Focusrite ISA428 MkII Lobbes Pro Audio User Guide

www.focusrite.con ISA428 MkII
User Guide

Important Safety Instructions

1. Read these instructions.

2. Keep these instructions.

3. Heed all warnings.

4. Follow all instructions.

5. Do not use this apparatus near water.

6. Clean only with dry cloth.

7. Do not block any ventilation openings. Install in accordance with the manufacturer’s instructions.

8. Do not install near any heat sources such as radiators, heat registers, stoves, or other apparatus (including amplifiers) that produce heat.

9. Do not defeat the safety purpose of the polarized or grounding-type plug. A polarized plug has two blades with one wider than the other. A grounding type plug has two blades and a third grounding prong. The wide blade or the third prong are provided for
   your safety. If the provided plug does not fit into your outlet, consult an electrician for replacement of the obsolete outlet.

10. Protect the power cord from being walked on or pinched particularly at plugs, convenience receptacles, and the point where they exit from the apparatus.

11.  Only use attachments/accessories specified by the manufacturer.

12. Use only with the cart, stand, tripod, bracket, or table specified by the manufacturer, or sold with the apparatus. When a cart is used, use caution when moving the cart/apparatus combination to avoid injury from tip-over.

13. Unplug this apparatus during lightning storms or when unused for long periods of time.

14. Refer all servicing to qualified service personnel. Servicing is required when the apparatus has been damaged in any way, such as power-supply cord or plug is damaged, liquid has been spilled or objects have fallen into the apparatus, the apparatus has  been exposed to rain or moisture, does not operate normally, or has been dropped.

WARNING: To reduce the risk of fire or electric shock, do not expose this apparatus to rain or moisture.
It is important that the apparatus shall not be exposed to dripping or splashing and that no objects filled with liquids, such as vases shall be placed on the apparatus.

• Do not expose this apparatus to drips or splashes.
• Do not place any objects filled with liquids, such as vases, on the apparatus.
• Do not install this apparatus in a confined space such as a bookcase or similar unit.
• Slots and openings in the cabinet are provided for ventilation and to ensure reliable operation of the product and to protect it from overheating. Please ensure adequate space around the apparatus for sufficient ventilation. Ventilation should not be  impeded by covering the ventilation openings with items such as newspapers, tablecloths curtains etc.
• The apparatus draws nominal non-operating power from the AC outlet with its POWER switch in the off position.
• The apparatus should be located close enough to the AC outlet so that you can easily grasp the power cord plug at any time.
• An apparatus with Class 1 construction shall be connected to an AC outlet with a protective grounding connection.
• The MAINS plug or the appliance coupler is used as the disconnect device. Either device shall remain readily operable when the apparatus is installed for use.
• No naked flames, such as lighted candles, should be placed on the apparatus.

WARNING: excessive sound pressure levels from earphones and headphones can cause hearing loss.
This equipment must be earthed by the power cord.

Important Safety Precautions

| CAUTION: TO REDUCE THE RISK OF ELECTRIC SHOCK, DO NOT REMOVE
COVER (OR BACK). NO USER-SERVICEABLE PARTS INSIDE. REFER SERVICING TO QUALIFIED SERVICE PERSONNEL.
---|---
| The lightning flash with arrowhead symbol, within equilateral triangle, is intended to alert the user to the presence of uninsulated “dangerous voltage” within the product’s
enclosure that may be of sufficient magnitude to constitute a risk of electric shock to
persons.
| The exclamation point within an equilateral triangle is intended to
alert the user to the presence of important operating and maintenance
(servicing) instructions in the literature accompanying the appliance.
WARNING| WARNING: TO PREVENT FIRE OR SHOCK HAZARD, DO NOT EXPOSE THIS APPLICANCE TO RAIN OR MOISTURE

Environmental Declaration
Compliance Information Statement: Declaration of Compliance procedure

Agoura Hills,
CA 91301
Telephone:| 800-994-4984

This device complies with part 15 of the FCC Rules. Operation is subject to the following two conditions: (1) This device may not cause harmful interference, and (2) this device must accept any interference received, including interference that may cause undesired operation.

