Gem Audio Labs Preceptor User manual

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Date 03.07.2012
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User’s Manual
Preceptor
analog compressor / limiter
model-A
Gem Audio Labs
Tel. : [phone]
[email protected]
www.gemaudiolabs.com

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CE Conformity
We declare with sole responsibility that this product complies with the following norms and
directives:
2006/95/EC LVD (Low Voltage Directive)
2004/108/EC EMC (Electromagnetic Compatibility)
DIN EN 55103-1 EMC of audio equipment- Emission
DIN EN 55103-2 EMC of audio equipment- Immunity
This declaration becomes invalid by any unapproved modification of the device.
Wroclaw, 28.07.2010 B. Radziszewski
SPLASH BARTOSZ RADZISZEWSKI
Wietrzna 36/1
53-024 Wroclaw
POLAND
VAT Reg. Nr : PL8862784446

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TABLE OF CONTENTS
INTRODUCTION ................................................................................................................................4
FOR SAFE OPERATION.....................................................................................................................4
CAUTION ..............................................................................................................................................5
FOR CORRECT OPERATION...........................................................................................................6
DESIGN ..................................................................................................................................................6
THE FRONT PANEL CONTROLS AND THEIR USE..................................................................9
THE REAR PANEL.............................................................................................................................13
BLOCK DIAGRAM............................................................................................................................14
TECHNICAL DATA...........................................................................................................................15
ENVIRONMENTAL PROTECTION..............................................................................................16
LIMITED WARRANTY.....................................................................................................................17

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INTRODUCTION
First of all, we would like to thank You sincerely for choosing this GEM AUDIO LABS
Preceptor which combines ease of operation with support for multiple usage environments.
As a company and first of all, as fans of pro audio devices, we do our best in our daily work
to satisfy your most sophisticated sound expectations. We put in your hands the highest
quality product, precisely designed and hand manufactured by our qualified staff, without
any compromise. To build our devices we use only the best, hand-selected electronic
components, we take care about all parameters repeatability and high quality of all our
products.
Please take a little time to read this manual thoroughly, as it will help You to entirely
understand how the Preceptor works and what is important to use it safely.
Gem Audio Labs team.
FOR SAFE OPERATION
INSTALLATION
Before You connect the power cord to the device please check fuses value and make
sure that the voltage switch setting reflects the correct local power line voltage. For
line voltages from 100V to 120V, set the switch to 115V and use 1,25A fuses (slo-blo;
5x20mm). The 230V position is good for all line voltages from 200-240Volts; fuses:
630mA (slo-blo; 5x20mm).
This unit is equipped with a three-pronged AC power cord. To reduce the risk of
electrical shock never remove or otherwise attempt to defeat the ground pin of the
power cord.
Do not allow water to enter this unit or allow the unit to become wet. Fire or electrical
shock may result.
Do not place a container with liquid or small metal objects on top of this unit. Liquid
or metal objects inside this unit are a fire and electrical shock hazard.
Do not place heavy objects, including this unit, on top of the power cord. A damaged
power cord is a fire and electrical shock hazard.

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OPERATION
Do not scratch, bend, twist, pull, or heat the power cord. A damaged power cord is a
fire and electrical shock hazard.
Do not remove the unit‟s cover. You could receive an electrical shock. If you think
internal inspection, maintenance, or repair is necessary, contact your dealer or
producer.
Do not modify the unit. Doing so is a fire and electrical shock hazard.
If lightning begins to occur, turn off the power switch of the unit as soon as possible,
and unplug the power plug from the electrical outlet.
If there is a possibility of lightning, do not touch the power plug if it is still connected.
Doing so may be an electrical shock hazard.
Use only the included AC power cord for this unit. Using other types may be a fire
and electrical shock hazard.
IN CASE AN ABNORMALITY OCCURS DURING OPERATION
If the power cord is damaged (i.e., cut or a bare wire is exposed), ask your dealer or
producer for a replacement. Using the unit with a damaged power cord is a fire and
electrical shock hazard.
Should this unit and AC cord be dropped or the cabinet be damaged, turn the power
switch off, remove the power plug from the AC outlet, and contact your dealer or
producer. If you continue using the unit without heeding this instruction, fire or
electrical shock may result.
If you notice any abnormality, such as smoke, odor, or noise, or if a foreign object or
liquid gets inside the unit, turn it off immediately.
Remove the power plug from the AC outlet. Consult your dealer or producer for
repair. Using the unit in this condition is a fire and electrical shock hazard.
CAUTION
INSTALLATION
Keep this unit away from the following locations:
-Locations exposed to oil splashes or steam, such as near cooking stoves, humidifiers,
etc.
-Unstable surfaces, such as a wobbly table or slope.
-Locations exposed to excessive heat, such as inside a car with all the windows closed,
or places that receive direct sunlight.
-Locations subject to excessive humidity or dust accumulation.
Hold the power plug when disconnecting it from an AC outlet. Never pull the cord. A
damaged power cord is a potential fire and electrical shock hazard.
Do not touch the power plug with wet hands. Doing so is a potential electrical shock
hazard.
To relocate the unit, turn the power switch off, remove the power plug from the AC
outlet, and remove all connecting cables. Damaged cables may cause fire or electrical
shock.

