Which Audiologic dac was the first to go 24 bit?

Pat and I have spoken a number of times regarding tubes in the M34, but I didn't want to steal his thunder. I have an M34DSB which, like Pat, I love and enjoy.

As regards your question about tube placement in the 34, looking from the front, the 12AU7 pair is on the left side (in line) and the 6DJ8 is on the right side (also in line).

As regards tube rolling, I had the occasion to speak with Jerry Ozment a few months back and he (to my hearing) confirmed my perception that the DAC is significantly more sensitive to 12AU7 selection than to 6DJ8 selection. I would suggest that you start there. I am a long way from trying everything but I have tried a few inclusive of Sylvania yellow labels, RCA's Black Plate 12AU7s, 5814a's and 5963's, and Siemens Silver Plates. Pat has used Amperex Bugle Boys so he will need to chime in on his comparison there (sorry Pat, I still have not gotten that done.

Observations: in my experience, the LARGEST improvement with this DAC and tubes has been isolation. When I put a Townshend Seismic Sink under the DAC, all of the rules changed. I would encourage anyone with this DAC to start there. It really levels the playing field. Yes, better tubes are still better, but the spread is definitely reduced.

As regards tube dampers, I think they are mandatory and the Herbies Halo-9's are a nice damper. I use 'em.

Tube observations: IMO, one of the best "affordable" tubes is the 1950's production Black Plate RCA 12AU7. Without isolation, they can be a bit bright and shrill, but put a sink under them and they get magic. They do cymbals wonderfully. A tube with a softer top end sound is the Black Plate 5814A. This was my preferred tube for quite some period of time. If you feel that CD playback has just a bit of an edge, try this tube.

My tube of choice at the present (as I have been fortunate enough to find a pair) is the Siemens Silver Plate ECC82. These tubes are scarce, but I just love them. Some have described them as the pinnacle of the 12AU7 family. All I can say is that they do everything just right for my tastes.

In terms of the 6DJ8 slot, I have used both Bugle Boys and Amperex PQ's. The PQ's were an improvment, but it was a SMALL improvement. On my list of to try tubes in this position are Brimar, Siemens and Tungsram.

If anyone is interested, email me off-line and I will send you a copy of my notes on tubes that you are interested in, and a slough of links to entertain yourself with.

Tburn, if you wish to try any of the above RCA's or Sylvania's, let me know. I have extras and would sell you enough inexpensively to get a good taste. These are inexpensive tubes.

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