API Audio 3124MB+ 4-Channel Mic Preamp/Mixer  From API

4 Channel Mic Preamp built around API's legendary sound with a built in mixer

API Audio

What We Think

Like the 3124+, this preamp remains to be a favorite among rock engineers and as a preamp for drums kits and percussion. It's classic, unforgettable API-famed sonic texture keeps clients coming back to it. The 3124+ is particularly noted by it's compact 1 rack size, and affordable price. The MB+ version adds a very useful and very high quality 4 x 2 mixer with individual channel pan pan and gain control.

API Audio 3124+ 4-Channel Microphone Preamp - Quick n’ Dirty

  The API 3124+ is a high quality, compact, 4-channel mic preamp. Top quality, military grade build and a distinct, aggressive sound that, when the situation calls for it, is nothing short of amazing. For hard rock or metal engineers, it’s pretty safe to say your preamp arsenal isn’t complete without at least 4 channels to cover your drums, guitars, and bass. This preamp is available for SoundPure’s Try-Before-You-Buy Program, so if you want to hear how it sounds in your studio with your gear, shoot us an email at ProAudio@SoundPure.com, or give us a call anytime at 919.682.5552. Thanks for watching!

Manufacturer's Description from API

Both the 3124+ and the 3124mb+ are designed with the professional engineer in mind, giving the highest possible quality 4 channel mic preamp and with the 3124mb+, an audio mixer with a transformer balanced output.that keeps the size and price at a reasonable level. Both models are equally at home in the control room, the studio, and news or recording truck, at the house console, on the stage, or at the artist's disposal for the source of his music.

The model 3124mb+ utilizes the same microphone preamp circuit that is used in all API consoles. It uses the RE-115 K mic input transformer and the same output transformer that is used in all API equalizers. All four mic inputs of the 3124mb+ are powered by an internal 48 volt phantom power supply, front panel switchable for each channel. Also provided is a front panel 20 dB pad switch that effects both the Mic and Line in.

The model 3124mb+ can provide up to 65 dB of gain to an output clip level of +30 dBm. The Hi-Z front panel input goes directly to the op-amp, allowing a low level input such as a guitar or bass to be amplified without a matching transformer or direct box. This Hi-Z input can accept input levels as high as +22, making it perfect for keyboards and other high level devices. The rear output is an XLR connector.

The model 3124mb+ is a 3124+ with the addition of a complete stereo mixer, plus a transformer balanced out. In conjunction with the gain control of the 3124+, the 3124mb+ adds a stereo panner with a level control, and a post "fader" aux send. The stereo panners and the aux sends are bussed to master output controls and then to the rear panel jacks. A stereo AUX return is provided to return effects or cascade additional mixers for more inputs. The unique aux return pot acts like a panner to balance the left/right signal, yet staying stereo. It can also be used as a mono return.


  • Uses API 2520 Op-Amp
  • Classic Console Circuit
  • Four XLR Mic Inputs
  • Four 1/4" Un-Balanced Inputs
  • Front Panel Polarity Switch
  • Front Panel 20 dB PadSwitch
  • Front Panel Mic/Line Switch
  • Front Panel 48V Power Switch
  • Output Clips at +30 dBm
API Audio

About Manufacturer

API (Automated Processes, Inc.) is world famous for its all-discrete audio products: studio and broadcast mixing consoles, and a full line of rack mount mic preamps, equalizers and processors. It all began with a dream. It was 1968. The company: Automated Processes Inc., formed by men with a vision. Best known for their now legendary "2520 amplifier", this unique amp has been and will continue to be the heart of all API discrete products. It continues to provide reliability and sonic purity unmatched by the competition. The resulting console met the needs of the music, commercial and broadcast industry. API became the leading audio broadcast console manufacturer for radio and television networks and high profile stations. In addition, recording studios, large and small, began using API.....and receiving rave reviews from engineers and producers. There are over 700 API consoles across the nation and around the world, including the three major networks. Over thirty years later, many of these consoles are still in daily use in some of the most prestigious recording and broadcast facilities in the world because, to date, there are few, if any consoles of equal sound quality at a cost-effective price.



Input Impedance:

1500 Ohms Mic, 470 K Ohms Un-Balanced, HI-Z in

Output Impedance:

Less than 75 Ohms Channel Outputs

Nominal Levels:

XLR Channel Output +4 dBu

Stereo Output Level:

Unbalanced: nominal -2

Balanced: +4

Clipping Level:

XLR Channel Output better than +28 dBm

Frequency Response:

+0, -5, 10 Hz to 20 kHz (-.5 at 10 Hz)

Noise EIN:

-129 Mic, -125 Un-Bal. Actual

Measured Noise:

Better than -91 dBm / below Nominal +4.


All Outputs at +4 out, .03%, at +22, .09% Max

Gain Range:

150 Ohms Input 10 dB Min., 65 dB Max (inc. PAD).

Un-Bal. Input 14 dB Min., 50 dB Max

VU Meter:

Calibrated for XLR Outputs, OVU=+4 dBu,

(-12, -6, -3, 0, +3, +6, +18)


GAIN, PAD (20 dB), 48Volts, POL (polarity),

MIC (mic/un-ba;), VU, AC

Power Consumption, Quiescent:

.66 Watts


19" X 1.75" (1U) X 10.5" Deep

Size (Boxed for Shipping):

23.25" X 6.5" X 16"

Actual Weight:

11.54 lbs.

Shipping Weight:

15.3 lbs.