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OPERATION
Do not cover this unit and use it only in a well-ventilated environment.
If you know you will not use this unit for a log period of time, such as when going on
vacation, remove the power plug from the AC outlet. Leaving it connected is a
potential fire hazard.
FOR CORRECT OPERATION
CONNECTOR PIN ASSIGNMENTS
XLR connectors (INPUT, OUTPUT) are wired according to the AES standard : Pin 1 =
shield, Pin 2 = hot (+), Pin 3= cold (-).
¼” TRS connectors (EXTERNAL SIDECHAIN) are wired according to the AES
standard: tip = hot (+), ring= cold (-), slave = shield
INFLUENCE ON CELL PHONE USAGE
Using a cell phone (mobile telephone) near this unit may induce noise. If noise occurs, use
the telephone away from the unit.
REPLACING ABRASIVE PARTS AND CLEANING THE UNIT
The performance of components with moving contacts, such as toggle switches, rotary
switches and connectors, deteriorates over time. The rate of deterioration depends on the
operating environment and is unavoidable. Consult your dealer or producer about replacing
defective components. Clean this unit only with lint-free damp cloth and do not use cleaning
agents.
DESIGN
The GEM AUDIO LABS Preceptor is a two channel (stereo/dual mono) pure analog (Class-A,
discrete) dynamic processor, in which the gain reduction is made by a discrete VCA based on
bipolar transistors and Zener diodes. In fact, there are two independent mono blocks sharing
common enclosure, ON/OFF switch and LINK/DUAL MONO switch.
ENCLOSURE
Preceptor’s enclosure is a solid (3U high) and compact construction based on aluminum and
steel. It has been designed according to EIA 19” standard. For enclosure painting the best
coating powders have been used (scratches and cracks resistant). Such a solid design reduces
the risk of any mechanical damages, and lets you enjoy the trouble-free device not only
working for the warranty period.

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POWER SUPPLY SECTION
Special care has gone into the design of the power supply of the Preceptor because the power
supply is the heart of any electronic system, and the better it is, the better the whole system
works. In an audio system, this translates into a better sound quality, lower noise and
unwanted distortion elimination.
Preceptor’s power supply is based on a 70VA toroidal transformer, which is made on our
special order from properly selected cores. It is characterized by the highest quality, good
supply of power, silent operation and excellent electrical parameters. It has the core and
windings impregnation, electrical shielding (between windings) and magnetic (external
screen), its center is flooded with resin. The transformer has an anti-vibration mount.
Primary voltage can be switched between 230V~50 Hz and 115V~60 Hz via the switch
located on the rear panel.
The device is connected to the line by a standard 3 core cord with an IEC plug.
There are two safety fuses located in the mains input socket on the rear panel:
630mA (slo-blo; 5x20mm) for 230V~50 Hz
1,25A (slo-blo; 5x20mm) for 115V~60 Hz.
On the primary side of the transformer a special EMI filter is installed. It filters out any
interferences that may enter the device from the electric network. The signal sections are
separated from the power supply section by solid metal partitions.
Every channel has its own rectifiers and secondary voltages stabilizers. We have designed a
special filtering stage with high capacity capacitors (10000µF) and special active filters (based
on discrete elements) eliminating noise and ripple. Power of all stages is symmetrical and
every section has its own stabilization, which keeps the voltage range of +/- 0.01V. All the
voltage stabilizers are mounted to a common heat sink, which cools them evenly.
Furthermore, the heat sink acts as an additional shield.
Operational voltages:
First gain stage : +/- 20V,
Sidechain: +/- 20V,
Blender: +/- 18V,
Make up gain stage: +/- 28V,
Lights and relays : 12V.

