Focusrite ISA428 MkII User manual

User Guide
focusrite.com
FA0438-03
Four channel mic pre and optional A-D card with Dante
ISA428
MkII

2
CONTENTS
About this User Guide .....................................................................3
INTRODUCTION ..............................................................................4
ISA 428 MKII CONTROLS AND FEATURES ....................................................5
Front Panel ................................................................................5
Input Channel Controls ....................................................................5
Input Selection..........................................................................5
Mic Input Gain ..........................................................................5
Line Input Gain .........................................................................5
Instrument Input........................................................................6
Z In (Input Impedance)...................................................................6
+48V ...................................................................................6
Phase ..................................................................................6
Filter...................................................................................6
Insert ..................................................................................6
Channel Meters............................................................................7
A-D Card Clock and Sync Switches.........................................................7
Rear Panel ................................................................................8
AC Mains Inlet ..........................................................................8
Channel Mic Inputs......................................................................8
Channel Line Inputs .....................................................................8
Channel Outputs ........................................................................8
A-D Inputs 5–8..........................................................................8
Channel Insert Sends & Returns .........................................................8
A-D Option Card Slot ....................................................................8
A-D Option Card ...........................................................................9
PHYSICAL CHARACTERISTICS ..............................................................10
Power Requirements .....................................................................10
APPENDICES ................................................................................ 11
1. Connector Pinouts...................................................................... 11
2. Preamp Input Impedance ..............................................................13
3. Pro Tools Interfacing ...................................................................15
PERFORMANCE AND SPECIFICATIONS .....................................................16
Focusrite Pro Warranty and Service ......................................................18

3
About this User Guide
This user guide applies to the ISA 428 MkII mic pre. It provides information about installing and using
the unit, and how it can be connected into your system.
Also included is information relating to the optional ISA ADN8 A-D interface card, which will allow
audio from the Mic pre to be added to a Dante network.
If you feel that additional information might be of assistance, be sure to consult the site:
pro.focusrite.com/technical-support, which contains a comprehensive collection of common
technical support queries.
Pro Tools® and Pro Tools | HDTM are trademarks or registered trademarks of Avid Technology, Inc. or its subsidiaries
in the United States and/or other countries.
Dante® and Audinate® are registered trademark of Audinate Pty Ltd.
Box Contents
• ISA 428 MkII unit
• AC power lead
• Safety information cut sheet

4
INTRODUCTION
Thank you for purchasing the Focusrite ISA 428 MkII.
The ISA 428 MkII is a high quality four channel microphone preamplier, which can be used to record
microphone, line-level or instrument sources. Microphones and line-level sources are connected via
the rear panel, whilst instrument inputs can be plugged directly into the front panel jack sockets.
The front panel also features gain and other settings such as phantom power and impedance for
each of the analogue inputs. LED metering is provided on each channel in dBFS, to indicate when the
level is reaching the digital clipping point.
To maintain pristine Focusrite quality in the digital domain, an Analogue-to-Digital interface card
may be tted into the option slot on the rear panel. This provides access to a Dante network and
features AES3, S/PDIF and ADAT signals.
With the A-D card installed, the internal/external clock sample rate and sync source can be selected
using the switches on the front panel.

5
ISA 428 MKII CONTROLS AND FEATURES
Front Panel
Applies +48V phantom power to the
mic input XLR
Inverts polarity (Phase) of the
selected input
Input Trim pot Mic/Line: 0 +20 dB
Instrument: +10 +40 dB
Applies the variable-frequency high-
pass Filter to the selected input
Filter frequency pot
Z In selects the input impedance for
the Mic and Instrument inputs
Switches the external Insert
return into the channel path
Input source selection
Selects the high (30-60 dB) mic
gain range for the Gain switch
10 dB stepped Mic/Line Gain switch
Mic: 0-30 / 30-60 Line: -20 +10
Input Channel Controls
Input Selection
Each press of the Input button steps through the three available input sources: Mic/Line/Instrument.
Mic Input Gain
The Gain switch adjusts the mic gain in three 10 dB steps. Its range is either 0–30 dB or 30–60 dB
when the 30–60 switch is pressed. An additional 0–20 dB of continuous gain adjustment is available
using the Trim control.
To avoid an excessive jump in level, It is recommended that the stepped Gain switch is turned to minimum before
pressing the 30-60 switch.
Before starting a recording, or if used for PA work, set the Trim control to near its centre position.This will allow for
some gradual gain adjustment up or down without the use of the stepped control.
Line Input Gain
The Gain switch adjusts the gain between -20 dB and +10 dB in 10 dB steps. Continuous gain
adjustment of up to 20 dB can be added using the Trim control.
Input channels
Power
switch
Instrument
inputs
LED
meters
A-D option card:
clock and sync
selection

