Focusrite Clarett OctoPre 8 CH Mic Preamp and AD/DA Converter User Guide

: June 6, 2024
: Focusrite

Table of Contents

OVERVIEW
Fe features
Box Contents
Hardware Features
Using the Clarett OctoPre
Digital Synchronisation
Example Setups
Physical and Electrical Characteristics
TROUBLESHOOTING
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User Guide
Version 2.0
focusrite.com

OVERVIEW

Introduction
Thank you for purchasing a Clarett OctoPre, an eight-channel mic-pre expansion unit incorporating high-quality Clarett analog pre-amplifiers with the unique Focusrite AIR function, plus send-and return insert points on each channel. As well as offering purely analog operation for stand-alone live use, the Clarett OctoPre includes both A-to-D and D-to-A conversion, providing a perfect solution for expanding your input and output capabilities via ADAT for recording.
This User Guide provides a detailed explanation of the hardware to help you achieve a thorough understanding of the product’s operational features. We recommend that you take the time to read through the Guide, whether you’re new to professional audio or a more experienced user so that you are fully aware of all the possibilities the Clarett OctoPre has to offer.
If the User Guide sections do not provide the information you need, please visit support.focusrite.com, which contains a comprehensive collection of answers to common technical support queries.

Fe features

The Clarett OctoPre is an eight-channel pre-amplifier for use with microphone, line, and instrument input signals. It converts the inputs into multi-channel, 24-bit digital audio at sample rates up to 192 kHz. Both analog and digital outputs are provided: the digital outputs are in ADAT format on optical TOSLINK connectors, which can be easily routed to ADAT inputs on your studio recording system, or any other ADAT-equipped interface using optical cables. The Clarett OctoPre can transmit and receive eight channels of audio at sample rates of 44.1, 48, 88.2, or 96 kHz, or four channels at 176.4 or 192 kHz.
A switchable analog INSERT function is provided on each input channel to permit the connection of external processors such as compressors or noise gates.
The OctoPre is an ideal “expansion” unit for adding eight more inputs to an existing audio interface such as other members of the Focusrite Clarett range.
The Clarett OctoPre is a bidirectional unit: it is also equipped with ADAT format digital inputs and balanced analog outputs. It incorporates an ADAT-to- LINE mode, making it the perfect interface for routing tracks from your DAW to an analog mixing console.
The Clarett OctoPre can be easily synchronized with other items of digital audio equipment in your studio, either as a follower to an external word clock signal or by acting as the leader clock source itself.
An important feature of all models in the Clarett range is the new design of the analog preamplifier. In addition to their class-leading dynamic range and ability to provide all the gain, you’re ever likely to need, the circuitry now includes the Focusrite AIR function. Individually selectable on each channel, AIR subtly modifies the pre-amp’s frequency response to model the impedance and resonance characteristics of Focusrite’s classic transformer-based ISA mic preamps. When recording with good quality microphones, you will notice enhanced clarity and definition in the important mid-frequency range, just where it is most needed for vocals and many acoustic instruments.

Box Contents

Along with your Clarett OctoPre, you should have:
• AC mains cable with IEC connector
The User Guide (in English, French, German and Spanish) can be downloaded from: focusrite.com/downloads

Hardware Features

Front Panel

The front panel includes all operational controls, metering for all channels, and two input sockets for mic, line, or instruments.

