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Phono Preamp Tube Rush

Is there such a thing as a tube phono stage that doesn't have tube rush? Is it just an inherent weakness of that type of pre or is it some combination of cartridge gain and preamp gain? I went from a silent solid state ASR Basis Exclusive to a Herron VTPH-2A (new home with space limitations) and now I'm using a Hagerman Trumpet with my Decca London Super Gold. Both the Herron and Hagerman have tube rush. The Hagerman beats the Herron in my setup and it really sounds incredible but in quiet passages and between songs, there's that hiss at high-medium and high volume. It's just there. No combination of new tubes, new cables, etc changes this fact. Same with the Herron. Anyone having a different experience with a tube phono preamp?
dhcod
three_easy_payments's avatar
three_easy_payments
2,097 posts
 
I had brought up the question earlier in the thread about why not use a 6922 instead of the 12AX7.  You definitely could get enough phono gain with the 6922 and this is commonly used in the Manley phono pre's (for example).  Now would the overall sound quality be as good in the overall circuit design compared to what Herron achieves in the VTPH-2A?...I have no idea.  I use the Herron VTPH-2A and am happy with it.  I may try a coupe of Roger's SLN tubes in the 1st gain stage soon and see if it makes a notable difference but either way I'm perfectly good with the Herron. ;-)
lewm
13,163 posts
 
three-easy, Manley, in the Chinook and in my Steelhead, use a hybrid cascode at the phono input.  "Hybrid", because the cascode is built out of a transistor (probably a JFET) and a tube (the 6922/6DJ8).  That is quite a bit different from using a 12AX7 all by itself to supply all needed gain.  A cascode per se will give you more gain and a wide bandwidth, plus shielding from input capacitance (because the JFET drives the 6922 via its cathode), compared to any single tube used in common cathode mode.  The trade-off is high output impedance of a cascode. The 6922 is well suited to this topology, because it has high transconductance, needed to take advantage of the drive from the JFET, rather than a high gain factor, in contrast to the 12AX7. 12AX7 has relatively low transconductance and very high gain.  You'd not use a 12AX7 in a cascode. Nor would you use a 6DJ8 by itself for the high gain needed at a phono input.
three_easy_payments's avatar
three_easy_payments
2,097 posts
 
@lewm 

I appreciate the detailed explanation!  I was unaware of the Manley hybrid design.
dhcod OP
710 posts
 
Interestingly, changing from my Herron VTSP-1/166 to a Lamm LL2.1 made a big difference, and not because the Lamm itself is quieter because it isn't. Could it be something with input impedance?
hagtech
175 posts
 
It’s all relative. There will always be phonostage hiss, whether tube or solid state. The goal is to get it quiet enough such that it is lower than silent groove noise. How much SNR is enough?

I just tested my system (Piccolo2 - Cornet3 - Tuba) at full volume into an HP400 AC meter. The difference between a silent groove (my best is the Hi-Fi News Analog Test LP) and the tonearm up is 9dB. Perhaps not numerically impressive, but it’s like night and day listening-wise. The uncorrelated groove noise sounds way louder.

Forgot to mention, this is with a Dynavector 20XL MC cart (0.3mV) into 100 ohm loading...
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