6
Channel Controls...
Instrument Input
The Instrument inputs are accessed via standard 1/4” mono jacks on the front panel. The level is set
using the Trim control only and is continuously adjustable from +10 dB to +40 dB.
Refer to the appendix on page 11 for connector pinouts.
Z In (Input Impedance)
With Mic input selected, pressing the Z In button steps through the four
transformer preamp input impedance options. The values are shown in the
table.
For additional information on impedance selection see Appendix 2, “Preamp Input
Impedance” on page 13.
With Instrument input selected, pressing the switch toggles between High
and Low impedance settings, as shown in the lower table.
The Line input impedance is xed at 10 kΩ and is not affected by the Z In
switch.
+48V
Pressing the +48V button applies phantom power to the Mic input XLR.
This switch does not affect the Line or Instrument inputs.
If you are unsure whether your microphone requires phantom power please refer to its handbook. Certain
microphones (most notably ribbon and unbalanced mics) could be damaged by applying phantom power.
Phase
Pressing Phase inverts the polarity of the selected input. This can be useful when multiple mics are
used in close proximity (ie., on a drum kit).
Filter
Pressing the Filter button inserts the 18 dB/octave high-pass lter into channel path; it is applied
to whichever input is selected. The High Pass Filter control allows the roll-off frequency to be set
within the range 16 Hz to 420 Hz.
The lter is useful for removing any unwanted low frequencies, eg., rumble transmitted through oor mounted
mic stands, etc.
Insert
Pressing Insert places the Insert Return signal into the channel path before the Output connector,
allowing the inclusion of external effects units.
The Insert Send is always available and is post the input Gain and Filter controls.
Low 600 Ω
ISA 110 1.4 kΩ
Med 2.4 kΩ
High 6.8 kΩ
Low 470 kΩ
High 2.4 MΩ
Mic Impedance
Instrument Impedance

7
Channel Meters
The front panel LED meter groups 1–4 and 5–8 display the audio level at two
different locations:
• Meters 1–4 display the signal level at the channel outputs.
The channel outputs are also routed to inputs 1-4 of the A-D option card.
• Meters 5–8 display the signal levels received at A-D Input connectors 5–8
The LED meters, therefore, always indicate the input levels at the A-D option card
prior to conversion.
The meter scales are in dBFS, ie., the level in dB, relative to maximum output
(reached when the red ‘0’ LED illuminates). ‘0’ indicates a level of 22 dBu which
corresponds to the maximum input level of the A-D card.
A-D Card Clock and Sync Switches
Clock select
Allows the user to select the internal sample frequency: 44.1kHz, 48kHz, 88.2kHz,
96kHz, 176.4kHz, or 192kHz.
Ext
Allows the ISA ADN8 A-D card to follow an external Word Clock source. Press the switch
to toggle between standard and Dante clock.
Lock LED
Indicates that the unit is successfully synchronised to the external Word Clock.

