Arrel Audio ER-100 User manual

ER-100 Eurorack
8 Channel Stereo,
Transformer Balanced Out Summing Mixer
User Manual
Issue 0.1

ARREL Audio
ER-100 User Manual, Issue 0.1 Page 2
SAFETY INSTRUCTIONS
WARNING
Always follow the precautions listed below to avoid any possibility of serious injury or even death from electrical shock, short-
circuiting, damages, fire or other hazards. These precautions include, but are not limited to, the following:
•Do not expose the instrument to liquids and rain. Do not use it near water or in damp or wet conditions, or place
containers on it containing liquids. If any liquid seeps turn off the power and unplug the power cord from the AC outlet.
•Do not put burning items, such as candles, on the unit. A burning item may fall over and cause a fire.
•This instrument contains no user-serviceable parts. Do not open the instrument or attempt to disassemble or modify the
internal circuit.
•Never insert or remove an electric plug with wet hands.
•Check the electric plug periodically and remove any dirt or dust which may have accumulated on it.
•Do not place the power cord near heat sources such as heaters or radiators, and do not excessively bend or otherwise
damage the cord, place heavy objects on it, or place it in a position where anyone could walk on, trip over, or roll
anything over it.
CAUTION
Always follow the precautions listed below to avoid any possibility of serious injury or even death from electrical shock, short-
circuiting, damages, fire or other hazards. These precautions include, but are not limited to, the following:
•Do not connect the instrument to an electrical outlet using a multiple-connector. Doing so can result in lower sound quality, or
possibly cause overheating in the outlet itself.
•When removing the electric plug from the instrument or an outlet, hold the plug itself and not the cord. Pulling by the cord can
damage it.
•Remove the electric plug from the outlet when the instrument is not to be used for extended periods of time, or during
electrical storms.
•Do not place the instrument in an unstable position where it might accidentally fall over.
•Before moving the instrument, remove all connected cables.
•When setting up the product, make sure that the AC outlet you are using is easily accessible. If some trouble or malfunction
occurs, immediately turn off the power switch and disconnect the plug from the outlet. Even when the power switch is turned
off, electricity is still flowing to the product at the minimum level.
•When you are not using the product for a long time, make sure to unplug the power cord from the wall AC outlet.
•Use only the stand/rack specified for the instrument. When attaching the stand or rack, use the provided screws only. Failure
to do so could cause damage to the internal components or result in the instrument falling over.
Information for Users on Collection and Disposal of Old Equipment
This special symbol on the products, packaging, and/or accompanying documents means that used electrical and electronic products
should not be mixed with general household waste.
For proper treatment, recovery and recycling of old products, please take them to applicable collection points, in accordance with your
national legislation and the Directives 2002/96/EC.
By disposing of these products correctly, you will help to save valuable resources and prevent any potential negative effects on human
health and the environment which could otherwise arise from inappropriate waste handling.
For more information about collection and recycling of old products, please contact your local municipality, your waste disposal service
or the point of sale where you purchased the items.
[For business users in the European Union]
If you wish to discard electrical and electronic equipment, please contact your dealer or supplier for further information.
[Information on Disposal in other Countries outside the European Union]
This symbol is only valid in the European Union. If you wish to discard these items, please contact your local authorities or dealer and
ask for the correct method of disposal.

ARREL Audio
ER-100 User Manual, Issue 0.1 Page 3
ARREL Audio Contacts
ARREL Audio
Via A. Mondadori, 7
00128 Rome – Italy
Tel [phone]
Fax: [phone]
Info: [e-mail]
Web: www.arrel-audio.com
Support: http://www.arrel-audio.com/support
ARREL Audio is continuously working to the improvement of its systems and related documentation.
In any case, we reserve the right to change the specifications without notice but in the respect to the current legislation.
Disclaimer:
The information contained in this manual has been carefully checked and we believed is accurate at the time of publication.
In any case, we do not assume any responsibility for inaccuracies, errors or omissions nor any liability for any loss or damage resulting either
directly or indirectly from use of the information contained in this manual.

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ER-100 User Manual, Issue 0.1 Page 4
TABLE OF CONTENTS
SAFETY INSTRUCTIONS...................................................................................................2
ARRELAudio Contacts........................................................................................................3
TABLE OF CONTENTS.......................................................................................................4
INTRODUCTION .................................................................................................................5
Housing................................................................................................................................5
ER-100 Front Panel Controls and Operations .....................................................................6
INPUT SECTION (CHANNELS 1-8)....................................................................................6
Input gain knob................................................................................................................6
Input pan knob .................................................................................................................6
Solo button.......................................................................................................................6
OUTPUT SECTION.............................................................................................................6
Insert Push Button ...........................................................................................................6
SEND/RETURN Left and Right Connectors.....................................................................6
Left and rigth master volume knobs.................................................................................6
Main L/R Out....................................................................................................................6
MONITOR SECTION...........................................................................................................6
MOnitor section GAIN ......................................................................................................6
Solo LED..........................................................................................................................6
AUX button.......................................................................................................................7
Headphones TRS jack .....................................................................................................7
Monitor Out ....................................................................................................................7
ER-100 FAQ.....................................................................................................................8
APPENDIXA: Front Panel.................................................................................................10
APPENDIX B: BLOCK DIAGRAM..................................................................................11
TECHNICAL SPECIFICATIONS........................................................................................12

