most people use the DI/O as a DAC, in beetween their CD player and their HiFi amplifier. In that case you are only using half the features of the little black box and you can very easily improve its performance by removing the 12AX7 tube (tube generates a lot of heat => hotter enclosure => hotter DACs => more noise generated)!
The first mod I made on the unit was to add an On/Off mini-switch next to the AC in socket.
I also upgraded the power transformer with on of bigger amperage (I honestly couldn’t hear any noticeable improvement).
On the digital dauther board of the ART DI/O, I replaced the C9 capactior (4700uF 50V) with one of 10000uF in order to improve the locking capacity of the DAC when used in ‘Ext sync’ mode. This is really a must try of you use the dac in that mode! Before I changed it, turning off a light in my flat would cut the sound comming out form the DAC. With this doubled capacity the DI/O almost never looses doesn’t lose sync in ext-mode!
Last but not least, stock ART DI/O units have a 100 Ohms digital input resistor (R10) terminators, which should be 75 Omhs according to the SPDIF specifications (and if you use a 75 Ohms coaxial cable). I replaced this resistor with a metal film 0.6W 75 Ohm resistor (it is located on the I/O board close to the digital input sockets).
I’m really pleased with the results. It’s impossible to use both the optical and coaxial inputs at the same time but it doesn’t bother me too much. I can’t hear the difference between the SPDIF and Optical inputs. And I freed one mains socket under my desk since I no longer need to power the SPDIF to optical converter!
It’s really surprising to rediscover songs… just use a different (better) DAC an you’ll hear subtleties you never heard before!
Hope you enjoyed this post.