INPUTS 1 & 2 – 2 x “Combo XLR” input sockets for Channels 1 and 2 – connect microphones or line-level signals via XLR or ¼” jacks: either TRS (balanced) or TS (unbalanced) jack plugs can be used for instruments or line-level signals. Note that the inputs for Channels 3 to 8 are on the rear panel [15].
INST 1 & INST 2 – two switches put Inputs 1 and 2 into “Instrument” mode. When INST is selected, the gain range and input impedance are altered (relative to LINE), and the input is made unbalanced. This optimizes it for the direct connection of instruments via a 2-pole (TS) jack plug. When INST is off, the inputs are suitable for the connection of line-level signals. Line level signals may be connected either in the balanced form via a 3-pole (TRS) jack or unbalanced, via a 2-pole (TS) jack. Each switch has an internal red LED to confirm the selection.
48V (1-4 & 5-8) – two switches, each enabling 48 V phantom power at the XLR contacts of four inputs: Channels 1 to 4 and 5 to 8 respectively. Each switch has a red LED indicating that phantom power is selected.
Input gain controls 1 to 8 – eight rotary controls: adjust the input gain for the signals in Channels 1 to 8 respectively.
O/L – each input channel has a red “overload” LED; this illuminates when the signal level reaches +19.5 dBu. Always adjust the signal level so that the LED does not illuminate: this will avoid clipping.
I NSERT/AIR –one “soft” switch per channel, which enables either the rear panel insert point for the channel, or the channel’s AIR function, depending on the setting of the INSERT and AIR main switches [8]. Each switch has an LED, which illuminates green when INSERT is selected or yellow when AIR is selected.
Input signal level meters: eight LED bargraphs, one per channel. Segments indicate -42, -18 & -12 dBFS (green), -6 & -3 dBFS (yellow) and 0 dBFS (red). Input signals are metered post the input gain controls, so you can see the levels being sent to the digital outputs.
INSERT and AIR function main switches two soft switches with internal LEDs (INSERT = green, AIR = yellow) which determine the function of the per-channel INSERT/AIR switches [6].
SAMPLE RATE – a soft switch that steps through the six available sample rate settings, the current rate is indicated by one of the adjacent green LEDs. The sample rate in use is stored in memory so that it is retained when the unit is switched off.
SYNC – a soft switch that steps through three available digital sync sources (Internal, ADAT, or Word clock), the current source is indicated by one of the adjacent red LEDs. The source in use is stored in memory so that it is retained when the unit is switched off.
– a green “Locked” LED which illuminates when the unit has locked to the available sync source, indicating that it is ready to use.
ADAT > LINE – this soft switch modifies the operating mode of the unit. When not selected, Channels 1 to 8 feed both the rear panel LINE OUTPUT connector (analog) and the ADAT ports (digital). When ADAT > LINE mode is selected, the LINE OUTPUT connector provides an 8-channel analog version of the incoming digital audio at the ADAT input ports instead. The adjacent red LED confirms that this mode is active. In this mode, the analog inputs (Channels 1 to 8) remain rooted to the ADAT digital outputs. The mode in use is stored in memory so that it is retained when the unit is switched off.
POWER – AC power switch and green LED.
Rack ears for mounting the Clarett OctoPre in a standard 19” equipment rack. The remainder of the Clarett OctoPre’s inputs and outputs are on the rear panel.
Rear Panel
INPUTS 3 to 8 – 6 x “Combo XLR” connectors; note that the inputs for Channels 3 to 8 do not have INST mode, but are otherwise identical to those for Channels 1 and 2.
INSERTS 1 & 2 – two ¼” TRS jack sockets, providing an access point for connecting external processing equipment into Channels 1 and 2. The inserts are enabled by the front panel INSERT/AIR switches [6] and [8], and are unbalanced. The sockets are wired as follows:
Jack contacts| Function
---|---
Tip| Send (output)
Ring| Return (input)
Sleeve| Ground

Note that the front panel O/L LED [5] monitors signal level pre the insert send so that excessive signal level is not sent to external equipment. are electrically identical to [16].