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ROTARY AND TOGGLE SWITCHES
Preceptor has only rotary and toggle switches installed to obtain the best repeatability of all
settings. Thus you can easily return to your favorite settings. By using 1% low-noise
metalized resistors and gold contact rotary switches, we succeeded to obtain (in the link
mode) the difference between levels and characteristics of two channels in a range of
+/- 0.1 dB.
SIGNAL PATH AND SIDECHAIN SECTION
The Preceptor has installed a high performance, no compromise, professional input
transformers made by Carnhill Transformers Ltd. All elements in the signal path and the
sidechain section are built from the high quality discrete elements (low-noise transistors,
ultra low-impedance electrolytic capacitors, precision film capacitors, precision silver-mica
capacitors, 1% low noise metalized resistors, etc.) Only in the blend section were used
transparent IC‟s for uncompressed (DRY) and compressed (WET) signals mixing.
The gain reduction is made by a discrete VCA based on bipolar transistors and Zener diodes.
There are 16 Zener diodes, of course manually selected and matched.

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THE FRONT PANEL CONTROLS AND THEIR USE
APOWER
Common POWER on/off switch. The amber light and panel meters will glow when the unit
is powered on. Please turn down the volume of your studio monitors before turning on or
turning off the Preceptor.
BBYPASS/IN
The bypass is a hard relay bypass. If the unit loses power, it will default to this hard relay
bypass. BYPASS- hard bypass is activated (panel meter is highlighted in orange ). IN- the
signal is going through the unit (panel meter is highlighted in yellow)
CINPUT GAIN
This switch lets You choose between HIGH or LOW input gains by changing input Z
(HIGH- 2k5Ω, LOW- 10KΩ)
DSIDECHAIN
In the INT mode the Preceptor acts as a normal compressor sending main INPUT signal to the
gain reduction stage. In the EXT position You can use another audio track (sending it to the
EXT SIDECHAIN input on the rear panel) to control the volume of the main INPUT signal.
If you want for example to control the volume of the synthesizer pad by the rhythm of a kick,
send kick‟s track to the EXT SIDECHAIN input and then send pads to the main INPUT. After
that activate the EXT mode and set proper volumes of two tracks to obtain expected gain
reduction.

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The wiring diagram:
Very interesting sound effects can be achieved by doubling the same signal in the INPUT and
in the EXT SIDECHAIN input with series equalizer connection. When You increase the level
of selected frequencies, the Preceptor will react compressing them more than other
frequencies and vice versa, when You decrease the level of selected frequencies, the Preceptor
will not compress them. This technique can really improve the quality of your music. Keep
experimenting!
The wiring diagram (hardware equalizer):
The wiring diagram (DAW equalizer):
TOTAL HARMONIC DISTORTION FUNCTION (THD)
There is another trick in the box. If the SIDECHAIN switch is in the EXT position and the
EXT SIDECHAIN input does not receive any signal, then the Preceptor turns into a pleasant
harmonic distortion generator. The amount of distortion depends on the Z and the INPUT
switches settings. The larger the signal, the more distortion is in the processed signal (at
extreme settings, it may be up to several % of THD). This is because there is no control signal
and the circuit is driven.