8
AC Mains Inlet
Standard IEC receptacle for AC mains. ISA 428 MkII features a ‘Universal’ PSU, enabling it to operate
on any supply voltage between 100 V and 240 V AC.
Channel Mic Inputs
Four latching XLR-3 female connectors.
Channel Line Inputs
Four balanced 1/4” TRS jack sockets.
Channel Outputs
Four XLR-3 male connectors. The outputs are connected to inputs 1–4 of the A-D option card.
A-D Inputs 5–8
XLR-3 female analogue inputs to channels 5–8 of the A-D option card.
These inputs have no function without the optional A-D card installed – however, LED meters 5–8 will still
indicate the incoming signal levels.
Channel Insert Sends & Returns
Analogue sends and returns on XLR-3 male and female connectors.
The return signal can be added into a channel path by pressing the front panel Insert switch.
A-D Option Card Slot
Slot for ISA ADN8 analogue to digital conversion card. See the following page for card details.
The card allows the audio outputs from the ISA 428 MkII, plus the four additional external inputs, to
be added to a Dante network. It also provides AES3, S/PDIF and ADAT signals.
See Appendix 1 on page 11 for connector pinouts.
Rear Panel
Mic inputsLine inputs
Insert Sends
& Returns
Channel
Outputs
Mains
inlet
A-D external
inputs 5-8
Slot for A-D
option card

9
A-D Option Card
The optional ISA ADN8 A-D card can be retrotted to an ISA 428 MkII at any time. Engineering
experience is not required as the card can easily be installed by the user.
Note that the ISA 428 MkII does not support the earlier ISA 8-Channel A-D card.
Once tted, conguration of the card is carried out over the network using either RedNet Control or
the Dante Controller software application.
The tting instructions and network software applications are included with the A-D card option.
Word Clock – Input
Allows the card to be synchronised to an external Word Clock source via the BNC connector.
Word Clock – Output
Provides an output of the external Word Clock source connected at the “Word Clock In” BNC connector
or, transmits the internal sample frequency of the A-D card.
• When the ISA 428 MkII is following other units within a larger digital system, the Word Clock
Out connector can be used to pass on the Word Clock signal to the next device.
• When the unit is not following another device and is in Internal Clock mode, the Word Clock
Out connector outputs the sample frequency selected on the ISA 428 MkII front panel.
Primary Network Port
Latching RJ45 connector for the Dante network. Use standard Cat 5e or Cat 6 network cable to
connect the ISA ADN8 to a local Ethernet switch which is connected to the Dante network. Adjacent
to each network socket are LEDs which illuminate to indicate a valid network connection and network
activity.
Secondary Network Port
Can be used as the Secondary Dante network connection where two independent Ethernet links are
being used (Redundant mode), or an additional port on an integral network switch on the primary
network (Switched mode).
ADAT 1 and 2
Two ADAT optical outputs using standard Toslink connectors. Provides 8 channels at 96kHz (using
S/MUX II). The ADAT channel count halves with every doubling of Sample Rate.
AES3 Outputs 1-8
Eight AES3 outputs on DB25 connector. The connector is wired to the Tascam digital standard.
See Appendix 1 on page 11 for the connector pinouts.

10
Case dimensions are illustrated in the diagram above.
ISA 428 MkII requires 2U of vertical rack space. Allow an additional 75mm of rack depth behind the
unit to allow for cables. ISA 428 MkII weighs 7.05 kg and for installations in a xed environment (eg.,
a studio rack), the front-panel rack mountings* will provide adequate support. However, if the unit
is to be used in a mobile situation (eg., ight-cased for touring, etc.), it is recommended that side
support rails or shelves are used within the rack.
*Always use M6 bolts and cage nuts specically designed for 19” equipment racks. An Internet search using the
phrase “M6 cage nuts“ will reveal suitable components.
Cooling vents are provided at each side; ensure that when mounted in a rack these vents are
not obstructed. Do not mount the unit immediately above any other equipment which generates
signicant heat, for example, a power amplier.
Note.The maximum operating environmental temperature is 40°C / 104°F.
Power Requirements
ISA 428 MkII is mains powered and incorporates a ‘Universal’ power supply which can operate on
any AC mains voltage from 100 V to 240 V. The AC connection is via a standard 3-pin IEC connector
on the rear panel.
A mating IEC cable is supplied with each unit – this should be terminated with a mains plug of the
correct type for your country.
Power consumption for ISA 428 MkII is 35 W.
Please note that there are no fuses or other user-replaceable components of any type in any unit.
Please refer all servicing issues to the Customer Support Team (see “Customer Support and Unit Servicing”
on page 18).
PHYSICAL CHARACTERISTICS
465.0mm / 18.3”
325.0mm / 12.8”
63.6mm / 2.5”