OPTICAL OUT – two TOSLINK connectors providing the digital outputs of the unit. Utilization of the two connectors is sample rate-dependent, as follows:
Sample Rate| OUTPUT 1 (RH port)| OUTPUT 2 (LH port)
---|---|---
44.1/48 kHz| Channels 1 to 8| Channels 1 to 8
88.2/96 kHz| Channels 1 to 4| Channels 5 to 8
176.4/192 kHz| Channels 1 & 2| Channels 3 & 4
OPTICAL IN – two TOSLINK connectors providing the digital inputs to the unit when used in the ADAT > LINE mode. Note that these are NOT “digital” inputs to Channels 1 to 8, and signals applied at these ports do not pass through the AIR circuitry, nor are available at the inserts. Utilization of the two connectors is sample rate dependent, as [18].
LINE OUTPUTS 1 to 8 – eight balanced analog line outputs on a 25-pin female D-sub connector. This connector is always active, and normally carries the outputs of Channels 1 to 8, enabling the Clarett OctoPre to be used as a stand-alone, high-quality 8-channel analog mic pre. In ADAT > LINE mode, the connector carries the signals applied at the OPTICAL IN ports [19]. The pinout of the connector follows the common “Tascam” standard for 8-channel analog interfaces:
Pin| Function| Pin| Function
---|---|---|---
1| Output 8 ‘hot’ (+)| 14| Output 8 ‘cold’ (-)
2| Output 8 GND| 15| Output 7 ‘hot’ (+)
3| Output 7 ‘cold’ (-)| 16| Output 7 GND
4| Output 6 ‘hot’ (+)| 17| Output 6 ‘cold’ (-)
5| Output 6 GND| 18| Output 5 ‘hot’ (+)
6| Output 5 ‘cold’ (-)| 19| Output 5 GND
7| Output 4 ‘hot’ (+)| 20| Output 4 ‘cold’ (-)
8| Output 4 GND| 21| Output 3 ‘hot’ (+)
9| Output 3 ‘cold’ (-)| 22| Output 3 GND
10| Output 2 ‘hot’ (+)| 23| Output 2 ‘cold’ (-)
11| Output 2 Gnd| 24| Output 1 ‘hot’ (+)
12| Output 1 ‘cold’ (-)| 25| Output 1 GND
13| n/c| |
WORD CLOCK OUT – a BNC connector carrying the Clarett OctoPre’s word clock; this may be used to synchronize other digital audio equipment forming part of the recording system. The source of sample clock synchronization is selected by the SYNC switch [10].
WORD CLOCK IN – a BNC connector for the connection of an external word clock signal; select by setting SYNC to WORD. Use this input if you have a leader reference clock that provides synchronization for all the digital audio devices in your studio.
AC mains – standard IEC receptacle. The Clarett OctoPre is fitted with a “Universal” power supply and will run from any AC mains voltage from 100 to 240 V, at 50 or 60 Hz.

Using the Clarett OctoPre

Combo Inputs
All eight of the analog inputs use “Combo XLR” connectors. These can accept male XLR connectors, TS (unbalanced) ¼” jacks, or TRS (balanced) ¼” jacks.
When an XLR connector is used, the pre-amp automatically configures gain and impedance to receive microphone level signals. If a ¼” plug is used, the pre- amp is able to accept balanced or unbalanced line-level signals. When INST mode is selected (on Channels 1 or 2), the 1/4” input reconfigures again to optimize for an unbalanced, high impedance signal.
Pre-amp Gain
The GAIN of each channel should be adjusted to suit the incoming level. Obviously, “hotter” sources will need a lower gain setting. Always use the LED meters to check the signal level on each channel. Start with the GAIN control set to a minimum. Ask the performer to play at the loudest level required by the song, and gradually increase the gain until the meter shows orange (-3 dB). Then lower the gain by a few dB. This should ensure that the signal level is unlikely to ever reach red (0 dB) and overload the A-to-D converter, which would result in distortion.
Note that the high headroom pre-amplifier design used in the Clarett range means that a switchable Pad is unnecessary. (See “Performance Specifications” on page 16 for input sensitivity specifications.)
The red O/L LED should never illuminate; if it does, the gain is set too high.