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ELIMIT/COMP
In the COMP position the Preceptor operates as a compressor with 2:1 compression ratio. In
the limit mode its behavior can be compared to the famous Fairchild 660 limiter.
FSPEED
This switch allows to choose between three attack and release speed modes:
“F”- fast mode,
“M”- medium mode
“S” – slow mode.
Depending on the processed signal and the aural effect you want to obtain, you should
choose speed mode at your own decision.
GATTACK
The ATTACK control (11-position gold contact switch) determines how fast the compressor
reacts.
Positions “1” (the fastest) to “10” (the slowest).
Position “11” is an additional auto mode (log curve)
HRELEASE
The RELEASE control (11-position gold contact switch) determines the time the compressor
needs to get back to the initial value after a level reduction.
Positions from “1” (the fastest) to “10” (the slowest)
Positions “11” is an additional auto mode (log curve)
The following table lists all attack and release times depending on the SPEED mode, the
ATTACK and the RELEASE settings.
ATTACK
position
SPEED MODE
RELEASE
position
SPEED MODE
F
M
S
F
M
S
1
0,5ms
1ms
1,5ms
1
25ms
50ms
75ms
2
1ms
2ms
3ms
2
50ms
100ms
150ms
3
2ms
4ms
6ms
3
65ms
130ms
190ms
4
3ms
6ms
9ms
4
75ms
150ms
220ms
5
4ms
8ms
12ms
5
100ms
200ms
300ms
6
5ms
10ms
15ms
6
260ms
500ms
800ms
7
8ms
17ms
25ms
7
500ms
1sec
1,5sec
8
12ms
24ms
36ms
8
1sec
2sec
3sec
9
16ms
32ms
48ms
9
1,5sec
3sec
4sec
10
20ms
40ms
60ms
10
2sec
4sec
6sec
auto (log)
5ms
10ms
15ms
auto (log)
140ms
280ms
420ms

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IINPUT
This is a 11-position gold contact audio taper switch that determines the level of the signal
entering the channel, as well as the threshold.
JOUTPUT
21-position gold contact switch set for +10dB/-10dB of gain control. Once the desired amount
of limiting or compression is achieved with the use of the INPUT control and the IN-GAIN
control, the OUTPUT control can be used to make up any gain lost due to gain reduction.
This control is used to set the amount of compressed (WET) signal in the blender stage.
KBLEND
11-position gold contact switch allows to mix compressed (WET) and uncompressed (DRY)
signals using only one knob. A single move changes mixing ratio by 10%. This technique is
known as parallel compression, or as New York compression. This technique usually needs
external mixing console, but not when You use our powerful Preceptor.
LS-CHAIN HPF
With this control (5-position gold contact switch) you can remove low frequency information
in the sidechain circuit from 40 Hz, 80 Hz, 120 Hz, 200 Hz, 320 Hz. It can be also turned off
by setting OFF position.
MLINK/DUAL MONO
When set to the up (LINK) position, the two channels of the Preceptor act as a single stereo
compressor, with equal gain reduction on both sides, even when there is transient activity
only on one channel. You only need to set all the functions on the left and right channel in
the same position. It is not a problem having only rotary and toggle switches installed in the
unit. In the down (DUAL MONO) position, the Preceptor operates as two separate
compressors, with the two channels operating completely independently of one another.
It is recommended to use the device in the LINK mode in the case of processing stereo
signals.

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THE REAR PANEL
aVOLTAGE SWITCH
Make sure that the voltage switch setting reflects the correct local power line voltage. For line
voltages from 100V to 120V, set the switch to 115V. The 230V position is good for all line
voltages from 200-240Volts.
bMAINS INPUT / AC FUSES HOLDER
The mains AC connector is a standard IEC-type 3 pin connector with a AC fuses (2 pieces)
holder. The ground of this AC connector is permanently internally connected to the chassis of
the Preceptor for safety. It is important to change the fuse before changing the supply voltage:
630mA (slo-blo; 5x20mm) for 230V~50 Hz
1,25A (slo-blo; 5x20mm) for 115V~60 Hz.
cINPUT
Balanced input XLR wired according to the AES standard : Pin 1 = shield, Pin 2 = hot (+), Pin
3= cold (-). In order to avoid hum, it is recommended to use the device only in balanced
connections.
dOUTPUT
Balanced output XLR wired according to the AES standard : Pin 1 = shield, Pin 2 = hot (+),
Pin 3= cold (-). In order to avoid hum, it is recommended to use the device only in balanced
connections.
eEXT SIDECHAIN
External sidechain input. ¼” TRS connector wired according to the AES standard: tip = hot
(+), ring= cold (-), slave = shield