11
APPENDICES
1. Connector Pinouts
Mic Input / A-D Input
Connector: XLR-3 female
Output
Connector: XLR-3 male
Pin Signal
1 Screen
2 Hot (+ve)
3 Cold (–ve)
Pin Signal
1 Screen
2 Hot (+ve)
3 Cold (–ve)
Instrument Input
Connector: Unbalanced (TS) 1/4” Jack socket
Line Input / Insert Send / Insert Return
Connector: Balanced (TRS) 1/4” Jack socket
Pin Signal
Tip Hot (+ve)
Ring Cold (–ve)
Sleeve Ground
Pin Signal
Tip Hot (+ve)
Sleeve Ground
Tip Ring Sleeve
Tip Sleeve

12
1. Connector Pinouts...
Network 1 & 2
Connector type: RJ-45 receptacle
Pin Cat 5/6 Core
1 White + Orange
2 Orange
3 White + Green
4 Blue
5 White + Blue
6 Green
7 White + Brown
8 Brown
1
8
ADAT Optical Interface
Connector: TOSLINK
Word Clock In & Out
Connector: BNC 75Ω
113
25 14
ISA ADN8 Option Card:
AES3 Outputs
Connector: DB25 female (AES59 digital)
Screw binding-posts use the standard UNC 4/40 thread
Inputs pins are not used
Pin Signal
1 Out channels 7/8 +
14 Out channels 7/8 –
2 Ground
15 Out channels 5/6 +
3 Out channels 5/6 –
16 Ground
4 Out channels 3/4 +
17 Out channels 3/4 –
5 Ground
18 Out channels 1/2 +
6 Out channels 1/2
19 Ground
7 In channels 7/8 +
20 In channels 7/8 –
8 Ground
21 In channels 5/6 +
9 In channels 5/6 –
22 Ground
10 In channels 3/4 +
23 In channels 3/4 –
11 Ground
24 In channels 1/2 +
12 In channels 1/2 –
25 Ground
13 n/c

13
Appendices...
2. Preamp Input Impedance
A major element of the sound of a mic pre is related to the interaction between the specic microphone
being used and the type of mic preamp interface technology it is connected to. The main area in which
this interaction has an effect is the level and frequency response of the microphone, as follows:
Level
Professional microphones tend to have low output impedances and so more level can be achieved by
selecting the higher impedance positions of the ISA 428 MkII mic preamp.
Frequency response
Microphones with dened presence peaks and tailored frequency responses can be further enhanced
by choosing lower impedance settings. Choosing higher input impedance values will tend to
emphasise the high frequency response of the microphone connected, allowing you to get improved
ambient information and high end clarity – even from average-performance microphones. Various
microphone/ISA 428 MkII preamp impedance combinations can be tried to achieve the desired
amount of colouration for the instrument or voice being recorded. To understand how to use the
impedance selection creatively, it may be useful to read the following section on how the microphone
output impedance and the mic preamp input impedance interact.
Switchable Impedance – In Depth Explanation
Dynamic Moving Coil and Condenser Microphones
Almost all professional dynamic and condenser microphones are designed to have a relatively low
nominal output impedance of between 150 Ω and 300 Ω when measured at 1 kHz. Microphones are
designed to have such low output impedance because the following advantages result:
• They are less susceptible to noise pickup
• They can drive long cables without high frequency roll-off due to cable capacitance
The side-effect of having such low output impedance is that the mic preamp input impedance
has a major effect on the output level of the microphone. Low preamp impedance loads down the
microphone output voltage, and emphasizes any frequency-related variation in microphone output
impedance. Matching the mic preamp resistance to the microphone output impedance (eg., making
a preamp input impedance 200 Ω to match a 200 Ω microphone) still reduces the microphone output
and signal to noise ratio by 6 dB, which is undesirable.
Impedance Setting – Quick Guide
In general the following selections will yield the following results:
High mic preamp impedance settings:
• Will generate more overall level
• Will tend to make low- and mid-frequency response of the microphone atter
• Will improve high-frequency response of the microphone.
Low preamp impedance settings:
• Will reduce the microphone output level
• Will tend to emphasise the low- and mid-frequency presence peaks and
resonant points of the microphone

