6
7. Operational Notes
The Manley ELOP+ follows certain traits and
traditions established by the UREI LA-2A and similar
historic leveling amplifiers.
These traits can be divided into two aspects -
electronic and operation.
The electronic concept is simple and rather clean,
use the audio to light up LEDs or lamps which shine
onto photo-resistors. These photo-resistors, in
combination with a fixed resistor, simply act as a
voltage divider to attenuate the signal. The tube
line amplifier functions to provide extra gain to
make up for attenuation losses and then acts as a
fine cable driver. Simple, elegant, and minimal.
Operation of this type of design is also simple,
elegant, and minimal. There are usually only
“threshold” and “gain” controls. Most have no user
adjustment of “attack”, “release”, “ratio” or
functions for de-essing or external side chains. To
put it one way, the user is “stuck” with fixed time
constants and a feature list that seems utterly
anemic compared to dynamic processors costing far
less...
...so why are “LA” style opto-based limiters so
popular? Several reasons.
To paraphrase Letterman, “The number one reason
why “LA” style limiters are favorites is because....
They work right on vocals.” This “rightness” has a
few aspects. The first is that “LA” style limiters
don’t leave much trace of limiting as they work.
This is partly due to the clean tube stages, the
simplicity of the opto circuit and partly because the
user can’t alter the attack and release.
Almost every VCA based design seems to leave
electronic personality on that critical vocal track.
This is usually undesirable. Our ELOP+ circuit has no
active limiting in the signal path. Tube circuits have
the potential to be musically more transparent than
transistors because tubes are generally more linear
devices and work with high voltages offering very
high headroom.
However, there are many poor examples of tube
circuits in the field, and many ways to butcher the
quality. We chose to use our favorite simple tube
line amplifier circuit which we also use in our Mic
Preamps, Enhanced Pultec Equalizers and the CORE.
Back to this matter with fixed time constants. We
get requests to modify our ELOP+ for more controls,
but we get even more people raving about how
great and useful the ELOP+ is now. The natural
attack, release, knee, and ratio (curve) are a
natural result of the LDR & LED Cell we chose to
use. The choice was based on the inherent attack
and release characteristics of this LDR & LED Cell
and is loved around the world for decades.
There is a major advantage of having fewer controls
and a reason for choosing this type limiter. You
simply adjust the Threshold for the desired limiting
amount and adjust the Gain for the desired level to
the recorder - then hit record! The limiter does
what its supposed to do - nothing more, nothing
less. Kinda like automatically right, strangely quick
and easy, and pretty much non-distracting.
We use the phrase “Set it and forget it”. This is a
very important feature that would be lost with a
variety of controls. A good engineer wants to be
ready to record “now” and does not want to be
fussing with controls while a lead vocal is going to
tape. Unfortunately most compressors drag the
engineer’s attention away (and often the singer’s
and producer’s attention away as well).
The time and slope characteristics of optical
elements are not easy to describe and probably even
more difficult to simulate. The attack is fast; not
super-fast “brick wall”, but fast enough to “catch”
consonants. It is also a function of level. At lower
reduction levels and lower peaks the LDR & LED Cell
is slower. It becomes faster with sharp peaks and
heavier levels of reduction. Release is similar but 10
to 20 times slower. Quick peaks are handled with
quick release and as gain reduction nears zero the
LDR & LED Cell gets slower like gentle braking to a
stop.
