Which Audiologic dac was the first to go 24 bit?

I think it was the 2400; I got a late model 34, and it had the 20-bit chips. Some of us upgraded our Model 34s to install the 24 bit chips.

The difference in sound was not really that much at all, and Jerry told me that before I made the switch; I only did it because I expected Classic Records to release a lot of great DADs (which they didn't) and because I liked the Purcell upsampler (which I still like, but after taking it out I think it added too much noise to the signal and lost some of the AL's delicacy) which could output a 24-bit signal. Unless you have a source that sends out a true 24-bit digital signal you're better off with the 20-bit chips, which Jerry apparently felt were very good. In my case, the 24-bit chips still are a plus, because I am friends with a couple of recording engineers (one professional, one amateur) who have 24-bit/96khz machines, so I can listen to their master tapes through my unit.

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.

Tab110s--read my review of the transformer upgrade for my impressions. Curious to see how others feel about it.