The Focusrite ISA 428 Pre Pack offers four high-quality transformer-based preamps and the 8-channel MH-442 A/D converter in one device.

From the lineage of the Focusrite ISA 110 comes the ISA 428 Pre Pack, which combines four high-quality transformer-based preamps in one device. When fitted with the optional MH-442 A/D card, the ISA 428 can be used as an 8-channel front end for your DAW or digital recorder.


The front panel of the ISA 428 stays true to the ISA heritage; the blue and gray panel is adorned with yellow knobs and red buttons and LEDs (see Fig. 1). What look like four oversize VU meters are actually peak meters in disguise, complete with LEDs that indicate channel overload. Beside each meter are buttons for +48V phantom power, phase reverse, and activating the send and return for each of the four preamp channels.

Below each meter are three knobs. The first knob sets the base gain amount in four 10 dB steps. The second knob is a continuously variable control that offers 20 dB of gain to the mic and line inputs and 30 dB of gain to the channel's instrument input. All four instrument inputs are located at the far left of the front panel, which keeps the cables conveniently out of the way when you're reaching for the controls.

One of my favorite features on any preamp is a variable low-cut filter, and the ISA 428 has one. The highpass filter ranges from 16 and 420 Hz, allowing you to block only subsonic frequencies or to drastically alter a source's sound. Given the 18 dB-per-octave rolloff of this filter, setting it anywhere above its middle range will thin the sound out considerably. My only gripe about the filter is a small one: only two landmarks are given between the extremes, and somewhat odd ones at that — 34 and 210 Hz. It would be nice to have a few more frequencies indicated.

Below the knobs are buttons for selecting the input source — Mic, Line, or Inst — and input impedance — Low, ISA 110, Med, or High (more on this in a moment). The rest of the front panel is dedicated to controls and meters for the A/D card: there's a Soft Limiter button; a Clock Select button, which determines a sampling frequency of 44.1 through 192 kHz; a Bit Depth Select button for choosing a 16-, 20-, or 24-bit word length (with dither added to the 16- and 20-bit output); and an Ext sync button for clocking the device from word clock or Superclock, using the rear-panel BNC jack. The Lock LED illuminates when the ISA 428 detects the clock input.

On the far right of the faceplate are eight 6-segment LED meters that indicate output levels — either analog only or analog and digital if the A/D card is installed. In digital mode, the meters are postlimiter and reflect the reduced level if the limiter is engaged and active. There are eight output meters instead of four because the MH-442 is an 8-channel converter. To take full advantage of this, the ISA 428 comes with four additional rear-panel line inputs that provide access to the extra channels, greatly increasing this product's value.

The rear panel features four mic inputs on XLR jacks, four balanced line inputs on TRS jacks, four analog outputs on XLR jacks, and individual balanced ¼-inch send and receive jacks for each channel (see Fig. 2). The A/D card has two BNC connectors for sync, two ADAT Lightpipe ports, and two 9-pin D-type connectors. Two ADAT ports are needed because at 88.2 and 96 kHz each port carries four of the available channels. At lower sampling frequencies, all eight channels appear at each port.


I first used the ISA 428 for a concert recording of a jazz trio. I used a pair of Neumann KM 184s for the drum overheads, and I sent the signal from the AES/EBU output to my Metric Halo Mobile I/O 2882 and into MOTU Digital Performer 4. The sound was clean, clear, and very detailed — as good as any drum sound I've recorded in that acoustically challenged room.

Back in the studio, I tried the ISA 428 on more drums, recording direct to 2-inch analog tape using an EV RE20 on the kick, a Shure SM57 on the snare, and a pair of Oktava MK012s on the cymbals. The results were excellent, with a sound that was thoroughly punchy and crisp.

One of the most impressive features of the ISA 428 is the switchable input impedance. The amount of impedance a mic signal sees at the preamp input plays an enormous role in the tonal characteristics of the amplified signal. The ISA 428's manual states that the “best” input impedance for a given mic is around ten times the mic's output impedance. This would lead you to expect a different impedance setting for each type of mic you use.

However, when I used three of my favorite mics, which have a variety of output impedance ratings — the Blue Dragonfly Deluxe is rated at 50ž, the RCA 77DX ribbon mic at 300ž, and the Schoeps 221B tube mic at 200ž — I ended up choosing the Low (600ž) impedance setting on the preamp. The same goes for the drum tracks noted earlier. To my ears, the Low setting sounded the smoothest in all but one case: when using the SM57 (rated at 150ž) on the snare drum, I used the High setting because it offered just the right amount of crispness to really make the drum stand out with a snap.

