Locomotive Audio MODEL 40AM-2 – 2-Channel Stereo Octal Tube Preamp
$4,398.00
Two-channel stereo octal tube preamp that delivers the big, heavy sound of 1940s American classics. Inspired by legendary designs like the RCA BA-11A and Gates SA-70, the Locomotive Audio MODEL 40AM-2Â offers thick, compressed tones with endless tonal shaping via input windings, a 5-position Response switch, and level controls. Whether tracking vocals, instruments, or re-amping mixes, the 40AM-2 infuses warmth, weight, and character into any source.
Locomotive Audio MODEL 40AM-2 – 2-Channel Stereo Octal Tube Preamp
OVERVIEW
Two Channels of Heavy 1940s American Tube Gain for Big, Thick, and Compressed Sound
The Locomotive Audio MODEL 40AM-2 brings the unmistakable sound of vintage 1940s tube gear into a powerful dual-channel design. Inspired by the RCA BA-11A and Gates SA-70, this stereo preamp delivers a thick, weighty, and harmonically rich character that has become a favorite for engineers chasing depth and warmth. With its dual 6SJ7 tubes per channel and in-house wound transformers, the 40AM-2 provides up to 52 dB of gain and a beautifully compressed response that enhances everything from vocals to drums.
The 40AM Experience
Beyond its vintage roots, the 40AM-2 offers modern flexibility. Its 5-position Input and Response switches, level controls, and selectable mic, line, and DI inputs allow you to sculpt tones ranging from subtle coloration to driven grit. Features like a 20 dB pad, 85 Hz low cut filter, phantom power, and dual LED metering per channel make it a versatile studio workhorse. Hand-built in the USA and backed by a lifetime warranty (excluding tubes), the 40AM-2 is a must-have preamp for those seeking both heritage tone and contemporary control.
Countless Tone Options – Set the Sound You Want
INPUT KNOB:
The 40AM features a versatile 5-position Input Switch, allowing users to select their preferred input transformer winding configuration in both MIC and LINE modes. This influences the frequency response and the signal level sent to the first 6SJ7 tube. Both the (500Ω) MIC INPUT and (LOW) LINE INPUT configurations provide approximately 4.5 dB of additional gain.
RESPONSE KNOB:
A 5-position Response Switch gives you complete control over the frequency response and harmonic footprint of any material processed through the 40AM. Position 5 enhances high and low frequencies, delivering a rich sound while minimizing distortion. Conversely, position 1 softens the highs and attenuates the lows, emphasizing the mid-range and adding subtle harmonic character. For the most neutral sound, we suggest position 4 as a starting point. The Response switch allows you to tailor the sound to your taste.
LEVEL KNOB:
The Level knob provides users with the flexibility to make precise signal level adjustments. It’s important to note that it interacts slightly with the response knob based on its setting. As the signal is attenuated, users may notice a subtle darkening of the sound. However, by working in tandem with the response knob, adjustments can be made to compensate for any changes in tone.
40AM InspirationÂ
Combining vintage circuits requires time and patience to achieve the perfect balance. However, when executed correctly, you can harness the strengths of each to create an exceptional hybrid. The RCA BA-11A pentode input paired with its triode output and the feedback structure of the Gates SA-70 come together to produce the rich, compressed sound of the 40AM, beautifully complementing its 86B and WT-72 siblings.
Unlock Your Creativity
Finding the right piece of gear to give your sound that “special something” might be one of the hardest parts of engineering. In our opinion, having an exciting combination of tools at your fingertips is the best way to get your creative juices flowing. The 40AM-2 will help to unlock your audio engineering mind and allow you to focus on creating truly impressive audio.
KEY HIGHLIGHTS
TRANSFORMERS:
Premium MuMetal shielded inputs and nickel & steel outputs are wound in-house!
TUBES:
Two octal 6SJ7 tubes (one used as a pentode & one strapped as a triode) amplify the signal with 52 dB of max gain.
RESPONSE KNOB:
A 5-position rotary switch allows the user to tailor the overall tonal balance for any given source.
LEVEL KNOB:
A level knob provides users with the flexibility to make precise signal level adjustments.
LINE MODE:
Dedicated XLR input connectors for sending audio ‘out-of-the-box’ without fear of phantom power being applied.
DUAL OUTPUT LEVEL LED:
A 3-colour LED indicator per channel shows signal level – Green -> Yellow -> Red
FEATURES
- Microphone, Line & high impedance instrument inputs
- Two 6SJ7 per channel
- 5-Position Input Switch:
- 500 Ω Mic
- 1.8K Ω Mic
- 20k Ω Line – Low Input transformer windings
- 20k Ω Line – High Input transformer windings
- DI 1.6meg Ω
- Polarity reverse switch
- 20 dB pad switch
- 85 Hz low-cut filter switch
- DI on for each channel
- +48 V phantom power​
- XLR mic input, line input, and line output connections
- Premium input and output transformers (wound in-house)
- Wima polypropylene capacitors in the signal path
- Built in the USA
- Heavy 16-gauge steel chassis
- 115 V/230 V AC mains option on rear
- Backed by lifetime warranty parts and labor – excluding tubes
TECHNICAL SPECS
Microphone Input Load Impedance: 500 Ω or 1.8k Ω
Line Input Load Impedance: 20k Ω
Output Impedance: 600 Ω
1/4″ DI Impedance: 1.6meg Ω
Dual Output Level LED Colour:
- Greater than -10 dBu = Green
- Greater than +10 dBu = Orange
- Greater than +18 dBu = Red
52 dB Gain Max (150 ohm source)
Frequency Response: Variable depending on setting
Maximum 20 Hz & 1 kHz Input Level for 1% THD: -18 dBu (+2 dBu with Pad)
Maximum Output Level: +24 dBu
THD+N: < 1%
S/N Ratio: > 70dB
Power Consumption (120/240VAC): 25 watts
Dimensions (2U Rackspace):
- Width — 19″
- Height — 3.5″
- Depth — 10″
Shipping Weight: 18 lbs.
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