Chandler Limited Zener Limiter User Manual

The EMI TG12413 Zener Limiter is the ultimate TG limiter issued in celebration of the 75th
birthday of Abbey Road Studios. The Zener Limiter was conceived by Chandler Limited designer
Wade Goeke and is based on the vintage EMI circuits used to record The Beatles and Pink Floyd.
It continues the tradition of EMI Limiters started in 1954 with the RS114 tube limiter and the 1968
RS168 Zener Limiter. The Zener Limiters were also part of the 1969 TG12345 console channel and
the 1974 TG12413. This newest version borrows from the RS168 Zener Limiter and TG12345 console
strip to make a new full featured and flexible unit for modern use.

The Zener Limiter is reissued to add features and flexibility to the powerful and vintage sounding TG limiter
circuits. Wade has added many new controls including switchable input impedance for hard or
soft driving of the unit, 11-position attack, 21-position release, side chain filtering, and Comp 1, Comp 2,
and limit settings.

NOTE ON FRONT PANEL LABELING - You will notice white and yellow markings on the controls
of the front panel. This is not a mistake :-) Because of the new controls and settings added to the
Zener we have used two colors for control labels. White labels designate a setting exactly as it
would have been on a vintage TG unit. Yellow designates expanded selections chosen by Wade.
This way you may accurately recall a standard

TG setting or purposely break all the rules.

ZENER LIMITER

Connections - All connections on the Zener are transformer balanced with pin 2 hot.

Power supply - This is designed to be used with Chandler Limited PSU-1 MKII power supply.

The power pin out is as follows:

1) chassis and audio ground

2) 48 volt

3) +28 volt

4) -28 volt

Notes on Grounding - On the back of the power supply are two black banana connectors.

These join the audio ground to earth ground with a solid wire between them. Depending on your
studio you may want this connected or disconnected. Turn up your monitors or headphones a bit
and experiment with which has a lower noise floor in your system. You may also need to join the audio
banana plug to other sections of your studio to obtain lowest noise floor. The audio banana is located
closest to the edge of the power supply case. Use something simple like a guitar cord and touch the
tip to other portions of your studio to find best results. In some cases it may be best to connect a
10 ohm resistor between banana plugs. Please contact the factory for any help in this area.

Controls and Features

FULL BYPASS - Each channel of the Zener may be fully bypassed by use of these pushbuttons.

Its main use is for direct comparison of dry and compressed sounds.

INPUT GAIN - The Zener has selectable input gain and input impedance via the input gain
toggle on the top right of the panel. This was added so the Limiter could more easily replicate
different versions of the RS168 and TG12413 Limiter. The high gain setting is 12db higher
and is similar to the “Vanderlism” setting of the RS168 Zener proto type (please refer to the book
“Recording the Beatles” for more). The low gain is closer to the TG12345 console input but is still
hotter than the unity gain input of the TG12413 mastering console version. Input impedance is
300 ohm in High and 1200 ohm in Low.

INPUT CONTROL - This is a 21-position gold contact audio taper switch that controls the level
going into the compressor/limiter. Simply turn it up to drive the unit into harder limiting.

THD - The THD toggle on the right top of each channel disengages the limiter threshold so that
the channel will stop limiting but signal still runs through the entire audio path and sidechain. The
effect is a smooth pleasing distortion with a high frequency bump caused by the discrete amplifiers
and zener diode limiting circuit. The INPUT switch is used to drive the signal to more or less
distortion and is marked in white on the front panel. Interestingly the THD function takes a clean
sine wave signal and gradually triangulates it as you increase the input control but importantly
does not clip the signal in anyway. It is possible to drive the THD past the 2% marking on the
front panel by increasing the signal into the Zener from an outside source.

IN LEFT

IN RIGHT

INPUT GAIN

HIGH

LOW

INPUT

1

2

3

4

5

6

7

8

9

10

11

2%

.04%

THD

INPUT

1

2

3

4

5

6

7

8

9

10

11

2%

.04%

THD

THD

LIMIT

Controls and Features continued

At unity gain input with the INPUT switch on full you will get about 2% THD. If this is increased
to +4-5db, distortion will increase to around 5%, which is many, many times that of tape
and without clipping.

One excellent use of this is to patch the two Zener channels in series and use the first to Limit
and the second for THD. You can then use the OUTPUT control of the first channel to drive the
second into higher THD percentages while lower the output of the second to control overall
level. Very retro!

OUTPUT GAIN - Another 21-position gold contact switch set for +/-10db of gain control in 1db
steps. Use this for Gain make up when hard limiting or to drive the second channel into a higher
THD range when in THD mode as described above.

COMP/LIMIT - A very important control for tailoring the overall tone of the unit. COMP 1 is a
2:1 ratio with slower time constants that was originally designed by EMI engineers to emulate
the Altec 436/RS 124 EMI modified Altec compressors. Limit is much faster and designed to
emulate the response curves of the much loved Fairchild 660. COMP 2 is a new setting designed
to put you halfway between the two original settings and essentially gives you the compression
curve of COMP 1 with faster release times similar to LIMIT.

-8

-6

-4

-2

0

+2

+4

-10

+6

+8

+10

OUTPUT

COMP 1

COMP 2

LIMIT