Manley TNT MICROPHONE PREAMPLIFIER - Manual (Page 10)

The Tube Channel
The left side (T) or channel one, is almost an exact
replica of the SLAM! Mic Preamplifier and audio
path. The only differences are the addition of the
Impedance switch and an additional shunt regulator
on the phantom power. The latter reduces noise and
provides a softer start & off with the phantom power
switching – less thump and less chance of input
transformer magnetization.
After being introduced, the SLAM! immediately
developed a reputation as one of the best and easiest
to use tube mic pres. It seems to particularly shine on
the traditionally most difficult sources like sax, brass,
raspy vocals, and most percussion. It might not be the
first choice for those looking for a dramatically colored
preamp or those looking for gobs of tube-warmth
(distortion) and it isn’t a one-trick-pony that stamps
its own personality on every sound. However, it does
have both an input transformer (Lundahl) and output
transformer (the one we developed for the SLAM!)
and it does have two stages using tubes and it is true
class-A from input to output, so yeah, it does have
some character and tube-magic, and a tasteful amount
of warmth. In other words, clean but not sterile, and
it is neither flavor-less nor overbearing. Perhaps, the
simplest description from a reviewer both describes
this tube preamp’s ‘sound’ and the designer’s actual
intention – “Just plug in a mic and it sounds great”.
There are twin tube gain stages based on one of most
rave-reviewed hi-fi phono preamps ever, the Manley
Steelhead. These gain stages can be described as
JFET-Tube cascode amplifiers. The FET is the first
stage to keep the noise floor low, and the tube provides
the bulk of the voltage gain. The beauty is that the
FET and tube are so arranged to cancel the distortion
of the other (complementary). The topology and
balancing of this circuit has such low distortion that
there is no need for negative feedback, (which might
be appreciated by audiophiles). The circuit is also set
up to compensate for both FET and tube variations
and their drift.
This preamp also tends to have a great deal of headroom
in most situations. While one can push the first stage
hard to get some clipping when desired, one really
has to try hard – this preamp wasn’t designed to be an
expensive fuzz-box. On the other hand, this is why it
tends to work so well with difficult and complex wave
sources and why it succeeds as a “plug the mic in and
hit record” preamp.
Are there any tricks to using it, anything in particular
to be concerned about or suggestions about its care
and feeding? Practically none. Set the GAIN TRIM
knob to near the middle or straight up as a starting
point, turn the monitors down when plugging in a
mic cable or switching phantom on or off (as usual),
adjust the GAIN rotary switch to get an good level,
hit record. The 4 LEDs on the far right are intended
as a rough starting point to set that “good level” but
there is ample headroom and low noise in the preamp
that the LEDs mostly serve as ‘signal present’ and
‘overload indicators’.
The IMPEDANCE switch can be set to taste. Probably
the 4K setting may be the brightest or hardest, and
the 600 setting the softest or phat-est. It affects the
instrument ¼” jack that way too when fed by magnetic
pick-ups. It probably won’t have any effect on guitars
or basses that have internal preamps, or after pedals,
and probably no effect on synths. And on that note,
before you write off a mono preamp as a last resort for
synths because they all have stereo outputs – usually
you can plug into just its left output and get the full
sound, save a track, and not be semi-forced into yet
another wide spread left-right synth sound. In the mix,
give it a position, and add some good convolution
reverb (especially authentic rooms), and maybe it
will begin to resemble a real-life instrument and not a
‘stereo-type’ wash.
There are two outputs, a balanced XLR and an
unbalanced ¼” jack. They sound a bit different and
you can get a little variation of tone that way too. The
XLR has a transformer in the path so it may sound
a little “warmer”, softer, rounder, and fatter - more
‘vintage’ or ‘classic’. The ¼” output interrupts the feed
to the transformer and the XLR, and sonically it might
be called a hair brighter, harder, more transparent,
or accurate, depending on who is trying to describe
subtle little details in sounds, what aspect they are
focusing on and what instrument is being fed through
it. Of course, life is never quite that simple. There is a
variable that can affect the XLR output and cause all
the above generalizations to be thrown out the window.
Transformers are dependant on the load. For example,
if there is appreciable capacitance in the cable because
it is a few hundred feet long, it’ll probably cause some
high frequency resonance (a few dB boost).
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