ISA 428 Pre Pack Specifications Analog Audio Inputs(4) XLR; (4) ¼" TRS; (4) ¼" TSAnalog Audio Outputs(4) XLRAdditional Analog Ports(4) ¼" TRS insert sends; (4) ¼" TRS insert returns;
(4) XLR A/D inputs (functional only with MH-442 card)Digital Ports (MH-442)(2) BNC word-clock I/O; (2) ADAT Lightpipe outputs;
(1) AES and S/PDIF 9-pin D-Sub output;
(1) AES-only 9-pin D-Sub outputBit Depths16, 20, or 24Sampling Rates44.1, 48, 88.2, 96, 176.4, or 192 kHzGain Rangeline input ±18 dB; mic input 60 dB;
instrument input 30 dBInput Impedanceline input 10 kž; mic input 600ž, 2.4 kž, 6.8 kž, and ISA 110 setting (variable); instrument input 1 MžSignal-to-Noise Ratio120 dBATotal Harmonic Distortion0.003% with 0 dBu, 1 kHz inputNoise Performanceline input -96 dB; mic input -128 dB
(EIN with 150ž input resistance at 60 dB of gain)Dimensions2U × 10" (D)Weight15.76 lb.


Next up was a session with woodwind specialist Aaron Bennett playing piccolo. Typically, I would use the Focusrite Green 1 Dual Mic-Pre because it ably captures the transparency and breathiness of wind instruments. Using the Blue, RCA, and Schoeps mics, I compared the ISA 428 with my Green 1. The difference between the two preamps was most noticeable with the ribbon mic: the ISA 428 brought out much more of the clarity and detail of the RCA than the Green 1, which by comparison sounded muddy and somewhat flat and two-dimensional. The differences between preamps were less obvious with the Blue and Schoeps mics, though the ISA 428 seemed a little crisper and cleaner, but at the same time more mellow with the shrill highest notes of the piccolo.

I also recorded Bennett playing baritone saxophone through the same setup. Whereas the Blue and Schoeps mics gave me a slightly richer sound through the ISA 428 than through the Green 1, the RCA really let me hear the differences between the two preamps. The ISA 428 offered a greater clarity in tone, especially on the rich harmonics produced by the low reed instrument. Multiphonics are one of Bennett's specialties, and the ISA 428 captured every nuance and complexity present in his tone.

I tested the ISA 428 further by comparing it with the Universal Audio 6176 and a Focusrite Platinum VoiceMaster. This time, the test subject was electric bass, both miked through an amp using an AKG 414 EB and running direct into the instrument input on the front of each of the preamps. I expected the preamps' tones to be drastically different, because the 6176's preamp is tube based and the VoiceMaster is part of Focusrite's lower tier of products. I was right — the ISA 428 had a tighter, less floppy low end than the 6176, and the high-mids were much smoother and almost sounded compressed. In addition, I was able to drive the ISA 428's gain much higher without the sound breaking up. The VoiceMaster held its own remarkably well, but the ISA 428 sounded cleaner in the low end and had a bit more shimmer. The ISA 428 gave me one of the best direct-bass sounds I have ever recorded, and I am usually not a huge fan of recording the bass direct.


I also compared the ISA 428's converters by sending its digital and analog outputs simultaneously into my Digidesign Digi 001's inputs and my Metric Halo Mobile I/O's AES/EBU input. The differences were subtle, because all three of these devices have above-average A/D converters. I was particularly impressed with how good the ISA 428 sounded next to the Mobile I/O, because Metric Halo's converters are widely heralded as some of the best available.

However, I was slightly less impressed with the ISA 428's Soft Limiter. Focusrite states that the Soft Limiter's opto circuit is a new design that should prevent digital overs entirely and minimize the “undesirable” distortion that standard limiter circuits generate. During my tests, digital overs did get through when I slammed the converters with a hot signal, and there was certainly undesirable distortion, though admittedly less than would have occurred without the limiter engaged. Although the limiting was hardly noticeable at normal-to-high operating levels, I did hear it pumping and popping when pushed to extremes. When engaged, it also seemed to drop the digital output level and negatively affect the tone somewhat. As a result, I would engage the Soft Limiter only when dealing with unpredictable sources that were prone to extreme transient peaks.


The ISA 428 Pre Pack is a versatile multipurpose preamp that sounds excellent and offers plenty of control of its very flexible tonal characteristics. Coupled with the optional MH-442 converter card, the ISA 428 serves as an easy, no-compromise way of adding eight inputs to a digital-recording rig.

At $500 a channel, the ISA 428 isn't the least expensive mic preamp you'll find. Nonetheless, Focusrite has lived up to its reputation for making quality gear, and it has done so at a competitive price point.

Eli Crewsco-owns and operates New, Improved Recording in Oakland, California. Read all about him or drop him a line



ISA 428 Pre Pack
mic preamp
MH-442 A/D converter $695


PROS: Clean sound. Sounds great on a variety of sound sources. Variable highpass filters. Switchable impedance on mic inputs. Inserts are bypassable using front-panel switches. Dithers to 20 and 16 bits. A/D card converts eight channels of audio. A/D card has a variety of digital output options.

CONS: A/D card gets very hot.


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