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ER-100 User Manual, Issue 0.1 Page 5
INTRODUCTION
ARREL Audio Eurorack Stereo Transformer Balanced Out Summing Mixer is the
answer to all stream mixing needs for EURORACK synthesizers. Its features set it apart
from other similar products on the market due to a very high fidelity approach used for the
design of the electronics together with the use of high quality line transformers to drive the
L and R outputs. The internal circuits of the ER-100 have been directly derived from the
ARREL Audio professional units in order to obtain maximum sonic performances.
The use of line transformers means a higher voltage output level (about 10 dB over the
competitors), suitable to drive all modern audio converters. Output transformers mean also
a very reliable connection in terms of unbalancing and ground loops problems.
The ER-100 is characterized by 8 input channels and a stereo output. Each channel is
characterized by a pan pot control, a volume control and a solo push button (active on the
monitor bus). A stereo insert (selection switch) is available on the main summing bus. The
monitor section is characterized by volume control and an auxiliary input (control switch)
(push button selection), suitable for monitoring DAC or general external inputs such us a
CD and different signal sources. Two LED VU meters are available on the output bus. The
AUX in can be used to send on line alternative mix.
Housing
The ER-100 is contained in a 28 TE Eurorack units (142 mm) and by a depth of about 40
mm. No specific air conditioning is required for the unit, provided that there is a free flow of
air through the rack from front to back and the temperature is maintained in the operating
range. Consequently, the racks may be stacked.

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ER-100 User Manual, Issue 0.1 Page 6
ER-100 Front Panel Controls and Operations
INPUT SECTION (CHANNELS 1-8)
INPUT GAIN KNOB
Rotate the level knob to change the gain. The level is controlled by a potentiometer (Fig.1).
On the front panel Input Gain control the optimum working level is indicated with a ticker
black line.
INPUT PAN KNOB
This is a -3.0 dB center pan, with S-Law shaping to help accurate panning to extremes of
left and right (F1g. 1).
SOLO BUTTON
Press the solo button to send the channel to the monitor bus, more than one solo buttons
in the on positions means that we will listen to the sum of the channels put in solo. Press
again to turn-off the solo function (Fig. 1).
OUTPUT SECTION
INSERT PUSH BUTTON
Push the insert button to select the insert on the R and L output channels (Fig. 1).
Press INSERT button to activate the insert. The INSERT is collocated on the main bus
after the sum and before the main L/R volume controls.
SEND/RETURN LEFT AND RIGHT CONNECTORS
3.5 mm jack for the send/return on the left and right channel.
LEFT AND RIGTH MASTER VOLUME KNOBS
Rotate the L and R knobs to adjust the master level. On the front panel Master volume
control the optimum working level is indicated with a ticker black line.
MAIN L/R OUT
3.5 mm jack for the L/R main balanced output.
MONITOR SECTION
MONITOR SECTION GAIN
Turn the MONITOR gain knob (Fig. 1) in order to select the required amount of gain for the
monitor outputs. On the front panel Monitor volume control the optimum working level is
indicated with a ticker black line
SOLO LED
LED on means that the SOLO function is activated.

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ER-100 User Manual, Issue 0.1 Page 7
AUX BUTTON
Push the button to select the auxiliary input (LED on). Press again to disconnect the
auxiliary input. The AUX input is active on the monitor bus only (Fig.2).
HEADPHONES TRS JACK
Connect the headphone to this TRS jack. The headphone amplifier is able to drive
headphones with impedance > 50Ω.
MONITOR OUT
3.5 mm jack for the L/R monitor output

