Focusrite ISA One Analogue Microphone Preamp

Give that microphone (and DI guitar or bass) tons of clean, transparent gain with this preamp, then add subtle character with its variable input impedance.

Craft a rich, colorful gain stage with the Focusrite ISA One analog microphone preamp. This preamp/DI will amaze you in the recording studio with its tone-shaping capabilities and versatility! Designed for portability, the ISA One is ruggedly built with a carrying handle right on top.

A Tribute to a Great Vintage Microphone Preamp

The Focusrite ISA One is based on the vintage ISA 110 module microphone preamplifier. It features the same circuitry and componentry as that legendary and celebrated unit, including the Lundahl L1538 transformer and bespoke zobel network. These were the preamps that made Focusrite a household name, and they have been lovingly recreated for this excellent-sounding pre. It is unquestionably a product reflecting many years of continued innovation.

The Nicest DI Box in the Room

Live or in the studio, the ISA One works as a fantastic direct input box when you want to run a high-impedance, line level, unbalanced output signal to a low-impedance microphone-level balanced input. As a DI, it delivers a great, noise-free sound. The DI channel is independent from the mic pre, and utilizes its own dedicated gain control.

Exceptional for Dual-Signal Application

Focusrite developed this innovative design to accommodate guitars or basses running via a DI while miking the amp cabinet simultaneously. The ISA One also serves well as a great single solution for musicians looking to run a direct guitar and vocals through the same preamplifier. read more

Versatile and Intuitive I/O

The Focusrite ISA One preamp has a single XLR and TRS line input. There is a switch for Active or Passive impedance to allow different signal sources to be routed quickly. A single TRS jack output is provided for routing to other amps. There is also an independent XLR output on the rear. The headphone output has a dedicated volume control.

Extensive Features for Tonal Crafting

The ISA One's variable impedance design allows you to switch between four different input impedance settings for more tonal variety. There is even an additional Insert Point where extra processors or FX can be introduced in between the preamp and the DI. Phase Reverse and a 75 Hz, 18 dB/octave high-pass filter round out the tonal shaping capabilities. The ISA One preamp also delivers phantom power.

A moving-coil VU meter with variable calibration gives you clear input metering for both channels. Helpfully, the meter calibrations utilize all the same reference points as Pro Tools, allowing your digital meters to sync perfectly to your analog meters.


- Variable impedance design with four switchable input impedance settings
- 1 x XLR and 1 x TRS instrument input
- 1 x TRS External ADC input
- 1 x TRS Return
- 1 x TRS Jack Send
- 1 x Balanced XLR Line Output
- 1 x XLR DI output
- 1 x TS Jack DI through
- 1 x headphone jack with independent volume
- 75 Hz high-pass filter
- Moving coil VU meter can be calibrated
WARNING: Cancer and Reproductive Harm -
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Mic Input Response
- Gain range = 0dB to 60dB in 10dB steps + 20 dB of variable gain
- Input Impedance, variable as follows (Switched Impedance setting Equivalent Input Impedance at 1kHz):
- Low = 600 Ohms
- ISA110 = 1400 Ohms
- Med = 2400 Ohms
- High = 6800 Ohms
- EIN (equivalent input noise) = -126dB measured at 60dB of gain with 150 Ohm terminating impedance and 22Hz/22kHz band-pass filter
- Noise at main output with gain at unity (0dB) = -97dBu measured with a 22Hz/22kHz band-pass filter
- Signal to noise ratio relative to max headroom (9dBu) = 106dB
- THD at medium gain (30dB) = 0.0009% measured with a 1kHz -20dBu input signal and with a 22Hz/22kHz band-pass filter
- Frequency response at minimum gain (0dB) = -0.5dB down at 10Hz and -3dB down at 125kHz
- Frequency response at maximum gain (60dB) = -3dB down at 16Hz and -3dB down 118kHz
- CMRR=98dB (Channel 1, 1kHz, maximum gain with +24 dBu input)
- Crosstalk Channel to Channel: with 10dB@1kHz input to chA, chB output =104dBrA. With 10dB@10kHz input to chA, chB output = 84dBrA

Line Input Response
- Gain range = -20dB to +10dB in 10dB steps + 20 dB of variable gain
- Input Impedance = 10kOhm from 10Hz to 200kHz
- Noise at main output with gain at unity (0dB) = -96dBu measured with a 22Hz/22kHz band-pass 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 band-pass filter
- Frequency Response at unity gain (0dB) = -0.3dB down at 10Hz and -3dB down at 200kHz

Instrument Input Response
- Gain range = 10dB to 40dB continuously variable
- Input Impedance:
- High = greater than1MOhm
- Low =greater than 300kOhm
- Noise at minimum gain (+10dB) = -92dBu measured with a 22Hz/22kHz band-pass filter
- Noise at maximum gain (+40dB) = -62dBu measured with a 22Hz/22kHz band-pass filter
- THD at minimum gain (+10dB) = 0.001% measured with a 10dBu input signal and with a 22Hz/22kHz band-pass filter
- Frequency Response at 10dB gain with -10dB input = 10Hz-100kHz +/- 0.6dB
- Frequency Response at 40dB gain with -40dB input = -2.5dB down at 10Hz and 0dB at 100kHz

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

- Moving coil (MC) meter is factory calibrated to 0VU = +4dBu with 1kHz sinewave. With the VU Cal button pressed the meter can be adjusted on the rear panel to allow 0VU to equal +10dBu to +26dBu with the centre detent being equal to +22dBu.