Phantom Power
The two 48V switches apply 48 V phantom power to Mic inputs 1 to 4 and 5 to 8 respectively. Phantom power is required by most condenser (capacitor) microphones, and also active ribbon microphones. Phantom power is only applied to the XLR contacts of the Combo connectors: thus if a group of four inputs is being used for both mic and line (or instrument) level signals, phantom power is only applied to the microphones.
Dynamic microphones do not require phantom power, but most will operate normally with phantom power supplied. Passive ribbon microphones do not require phantom power and may be damaged if supplied with phantom power.
If you are unsure about a microphone’s type, DO NOT apply phantom power without checking the manufacturer’s specifications first.
Line Outputs
By connecting the line outputs of the Clarett OctoPre to the analog line inputs of a mixing console (or any other device), the unit can be used either as a purely analog, 8-channel microphone preamplifier or as an analog “break- out box” for ADAT signals when in ADAT >
LINE mode.
The outputs are balanced; see [20] on page 7 for the pinout. Ready-made D25 -to-XLR or D25-to-jack breakout cables are available from professional audio suppliers. The maximum output signal level is +16 dBu.

Digital Outputs
Use the OPTICAL OUT ADAT port(s) [18] to connect the Clarett OctoPre to the ADAT input(s) of an audio device using TOSLINK optical cable(s).
The ports can transmit eight channels of audio at 44.1 kHz or 48 kHz sample rate via a single optical cable. At these sample rates, the two ports carry the same eight channels.
At 88.2 kHz or 96 kHz sample rates, each port can transmit four channels of audio. The right-hand port carries Channels 1 to 4, the left-hand port carries Channels 5 to 8; thus two TOSLINK cables are required to transmit all eight channels.
At 176.4 kHz or 192 kHz sample rates, each port can transmit two channels of audio. The right-hand port carries Channels 1 and 2, the left-hand port carries Channels 3 and 4. The OctoPre is restricted to four channels of digital audio at these sample rates; the outputs of Channels 5 to 8 are not available via the ADAT ports.
Use the SAMPLE RATE switch [9] to select the desired sample rate frequency. It is essential that the sample rate selected on the Clarett OctoPre matches the sample rate set on the receiving digital device.

Digital Synchronisation

Two synchronization options are available:
Clarett OctoPre as Clock Source Leader:
Connect the OctoPre to the receiving digital device via the OPTICAL OUT port(s) and ensure that the receiving device is set to source its clock from its ADAT input (and also that the sample rates on both devices match).
On the OctoPre, SYNC should be set to INTERNAL and the LED will illuminate.
An alternative method is to sync the receiving device to the Clarett OctoPre’s WORD CLOCK OUT using a BNC cable. In this scenario, the receiving device’s sync source will need to be set to its external word clock input.
Clarett OctoPre as Clock Source Follower:
Connect the OctoPre to the receiving digital device via the OPTICAL OUT port(s) and connect a BNC cable from the digital system’s leader word clock to the OctoPre’s WORD CLOCK IN connector (also ensuring that the sample rates on all devices match). On the OctoPre, SYNC should be set to WORD and the LED will illuminate.

Digital Inputs
Use the OPTICAL IN ADAT port(s) [19] if you need to convert digital audio (e.g., the output of a DAW) to analog, using the Clarett OctoPre’s ADAT > LINE mode. The right-hand port can receive eight channels of audio at 44.1 kHz or 48 kHz sample rate via a single
optical cable.
At 88.2 kHz or 96 kHz sample rates, each port can receive four channels of audio. The right-hand port carries Channels 1 to 4, the left-hand port carries Channels 5 to 8; thus two TOSLINK cables are required to receive all eight channels.
At 176.4 kHz or 192 kHz sample rates, each port can receive two channels of audio. The right-hand port carries Channels 1 and 2, the left-hand port carries Channels 3 and 4. The OctoPre is restricted to four channels of digital audio at these sample rates.
Use the SAMPLE RATE switch [9] to select the desired frequency. It is essential that the sample rate selected on the Clarett OctoPre matches the sample rate set on the transmitting digital device.