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BLOCK DIAGRAM

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TECHNICAL DATA
Inputs: Balanced XLR
Outputs: Balanced XLR
Ext. sidechain inputs: Balanced TRS
Signal transformers: Carnhill
Bypass: hard relay bypass
Input impedance: 2k5Ωor 10kΩswitched on the front panel
Output impedance: < 50Ω
Frequency response: 20-22.000Hz
Maximum input level : + 21 dBu @ sensitivity +4 dBu
Maximum output level: +23 dBu
S/N ratio (A-weighted) : better than 85dBu
Meter: 0 to -20dB gain reduction
Signal path: Class-A, discrete
VCA: bipolar transistors biased by Zener diodes
Dynamic modes: limiter, compressor
Speed modes: fast, medium, slow
Attack: 0,5ms –60ms
Release: 25ms –6s
External sidechain: YES
Sidechain filtering : OFF, 40Hz, 80 Hz, 120 Hz, 200 Hz, 320 Hz
Blender (parallel compression) : yes
PSU: internal
Fuses type: 230V : 630mA (slo-blo; 5x20mm) /115V : 1,25A (slo-blo; 5x20mm)
Power consumption: 70W
Dimensions (WxHxD) : 483x133mm (3U) x 245mm
Weight: 6,4kg
Subject to change without notice.

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ENVIRONMENTAL PROTECTION
At the end of its operating life, this product must not be disposed of with regular household
waste but must be returned to a collection point for the recycling of electrical and electronic
equipment. The wheelie bin symbol on the product and user„s manual indicates that. The
materials can be re-used in accordance with their markings. Through re-use, recycling of raw
materials, or other forms of recycling of old products, you are making an important
contribution to the protection of our environment. Your local administrative office can advise
you of the responsible waste disposal point.
Our devices are packaged in environmentally friendly packaging that can be reprocessed.
Remember about waste segregation.

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LIMITED WARRANTY
Should you need to use our warranty service on this product, we refer you to the terms and conditions stipulated
below.
This warranty is valid for one year from the date of purchase by the consumer and is not transferable.
SPLASH BARTOSZ RADZISZEWSKI, Wietrzna 36/1, 53-024 Wroclaw, POLAND (called the PRODUCER
hereafter) selling products under Gem Audio Labs trade mark will only give warranty on products
purchased through authorized dealers or directly from the producer.
PLEASE RETAIN YOUR SALES RECEIPT. IT IS YOUR PROOF OF PURCHASE COVERING YOUR
LIMITED WARRANTY. THIS LIMITED WARRANTY IS VOID WITHOUT SUCH PROOF OF PURCHASE.
This limited warranty does not cover the product if it has been electronically or mechanically modified in any
way.
This limited warranty is invalid if the factory-applied serial number has been altered or removed from the
product.
Natural wear is not covered by this warranty.
Damage/defects caused by the following conditions are not covered by this limited warranty: improper
handling, neglect or failure to operate the unit in compliance with the instructions given by the PRODUCER‟s
user manual; connection or operation of the unit in any way that does not comply with the technical or safety
regulations applicable in the country where the product is used; damage/defects caused by acts of
God/Nature (accident, fire, flood, etc.) or any other condition that is beyond the control of the PRODUCER.
Warranty will not apply because of incorrect storage, dropping, excessive shocks, corrosions, dirt, water or
sand damages.
To confirm your warranty please register your Gem Audio Labs product shortly after purchase. Please fill out
your user registration card (included in the original packaging) and send it via e-mail to
[email protected]om or via mail to: SPLASH BARTOSZ RADZISZEWSKI, Wietrzna 36/1, 53-024
Poland.
All returns must be in the original packaging, accompanied by the return authorization. Please fill out your
return authorization form (included in the original packaging) and send it to your local distributor from
whom You purchased the unit. If the unit has been purchased directly from producer, please send the return
authorization form via e-mail to [e-mail] or via mail to: SPLASH BARTOSZ
RADZISZEWSKI, Wietrzna 36/1, 53-024 Poland.
All returns must be shipped via insured freight at the customer's own expense.
In case when a product must be returned to the factory from a country outside Poland, the customer shall
adhere to specific shipping, customs, and commercial invoicing Instructions given with the return
authorization as the PRODUCER will not be responsible for transportation costs or customs fees related to
any importation or re-exportation charges whatsoever.
After repair, a product will be returned to the customer via prepaid, insured freight, method and carrier to be
determined by the PRODUCER
All damages caused by transport are not covered by this warranty.
Contact data
For the warranty confirmation, technical support and return authorizations, please contact:
SPLASH BARTOSZ RADZISZEWSKI
Wietrzna 36/1
53-024 Wroclaw
Poland
[e-mail]