For USA To the User:

1. Do not modify this unit! This product, when installed as indicated in the instructions contained in this manual, meets FCC requirements. Modifications not expressly approved by Focusrite may void your authority, granted by the FCC, to use this product.
2. mportant: This product satisfies FCC regulations when high quality shielded cables are used to connect with other equipment. Failure to use high quality shielded cables or to follow the installation instructions within this manual may cause magnetic interference with appliances such as radios and televisions and void your FCC authorization to use this product in the USA.
3. Note: This equipment has been tested and found to comply with the limits for a Class B digital device, pursuant to part 15 of the FCC Rules. These limits are designed to provide reasonable protection against harmful interference in a residential installation. This equipment generates, uses and can radiate radio frequency energy and, if not installed and used in accordance with the instructions, may cause harmful interference to radio communications. However, there is no guarantee that interference will not occur in a particular installation. If this equipment does cause harmful interference to radio or television reception, which can be determined by turning the equipment off and on, the user is encouraged to try to correct the interference by one or more of the following measures:
   • Reorient or relocate the receiving antenna.
   • Increase the separation between the equipment and receiver.
   • Connect the equipment into an outlet on a circuit different from that
   • to which the receiver is connected.
   • Consult the dealer or an experienced radio/TV technician for help.

For Canada To the User:
This Class B digital apparatus complies with Canadian ICES-003
RoHS Notice
Focusrite Audio Engineering Limited has conformed and this product conforms, where applicable, to the European Union’s Directive 2002/95/EC on Restrictions of Hazardous Substances (RoHS) as well as the following sections of California law which refer to
RoHS, namely sections 25214.10, 25214.10.2, and 58012, Health and Safety Code; Section 42475.2, Public Resources Code.

Hardware Overview – Rear Panel

XLR (audio) inputs and outputs
All 3-pin XLR balanced audio connectors (Output, Mic IP and EXT A/D IP) are wired as follows:
Pin 1 Screen/Chassis Pin 2 Audio 0° Pin 3 Audio 180°
Line inputs and insert sends and returns
1/4” balanced jack wired as follows:
Tip Audio 0° Ring Audio 180° Sleeve Screen/Chassis
Instrument Hi Z inputs
1/4” unbalanced jack wired as follows:
Tip Audio 0° Sleeve Screen/Chassis
Mic / line / instrument hi Z inputs (front panel)
Any one of these inputs may be used as the input to the ISA428 MkII channels 1-4. Signals routed to these inputs are referred to as the ‘internal’ channels or signal paths.
Outputs – Channels 1-4
These outputs are used as the main analogue signal outputs, and are fed by whatever is connected to the Mic Inputs, Line Inputs, or Instrument Inputs. These outputs also connect to the ADC ‘internal’ channels 1-4.
Insert send and return
Allows an external unit, such as a Red 3 Compressor or Red 2 EQ, to be placed within the signal chain, prior to the output and post the high pass filter.
ADC inputs 5-8
The ADC inputs 5-8 act as line level inputs and are used to route ‘external’ signals to the optional ADC channels 5-8. Using these inputs in conjunction with a single optional ADC card, up to eight analogue inputs can be routed to the eight digital outputs. Using these inputs in conjunction with a second ISA428 MkII unit and a single optional ADC card, eight pre amps can be routed to all eight ADC channels. (See ‘Two ISA428 MkII units used as a single 8 channel ADC’ on page 14.)
Retrofitting the optional ADC
The optional ADC can be retrofitted to a standard ISA428 MkII at any time. The card can be fitted easily by the user – no engineering experience is required. Full fitting instructions for this option are included along with the ADC.

Hardware Overview – Front Panel

Power
Applies power to the unit. Turn on the ISA428 MkII before powering up devices to which the outputs are connected.
Instrument inputs Instrument sources may only be connected via the front panel. Four unbalanced Instrument input connectors are located to the far left of the front panel and are numbered 1-4, correlating to each of the four channels.
These connectors are used primarily for connecting low level unbalanced signals such as those from passive guitars and basses, or from active instruments such as keyboards and electro-acoustic guitars.
Analogue/ADC dBFS output meters These vertical columns of LEDs indicate the peak signal levels of channels 1-8 in one of the two following modes:

Mode 1. Analogue only unit (no optional ADC card fitted).
Meters 1 to 4 indicate the analogue level at the ISA428 MkII XLR output connectors for channels 1 to 4. 0dBFS (reached when the red LED is lit) indicates that a signal level of +22dBu is present at the output. Therefore –18dBFS indicates that there is a signal level of +4dBu at the output. Meters 5 to 8 have no function in this mode.
Mode 2. Digital (optional ADC card fitted).
Meters 1 to 8 indicate the signal level that exists in the signal path just before the point of conversion on the optional ADC card. 0dBFS (reached when the red LED is lit) indicates the maximum signal level that can be converted by the optional ADC card and should only be lit for very short durations to ensure a good quality recording with no digital overload.

