Focusrite ISA 828 User Guide

ISA 828

User Guide
Mode d’emploi

FA0145-04

WARNINGS & CAUTIONS

THE APPARATUS SHALL NOT BE EXPOSED TO DRIPPING OR SPLASHING, AND NO OBJECTS FILLED WITH LIQUIDS,
SUCH AS VASES, SHALL BE PLACED ON THE APPARATUS

VENTILATION SHALL NOT BE IMPEDED BY COVERING THE VENTILATION OPENINGS WITH ITEMS, SUCH AS
NEWSPAPERS, CLOTHS, CURTAINS ETC.

NO NAKED FLAME SOURCES, SUCH AS LIGHTED CANDLES, SHOULD BE PLACED ON THE APPARATUS

MAINS LEAD - THIS EQUIPMENT MUST BE EARTHED AND FITTED WITH THE CORRECT LEAD FOR THE COUNTRY
OF OPERATION. THIS WILL NORMALLY BE ACHIEVED FROM THE CORRECT MAINS SUPPLY SOCKET

DO NOT USE A DAMAGED OR FRAYED POWER CORD

IF THE MAINS PLUG SUPPLYING THIS APPARATUS INCORPORATES A FUSE THEN IT SHOULD ONLY BE REPLACED
WITH A FUSE OF IDENTICAL OR LOWER RUPTURE VALUE

SHOULD THE APPARATUS OR SUPPLY CORD BECOME PHYSICALLY DAMAGED THEN IT SHOULD NOT BE POWERED,
AND ADVICE SOUGHT FROM SUITABLY QUALIFIED PERSONNEL

THIS UNIT MUST BE EARTHED BY THE POWER CORD

UNDER NO CIRCUMSTANCES SHOULD THE MAINS EARTH BE DISCONNECTED FROM THE MAINS LEAD

This unit is capable of operating over a range of mains voltages as marked on the rear panel. Ensure correct mains
voltage setting and correct fuse before connecting mains supply. Do not change mains voltage settings while mains
supply is connected. To avoid the risk of fire, replace the mains fuse only with the correct value fuse, as marked on the
rear panel. The internal power supply unit contains no user serviceable parts. Refer all servicing to a qualified service
engineer, through the appropriate Focusrite dealer.

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Contents

Getting Started and Powering Up . . . . . . 4

Front Panel . . . . . . . . . . . . . . . . . . . . . . . . 5

Rear Panel . . . . . . . . . . . . . . . . . . . . . . . . . 8

Digital Options . . . . . . . . . . . . . . . . . . . . . 10

Applications . . . . . . . . . . . . . . . . . . . . . . . 12

FAQs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Specifications . . . . . . . . . . . . . . . . . . . . . 18

Warranty . . . . . . . . . . . . . . . . . . . . . . . . . 19

Mode d’emploi . . . . . . . . . . . . . . . . . . . . . 22

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Getting Started and Powering Up

The ISA 828 is a high quality eight-channel microphone preamplifier, which can be used to record microphone, line-level
or instrument sources. Microphones and line-level sources for all eight inputs are connected on the rear panel, whilst
instruments are plugged directly into the front panel (inputs 1-4 only). The front panel also features level controls and
other settings such as phantom power and impedance for each of the eight analogue inputs. LED metering is provided on
each channel in dBFS, to indicate when the level is reaching the digital clipping point, with a dial on the rear panel for
calibration.

If wanting to maintain pristine Focusrite quality in the digital domain, an optional digital output card can be installed, for
connecting an AES, S/PDIF or ADAT™ signal directly to the DAW. With the card fitted, the clock sample rate and sync
source can be selected with switches on the front panel.

A 2-way switch labelled

Power supplies power to the unit, providing the supplied IEC mains lead is connected to the
input on the rear panel. Make sure that the ISA 828 is turned on before powering up any devices connected to the
outputs.

The IEC mains lead supplied with the unit should have the correct moulded plug for your country. The wiring colour code
used is:

For units shipped to the USA, Canada, Taiwan and Japan:

Live - Black Neutral - White Earth – Green

For units shipped to any other country:

Live - Brown Neutral - Blue Earth - Green and Yellow

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Front Panel

Input Stage

Eight numbered sections are included on the front panel for setting up each of the eight analogue inputs.

