Which Audiologic dac was the first to go 24 bit?

Thanks Gary, you said it better than I could !!
BTW, the RCA 12AU7's are sounding primo.
The other side is running a pair of Cryo'd Russian 6H23N-EB's, life is good.

Hi Jeffcott - thanks so much for your detailed discussion. As I don't consider myself a "paying" customer, I didn't feel it right to infringe upon Mr. Ozment's time concerning tube selection. It's apparent that you gentlemen have spent quite some time and effort in the quest, so I am very appreciative of your willingness to offer your observations to this neophyte.

After the aforementioned household move, my 2 ch. system will reside in a dedicated room, along with the components finding a new resting position upon a Sistrum SP-4 rack - so I'm hoping that this will adequately address the isolation enhancement you feel is important. (As an aside, I recently made the acquaintance of a local Audiogoner thru the forum, and I'm sure he would attest to my current hodge-podge 2 ch/ HT arrangement - I'm chomping at the bit to get things set-up properly. It perhaps may be a mistake to make all these changes - room, rack, tube rolling, etc - at once, but am afraid I don't have the patience any longer to do it methodically.) I will also act upon your suggestion for using the tube dampeners.

And thanks for the offer - I'll be in touch via email.

Cheers,
Tom

I'll chime in:

1. Isolation does make a difference with this DAC. I use a K-Works IsobaseK, and prior to that a Seismic Sink. Both made a big difference, as noted above.

2. For tubes, I agree in the units without the transformer upgrade, the 12AU7s have the biggest effect on the sound. I've always been a Telefunken fan, and I used both Tele 12AU7s and ECC802s in there. The Teles probably are a little rich around 200hz or so, because after I got the transformer upgrade I could hear a slight dip at that crossover frequency in my speaker system, where the satellites pass over to the woofers (fixed that with a phase control). Jerry used to use Mullards in there, which I found lively but with just a little too much glare for me. For the 6922s/6DJ8s, I've settled on Siemens, both Ccas and ECC88s as my tubes of choice. The Sovteks are OK, but not in the same league. I've also heard people claim the NOS Sylvanias work well in this DAC; perhaps if Joe Kubala is around he'll elaborate.

Hey - thanks to all you guys who've responded about tubes here. I will never ceased to be amazed at the level of knowledge you fellas possess for this hobby. Talk about feeling like a ditch-digger at an Aeronautical Engineering Society luncheon - sheesh!
Have a great weekend ...
Tom

Hoe does the transformer upgrade improve the sound?