Input Stage

Three input options are provided to give compatibility with microphone, line or instrument level sources.
Input
Pressing INPUT steps through each of the three inputs, as indicated by the corresponding LEDs. When the mic LED is lit, the microphone input is active etc. Hence a mixture of microphone, line and instrument inputs may be selected across the four channels simultaneously.
Mic input gain
With the mic input selected, the user has access to the full gain range in 10dB steps from 0dB to +60dB. The gain range is split between two gain modes depending upon the status of the 30-60 switch.
Mode 1 Mic Gain Range 0-30
With the 30-60 switch off, the rotary gain knob operates over a gain range of 0dB to +30dB, the level of gain chosen being indicated on the front panel by the outer arc numbers around the gain knob.
Mode 2 Mic Gain Range 30-60
With the 30-60 switch on (illuminated), the rotary gain knob operates over a gain range of 30dB to 60dB, the level of gain chosen being indicated on the front panel by the outer arc numbers around the gain knob. An additional 20dB of gain can be applied to the
signal after the mic/line gain knob using the Trim knob. See ‘Trim’ control text below for full explanation.
Line input gain
With the line input selected, the user has access to gain settings ranging from –20dB to +10dB, indicated on the front panel by the inner arc of numbers around the gain knob. The 30-60 switch is inactive when the line input is selected, as the gain range for Line
level input is restricted to –20dB to +10dB in 10dB steps.
An additional 20dB of gain can be applied to the signal after the mic/line gain knob using the Trim knob. See ‘Trim’ control text below for full explanation.
Instrument input gain
With the instrument input selected, gain is applied to the input signal by using the trim control only, which allows +10dB to +40dB of gain range. The level of gain chosen is indicated on the front panel by the outer arc of numbers around the trim knob. This input is suitable for high impedance sources such as guitar or bass pickups (which may be connected directly without the need for an external DI box) or vintage synthesizers with high impedance outputs.
Trim
The Trim control provides additional variable gain of 0dB to +20dB when Mic or line inputs are selected. The level of trim chosen is indicated on the front panel by the inner arc of numbers around the trim knob.
Note: When using the instrument input the Trim control is used to adjust gain.
The additional 20dB of gain that can be applied to the Mic or Line signal is very useful for two reasons:
When high gain is required
The trim used in conjunction with the Mic gain of 60dB will give a total of up to 80dB of pre-amp gain, making it very useful for getting good digital recording levels from very low output dynamic and ribbon microphones.
Gain adjustment during recording
When small amounts of gain adjustment are needed to correct for performance level variations during recording, use the trim knob rather than the stepped Mic/Line gain knob, as switching the 10dB gain steps would be much too intrusive. It is therefore good practice to apply some Trim gain before using the 10dB stepped gain knob to find the optimum recording level so that the Trim control can be used to gently add or take away gain later, if so required.
+48V
Pressing the +48V switch provides +48V phantom power, suitable for condenser microphones, to the rear panel XLR microphone connector. This switch does not affect the other inputs. If you are unsure whether your microphone requires phantom power, refer to its handbook, as it is possible to damage some microphones (most notably Ribbon Microphones) by providing phantom power.
Phase
Pressing PHASE inverts the phase of the selected input, to correct phase problems when using multiple microphones, or when incorrect wiring polarity has occurred.
Insert
Pressing the INSERT switch (illuminated) breaks the signal path of the channel, so that the channel input signal is sent out of the unit from the rear panel Insert Send connector and returned to the same point in the signal chain via the rear panel Insert Return connector.
Filter
Pressing the FILTER switch makes the Hi pass filters active in the audio path. The filter provides 18dB/octave roll-off. A variable control allows the roll- off frequency to be set within the range of 16Hz to 420Hz.

