Focusrite Red 1 500 Series Mic Pre

By Barry Rudolph

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Focusrite Red 1 500 Series Mic Pre

In a way the Focusrite Red 1 500 Series Mic Pre is the modern return of the microphone pre-amp design and sound used in the original Focusrite Red Range line of 2U processors. The Red 1 Quad Mic-Pre, Red 6 Mono Mic-Pre Equalizer, Red 7 Mono Mic-Pre & Dynamics and the Red 8 Dual Mic-Pre variants all used that same pre-amp circuit topology. The Red Range was first released in 1992 and then discontinued in 2010 but its lineage goes back to the mid 1980's with the Focusrite ISA 110 Mono Mic-Pre & Equalizer. The vertically mounted ISA 110 was Rupert Neve's design work product as a result of being commissioned to supply 16 extra inputs for a Neve console at AIR Studios.

Let's Get Vertical

The Red 1 500 Series module fits standard 'lunchbox' racks as a single space unit housed in an all-steel 'clam shell' style shielded enclosure. Internal construction is first class with surface mount components on thick circuit boards.

The Red 1 uses an internal steel frame to support three circuit boards: the main circuit board; a second board with a miniature backlit Nissei VU meter and 12-position Grayhill gold-plated military-grade rotary gain switch; and a third holds the ISA-style lighted polarity flip and phantom on/off push buttons. The three boards connect to each other using high-grade interconnecting cables (not ribbon) and sockets.

The gain control shaft is topped with a machined aluminum knob. The knob plus both switches and VU meter are recessed and seen through chamfered holes made in the red anodized aluminum front panel. This presentation stays true to form of the original Red Range rack units.

A Look Inside

There are two, three-terminal voltage regulators on the main board that down-regulate the 500 rack's +/- 16-volt rails and also filter out any possible high frequency switch mode noise that might come from the rack's power supply. The Red 1 500's nominal slot current drain is 150mA for the +16-volt rail and 90mA for the -16volt rail--well within VPR spec.

The microphone input and output transformers are big part of the sound of the original Focusrite Red mic pre-amp. Like the original's design, the Red 1 500 uses a shared gain structure with the Lundahl input transformer offering 14dB of gain, the Carnhill output transformer giving 6dB of gain and the active amplifier circuit producing the remaining 40dB.

A Zobel input network (specifically configured for the ISA design by Rupert Neve) and the identical dual-primary Lundahl LL1538 mic input transformer are used. The input impedance is 1,200 ohms.

The same Carnhill bifilar-wound toroidal output transformer is used--just made to fit the size-constraints of a single-slot 500 series module. With its leads directly soldered to the main circuit board, this large transformer (that looks more like a power supply transformer) is bolted to the steel enclosure's wall and dominates the interior of the Red 1 500 module.

The Red 1 500 has 12 fixed pre-amp gain settings in 6db steps from -6 to +60dB. There is no variable output level control or switchable high pass filter. On the rear of the module is a slide switch that pads the meter's 0VU = +4dB calibration by 6dB. When engaged, it minimizes excessive needle pinning with the up to +25.5 dBu output level possible.

 Focusrite 1980s 
The Red 1 500 uses 5532 and 5534 operational amplifiers and a discrete transistorized Class-AB amplifier drives the output transformer.

Rob Jenkins from Focusrite comments:

"The original design used 5532 and 5534 op amps. They were the state-of-the-art amplifiers back in 1980s when this preamp was first designed. There are faster more modern op amps today however they don't have the same sound so we stick with the originals as they are a part of the signature sound."

In the Studio

I plugged the Red 1 500 module into my six-slot, 500 6B API lunch box. I left the VU attenuator switch in the -6dB position for all tests. I used either Pro Tools 10 HD or 11 HDX, 24-bit/88.2kHz, and standard -18dBu (18 dB headroom) I/O reference set up on my Avid interface. I liked the mini VU as a sort of signal present indicator but a peak indicator LED would be helpful for spotting a problem from across the control room.

Kicks, Toms, Snares

For my first studio test, I used a mic splitter box with a Jensen JT-MB-E transformer inside to route a single drum mic to both the Red 1 and another mic pre-amp at the same time. My splitter presents the same 150-ohm source impedance to all connected pre-amps.

I started with a 22-inch DW kick drum with a hole in the front head. I placed a Shure Beta 52 in the hole aimed at the beater head. I compare the Red 1 500 set to 30dB of gain to my 'go to' mic pre-amp, a 2-channel RTZ Professional 9762 Dual-Combo--a high-end remake of the Class-A Neve 1272 microphone preamp. The RTZ was also set to 30dB. The Red 1 had a clear sound with good attack while the RTZ had less attack and was rounder and (by comparison) muddy sounding.

