Dual Channel Multi-tap Input Transformer Coupled Discrete Mic Preamp


Using the MPA681 preamp is a treat for both the engineer and the artist! It gives me the ability to dial in my own sound by balancing my choice of the clean sounding discrete JFET input with the fullness of the Class A Output. I don't have to use an EQ to "correct" the sound of my preamp anymore - it already sounds good! More importantly, it also gives the artist a chance to be excited about their vocal sound again!

Matt Leatherman at Rodney Mills Masterhouse

The pre is really nice. It sounds great. Compared to the 1272, it is clearer on the bottom with a quicker top. The 1272 is beefier on the bottom. I multed mics through both on several things and let the artist pick what worked for their instrument. On bass, a punk-rocker playing through a loud SVT chose yours for it's clearer bottom, and the way the amp distortion cut through. For a round toned whole note bass, the 1272 was the pick. With a guitarist, he picked yours for one track and the Neve for another one, based on the way the instrument was sitting in the track. Neither artist had any idea what I was asking them to compare. I have also used it on some drum room mics, where it also performed well. The engineers in the studio commented positively on two features - the multiple impedence options (a brilliant idea), and the DI thru.

David Barbe at Chase Park Transduction


  • User Selectable Input Impedance Available to Shape Audio Tones
  • Direct Input with Loop-Through for Full Direct Box Capability
  • Extended Frequency Response
  • Ultra-Linear Phase Response
  • 100% Discrete JFET Input/Class A Output Amp Design
  • Transformer Coupled Input / Output Using Jensen, Sowter and Other Options
  • Good EMI Shielding

The Ingram Engineering MPA681 provides two channels of semiconductor based amplification of microphone and instrument signals.

The pre-amp uses input and output transformer coupling for high CMRR, best noise performance and tonal character. Input / output Transformer coupling is accomplished via combinations including Jensen and Sowter transformers, among others. The input transformer is a multi-tap variety in order to provide optimum noise matching over a wide range of mic impedances and mic output noise. The multi-tap transformer input also enables mics to be loaded with different impedances by simply changing a front panel switch. The input impedance range is best suited for passive mics and active mics that operate into low to low-medium load impedances. The MPA681 is designed to provide the input transformer with constant impedance load, independent of pre-amp gain and / or attenuation settings, therefore guaranteeing excellent transient response and optimum noise matching.

Amplification is provided by an all-discrete JFET input / Class-A Output circuit. Rather than using a 20dB input pad, a combined variable-attenuator / gain stepped switch control by Goldpoint provides the ability, unique among most pre-amp designs, of optimizing signal to noise and dynamic range for any audio signal level and any pre-amp setting. A balanced, buffered output stage isolates the gain stages from cable effects.

Full Direct Box capability is provided via an unbalanced JFET buffered instrument direct input. A front panel DI loopthrough is provided for simultaneously recording and routing the signal to a speaker cabinet or processing equipment.

A regulated +48V power supply provides reliable power for phantom power mics. Clip detector circuit LED indicates positive or negative audio peaks over the full audio spectrum.

Top quality electronic components include long life Panasonic HE Series and Nichicon Fine Gold Electrolytic Capacitors, polypropylene and metallized polyester non-electrolytic capacitors, low noise 1% Vishay/Dale RN55/RN60 Resistors, stepped switch by Goldpoint for recalling exact pre-amp settings, and continuously variable output level control using long life ETI noiseless level control pots with high rotational life expectancy.

Key Specifications

Input transformer options provide the following mic impedance loads:

  • 60 Ohm
  • 200 Ohm
  • 600 Ohm

Max Gain, Mic Input, Mic Output Impedance = 150 Ohms:

  • 60 Ohm Switch Position: 71 dB
  • 200 Ohm Switch Position: 65 dB
  • 600 Ohm Switch Poisition: 60 dB

Max Gain, Direct Input: 56 dB

Frequency Response, ±0.25 dB, with Gain Setting = 0:

  • 60 Ohm Switch Position: 30 Hz to >45 kHz
  • 200 Ohm Switch Position: 30 Hz to >60 kHz
  • 600 Ohm Switch Position: 30 Hz to >85 kHz
  • Direct Input: <10 Hz to>100 kHz

High Pass Filter -3 dB Cutoff Frequencies:

  • 70 Hz
  • 140 kHz

>+24 dBu into 100k Ohms at 0.05% THD, >+21 dBu into 600 Ohms at 0.05% THD

THD = 0.008 % at +4dBu, 100k Ohm Load

Dynamic Range = 125 dB