Re: Re: [Harp-L] Re: Art Tube MP

["Tim Moyer" <wmharps@xxxxxxxxxxxxxxxxxxxx>]

Uncle Ed Kliman wrote:
> Since this thread is about *tube* gear, the tube involved has a 
> great deal to do with whether this piece of equipment works for 
> harp.  A 12AX7 tube is a great preamp tube, but not necessarily 
> what you want for harp.  Switching the 12AX7 out for a 12AU7 or 
> even a 12AT7 will help the sound quite a bit.

I have to say, I wondered about this statement, so -- being in the 
market for a new tube preamp -- I did a little experiment.  The 
preamp I chose was the Studio Projects VTB1.  This preamp differs 
from many in that it has both tube and solid state preamp circuitry 
with a "blend" control that determines the mix between the two on a 
single circuit.  This is the same design as the PAiA Tube Head two-
channel rack unit I've been using for a decade.  

The VTB1 ships with an 12AX7, so when I bought it I ordered a 12AU7 
Groove Tube as well.  I ran the unit into my solid state amplifier, 
first stock, then swapped out the tube and tried it again.  I ended 
up going back to the 12AX7.  

It is true that the lower-power tube lets you crank the output more 
without clipping as much.  But the combination of input/output 
levels and the tube blend control give a lot of flexibility in 
shaping the tone.  Using the 12AU7, I could crank the input level 
all the way up, set the blend to all tube, and get a fat, warm tube 
sound with minimal clipping artifacts.  But sometimes I *like* those 
artifacts.  It turns out that with the higher power tube I get the 
same tone by just not cranking it as much.  I didn't like the fact 
that the tone I wanted had the knobs twisted all the way one 
direction.  It sort of implied that I was taking what the unit was 
giving, not selecting something from a spectrum of sounds.  

With the 12AX7 tube, I set the tube blend to full tube, and simply 
lower the input stage so it doesn't clip (the VTB1 has both internal 
and output level LEDs), then adjust the output appropriately (again, 
using the level LEDs), and get the same tone as the 12AU7 on full 
crank.  If I want something that's sort of a caricature of 
overdriven amp tone, I can still drive the higher powered tube to 
clip, and adjust the output levels.  

After my own tests, I like the higher power tube.  Your mileage may 
vary.  The lower power tube MIGHT work better in a preamp with a 
different topology.  But I like having the range to go either way 
(more or less distorted) when the application calls for it.

By the way, I was VERY impressed with the Studio Projects VB1.  It's 
very nice quality, a lot of flexibility in adjustment, and not out 
of range of what the other tube preamp stomp boxes sell for.  My 
only complaint is that I wish it had an on/off switch!

-tim