14
2. Pre Amp Impedance...
To minimise microphone loading, and to maximise signal to noise ratio, preamps have traditionally
been designed to have an input impedance about ten times greater than the average microphone,
around 1.2 kΩ to 2 kΩ. (The original ISA 110 preamp design followed this convention and has an
input impedance of 1.4 kΩ at 1 kHz.) Input impedance settings greater than 2 kΩ tend to make the
frequency-related variations of microphone outputs less signicant than at low impedance settings.
Therefore high input impedance settings yield a microphone performance that is atter in the low
and mid frequency areas and boosted in the high frequency area when compared to low impedance
settings.
Ribbon Microphones
The impedance of a ribbon microphone is worthy of special mention, as this type of microphone is
affected enormously by preamp impedance.
The ribbon impedance within this type of microphone is very low, around 0.2 Ω, and requires an
output transformer to convert the low voltage it generates into a signal capable of being amplied by
a preamp. The transformer uses a ratio of around 1:30 (primary:secondary) to increase the ribbon
voltage to a useful level. This transformer ratio has the effect of increasing the output impedance of
the mic to around 200 Ω at 1 kHz.
The transformer impedance, however, is very dependent upon frequency – it can almost double at
some frequencies (known as the resonance point) and tends to roll off to very small values at low
and high frequencies. Therefore, in common with dynamic and condenser microphones, the mic
preamp input impedance has a signicant effect on the signal level and frequency response of the
ribbon microphone output transformer, and the associated ‘sound quality’ of the microphone. It is
recommended that a mic preamp connected to a ribbon microphone should have an input impedance
of at least 5 times the nominal microphone impedance.
For a ribbon microphone impedance of 30 Ω to 120 Ω, the input impedance of 600 Ω (Low) will work
well. For 120 Ω to 200 Ω ribbon microphones, the input impedance setting of 1.4 kΩ (ISA 110) is
recommended.

15
Appendices...
3. Pro Tools Interfacing
• Analogue out to Pro Tools | HD
• Dante to Pro Tools | HD
ISA 428 MkII
ISA 428 MkII
Red 16Line
RedNet HD32R
4 x XLR-3 female – DB25 male analogue
RJ45 – RJ45 network
RJ45 – RJ45 network
Pro Tools interface
Inputs to
ch. 5 – 8
Channels
1 – 4
Pro Tools interface
Dante Network

16
PERFORMANCE AND SPECIFICATIONS
Microphone Inputs
All measurements taken at minimum gain, Z In: medium, unless otherwise stated. Measurements taken at the analogue outputs
Gain Range 0 to 30 dB or 30 to 60 dB (with ‘30-60’ switch enabled), in 10 dB steps,
plus 0 to 20 dB of continuous trim
Maximum Input Level +7 dBu
Input Impedance Transformer balanced, Low: 600 Ω, ISA 110: 1.4 kΩ, Medium: 2.4 kΩ, High: 6.8 kΩ
Signal-to-Noise Ratio 122 dB ‘A’-Weighted (typical), maximum gain
Frequency Response 20 Hz – 20 kHz ± 0.2 dB | 10 Hz – 110 kHz ± 1.5 dB
THD + N -92 dB (0.0025%) @ -1 dBr
High-Pass Filter 75 Hz knee frequency, 18 dB/octave, switchable per channel
EIN <-123 dBu ‘A’-Weighted (typical), maximum gain
Common Mode Rejection
Ratio
-93 dB @ 1kHz
Line Inputs
All measurements taken at minimum gain, Z In: Low, unless otherwise stated, RS= 50 Ω. Measurements taken at the analogue outputs
Gain Range -20 to +10 dB in 10 dB steps, plus 0 to 20 dB continuous trim
Maximum Input Level +25 dBu
Input Impedance Electronically balanced 10 kΩ
Signal-to-Noise Ratio 122 dB ‘A’-Weighted (typical), maximum gain
Frequency Response 20 Hz – 20 kHz ± 0.1 dB | 10 Hz – 122 kHz ± 3 dB unity gain
THD + N -91 dB (0.0028%) @ -1 dBr
High-Pass Filter 75 Hz knee frequency, 18 dB/octave, switchable per channel
Common Mode Rejection
Ratio
-65 dB @ 1 kHz
Instrument Inputs
All measurements taken at minimum gain, Z In: Low, unless otherwise stated, RS= 600 Ω. Measurements taken at the analogue outputs
Gain Range +10 to +40 dB continuous, using Trim pot
Maximum Input Level +18 dBu
Input Impedance Low: 470 kHz, High: 2.4 MΩ
Signal-to-Noise Ratio 100 dB ‘A’-Weighted
Frequency Response 20 Hz – 20 kHz ±0.1 dB | 10 Hz – 110 kHz ± 1.2 dB
THD + N -83 dB (0.0071%) @ -1 dBFS
High-Pass Filter 75 Hz knee frequency, 18 dB/octave, switchable per channel