Z In – Impedance
Pressing the Z IN switch steps through each of the four transformer pre-amp input impedance values, as indicated by the corresponding LEDs. By selecting different values for the impedance of the transformer input, the performance of both the preamp and
the microphone connected can be tailored to set the desired level and frequency response. The impedance values are as follows:
Low – 600 Ω
ISA 110 – 1k4 Ω
Med – 2k4 Ω
High – 6k8 Ω
A guide to setting input impedance is available in the Applications section.

8 Channel Digital Output Option

The optional ADC can be retrofitted to a standard ISA428 MkII at any time. No engineering experience is required as the card can be fitted easily by the user. Full fitting instructions for this option are included along with the ADC.
The ISA428 MkII can be used as a high quality 8 channel ADC for analogue transfer to digital with the addition of the optional digital output board. The 4 external ADC inputs and the main channel inputs can all be fed to the ADC, ensuring eight super-clean, highquality paths to digital. A single ISA428 MkII unit can act as an 8-channel digital input expansion unit to any DAW. Channels 1-4 always route respectively to ADC output channels 1-4.
Alternatively, two ISA428 MkII units with a single ADC option can be used to create an 8-channel mic pre to ADC system. Digital formats available on the ADC are AES/EBU, SPDIF and ADAT™ optical format.  Digital outputs (AES, S/PDIF)
A 25-pin (Tascam DB-25FM) connector allows up to 8 channels of 24-bit digital audio (AES or S/PDIF) to be transmitted to a DAW or other digital storage medium. The card can be configured using jumpers (on the card) and using two push button switches on the rear panel. The table on page 10 shows the pinout details for all available configurations. Below is a brief description of the overall functionality available.
Jumper position
The digital card has four jumpers (movable plastic clips) that can be positioned so as to disable AES outputs 5-8, and therefore make the ISA428 MkII pin to pin compatible with a Pro Tools HD™ 192 interface using a standard 25-pin to 25-pin cable. With the jumpers in the disabled position (default), channels 1-8 are available at 44.1-96kHz and channels 1-4 at 176.4/192kHz. Depending on the position of 1-wire/2-wire switch. (See Appendix 1 for details of the cable pinout for recording all 8 channels to Pro Tools™ at 192kHz – jumpers are in the enabled position in this case.) (See Appendix 2 for details on adjusting the Jumper positions.)
AES, S/PDIF switch
This switch selects whether the signal is professional (AES) or consumer (S/PDIF) digital format. With the switch out, channels 1-8 are in AES format and are duplicated across the connector, allowing 16 outputs (dependent on wire mode switch). With the switch in, channels 1-8 are available as S/PDIF and AES formats (number of channels available in AES format is dependent on wire mode switch). See the table on page 10 for pinout details.
1-Wire/2-Wire AES mode switch
For sample rates from 88.2 to 192kHz, a dual-wire mode is available for connecting to older equipment with AES inputs, which can only receive speeds up to 192kHz by using both digital channels of a single AES connection (known as ‘2-wire’). Engaging this switch ‘splits’ the digital signal and activates dual wire mode, which means that half the number of channels are transmitted down the same number of wires. Transmitting channels 1-8 in 2-wire mode requires all of the pins of the DB25 connector. Therefore, if the S/PDIF mode is selected, only channels 1-4 can be transmitted as AES format. (See the table on page 10 for pinout details.)
ADC card DB25 pin out configurations

