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Eight channels of classic ISA 110 tone, with expanded digital options and Dante

Review by Paul Vnuk Jr.

The ISA 110 preamp is one of the most significant achievements in Focusrite history. Rupert Neve designed it, and in the mid-80s it was one of the first standalone preamps on the market in addition to being found in Focusrite Forte consoles. The Focusrite ISA 828 MkII packs eight ISA 110 preamps into a 2U space. An expanded feature set makes it equal parts preamps, ADAT and Dante expansion box, and analog conversion interface.

An ISA primer

ISA stands for Input Signal Amplifier. Current models include the ISA One (reviewed August 2009), the two-channel ISA Two, the four-channel ISA 428 MkII and ISA 828 MkII—all containing Lundahl LL1538 transformers. The MkII units feature updated digital card options with Dante Audio-over-IP network capability and an updated ultra-efficient power supply.

ISA 110 x 8

The ISA 828 MkII features eight matching preamp channels with +48v phantom power, phase switching, highpass filters (18dB at 75 Hz), and a channel insert. You also get a choice of mic, line or instrument input (channels 1-4), four levels of input load impedance, and a six-step LED input meter.

The gain train

Gain is set by a pair of yellow knobs. The first is a four-position stepped pot offering -20 to +10dB of line gain in 10dB steps, or two levels of microphone gain selectable with a 30-60dB button (0 to 30dB or 30 to 60dB in 10dB steps).

A variable trim pot offers an additional 20dB of gain for both mic and line signals, giving the 828 MkII an impressive 80dB of microphone gain and 30dB of line level gain.

This is also the sole level control for the four front-panel 1/4 instrument inputs located on the unit’s far left. These offer from 10 to 40dB of gain on channels 1-4 only.

Catching some z’s

Each channel also offers selectable input impedance for the microphone input with a choice of Low (600 Ω), the original ISA 110 setting (1.4 kΩ), Med (2.4 kΩ) and High (6.8 kΩ). When an instrument input is used, there’s a choice of Low (470 kΩ) or High (2.4 MΩ).

Also on the front panel are digital clock and sample rate selection, a pre-ADC monitoring button for when the unit is fitted with one of the digital expansion cards, and a master power switch.

Making the connection

Each input type has a dedicated input on the back with no combo jacks or shared inputs. There are eight XLR inputs and eight 1/4” TRS inputs. Analog line outputs 1-8 are on a DB-25 connector, convenient if you’re going straight into a D-Sub equipped patch bay or interface, but it will require a Male XLR or 1/4” TRS breakout snake if not.

Above the analog output is a second DB-25 connector labeled A-D External Inputs. This is the input for the digital channel insert when used with the A-D option card.

Finally, there is an IEC mains connector on the back for power.

Focusrite ISA 828 BackDigital expansion

Adding one of the two available digital expansion cards opens up additional connective features. Card options include the two-channel ISA ADN2 and the eight-channel ISA ADN8. Both offer BNC Word Clock I/O and a set of RJ45 Dante output ports. The ISA ADN2 has a choice of stereo digital out over ADAT, S/PDIF, or XLR-based AES3.

The ISA ADN8 is an eight-channel card with dual ADAT ports for high-sample rates and eight channels of AES3 over DB-25.

Both cards are analog to digital only, making the ISA 828 MkII more of an expansion box or a Dante input device than a proper audio interface. The unit offers no digital to analog conversion or monitoring facilities. Sample rates up to 192 kHz are supported, as are external Word Clock and Dante clocking choices.

And now, the inserts!

Next, we come to the insert capabilities of the ISA 828 MkII. This feature is dormant when used solely as an analog preamp. However, when connecting the unit digitally to another interface or Dante network, the analog outputs can be re-purposed as the channel insert sends, and the A-D External Inputs handle the returns. This allows for easy inline connection of a favorite EQ or dynamics processor.

The 828 MkII in action

My assessment of the ISA sound remains similar to when I reviewed the ISA One twelve years ago. It’s a perfect example of a classic console sound that is neither heavily colored nor ultra-transparent. I would place the ISA sound between the Neve and API camps, gently leaning toward the smooth low-mid saturation of Neve while offering more upper-end focus. Thanks to the obscene amount of possible gain and available headroom, there’s no microphone—loud, quiet, high or low output—that the ISA 828 MkII cannot handle.

This also means that there’s no instrument, vocal range or musical style that this preamp cannot easily navigate.

Choose your impedance

I’m a big fan of impedance switching preamps, as they offer a great way to milk subtle tonal nuances out of mics by altering their reactive relationships with the preamps. These changes are more noticeable in passive microphones, but a mic pre’s input impedance affects all mics.

I used a microphone splitter to send a single microphone to four preamp channels, each set to a different impedance load. Then I layered a quick test song of acoustic guitar, vocals, cajón kick, snare, and some shakers and tambourine. I also tracked some direct bass with the high and low settings.

The low setting was the most weighted and offered the most low-end extension of the bunch, especially with an AEA R44CE ribbon microphone; the ISA 110 setting is the sound of this classic preamp, and the most balanced across the board. Medium offered a nice upper-mid punch and forward detail well suited to my Shure SM7B. Finally, the High setting reigned in the low-end of a vintage tube mic and more so the AEA ribbon, while gently accentuating the top-end clarity. That said, these tonal changes in each instance are subtle—in the 10-15% range, especially on modern condenser mics. Moving to direct instruments, on my Rickenbacker 4003 bass I found the Low setting gave the bass a more diffuse, laid-back sound, while High (the usual instrument impedance on most preamps) offered the upper mid punch and aggression I know and love with this bass.

Diggin’ in the digital

My other favorite feature of the ISA 828 MkII is the ISA ADN8 expansion card’s added flexibility. If your audio interface offers multichannel ADAT optical input, the ISA 828 MkII instantly grants you an additional eight analog input channels. In my studio, it easily connected to my Universal Audio Apollo x8p, and it also made a great companion to the similarly ADAT-equipped Focusrite Red 8Line interface (review coming soon). My MacBook Pro is equipped with the Audinate Dante Virtual soundcard, so it was also easy to add the ISA 828 MkII to my Dante network for the remote recording and live streaming that I do weekly for my church. Note, you can also use Focusrite RedNet Control. I also often like to track drums and piano in the sanctuary, and using Dante makes light work of the task and offers a significant preamp upgrade over the Dante-equipped digital consoles in the building.

As an added bonus, when you purchase an ISA 828 MKII you also get a free copy of the  Brainworx BX_Console Focusrite plugin (review coming soon).

Wrap-up

The ISA 110 preamp is already a classic, and having eight of them at your disposal is an excellent option for any source and style of music. Adding the ISA ADN8 with its new Dante connectivity makes the ISA 828 MkII more versatile, full-featured and future proof, for both studio and stage.

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