Manley ELECTRO-OPTICAL LIMITER User Manual

OWNER'S MANUAL

MANLEY

ELECTRO-OPTICAL

LIMITER

MANLEY

LABORATORIES, INC.

MANLEY LABORATORIES, INC.

13880 MAGNOLIA AVE.

CHINO, CA. 91710
TEL: [phone]
FAX: [phone]

email: emanley @ netcom.com

http://www.manleylabs.com

CONTENTS

SECTION PAGE

INTRODUCTION 3

MAINS CONNECTIONS 4

OPERATION NOTES 5 & 6

FRONT PANEL 7

REAR PANEL 8

TROUBLE SHOOTING 9 & 10

INTERNAL ADJUSTMENTS 11

SPECIFICATIONS 12

WARRANTY 13

WARRANTY REGISTRATION 14

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INTRODUCTION

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WARNING!

TO PREVENT THE RISK OF ELECTRIC SHOCK

DO NOT OPEN THE CABINET

REFER SERVICING TO

QUALIFIED PERSONEL

THANK YOU!...

for choosing the Manley Stereo Electro-Optical Limiter. This Limiter follows in the tradition of the
vintage LA-2A Leveling Amplifier using a passive electro-optical device to control gain. The
advantage of a passive device is that it eliminates the need to push the music through many transistors
and / or ICs as would be the case in a VCA based Limiter. Also like the LA-2A, the Manley utilizes
a tube line amplifier for make-up gain. This is one of our favorite clean and powerful line drivers.
We achieve true tube "warmth" with fidelity rather than with distortion. Other owners of this unit
love the way they can drastically (10 dB) limit without introducing unmusical harshness. An
important feature is that it is quick and easy to use. Also rare is that it limits in a way that engineers
expect when they patch in a limiter. For critical vocal tracks - this is the one to demand.

Unlike the LA-2A, we use LEDs to illuminate the photo-resistor rather than electro­luminescent elements which are often slow and unreliable. We also use a solid state side-chain to
drive the LEDs. The Limiter also features a BYPASS switch that retains the tube section at unity gain
as well as an innovative BALANCE control to "fine tune" the stereo image in LINK mode. Around
Manley Labs we call the unit "The ELOP".

Please take a few moments to read through this manual carefully as it contains information essential
to proper operation of this unit. Thank you again, and please enjoy

GENERAL NOTES

LOCATION & VENTILATION

The Manley Electro-Optical Leveling Amplifier must be installed in a stable location with ample
ventilation. It is recommended, if this unit is rack mounted, that you allow enough clearance on the
top and bottom of the unit such that a constant flow of air can move through the ventilation holes.

WATER & MOISTURE

As with any electrical equipment, this equipment should not be used near water or moisture.

SERVICING

The user should not attempt to service this unit beyond that described in the owner's manual.
Refer all servicing to Manley Laboratories.

!

MAINS CONNECTIONS

Your Limiter has been factory set to the correct mains voltage for your country. The voltage
setting is marked on the serial badge, located on the rear panel. Check that this complies with
your local supply.

Export units for certain markets have a moulded mains plug fitted to comply with local re­quirements. If your unit does not have a plug fitted the coloured wires should be connected to
the appropriate plug terminals in accordance with the following code.

GREEN/YELLOW EARTH terminal
BLUE NEUTRAL terminal
BROWN LIVE terminal

As the colours of the wires in the mains lead may not correspond with the coloured marking
identifying the terminals in your plug proceed as follows;

The wire which is coloured GREEN/YELLOW must be connected to the terminal in the plug
which is marked by the letter E or by the safety earth symbol or coloured GREEN or GREEN
and YELLOW.

The wire which is coloured BLUE must be connected to the terminal in the plug which is
marked by the letter N or coloured BLACK.

The wire which is coloured BROWN must be connected to the terminal in the plug which is
marked by the letter L or coloured RED.

DO NOT CONNECT/SWITCH ON THE MAINS SUPPLY UNTIL ALL OTHER
CONNECTIONS HAVE BEEN MADE.

Note: This unit has been factory wired for your country. If you plan to take the unit to
countries with a different mains voltage you will need to send the Limiter to Manley Labs
for the correct power transformer - or use AC voltage converters.

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OPERATION NOTES

TheManley Electo-Optical Limiter follows certain traits and traditions established by the UREI
LA-2 and similar levelling 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 only functions to provide extra gain
to make up for attenuation losses and then act as a fine cable driver. Simple, elegant and minimal.
Operation aspects are also simple, elegant and minimal. There are usually only a "threshold" and "gain"
control. Most have no user adjustment of "attack", "release", "ratio" or functions for de-essing or external
sidechains. The user is "stuck" with fixed time constants and a feature list that seems 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 tubes, partly to 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 Opto circuits 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. However, there are many poor examples of
tube circuits in use, and many ways to butcher the quality. We chose to use our favorite simple tube line
amplifier circuit which we also use in the 40 dB Mic Pre and Enhanced Pultec Equalizers (rather than
copy UREI designs) because frankly our circuit sounds better and cleaner.

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 attack,
release, knee and ratio (curve) are a function of the Vactrol Cell we chose to use. The choice was based
on the attack and release characteristics. Changing the time values in this circuit involves different
choices of Vactrols. Not practical. Not in a "LA" style limiter. There is a major advantage to fewer
controls. You simply adjust the Threshold for the desired limiting amount and adjust the Gain for the
desired level to tape - then 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 Opto 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 Vactrol 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 Vactrol gets
slower like gentle braking to a stop. It is possible to"trick out" an opto circuit for conventional operation
but generally the results have been not well liked.

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