Pin No.| Jumpers disabled (default) ProToolsTm Compatible 44.1 – 96kHz| Jumpers disabled ProTools,” Compatible
Dual Wire Mode 88.2 – 192kHz| Jumpers enabled Single Wire Mode 44.1 – 192kHz| Jumpers enabled + S/ PDIF
Switch In – Single Wire Mode 44.1 – 192kHz| Jumpers enabled +
Dual Wire Mode 88.2 – 192kHz| Jumpers enabled + S/ PDIF
Switch In + Dual Wire
Mode 88.2 -192kHz
---|---|---|---|---|---|---
1| NC| NC| AES 7/8+| AES 7/8+| AES 8+| AES 4+
2| GND| GND| GND| GND| GND| GND
3| NC| NC| AES 5/6-| AES 5/6-| AES 7-| AES 3-
4| NC| NC| AES 3/4+| AES 3/4+| AES 6+| AES 2+
5| GND| GND| GND| GND| GND| GND
6| NC| NC| AES 1/2-| AES 1/2-| AES 5-| AES 1-
7| AES 7/8+| AES 4+| AES 7/8+| SPDIF 7/8+| AES 4+| SPDIF 7/8+
8| GND| GND| GND| GND| GND| GND
9| AES 5/6-| AES 3-| AES 5/6-| SPDIF 5/6+| AES 3-| SPDIF 5/6-
10| AES 3/4+| AES 2+| AES 3/4+| SPDIF 3/4+| AES 2+| SPDIF 3/4+
11| GND| GND| GND| GND| GND| GND
12| AES 1/2-| AES 1-| AES 1/2-| SPDIF 1/2-| AES 1-| SPDIF 1/2-
13| NC| NC| NC| NC| NC| NC
14| NC| NC| AES 7/8-| AES 7/8-| AES 8-| AES 4-
15| NC| NC| AES 5/6+| AES 5/6+| AES 7+| AES 3+
16| GND| GND| GND| GND| GND| GND
17| NC| NC| AES 3/4-| AES 3/4-| AES 6-| AES 2-
18| NC| NC| AES 1/2+| AES 1/2+| AES 5+| AES 1+
19| GND| GND| GND| GND| GND| GND
20| AES 7/8-| AES 4-| AES 7/8-| SPDIF 7/8-| AES 4-| SPDIF 7/8-
21| AES 5/6+| AES 3+| AES 5/6+| SPDIF 5/6+| AES 3+| SPDIF 5/6+
22| GND| GND| GND| GND| GND| GND
23| AES 3/4-| AES 2-| AES 3/4-| SPDIF 3/4-| AES 2-| SPDIF 3/4-
24| AES 1/2+| AES 1+| AES 1/2+| SPDIF 1/2+| AES 1+| SPDIF 1/2+
25| GND| GND| GND| GND| GND| GND

24-bit/192kHz ADAT™ interface operation

The card provides digital outputs for all eight ISA428 MkII channels, which operate over the sample frequency ranges 44.1-192kHz.
The card features two ADAT™-type ‘lightpipe’ output connectors. For speeds up to 48kHz, both connectors transmit all 8 channels simultaneously. However, ADAT™-type connectors are bandwidth-limited at sample rates 88.2kHz and 96kHz – each audio channel uses two ADAT™ digital channels to accommodate the increased quantity of data (SMUXII). At sample rates 176.4kHz and 192kHz, each audio channel uses four ADAT™ digital channels to accommodate the increased quantity of data (SMUXIV).
The ADAT™ output connectors operate as follows:
44.1/48kHz sample rates:
Connector 1 = channels 1 to 8
Connector 2 = channels 1 to 8 (identical to connector 1)
88.2/96kHz sample rates:
Connector 1 = channels 1 to 4
Connector 2 = channels 5 to 8
176.4/192kHz sample rates:
Connector 1 = channels 1 and 2
Connector 2 = channels 3 and 4
Word clock in and out
The optional ADC can be synchronised to an external word clock. By pressing the front panel Ext switch, the synchronisation mode can be switched between standard external word clock and 256X external word clock. Both types of external word clock should be
connected to the ISA428 MkII ADC card at the Word Clock In BNC connector.
The Word Clock Out BNC connector either regenerates the external word clock connected at the Word Clock In BNC connector, or transmits the internal sample frequency of the ADC card. Where the ISA428 MkII is being used as a slave device within a larger digital system, the Word Clock Out BNC connector can be used to pass on the external word clock signal to the next device. When the unit is not slaved to another device and is in internal clock mode, the Word Clock Out BNC connector outputs the sample frequency selected on the ISA428 MkII front panel.
Digital output front panel controls Clock select
Pressing this switch allows the user to select between sample frequencies of 44.1kHz, 48kHz, 88.2kHz, 96kHz, 176.4kHz, and 192kHz.
Ext
Pressing this switch allows the ISA428 MkII to be slaved to an external word clock source. Selecting 256X allows the ISA428 MkII to be slaved to an external clock running at 256 times faster than the sample frequency and enables connection to systems such as the Digidesign ‘Superclock’ or other 256X slave clock devices.
Lock LED
When lit, LOCK indicates that the unit is successfully synchronised to an external clock. Note: When using 256X external clock, no lock indication is given, if audio can be heard in this mode then 256X clock is locked.

