I started a new thread on this, but thought I'd add same here:
As mentioned last year in some comments I placed in one of the mhdt Pagoda threads, I upgraded from Havana Balanced to Pagoda and Atlantis in my systems. I promised further commentary after I had extended time with these DACs. After getting some long-awaited comparative listening time I got to some definitive views particularly on the choice of tubes.
For all you TL;DR types out there in today's web, the net is that the way to reach a breakthrough in mhdt 24/192 R2R DACs is to dispense with the 5760-2c51-6385-6cc42-6n3p family of tubes entirely in favor of ecc88-to-6n3 converter sockets enabling you to run a high-grade 6922, e88cc/ecc88 or CCa in the output sockets. The boost in vividness, dynamic realism and tone density is startling, and yet doing this nicely balances the sharper, more articulate sound of the Pagoda and Atlantis that seems aggravated when you use a Bendix 2c51 for instance, that was otherwise so good at waking up the Havana.
For anyone else interested in the discovery path that got me from trying my full gamut of preferred Havana tubes to where I landed with CCa and CV2492 tubes in my DACs.
The first time I listened to the mhdt Pagoda, it sounded at once right and wrong relative to the already-sorted Havana Balanced DACs I had in my two hifi systems. The Havanas were organic, toneful and slightly "dark" sounding. A little soft on the top and and out-of-the-box were dynamically reticent but absent annoying, common, digital artifacts. I bought them on pure speculation that their R2R ladder foundation would give me something worth working through. On my Zu Definition 4 system, I arrived at configuring the Havana Balanced with Analog Devices AD1856 chips, with Bendix NOS 6385 tubes. On my Zu Druids V system, I configured the Havana Balanced with PCM-56K chips and replaced the stock 0.22mfd caps with Hovland Supercaps, and Bendix 2c51 tubes. In both cases, placing the Havana DACs on Aurios Media Bearings was a crucial element, for best dynamics, bass solidity and full-frequency shove. Aurios is out of business but I strongly recommend a bearing type footer under any mhdt DAC.
Getting the Pagoda, Pagoda Balanced and Atlantis DACs in place for evaluation was initially disconcerting. Accustomed to the leavened, organic, natural tone of the painstakingly-configured Havanas, the 24bit mhdts at first seemed by comparison spiky and over-emphasizing of transients. Very clean and articulate, however and spatially generous. I figured the PCM1704 and the discrete transistor I/V stage in each DAC must have fundamentally changed the familiar mhdt voicing into a new and different balance or proportioning of leading transient detail and follow-through tone. So different thinking was necessary.
The 24/192 DACs responded to placement on bearings exactly the same way as the older PCM56-based Havana. So no change there. I haven't gotten the time to consider capacitor changes, though my prior experience with the relatively compact Hovland Black Supercaps suggests they will be nothing but positive for the newer DACs. But to get these 24/192 DACs into their proper zone, I started with the tube(s).
Starting with stock GE 5670 and several variants, all broken in, did not prove a productive path. The 5670 smooths the spikiness of the native Pagoda and Atlantis voicing but also dumbs down dynamic contrast and shallows bass. However, the magic bullet 2c51 sharpened the saw teeth on the newer DACs to a degree that undermined mhdt's older and excellent house balance of leading edge vs. natural tone. To much of the former and you get hi-fi instead of music. Too much of the latter and it's all syrup. The 2c51 pushes the 24/192 mhdt DACs too much toward the undesirable aspects of hi-fi sound, which the older Havana needs a little of.
Several variants of 5670, 2c51, 6386, 6n3p weren't zeroing in on a clear improvement. They all presented not-quite-right points on a polar graph of attributes, each one a trade-off against good results from others. I was tempted to go back to my Havana Balanced DACs for both systems. I got past that with the NOS Tesla 6cc42. Really convincing musicality that was only a little short of the transient dynamics I expected over Havana. That was quite good and was equally effective in Atlantis and the Pagoda Balanced. This is a pretty affordable and available tube which I think will work for most people. After a few weeks gaining familiarity with the Tesla, I then tried and settled on the scarce and expensive NOS Bendix 6385 as ideal, if you can find it. That tube reconciled the tone/detail balance to near perfection without the older Havana's relative tonal darkness, and without the Tesla's slight dynamic reticence.
Then one day wandering around eBay I happened upon sources for tube socket converters. Prowling that list, I found a source in China for ecc88/e88cc/6922 > 6n3p/5670 converters. This would allow running 6922/cv2492/CCa dual triodes in mhdt DACs. No brainer to order some. First up, the Pagoda single-ended. Out with the Bendix and in with the converters plus NOS Mullard CV2492. It was an idea to try; I had no particular expectations. I wouldn't have been surprised to have this be a step backward.
But no. It's sensational! Current draw is similar to the 5670, so this isn't a strain on the power transformer. I assume mhdt's decision to select the 5670 family was driven by the facts that they are cheap, plentiful and very good, and the extended family of substitution tubes is extensive. Nevertheless, go converters + premium 6922 family and I think you'll be seriously startled by the gains in dynamics, musicality, tone density, transient life and an especially notable extension of deep bass response from Pagoda and Atlantis. I also hear a more fully dimensioned soundstage, including depthwise. Overall a more spatially scalable sound where it's appropriate.
All of my inventory of 6922 family tubes is comprised of premium NOS. Siemens, Siemens-Halske, Amperex PQ, Mullard, Telefunken, Valvo CCa, CV2493, e88cc, etc. I settled on Mullard CV2492 in Atlantis, Siemens CCa in Pagoda, CV2492 in Pagoda Balanced. The differences between these premium tubes are discernible but not gaping. Running a step down Siemens e88cc or Amperex PQ 6922 is still going to be completely in the realm. I don't have any cheap and current production 6922 family tubes, but will get some and report back. The tube socket converters run something like eight bucks. If current production tubes yield same or similar effects, then this can be a very inexpensive sonic improvement.
The differences aren't subtle. I will stick with this combination for a few weeks and see if it sticks. In a separate post I'll get into the differences between Atlantis and Pagoda.
Phil