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 eight channels simultaneously. Note that only inputs 1-4 can be used for instruments however.

XLR inputs for microphones and TRS 1/4” inputs for line-level sources are available on the rear panel. TS 1/4” inputs for
instruments are available on the front panel (inputs 1-4 only).

Mic Input Gain

With the Mic input selected, the user has access to the full gain range in 10dB steps from 0dB to +60dB (yellow legend).
The gain range is split between two gain modes depending upon the status of the 30-60 switch (see description on page 6).

Instrument Inputs (Inputs 1-4)

Switch Input metering to pre
ADC (when using Inserts for
external processing of Inputs)

Digital Options (for optional card)

Power
switch

Controls for Inputs 1-8

Phantom Power switch

Activates a gain range
of 30-60 across the
Gain (stepped) dial
(the default is 0-30)

Selects type of input

Meter in dBFS

Selects input impedance to
600, 1k4, 2k4 or 6k8 Ohms

Selects the gain of the input
in stepped values of 10

Allows an additional 20dB of gain to be applied
to a mic or line signal, or sets the gain of the
instrument to between 10 and 40dB

Routes channel 2 of the ADC Input on
the rear panel to the optional digital
card, instead of the direct mic/line/inst
signal for input 2

Inverts phase of signal

Activates a high-pass filter

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Mode 1 Mic Gain Range 0-30

With the 30-60 switch off, the stepped gain dial operates over a gain range of 0dB to +30dB, the level of gain chosen
being indicated on the front panel by the outer arc of yellow numbers around the gain knob.

Mode 2 Mic Gain Range 30-60

With the 30-60 switch on (illuminated), the stepped gain dial operates over a gain range of 30dB to 60dB, the level of
gain chosen being indicated on the front panel by the outer arc of yellow 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 the
‘Trim’ control text below for a 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 arc of white numbers around the gain knob. The 30-60 switch is inactive when the line input is selected,
as the gain range for Line level inputs 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 the ‘Trim’ control text below for a full
explanation.)

Instrument Input Gain

With the instrument input selected (inputs 1-4 only), 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
yellow numbers around the gain 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 gain chosen is indicated on the front panel by the inner arc of white numbers around the gain knob. 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

Using trim in conjunction with the mic gain of 60dB gives 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 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 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.

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Insert In

Activating the INSERT switch (illuminated when active) breaks the signal path of the channel, so that the signal
connected to the ADC Input 25-pin connector on the rear panel routes to the digital output card (if connected) rather
than the direct mic, line or instrument signal. Note that the mic, line or instrument signal will still route to the analogue
output on the rear panel with this switch active. This switch is designed to allow the input signal to be routed to other
hardware for processing (out of the analogue output) and then back into the 828 (using the ADC input) for digital
conversion. The

Meters Pre ADC switch on the front panel allows the ‘return’ signal level to be viewed on the LED

strip meters before conversion (see the Metering section below for details).

HPF

Pressing the HPF switch makes the High Pass Filter for that channel active in the audio path. This is useful for
removing any unwanted bass caused by proximity effect or rumble. The filter provides a 75Hz knee frequency with
18dB/octave roll-off.

Input 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 ISA 828 transformer input, the
performance of both the ISA 828 pre-amp 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.

The impedance switch is also active on the instrument input. In this case, pressing the Z In switch toggles between
High and Low impedance settings. The impedance values are as follows:

Low – 470 k

Ω

High – 2.4 MΩ

Metering

The vertical columns of LEDs indicate the peak signal levels of channels 1-8 in one of two modes, defined by the state
of the ‘Meters Pre ADC’ switch on the front panel:

Mode 1. Meters Pre ADC switch disengaged

This is the default state and the mode to use when no digital output card is installed. Meters 1 to 8 indicate the analogue
level directly after the Gain stages set on the front panel. 0dBFS (reached when the red LED is lit) indicates that a signal
level of +22dBu is present at the analogue output. -18dBFS (unless recalibrated on the rear panel, see description on
page 8) therefore indicates that there is a signal level of +4dBu at the analogue output.

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