ARREL Audio
ER-100 User Manual, Issue 0.1 Page 8
ER-100 FAQ
FAQ 1: Why the ER-100 is equipped with transformers on the line out L and R
channels?
The two high quality (large bandwidth and high output level) output transformers are
fundamentals in order to:
1. Increase the signal output level over the Eurorack standard level that is
limited by the low power supply voltages (+12V/-12V).
2. Avoid any problem with ground loops due to the transformer galvanic
isolation.
3. Avoid any problem when the output will be unbalanced. Transformer
galvanic isolation assures that the output signals are floating with respect
to the ground so you can unbalance without problems. The possibility to
unbalance the L and R output signals can be very useful in a lot of live
situation.
FAQ 2: Why the ER-100 is not a cheap equipment ?
The ER-100 is a high quality 8 channel mixer in a very compact format. The cost of the
unit is high due to the following reasons:
1. ER-100 uses two high quality audio line transformers on the Land R line
outputs, high quality transformers are very expensive.
2. The ER-100 is extremely compact. Please take into account that we offer,
8 channels, solo function, pan-pot, monitor out with high quality
headphone amplifier supporting 50 ohm headphones, insert point,
auxiliary input, and a flexible and accurate VU metering system.
Implementing all these functions in the 28U format in about 40 mm of
depth is a real engineering challenge. The unit is composed by 6 boards
mounted over a motherboard so 7 boards in total so very compact and
complex.
3. The ER-100 is based on high quality integrated circuits for audio
applications. We have applied our experience in very high quality audio
units for recording and live into the Eurorack world...
4. All the electromechanical components (potentiometers, switches, push
buttons and jacks) used in the ER-100 are of top quality. We know very
well that these components are the most critical for reliability. Moreover
whenever possible we use the concept of "Electromechanical Fault
Tolerance (see KEY-TECNOLOGIES link) to ensure very high reliability to
our units.
FAQ 3: What is the function of the auxiliary input (AUX IN)?
The ER-100 AUX IN has exactly the same role as in a traditional mixer it is conceived as
an auxiliary input on the Monitor. This input is not added to the 8 channels. When you
select theAUX IN you disconnect the monitor from the summing solo bus and connect the
auxiliary in to the monitor in order to hear only the signals connected to this input. The
typical situation is when you have to monitor a recording. If you want easily check the song
recorded with your Eurorack synth you can connect the recorder output to the AUX IN and
easily check "on the fly" the recorded song just by switching the aux in on position. The
AUX in can be used to check an alternative mix before send it on line.

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ER-100 User Manual, Issue 0.1 Page 9
FAQ 4: What is the function of the solo button?
1. The solo button permits to listen only the channels corresponding to the
SOLO button switched in ON position all the others channels are muted.
The function works on the Monitor Bus only. For example, if you want to
listen only channel four (Monitor Out) you have to select SOLO ON on
channel 4. If you want to listen the mix of channels 2 and four you have to
select SOLO ON also on channel 2.
FAQ 5: Why there are no Control Voltages (CV) on the ER-100 ?
Because ER-100 is a very high quality traditional mixer in the Eurorack format. It is
characterized by the maximum transparency and linearity with very low distorsion in order
to reproduce with maximum fidelity your sounds. The implementation of an amplifier or a
pan pot controlled by a voltage means the use of VCAs (Voltage Controlled Amplifiers) or
similar technologies that inevitably deteriorate the sound quality. ER-100 has not been
conceived to be a "creative" mixer (in the sense of CV). ER-100 viceversa permits to the
Eurorack user to have in his Eurorack case the power of a very high quality traditional
mixer able to preserve all the sounds generated by the artist.
FAQ 6: How the ER-100 INSERT works ?
The stereo INSERT point of the ER-100 is connected to the main summing bus before the
main L/R volume controls. You can easily use this stereo insert to connect whatever effect
you want (compressors, EQs etc.) that works at line level. The insert can also be used for
"on the fly" monitoring of a different signal source. To do this, connect the signal source
output to the RETURN jack (the SEND jack is not used). The jack insertion disconnects
the mixing bus from the L/R outputs and connects the alternative signal source to the L/R
bus so can monitor whatever you want just by a jack insertion in the RETURN plug.

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ER-100 User Manual, Issue 0.1 Page 10
APPENDIX A: Front Panel
FIG. 1 ER-100 Front Panel

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ER-100 User Manual, Issue 0.1 Page 11
APPENDIX B: BLOCK DIAGRAM
FIG. 2 ER-100 Block Diagram

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ER-100 User Manual, Issue 0.1 Page 12
TECHNICAL SPECIFICATIONS
Number of Channels
8
Power Supply
From the Eurorack power supply unit
Operating Voltage
+/- 12 VDC
Power Consumption
3.5 W
Input
Electronically unbalanced, Level -6 dBu max +30
dBu Impedance > 5 KΩ
Master Output
Transformer balanced and floating,
Output Impedance optimum load impedance > 5KΩ)
Master Level
Level +4dBu, Max +26dBu,
AUX Input (DAC)
Stereo. Level 0 dBu, Imp. 10kΩ, unbalanced
Bandwidth
5 – 60.000 Hz -1dB, perfect square wave up to 20
KHz
Distortion + Noise
<0.005% ( typical 0.001 %)
Front Panel Controls (each channel):
Input Section
Channel Level control
Pan Pot control
Solo in Place button (LED)
Front Panel Controls: Insert Section
Stereo insert on Left and Right
Selected by a button
Front Panel Controls: Master Section
Volume knob
Front Panel Controls: Monitor
Section
Volume Knob
Front Panel Indicators
LED VU meters
Front Panel Connnectors
8 x 3.5 mm jack for the input ,
4 x 3.5 mm jack for the stereo insert
1 x 1/4” stereo jack for headphones Imp. >50Ω
2 x 3.5 mm jack for the output
2 x 3.5 mm jack for the AUX input
2 x 3.5 mm jack for the monitor out
Rear Panel Power Supply
Connectors
Eurorack power supply connector
Construction
28U TE Units (142mm)
Dimensions
142 mm x 128 mm (w x h)
Weight
500 g