Later I replaced the B52 with an AKG D112 in exactly the same positioning and reduce pre-amp gain for both pre-amps for this higher output microphone. For the mid-tempo track, the AKG mic was a better choice for this particular kick drum. I got more subsonic energy and mid-range "cut" but again, it was a close call between the two, with the Red 1 offering a clarity that was missing from the RTZ. In this situation, my temptation was to clean up with EQ the RTZ's sound whereas the Red 1 was good to go.

Focusrite Red 1 500 Series Mic Pre With the same pre-amps and splitter, I used a Sennheiser MD 421-II close in to record rack and floor toms. In this case, there was no difference in the sound--either pre-amp sounded great. But the floor tom through the RTZ had less attack and was thicker while the Red 1 500 was a slightly thin. Gain was set to 25-30dB for both pre-amps.

For recording the drummer's Ludwig Black Beauty snare, I used the same splitter rig but switched from the RTZ over to the studio's API 1608 console mic-pre. I placed a Shure SM57 in my usual starting mic position--inches away and aimed directly at the center of the head.

The API 1608 mic pre was set at minimum gain and without the 20dB pad. It sounded fine although the console fader's position was down closer to the bottom of its range and a bit touchy to adjust and work with. Switching in the pad allowed for more fader travel and adjustability but didn't improve the sound.

To obtain the same recording level, I used 24-30dB of gain on the Red 1 and the sound was fat, full and noticeable thicker than the API. I found the 6dB stepped gain increments worked great to get any recording level. Later, I put a Neumann KM184 in the same position on the snare drum and it sounded like it should with the Red 1 dialed down to only 6dB of gain. The API pre required the pad and sounding somewhat compressed by comparison.

I found it a big plus to not use an attenuator pad and be able to dial mic gain on the Red 1 500 down to (essentially) line level to handle modern, high output condenser microphones placed closed to loud sound sources--like Audio-Technica's AT5040 Cardioid Condenser Microphone


Next was a male lead vocal recording session and I chose a Neumann M 149 condenser microphone set to cardioid. With the singer about a foot away from the pop screen, the high output of this mic only required about 18dB gain on the Red 1. For louder singing, I clicked one notch down to 12dB. Whatever gain was required, the sound was superb with good detail of my singer's voice, the affect of the room's sound, and his positioning in and around the mic--changes all easily heard.

For quieter vocals, I switched to 30dB of gain and found it convenient to quickly return to the lower gain setting if needed and at the same time maintain the same "ballpark" amount of compression from the following UA 1176LN Peak Limiter. I also found the 1176LN's 'grit' nicely complimented the generally smooth and clean tone of the Red 1 500 and M 149 combination.

Acoustic Guitar

Next I recorded an Alvarez AJ60S acoustic guitar with a Gauge Precision ECM-84 small diaphragm cardioid condenser without using the pad or roll-off. For rhythm strumming, 24dB of gain was all I needed when about six inches over the 12-fret or about 36dB when I pulled the mic back 2-feet from over the sound hole. Subtle changes in microphone positioning are easy to hear using this pre-amp and mic combination and I found the sound to be honest--realistic and lush sounding with excellent dynamic range--what I am used to--not overly bright or excessively boomy and Mix-ready.

Focusrite In The 500 Rack!

If you missed the Red Range Red 1 the first time around, the Red 1 500 with its high build quality, classy looks, and clarity of sound will be a great introduction to the Focusrite sound. For me it's a '80s flashback in a good way and I highly recommend it as a great addition to any 500 rack!

 Try This! 
An old trick is to connect line level sources to microphone pre-amps and purposefully distort with excessive gain. I fed a line level signal from my HD interface into an inline XLR -15dB T-pad and connected that to the input XLR on the Red 1 500 mic pre. I experimented with reducing the Red 1's output with another pad but found it was easier to put the Trim plug-in on the Aux input fader back in Pro Tools that received the pre's output signal. I would "juggle" pre-amp gain setting with the Trim plug-in fader and found this adds "hair" to drum loops, DI guitar and bass and also super clean guitar solos.

Barry Rudolph
 Barry Rudolph 
Barry Rudolph is a recording engineer/mixer who has worked on over 30 gold and platinum award-winning records. He has recorded and/or mixed Lynyrd Skynyrd, Hall & Oates, Pat Benatar, Rod Stewart, The Corrs, and more.

Barry has his own futuristic music mixing facility called Tones 4 $ Studios and also teaches audio engineering at: Musician's Institute, Hollywood, CA..

He is a lifetime Grammy-voting member of NARAS, the 'New Toys' columnist for LA's Music Connection Magazine, and a contributing editor for Mix Magazine.

 Focusrite Novation Inc 
Web Site:

Product: Focusrite Red 1 500 Series Mic Pre

Price: $999

Pros: Super clean gain, easily recallable, built like a Bentley GT Speed

Cons: Could use a peak LED.

Barry Rudolph is an L.A.-based recording engineer. Visit his Web site at: WWW.BARRYRUDOLPH.COM

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