- Peak LED meters calibrated in the detent position for 0dBFS = +22dBu, calibration is adjustable on the rear panel to allow 0dBFS to equal +10dBu to +26dBu

- Routing for MC and Peak1 meter is after the HPF, pre insert send or switched post insert return. Peak2 is always pre ADC channel 2, which can be fed by external input or Instrument input.

- LED levels are as follows when peak calibration is set to center detent on the rear panel. (This is when using the internal ADC).

0 = +22dBu
-2 = +20dBu
-6 = +16dBu
-12 = +10dBu
-18 = +4dBu
-42 = -20dBu

Front and Rear Connectivity

Analogue Channel Inputs:
- Mic input: XLR x 1
- Line input: XLR x 1 and TRS x1
- Instrument input TRS Jack: XLR x 1
- External ADC input: TRS Jack x 1
- Return: TRS Jack x 1

Analogue Channel Outputs:
- Send: TRS Jack x 1
- Balanced line output: XLR x 1
- DI output: XLR x 1
- DI through: TS Jack x 1

Analogue Channel Additional I/O:
- Cue mix left input: TRS Jack x 1
- Cue mix right input: TRS Jack x 1
- Headphones output: 1/4 in. TRS Jack x 1

Case NOT Included.

Weight: 3.9kg, 8.6 lbs
Dimensions and Weight in Packaging
Base Item
Shipping Weight: 13 lbs
Shipping Dimensions: 16 x 16 x 10 in
Manufacturer Part Number (MPN): AMS-ISA-ONE
Warehouse Resealed
Shipping Weight: 13 lbs
Shipping Dimensions: 16 x 16 x 10 in
Manufacturer Part Number (MPN): AMS-ISA-ONE

For support or warranty questions, please contact the manufacturer:
Phone: 310-322-5500

Focusrite ISA One Microphone Preamp

Featuring a rugged, portable all-metal enclosure, the ISA One combines the classic Focusrite microphone preamp with a flexible, independent DI channel and optional 192kHz precision A/D conversion.

Back in the mid-1980s, Sir George Martin commissioned console design legend Rupert Neve to build a series of new, 'no compromise' console modules for AIR studios. They were an enormous hit and formed the basis of the Focusrite Studio Console, widely regarded as the best-sounding analogue recording console of all time. Today, the descendants of those modules are used in leading studios around the world, and their sought-after Focusrite Heritage Sound lies behind hundreds of hit records. Today's ISA Range from Focusrite puts the classic sound of Focusrite into your own studio or live performance.

At the heart of the ISA range is the microphone preamplifier with its Lundahl input transformer -- essentially the same circuit, based on the original ISA110, that has been used for 30 years in successive Focusrite designs. The input transformer imparts a special character to the sound that can't be truly emulated in any other way: inseparable from the microphone itself, the transformer input stage is ideal for use with classic microphones. But this mic pre has a twist the original didn't have, which makes it far more versatile: four carefully-selected impedances allow you to match microphone to input in different ways. Bring out the character of a classic mic or emphasise a special feature, or go for a totally transparent, modern sound -- it's up to you.

Whether you're an artist, engineer or producer, you'll appreciate the versatility of the ISA One, with its front-panel DI input. The DI includes low/high impedance switching and an amplifier output, and its own feed to the optional A/D converter and separate rear-panel XLR output.


- ISA series transformer-based preamplifier: Encased in a rugged and portable chassis, ISA One offers the classic Focusrite microphone preamplifier in a highly cost-effective and flexible package.
- Flexible, independent DI channel: ISA One is ideal for both engineers and demanding performers alike, featuring independent gain control, an output for routing to an amp, an independent XLR output on the rear and routing to the optional A-D converter.
- Switchable impedance: Choose one of four carefully selected input impedances, including the original ISA110 setting, to suit any microphone.
- Headphone output with volume control: ISA One can feed either a sum of the two inputs to the headphones output, or an external stereo cue mix (such as a stereo feed from an interface) via two TRS jack inputs on the rear of the unit.
- Dedicated insert point: Allows you to place extra processing between the preamplifier or DI and the optional converter, such as an EQ or compressor.
- Optional stereo 192kHz A-D converter: You can choose to upgrade your unit with an optional digital card that delivers the best A-D performance in its class, with a dynamic range of 118dB.
- Lundahl LL1538 Input Transformer: The original mic transformer used in the original Red modules helps to provide the unique sound and performance of this groundbreaking design.
- Backlit VU meter with variable calibration: ISA One has a moving coil VU meter with variable calibration to suit analogue and digital recording media, alongside two six-LED peak meters; inputs can be metered either pre- or post-insert.

Reviewers gave this product an overall rating of 5 out of 5 stars. (16 ratings)
Submitted July 25, 2011 by a customer from

"The most versatile ore under $1000?"

Overall: 5 out of 5 stars
(see rating details)
Verified Customer zZounds has verified that this reviewer made a purchase from us.
Clean and clear but can add some warmth if pushed. Very versatile and the multi-impedance settings allow for a wide range of custom tailoring of your mics.
It has a very versatile preamp section and a separate and simultaneously usable DI section that includes re-amping capabilities. The variable impedance and extremely wide gain range make it a very usable and versatile pre amp that can make any mic sound really, really good.
Ease of Use
Easy as can be!
The knobs and buttons while requiring little force still manage to offer a distinct and positive feel and when the small buttons are pressed, they engage with a solid click.

Musical Background:

Recording Engineer, Semi-Pro Musician
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