If
you want to pick nits, a 'tube limiter' is a limiter that uses
a tube as the gain reduction element. That means an LA-2A is
not a tube limiter-it's an electro-optical limiter. There are
tube-based amplifier circuits in the input and output stages
of the box, but that doesn't make it a tube limiter. You could
correctly call it a 'tube leveling amplifier' without error if
you so choose.
Why does this matter? Well, one important reason is that there
are tube compressor/limiters, and the term is most appropriate
when talking about them.
During the 1950s, several different manufacturers began using
the rather common GE-6386 tube in a variable gain configuration
for their broadcast limiters. The circuit works with the bias
of the dual triode tube, and therefore the output is changed
by side-chain control voltages.
Among the devices based on the 6386 were broadcast limiters
by Gates, Altec, Collins... and Fairchild, who designed a stereo
limiter and continued to use the 6386 tube in a variable gain
circuit. The result, the Fairchild 670, was a widely used mastering
limiter that later became a widely used mixing limiter.
The 670 is long out of production and has become possibly
the most expensive piece of outboard audio gear in the world,
with prices well north of $25,000. In fact, the 6386 tube is
no longer made and has become fairly rare (and fairly expensive
if you can find them).
The folks at Pendulum Audio decided to build a tube limiter
with the same characteristics as the as the venerable Fairchild
670 - not only its time constants (attack and release times)
but also the way its compression ratio increases with gain reduction.
The design goal was to maintain the 'dynamic signature' of the
670 but come up with a more accurate and less colored signal
path.
Initially, they used the 6386 as a gain control tube, and
then coupled that with class-A amplification that had an active-balanced
output stage rather than the transformer output used in the original.
The result is the
Pendulum 6386 ($3995), for users who insist on the real thing
where the tubes are concerned.
Realizing that the 6386 tube is becoming much harder to find,
they set out to find another tube that could duplicate the Fairchild
compression curve and time constants.They found it in the 6ES8,
which led to the introduction of today's subject: the ES-8 Variable
Mu Tube Limiter.
Swinging back and forth
The Pendulum ES-8 is a stereo/dual mono limiter. When linked
for use as a stereo limiter the threshold and time constants
are controlled entirely by Channel 1; in the dual mono mode each
channel is completely independent.
The solid-state side chain offers three modes of processing.
Its Fast mode is self-explanatory, with attack and release times
of 0.5 ms and 50 ms respectively. The Preset mode offers program
settings identical to the 670 (more on the program settings in
a bit), and the Manual setting gives you control over both the
attack and release times to suit the application.
Controls
The input control is actually a passive attenuator placed
before the input transformer. Its normal operating position is
at it maximum unless the overall input level is overloading the
input transformer or gain stage. TheThreshold control determines
how much gain reduction is applied to the source material, and
the Output control is for gain make-up after compression.
Each channel also has a meter switch, allowing you to monitor
the input level, output level, or gain reduction. The manual
attack and release controls are active when the Mode switch is
set to Manual; the attack times
are adjustable from 1 ms to 100 ms and the release times from
a tenth of a second to 2 seconds.
One setting on the Mode switch is Presets, which accesses
six settings that are identical to the time constants of the
Fairchild. These Presets are labeled by their release times,
though the attack times vary as well. The first four settings
offer fixed attack and release times, while the last two have
a quick initial release followed by a longer decay time to zero
gain reduction. (Interestingly, this type of release is a characteristic
of electro-optical compressors like the LA-2A.)
The available release settings are 0.1 s, 0.3 s, 1 s, and
2 s, with 1 to 4 seconds and 0.5 to 20 seconds on the program-dependent
settings. All controls, including a hard-wired bypass switch,
are duplicated for the second channel. And when the two channels
are linked, Channel 2 is also bypassed by the Channel 1 switch
-a neat idea.
The rear panel has the both XLR and TRS I/O (the TRS plugs
can be run unbalanced), along with inserts for an equalizer into
the sidechain detector circuit. There is an IEC connector for
AC power, a power switch, and fuse holder.
Observations
The ES-8 is an interesting box. On one hand it aims to duplicate
the compression characteristics (a large part of the sound) of
the Fairchild 670, while avoiding the use of output transformers
(also a large part of the Fairchild sound). So rather than attempting
to do any sort of a comparison-which would really be hard, since
I don't happen to have the $25 grand to purchase a 670 of my
own!-we'll discuss it on its own terms. And
as a high quality compressor/limiter, it works extremely well.
When I needed to control single instruments and lead voices
without noticeable compressor artifacts, the Fast setting was
often just the ticket. And the program-dependent settings (especially
number 5, with a 1
to 4 second release) were great when I wanted just a bit of an
optical vibe. But most of my play time was spent using the ES-8
as a stereo compressor/limiter. To my ears, that's where its
strength lies.
When set within the typical operating
parameters of the unit (that is, without going for huge amounts
of added gain), the ES-8 is sonically as neutral as any compressor
I've heard. When you wish to rein in the dynamic range of a mix
without adding any coloration, this is the box to do it with.
Even with dramatic amounts of gain reduction, the output maintained
a remarkable transparency.
I'm a firm believer in Bypass switches for signal processing
devices, and a hardwire bypass that routes the input directly
to the output (bypassing all electronics) always gets bonus points.
While I usually use the bypass switch to
make sure I'm not making the sound worse, with the ES-8 I kept
having to check to make sure I was indeed compressing the signal!
The flip side of that is that sometimes you want a less transparent
limiter. But it would be silly to applaud a piece of equipment
for meeting its design goals so well and then turn around and
complain that it meets
its design goals so well.
Thus
The Pendulum Audio ES-8 is an extremely
high quality tube limiter that I'd recommend to anyone looking
for transparent level control without the sonic artifacts typically
associated with variable mu limiters. At $ three and a
half grand the ES-8 could hardly be called inexpensive, but then
the good stuff seldom is.
Price: $3495
More from: Pendulum Audio, Inc., P. O. Box 339, Gillette,
NJ 07933. vox/fax
908/665-9333, www.pendulumaudio.com.
