VAC Signature MK2a pre "phono tube questions"

Hello Dev,

You asked me to report back on tube rolling the phono section of my Phi Beta, which has the same circuit as your Sig 2a. I've had it for a week now and I'm ready to make a few preliminary observations after rolling a variety of high-quality 12AX7s, including 1964 Med Grade Amperex (very pricey), mid-'50s RCA long blackplates (one of my favorites), late-'50s Tele ribbed plates, and mid-'60s Lorenz (German-made Amperex). I have several pairs of each and I've tried them in different permutations in the first two positions. Because this circuit is so transparent, all changes in tubes affect the sound quite dramatically. Much to my surprise, however, so far the stock VAC tubes sound best to me. They are very balanced with excellent soundstage and tonality, weight and authority. They just sound "right," perhaps because VAC spends quite a bit of time tuning the sound by ear. I do find myself wanting a tiny bit more extension in the treble, and slightly faster transients, but this is perhaps because my tubes have quite a bit of time on them. I've ordered some Psvanes (I had a pair but wrecked one), which I expect to match this circuit very well since they appear to be of the same manufacture as the stock tubes (Shugang) but at a higher level of quality. I'll report back when I've tried them.

I'll add that I'm extremely impressed with the phono section itself. It's quite a bit better than I was expecting, and holds its own extremely well against my Steelhead II. I'm actually not sure which one I prefer. The Manley (which I've rolled extensively and optimized to my ear) is perhaps more dynamic, with more drive and extension. And it's more flexible in that it allows gain and capacitance adjustment. But the VAC is perhaps a bit more organic and natural. And it has plenty of gain even for a .2 mV cartridge. I could easily live with either, though I'm glad to keep both. Mine is MC/MC. At my request, Brent modified it to allow manual adjustment of impedance loading, unlike the stock Phi Betas, which have user-chosen fixed loading. He built these ingenious screw terminals that allow me to slide in resistors of my choice (I use nude Vishays) so I can really fine-tune the loading for any cartridge. For 100k loading, e.g., I use 10k resistors. It's both extremely flexible and extremely transparent. What a great company! I'm completely in love with this preamp. And you're right, it's a brilliant match with the Bryston 28B-SST2.

Hi Wrm57,

thanks for that information in relation to the phono section, look forward to your further results when you get your tubes.

Great to read that you are also happy with the pairing, I know of a few others whom also pulled the trigger and now have the same combo and truly enjoying.

Follow up: I found the VAC 12AX7s to be better than the Psvanes in this phono stage--more open and balanced. The Psvanes are tonally richer but and not as extended in the highs. I just ordered another set from VAC as back ups.

Wrm57,

thanks for the update, how many hours does your unit have on it now.

Kinda wondering if it is broken-in as of yet.

If so a recap of comparisions to your Manley specifically, once I have my 500 or so hours logged in with my 450's then at that time I will be wanting to do some phono comparisons.

When talking to Brent or Kevin did you happen to get any information in relation to the phono they have been working on.

My preamp is a dealer demo so it had a lot of time on it. The phono stage, however, had a cap replaced and the screw terminals for impedance loading installed, so those changes require some break-in, as do the nude Vishays I use for loading. In my hands, the unit's been on for three weeks with probably 130 hours of playing time (I work at home and listen while I work). So, you're right, the phono section is probably not quite fully burned in, but close.

I probably should have mentioned that the Psvane tubes are not fully burned in yet. Psvane recommends around 100 hours and I have probably half that on them, so their character might change. But the sound has stayed pretty consistent so I doubt they'll change much. Brent was pretty emphatic that the VAC 12AX7s are his favorites in the Sig phono circuit. He has quite a collection of NOS 12AX7s but prefers the stock ones in there. I have to agree.

I'm coming to the conclusion, subject to revision, that the Manley phono stage is a bit better. The VAC is excellent, don't get me wrong. I completely enjoy it and could easily be happy with it alone (if I only needed two MC inputs). But the Steelhead, right now, anyway, is more dynamic and throws a deeper, more articulate sound stage. My cartridges are all pretty low output, ranging from .2 to .28 mV. The VAC MC sections provide 60 db of gain, which is certainly enough for all of them to sound great. But the Steelhead may be selected for more gain yet, hence the increased dynamics. Running through the VAC linestage, the Manley sounds superb, better than I've ever heard it.

Since I'm running three arms (soon to be four) on two tables, it's good to be able to choose different phono sections for different arm/cartridge combos. But if I had to choose, at this point, anyway, I'd take the Manley. I haven't talked to VAC about the new stand-alone phono stage.