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FOCUSRITE ISA828 PRE-AMPLIFIER

FOCUSRITE ISA828 PRE-AMPLIFIER

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The ISA828 eight channel microphone pre-amplifier provides eight original ISA transformer-based pre amps in a single robust 2U chassis, offering the Focusrite signature sound at its lowest cost per channel to date.

The eight ISA-series transformer-based microphone pre amps feature the same classic microphone pre-amplifier design as the original ISA110 module from Focusrite's critically acclaimed Forte console (including the original Lundahl L1538 transformer and bespoke zobel network).

The pre-amps are complemented by eight line inputs, eight line outputs and an optional eight channel 192kHz ADC boasting the widest dynamic range of any converter to date. Thanks to its convenient 25 pin D-Type connectors, the ISA828 also integrates quickly and seamlessly with ProTools HD, as well as other popular hard disc recorders and mixing desks.

The microphone input stage additionally has a variable impedance circuit, allowing the user to switch between four carefully selected input impedance settings. The original ISA110 setting is supplemented by three further impedance settings to either perfectly match the pre-amp with any microphone, thus maximizing level, or to use different settings creatively to shape the sound of the microphone being used.

The four front panel instrument inputs also feature high and low impedance options to provide a comprehensive and accessible DI solution. Insert switches are also featured on every channel, should the need arise to place extra processing between the pre amp and converter. Vintage design 75 Hz / 18dB per octave high pass filters are also provided on every channel, ensuring unwanted low frequencies are effectively eliminated.

The ISA828's new optional eight-channel 192kHz ADC is the first audio ADC to utilise Texas Instruments Burr-Brown Pro Audio Amplifiers and Flagship Analog to Digital Converter PCM4220 chips. This cutting-edge technology is encompassed within Focusrite's own custom analogue circuitry to provide eight channels of unparalleled A/D conversion, delivering a dynamic range of 122dB and jitter at less than 250 picoseconds.

Finally, every channel features a six LED input meter, complete with global precise meter trim. Metering was specifically designed to utilise the same reference points as Digidesign's Pro Tools HDsystem and provides clear and accurate input metering, independent of the DAW.

Key Features

  • Eight ISA series transformer-based pre amps
    In a single robust 2U chassis, offering the classic Focusrite pre at its lowest cost-per-channel to date.
  • New Optional Eight Channel 192kHz ADC
    Embodies cutting-edge conversion technology, incorporating Focusrite analogue circuitry to deliver the best A/D performance on the market, bar none
  • Convenient 25 pin D-Type connectors
    The ISA828 integrates quickly and seamlessly with ProTools HD, as well as other popular hard disk recorders and mixing desks.
  • Switchable Impedance
    Selectable per channel; choose one of four carefully selected input impedances, including the original ISA110 setting, to suit any microphone.
  • Direct Instrument inputs
    Each instrument input features high and low impedance options to provide a comprehensive and accessible DI solution.
  • Inserting available on every channel
    Allows external devices to be inserted between the pre amp and the ADC, using the 25-pin D-type cable.
  • High pass filter, Phase reverse and Phantom power
    Each has a dedicated switch, independent on each channel.
  • Six LED input meter
    Complete with precise meter trim - Designed to utilise the same reference points as Digidesign's HD

FAQs

Q: Which applications is the ISA 828 suitable for?
A: The ISA 828 can be used as a multi-channel high quality front end for Digital Audio Workstations, allowing multi-channel recording to HD. Equally, it can be used simply as the perfect interface or A/D converter for synths/other line-level devices. It also provides additional channels for anyone who has run out of microphone pres on their analogue console (either live or recording), and is especially useful as a source of additional microphone pres for digital consoles.

Q: What are the basic features of the ISA 828?
A: Eight Focusrite microphone pres, eight line inputs, four instrument inputs, optional 8-channel 192kHz A/D conversion.

Q: Which Focusrite pre is featured in the ISA 828?
A: It's essentially the same original transformer-balanced microphone pre that featured in the classic analogue Focusrite consoles in the 1980s, and the one that features in the ISA 430 MKII and 428, as far as design and topology go. All these designs utilise a Lundahl LL1538 input transformer. The main improvements to the design are switchable impedance (including an ISA 110 setting to replicate the original device) and 10dB of extra Gain.

Q: Which Focusrite pre is featured in the ISA 828?
A: It's essentially the same original transformer-balanced microphone pre that featured in the classic analogue Focusrite consoles in the 1980s, and the one that features in the ISA 430 MKII and 428, as far as design and topology go. All these designs utilise a Lundahl LL1538 input transformer. The main improvements to the design are switchable impedance (including an ISA 110 setting to replicate the original device) and 10dB of extra Gain.