Applications

Mic preamp input impedance
A major element of the sound of a mic pre is related to the interaction between the specific microphone being used and the type of mic pre-amp 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 ISA428 MkII mic pre-amp.
Frequency response
Microphones with defined 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/ISA428 MkII pre-amp 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 pre¬amp 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 150Ω and 300Ω when measured at 1kHz. 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 pre-amp input impedance has a major effect on the output level of the microphone. Low pre-amp impedance loads down the microphone output voltage, and emphasises any frequency-related variation in microphone output impedance. Matching the mic pre-amp resistance to the microphone output impedance, (e.g. making a pre-amp input impedance 200Ω to match a 200Ω microphone) still reduces the microphone output and signal to noise ratio  by 6dB, which is undesirable.
To minimise microphone loading, and to maximise signal to noise ratio, pre- amps have traditionally been designed to have an input impedance about ten times greater than the average microphone, around 1.2kΩ to 2kΩ. (The original ISA110 pre-amp design followed this convention and has an input impedance of 1.4kΩ at 1kHz.)
Input impedance settings greater than 2kΩ tend to make the frequency-related variations of microphone output less significant than at low impedance settings. Therefore high input impedance settings yield a microphone performance that is more flat 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 pre-amp impedance. The ribbon impedance within this type of microphone is incredibly low, around 0.2Ω, and requires an output transformer to convert the extremely low voltage it can generate into a signal capable of being amplified by a pre-amp. The ribbon microphone output transformer requires a ratio of around 1:30 (primary: secondary) to increase the ribbon voltage to a useful level, and this transformer ratio also has the effect of increasing the output impedance of the mic to around 200Ω at 1kHz.
This 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, as with the dynamic and condenser microphones, the mic pre-amp input impedance has a massive effect on the signal levels and frequency response of the ribbon microphone output transformer, and thus the ‘sound quality’ of the microphone. It is recommended that a mic pre-amp connected to ribbon microphone should have an input impedance of at least 5 times the nominal microphone impedance.
For a ribbon microphone impedance of 30Ω to 120Ω the input impedance of 600Ω (Low) will work fine and for 120Ω to 200Ω ribbon microphones the input impedance setting of 1.4kΩ (ISA110) is recommended.
Impedance Setting Quick Guide
In general the following selections will yield the following results:
High mic pre-amp impedance settings

• Will generate more overall level
• Will tend to make low- and mid-frequency response of the microphone flatter
• Will improve high-frequency response of the microphone.

Low pre-amp 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

Example Signal Connections

Recording from analouge outputs to DAW Digital connections Two ISA428 MkII units used as a single 8 channel ADC

Specifications

Mic inputs

• Frequency response at minimum gain (0dB): -0.35dB at 20Hz and –3dB at 122kHz.
• Frequency response at maximum gain (60dB): –2.5dB at 20Hz and –3dB 103kHz.
• Gain range: 0dB to +60dB in 10dB steps, plus 0dB to +20dB continuously variable trim.
• Maximum headroom: +7.4dBu.
• THD+N: 0.0009% (measured at 1kHz -20dBu input signal, at 30dB gain setting, with a 20Hz/22kHz bandpass filter).
• Noise EIN: -126dB (measured at 60dB of gain with 150Ω termination and 20Hz/22kHz bandpass filter).
• Noise at main output with unity gain: -98dBu (measured with a 20Hz/22kHz bandpass filter).
• SNR: 123dB (relative to max output 25dBu).
• SNR: 120dB (relative to 0dBFS (+22dBu).
• CMRR: 88dB.
• Input impedance, variable as follows:

Line inputs

• Frequency response at unity gain (0dB): -0.3dB at 20Hz and –3dB at 94kHz.
• Gain range: -20dB to +10dB in 10dB steps, plus 0dB to +20dB continuously variable trim.
• Maximum headroom: +25.4dBu.
• THD+N: 0.002% (measured with +4dBu input signal, 0dB gain setting, with a 20Hz/22kHz bandpass filter).
• Noise at main output with unity gain: -91dBu (measured with a 20Hz/22kHz bandpass filter).
• SNR: 116dB (relative to max output 25dBu).
• SNR: 113dB (relative to 0dBFS +22dBu).
• Input Impedance: 10kΩ.