AIR mode
An important feature of all models in the Clarett range is the new design of the analog preamplifier. The circuitry now includes a new AIR function, individually selectable on each channel. AIR subtly modifies the pre-amp’s frequency response to model the impedance and resonance characteristics of Focusrite’s classic transformer-based ISA mic preamps. When recording with good quality microphones, you will notice enhanced clarity and definition in the important mid-frequency range, just where it is most needed for vocals and many acoustic instruments.

Inserts
Each pre-amplifier channel includes a switchable insert point for the connection of external processing equipment such as compressors or noise gates. The insert comprises a send (the output of the channel’s input stage) and a return (an input to the channel’s output stage): with no plugin in the INSERT socket, the channel signal path is uninterrupted. The insert send and return are both unbalanced. Use a TRS jack wired with the tip (send) and ring (return) of the jack wired to two separate cables; such cables (often referred to as ‘Y-cables”) are available from professional audio suppliers.
The insert point is to post the AIR circuitry (thus external equipment will receive a signal modified by AIR), and also post the front panel GAIN controls [4]. When using an insert point, try to adjust the input and output levels of the external processor so that the return signal is about the same level as the send. If the external processor has too much gain, you run the risk of overload within the OctoPre, so use the channel meters [7] to check the return signal level.

Use the front panel INSERT/AIR buttons [6] to enable the insert point. (First, select INSERT using the main switch [8].) The channel LED will illuminate green to confirm the selection.

ADAT-to-Line mode
Selecting ADAT > LINE mode ([12] on the front panel) reassigns the eight sources for the analog LINE OUTPUTS D-sub connector [20]. In normal operation, the outputs of the mic pre-amplifier channels are available at this D-sub connector; in ADAT > LINE mode, the D-sub connector is fed with the ADAT digital signals at the OPTICAL IN port(s), following D-to-A conversion.

This mode enables the Clarett OctoPre be used to connect an 8-channel ADAT format output (from a DAW, for example) to a set of analog inputs, typically the channels of an analog mixing console, to permit such a mixer to be used to mix down DAW tracks.
When ADAT > LINE mode is enabled, the eight Clarett microphone pre-amplifiers are still operational, and their outputs remain available at the OPTICAL OUT ports.

Example Setups

1 . Clarett OctoPre with an audio interface: OctoPre as clock source Leader

Here the OPTICAL OUT on the Clarett OctoPre is connected to OPTICAL IN o n a Focusrite Clarett 8Pre audio interface with a single optical cable. Both units are running at a 44.1 kHz sample rate. The OctoPre’s clock source is set to INTERNAL, and the 8Pre is synchronized to it because its clock source is set to ADAT (via Focusrite Control).
This setup would, for example, enable up to 16 mic or line sources to be recorded in a DAW simultaneously, and would thus be ideal for recording a live band. It would also be appropriate for any other audio interface which has an ADAT input.

2 . Clarett OctoPre with an audio interface: the audio interface as a clock source Leader

Here OPTICAL OUT on the Clarett OctoPre is connected to OPTICAL IN on a Focusrite Clarett 8PreX audio interface with a single optical cable. Both units are running at a 44.1kHz sample rate. The OctoPre’s clock source is set to WORD, and its WORD CLOCK IN input is connected to WORD CLOCK OUT on the Clarett 8PreX with a BNC cable. The Clarett 8PreX’s clock source is set to INTERNAL (via Focusrite Control), thus making it the sync leader. It would also be appropriate for any other audio interface which has an ADAT input and a word clock output.

3 . Clarett OctoPre with Clarett 8PreX – SMUX-II and SMUX-IV modes

This example shows the same setup as Example 2, but running at a sample rate of 96 kHz (“SMUX-II” mode). Both units must be set to 96kHz; two optical cables are used, carrying four channels of audio each. The Clarett 8PreX is the sync leader as before.
This setup is also applicable with a 192 kHz sample rate (“SMUX-IV” mode); each optical cable will then carry two channels of audio.
The setup in this example would also be appropriate for any other 96/192 kHz- capable audio interface with two ADAT inputs and a word clock output.
4 . Clarett OctoPre with analog mixing desk