Q: Do the pres have the usual phantom power and High-Pass Filter controls?
A: Yes, and more... each pre has switchable microphone impedance so that you can match to your chosen mic's impedance, or ‘mismatch" for creative ‘input response colours". Also, there are inserts per channel, plus fixed 75Hz HPF, phase reverse, and phantom power.

Q: What's significant about the impedance switching for each pre?
A: Each pre can either be matched perfectly to any microphone (vintage or modern), or offset to offer a variety of ‘response colours" by interacting with any particular microphone. The impedance of each preamp is switchable (via a single switch labelled ‘Z In") between 4 settings: original ISA 110 (Zobal network influence for the classic Vintage Focusrite sound), Low (600 Ohms), High (2.4k) and Higher (6.8K, relatively lively, great for room ambience). For more information, read the impedance guide in the Applications section.

Q: Are insert points featured?
A: Yes, switchable in- or out- of circuit on each of channels 1-8.

Q: What do the insert switches actually do?
A: Activating an insert switch for an input switches the signal fed to the ADC (for that channel) to the corresponding one received at the ADC Input on the rear panel. This is so that the mic/line/inst signals can be sent to additional hardware such as compressors (using the analogue outputs) before being converted by the optional digital card.

Q: What are the four extra inputs on the left hand side of the front fascia for?
A: They are unbalanced inputs that enable you to easily connect unbalanced sources like guitars/basses to the unit without the need for an external DI box.

Q: What's the specification of the A/D option?
A: AES (both single and dual wire specs), S/PDIF and ADATTM formats, sample rates selectable between 44.1, 48, 88.2, 96, 176.4 and 192kHz, (ADATTM above 48kHz is, of course, via 2 ports), internal or external word clock, and 256X clock, S/N Ratio better than 121dBFS ‘A weighted to AES17". Connections are via a 25-pin D-type connector and standard lightpipes, word clock is via BNC in and out.

Q: Does the ISA 828's A/D option feature word clock as standard?
A: Yes, word clock may be fed in via a BNC connector on each A/D to allow the 828 to synchronise to any word clock master source.

Q: Why do I need word clock anyway?
A: When using multiple pieces of digital equipment, it is necessary to make sure that their bit streams are all in sync. In order to do this, all equipment needs to be synchronized to a common word clock system. Somewhere in this system a word clock ‘master" must be dictating the word clock for the rest of the equipment (‘word clock slaves") to follow. Failure to sync all pieces of digital equipment to a common word clock source will result in audible clicks and glitches
in programme material. Note that the 828 regenerates word clock at its BNC output, further boosting word clock stability.

Q: How many rack spaces does ISA 828 take up?
A: The ISA 828 is a 2U device.

Specifications

Mic Input Response
Gain range: 0dB to 60dB in 10dB steps
Input Impedance, variable: 600Ω, 1k4Ω, 2k4Ω, 6k8Ω
EIN (equivalent input noise): -126dB measured at 60dB of gain with 150 Ohm terminating impedance and 22Hz/22kHz bandpass filter
Noise at main output with gain at unity (0dB): -97dBu measured with a 22Hz/22kHz bandpass filter
Signal to noise ratio relative to max headroom (9dBu): 106dB
THD at medium gain (30dB): 0.0008% measured with a 1kHz -20dBu input signal and with a 22Hz/22kHz bandpass filter
Frequency response at minimum gain (0dB): -0.5dB down at 10Hz and –3dB down at 110kHz
Frequency response at maximum gain (60dB): –3dB down at 16Hz and –3dB down 85kHz
CMRR: 91.8dB (Channel 1, 1kHz, maxiumum gain)
Crosstalk Channel to Channel: with 10dB@1kHz input to chA, chB output =102dBrA. With 10dB@10kHz input to chA, chB output = 84dBrA

Line Input Response
Gain range: -20dB to +10dB in 10dB steps
Input Impedance: 10kΩ from 10Hz to 200kHz
Noise at main output with gain at unity (0dB): -96dBu measured with a 22Hz/22kHz bandpass filter
Signal to noise ratio relative to max headroom (24dBu): 120dB
Signal to noise ratio relative to 0dBFS(+22dBu): 118dB
THD at unity gain (0dB): 0.001% measured with a 0dBu input signal and with a 22Hz/22kHz bandpass filter
Frequency Response at unity gain (0dB): 0.3dB down at 10Hz and –3dB down at 122kHz

Instrument Input Response
Gain range: 10dB to 40dB continuously variable
Input Impedance: 1MΩ or 300kΩ
Noise at minimum gain (+10dB): -90dBu measured with a 22Hz/22kHz bandpass filter
Noise at maximum gain (+40dB): -62dBu measured with a 22Hz/22kHz bandpass filter
THD at minimum gain (+10dB): 0.002% measured with a 10dBu input signal and with a 22Hz/22kHz bandpass filter
Frequency Response at 10dB gain with -10dB input: 10Hz-200kHz +/- 0.6dB
Frequency Response at 40dB gain with -40dB input: -2.5dB down at 10Hz and 0dB at 200kHz