Instrument inputs

• Frequency response at +10dB gain: -0.2dB at 20Hz and 0dB at 200kHz.
• Frequency response at +40dB gain: -3dB at 20Hz and –3dB at 38.4kHz.
• Gain range: +10dB to +40dB continuously variable.
• Maximum headroom: +11.5dBu.
• THD+N: 0.006% (measured with –20dBu input signal, at minimum gain (+10dB), with a 20Hz/22kHz bandpass filter).
• Noise at main output with minimum gain (+10dB): -95dBu (measured with a 20Hz/22kHz bandpass filter).
• Input Impedance >1MΩ.

High pass filter

• Roll off = 18dB per octave 3 pole filter.
• Frequency range: 16Hz to 420Hz (continuously variable, measured at the 3dB down point).

Meters

• 6 LED meter is calibrated 0dBFS = +22dBu (the maximum level which can be correctly converted by the optional internal A/D converter before overload occurs). The meter calibration points are as follows:

Front and rear connectivity
Analogue channel inputs (inputs 1-4) (ACD inputs 5-8)

• 4 instrument ¼” TS jack inputs on front panel
• 4 microphone XLR inputs on rear panel
• 4 line ¼” TRS jacks on rear panel
• 4 insert return ¼” TRS jacks on rear panel
• 4 ADC XLR inputs on rear panel

Analogue audio outputs (outputs 1-4)

• 4 line XLR outputs on rear panel
• 4 insert send ¼” TRS jacks on rear panel

Other I/O

• IEC power input connector 100Vac – 240Vac

Front panel indicators

• 8 output meters 6 segment
• 4 30-60 mic gain range selection indicator
• 4 +48V phantom power indicator
• 4 Phase indicator
• 4 Insert indicator
• 4 Filter indicator
• 4 Input selection indicators (Mic, Line, Inst)
• 4 Z In microphone input impedance selection indicators (Low, ISA110, Med, High)
• Clock select indicators (44.1, 48, 88.2, 96, 176.4, 192)
• Ext clock indicators (Lock, Word clock, 256X)

Weight and dimensions

• Dimensions: approx. 480mm x 88mm x 280mm (W x H x D)
• Net Weight: 5.5kg

Appendix 1

Recording AES Outputs 1-8 to Pro Tools ™ HD at 192kHz
To record all eight channels digitally to Pro Tools™ HD at 192kHz, all eight AES channels need to be enabled on the ISA428 MkII (jumper positions shown on Appendix 2) and 2 Digital cards must be fitted in the HD192 interface. A 25-pin to two 25-pin cable must then be used, with the following pinout:

Pin No.| ISA428 Mk!! ADC Connector| HD 192 Break Out Connector 1| HD 192 Break Out Connector 2
---|---|---|---
1| AES 8+| NC| NC
2| GND| GND| GND
3| AES 7-| NC| NC
4| AES 6+| NC| NC
5| GND| GND| GND
6| AES 5-| NC| NC
7| AES 4+| AES 4+| AES 8+
8| GND| GND| GND
9| AES 3-| AES 3-| AES 7-
10| AES 2+| AES 2+| AES 6+
11| GND| GND| GND
12| AES 1-| AES 1-| AES 5-
13| NC| NC| NC
14| AES 8-| NC| NC
15| AES 7+| NC| NC
16| GND| GND| GND
17| AES 6-| NC| NC
18| AES 5+| NC| NC
19| GND| GND| GND
20| AES 4-| AES 4-| AES 8-
21| AES 3+| AES 3+| AES 7+
22| GND| GND| GND
23| AES 2-| AES 2-| AES 6-
24| AES 1+| AES 1+| AES 5+
25| GND| GND| GND

Appendix 2

Digital Card Jumper Positions – Disabling AES Outputs 5-8
Four jumpers on the digital card can be made to disable channels 5-8 on the AES Output. This is so that a standard 25-pin to 25-pin Pro Tools™ cable can be used to record channels 1-4 at 192kHz. (Half of the connections on the Digidesign Digital connector are used for receiving and the other half for transmitting.) For more information, consult the relevant section of the Pro Tools™ User Guide.
As shown on the card, with the jumpers in the lower position (on the bottom two pins), outputs 5-8 are enabled.
Removing the jumpers and placing them in the upper position (on the top two pins) disables outputs 5-8, as shown:
AES Outputs 5-8 disabled (default)

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