17
Performance and Specications . . .
Crosstalk
All measurements taken at minimum gain, Z In: Medium
Microphone Inputs -60 dB, 20 Hz – 20 kHz
Line Inputs -80 dB, 20 Hz – 20 kHz
Instrument Inputs -80 dB, 20 Hz – 20 kHz
Power
PSU 1 x Internal, 100 – 240 V, 50 / 60 Hz
Consumption 35 W.
Dimensions
Height 88mm / 3.46”
Width 482mm / 18.98”
Depth 325mm / 12.8”
Weight
Weight 7.05 kg / 15.55 lbs
Environmental
Operating Temperature 40°C / 104°F Maximum ambient operating temperature
Connectivity
Front panel
Instrument inputs 4 x 1/4” mono jack
Rear Panel
Microphone inputs 4 x XLR-3 female
Line level inputs
Line level outputs
4 x 1/4” balanced jack
4 x XLR-3 male
Insert sends
Insert returns
4 x 1/4” balanced jack
4 x 1/4” balanced jack
A-D inputs 4 x XLR-3 female
Digital Card Slot
Compatible card ISA ADN8

18
Focusrite Pro Warranty and Service
All Focusrite products are built to the highest standards and should provide reliable performance for
many years, subject to reasonable care, use, transportation and storage.
Very many of the products returned under warranty are found not to exhibit any fault at all. To
avoid unnecessary inconvenience to you in terms of returning the product please contact Focusrite
support.
In the event of a Manufacturing Defect becoming evident in a product within 36 months from the date
of the original purchase Focusrite will ensure that the product is repaired or replaced free of charge.
A Manufacturing Defect is dened as a defect in the performance of the product as described and
published by Focusrite. A Manufacturing Defect does not include damage caused by post-purchase
transportation, storage or careless handling, nor damage caused by misuse.
Whilst this warranty is provided by Focusrite the warranty obligations are fullled by the distributor
responsible for the country in which you purchased the product.
In the event that you need to contact the distributor regarding a warranty issue, or an out-of-warranty
chargeable repair, please visit: pro.focusrite.com/rest-of-the-world
The distributor will then advise you of the appropriate procedure for resolving the warranty issue.
In every case it will be necessary to provide a copy of the original invoice or store receipt to the
distributor. In the event that you are unable to provide proof of purchase directly then you should
contact the reseller from whom you purchased the product and attempt to obtain proof of purchase
from them.
Please do note that if you purchase a Focusrite product outside your country of residence or business
you will not be entitled to ask your local Focusrite distributor to honour this limited warranty,
although you may request an out-of-warranty chargeable repair.
This limited warranty is offered solely to products purchased from an Authorised Focusrite Reseller
(dened as a reseller which has purchased the product directly from Focusrite Audio Engineering
Limited in the UK, or one of its Authorised Distributors outside the UK). This Warranty is in addition
to your statutory rights in the country of purchase.
Registering Your Product
To access optional bundled software, please register your product at: focusrite.com/register
Customer Support and Unit Servicing
You can contact our Customer Support team free of charge:
Email: [e-mail]
Phone (UK): [phone]
Phone (USA): [phone]
Troubleshooting
If you are experiencing problems with your ISA 428 MkII, we recommend that in the rst instance, you
visit our Support Help Centre at: pro.focusrite.com/help-centre