High Pass Filter
Roll off: 18dB per octave 3 pole filter
Fixed Frequency 75Hz measured at the 3dB down point

Weight
8.84kg
19.5Ibs

Dimensions
484mm (W) x 85mm (H) x 305mm (D) (350mm depth with heat sink)
19" (W) x 3.5" (H) x 12" (D) (13.8" depth with heat sink)

The ISA Pre

The ISA microphone pre-amplifier was first introduced back in 1985. This transformer-based pre-amplifier formed the first half of the ISA110 mic-pre and EQ module on Focusrite's critically acclaimed Forte console. This console, and the later Studio console were hailed by many as the finest sounding consoles ever built.

The ISA microphone pre-amplifier went on to form the cornerstone of all ISA and RED Focusrite products. The topology has never changed, except for the addition of a variable impedance circuit, allowing ISA users to either perfectly match the pre-amp with any microphone, thus maximizing level, or to use different settings creatively to shape the sound of the microphone being used. The original ISA110 setting was supplemented by three further impedance settings.

The Focusrite pre amp is renowned for its transparency, but there's also that subtle warmth that transformer core saturation contributes. This seeming contradiction of warmth plus beautifully open, unrestricted high frequencies, is a classic hallmark of the mid 80's Focusrite designs.

With processors whose bandwidth is strictly limited to the audible (20Hz to 20kHz) bandwidth alone, significant roll-off can still occur, affecting the higher audible frequencies of the signal. Therefore, in order to capture every subtle nuance, exactly as it occurs whilst avoiding any roll-off, the pre-amp must operate over a far greater bandwidth. The extremely broad frequency response of Focusrite pre-amps - close to 200kHz at the top end - guarantees accurate phase response across the much narrower range of human hearing, the roll-off point being moved entirely outside of the audible hearing range.

All critical inputs are transformer-coupled, providing a dual gain structure - an expensive option, but the optimum route to high quality signal handling. Focusrite use Lundahl LL1538 transformers.

Also originally employed was a 'Zobel network' to counteract the reactance of the primary coil of the transformer. A Zobel network is a damping circuit that is applied across the secondary of the microphone input transformer. This damping network tailors the naturally occurring high frequency resonant point of the input transformer. The Zobel network featured in ISA and RED pre amps was set by ear, has never changed, and as such is a key contributor to the Focusrite sound.

Finally, all the components featured in the ISA pre-amp were always chosen with a specific frequency response in mind. Rather than accepting the effect of the components chosen, the designer worked diligently with the values of every component in a relentless effort to achieve the desired response.

Reviews

Reverb Magazine review quotes
January / February 2008
vol 02 iss 07

"The ISA828 provides a massive degree of flexibility with the sources you can record and recordings you can use it on. It's sound is subtle yet distinct, with just the amount of presence so as not to overpower other elements in your mix. If you"re finding that your recordings are somewhat lack lustre and missing that professional edge, probably due to the use of a cheap interface, then the ISA 828 is the solution for you."

Future Music Magazine review quotes
February 2008

"As a testament to the quality of the pres design, noise is super-low even at high gain settings and it's difficult to get any audible distortion. It's one of the quietest pres I"ve used in this respect and there's no way you"d ever be short of headroom.

Where it excels is on bass/acoustic guitar and on punchy sounds where the pre really retains and emphasises the attack transients.

I can see the ISA 828 getting used in many different applications including as a standalone converter, (using the ADC card) as a front end for your DAW and generally if you want eight excellent workhorse pres in a compact unit you need to consider this box seriously"

Sound On Sound Magazine review quotes
October 2007
Paul White

"Even discounting the optional digital capabilities included with the review model, the ISA828 provides the most cost-effective ‘per channel" means of buying this particular design of preamplifier."

With its Rupert Neve heritage, the ISA preamp - in its various guises - is a popular piece of kit, and is used in many top studios around the world, so it doesn't really need any help from me to establish its credentials. What the ISA828 offers is a very cost-effective way of adding eight channels of ISA preamp to any studio system, with the highly-specified digital output card available as an option, which means you don't have to pay for it if you don't need it. Having to buy cables to mate with the D-Subs is a minor inconvenience, but it is more than made up for by the space-saving format and does benefit Pro Tools HD users. Because the price is so attractive, those project-studio owners prepared to spend a little more on quality equipment can now afford to add truly professional, transformer-input preamps to their own systems."

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FOCUSRITE

Focusrite warrants its products to be free from defects for 1 year from the date of purchase.

FOR SUPPORT WITH YOUR PRODUCT CONTACT:
800-431-2609