This setup uses the Clarett OctoPre’s mic pre-amplifiers and AIR mode to provide a high-quality “front end” for an analog mixing desk. Use an 8-way loom to connect the OctoPre’s LINE OUT socket to eight line inputs on the mixing desk; this will need a 25-way D-sub on one end and eight connectors appropriate to the desk’s line inputs on the other. (Pre-made looms are available from professional audio suppliers.)
This setup would also be appropriate to use the OctoPre as an input stage with any type of 8-channel analog device.
Because the Clarett OctoPre’s ADAT OUT ports are always active, you can also simultaneously record the performance on a DAW (or another recording device) with an ADAT interface.
5 . Clarett OctoPre in ADAT > Line mode

This example shows how to connect a greater number of DAW tracks to an analog mixing desk for mixdown. The 10 analog outputs of a Clarett 8PreX interface are connected to desk Channels 1 to 10. It’s OPTICAL OUT ports are connected to the OPTICAL IN ports of two Clarett OctoPres with ADAT > LINE mode selected on both. A loom similar to that used in Example 4 is then used to connect the two OctoPres to Channels 11 to 26 of the desk.
The Clarett 8PreX would normally be the sync leader in this situation, so its clock source is set to INTERNAL (via Focusrite Control). The clock source on both Clarett OctoPres is set to ADAT, so both are synchronized to the Clarett 8PreX via the ADAT optical connections.
The setup in this example would allow 18 DAW tracks to be connected to the desk if only a single Clarett OctoPre was in use.
The above channel counts are applicable at a 44.1/48 kHz sample rate, providing that a Clarett 8PreX is used as the primary interface.
6 . Using Clarett OctoPre’s inserts to record drums

When recording acoustic drums, dynamics control may be applied in various ways to get the sound you’re after. Compression is frequently added to kick and snare drums to thicken up the sound, while noise gates are effective on tom- toms to minimize spillage between the various drum mics.
Use looms with a TRS jack on one end wired to two XLRs, TRS jacks or TS jacks as appropriate to the outboard processors. The “ring” of the TRS jack at the OctoPre end should go to the input of the processor, the “tip” to the output.

CLARETT OCTOPRE TECHNICAL SPECIFICATIONS
Performance Specifications
(All performance figures are measured to the AES17 standard).

Sample Rates

Physical and Electrical Characteristics

Analogue Inputs 1 & 2

Connectors| “Combo XLR” sockets on front panel; for Line use ¼” TRS jack, for Inst use ¼” TS jack.
Mic/Line switching| Automatic
Line/Instrument switching| via front 2 x front panel switches
Phantom power| +48 V, switchable Chs. 1-4, 5-8 in groups
Analogue Inputs 3 to 8
Connectors| “Combo XLR” sockets on rear panel; for Line use ¼” TRS jack.
Mic/Line switching| Automatic
Phantom power| +48 V, switchable Chs. 1-4, 5-8 in groups
Outputs
Analog outputs| 8 x balanced, on rear panel 25-way female D-sub
Other I/O

ADAT I/O

| 4 x TOSLINK optical connectors:

8 channels at 44.1/48 kHz (both ports)

8 channels at 88.2/96 kHz (Chs 1-4, 5-8)

4 channels at 176.2/192 kHz (Chs 1 & 2, 3 & 4)

Word clock output| 2.5 V (correctly terminated); BNC connector
Word clock input| BNC connector
Weight and Dimensions
W x D x H| 482 mm (1U) x 44.5 mm x 286 mm

19.0” (1U) x 1.75” x 11.3”

Weight| 4.15 kg

9.15 lbs

TROUBLESHOOTING

For all troubleshooting queries, please visit the Focusrite Help Centre at support.focusrite.com.
COPYRIGHT AND LEGAL NOTICES
Focusrite is a registered trademark and Clarett OctoPre is a trademark of Focusrite Audio Engineering Limited.
All other trademarks and trade names are the property of their respective owners. 2016 © Focusrite Audio Engineering Limited. All rights reserved.