MPA685 Microphone Preamplifier


Dual Channel Variable Input Impedance Transformer Coupled Discrete Mic Pre, Direct Box & Re-Amplifier


Click here to access a library of audio samples recorded using the MPA685
All samples may be streamed or downloaded



MPA685 Reviews


Royer Ribbon Microphones"Recently we had the opportunity to audition the Ingram MPA 685 microphone preamplifier in our lab. We were impressed with the build quality and features of the MPA 685 and were further impressed with its performance. The preamplifier has ample gain required for passive ribbon microphones and a proper phantom supply for active ribbon microphones such as the R-122. A switchable impedance switch allows for correct matching for passive ribbon models and we found the MPA 685 to be quiet and transparent. Owners of Royer or any other ribbon microphones should find the MPA 685 to be a very good marriage."

Rick Perrotta
President / Royer Labs



  • User Selectable Input Impedance Available to Shape Audio Tones
  • Transformer Coupled Input / Output Using Custom Sowter and Jensen
  • 100% Discrete JFET Input/Class A Output 2-Stage Amp Design
  • Low Noise and High Headroom for Wide Dynamic Range
  • Extended Frequency Response with Ultra-Linear Phase Response
  • Excellent Pulse Response for Smooth Tones
  • Direct Input with Loop-Through
  • Full Direct Box Capability
  • Re-Amping Capability
  • Excellent Gain Matching Between Channels
  • Combined Input Attenuator / Gain Adjustment via Goldpoint 24-Position Stepped Switch for Optimal Noise Performance and Dynamic Range (No Input 20dB Pad)
  • Buffered Output for Optimum Load Isolation and Current Drive Capability
  • Variable Output Level Control Using Long Life Noiseless Level Control Pot
  • 2nd Order High Pass Filter, Switchable Between 70 Hz and 140 Hz
  • Overload Indicator Accurately Detects Distortion to Ultrasonic Frequencies
  • Internal Power Supply with Regulated +48V phantom power
  • 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


The Ingram Engineering MPA685 provides two channels of 100% discrete semiconductor based amplification of microphone and instrument signals. Input impedance is selectable via a front panel three-position switch. Each pre-amp is configured at the factory for one of two input impedance range options, specified when ordering: Range 1 is best suited for passive mics and active mics that operate into low to low-medium load impedances; range 2 is best suited for condenser or ribbon mics whose circuits require a high impedance load for best operation.


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 custom Sowter transformers, among others. The MPA685 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 a 2-stage 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.  The MPA685 can also be used for re-amping recorded tracks. 


Extremely tight gain matching between channels, along with the transformer usage and discrete circuit design, also makes the MPA685 an excellent choice for stereo make-up gain applications.


High voltage rails enable excellent headroom and provide high output level.  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:
  •   Range Option 1 Range Option 2
    • Lo:  60 Ohm
    • Med:  200 Ohm
    • Hi:  600 Ohm
    • Lo: 600 Ohm
    • Med: 1.5k Ohm
    • Hi: 2.5k Ohm
  • Max Gain, Mic Input:
  •   Range Option 1 Range Option 2
    • Lo: 79 dB
    • Med: 73.5 dB
    • Hi: 67.5 dB
    • Lo: 70 dB
    • Med: 75 dB
    • Hi: 76 dB
  • Max Gain, Direct Input: 69 dB
  • Frequency Response, Mic Input, ±3 dB, Gain Setting = 0:
  •   Range Option 1 Range Option 2
    • Lo: 10 Hz to >100 kHz
    • Med: 10 Hz to >100 kHz
    • Hi: 10 Hz to >100 kHz
    • Lo: 10 Hz to >90 kHz
    • Med: 10 Hz to >98 kHz
    • Hi: 10 Hz to >98 kHz
  • Frequency Response, Direct Input, ±3 dB, Gain Setting = 0: <10 Hz to >500 kHz
  • High Pass Filter -3 dB Cutoff Frequencies:
    • 70 Hz
    • 140 Hz
  • THDMIN = 0.003% at +14dBu, 1kHz, 1.5k Ohm pre-amp impedance
  • Dynamic Range = 133dB
  • Max Input Level = +20dBu
  • Max Output Level = >+30 dBu with <1.0% THD, 1kHz, 100k Ohms Load Impedance


Ordering Information


Input impedance range must be specified when ordering. This can be selected from the drop down menu below. Low impedance option includes 60, 200, 600 Ohms. High impedance option includes 600, 1.5k, 2.5k Ohms.


Contact Ingram Engineering for current pricing.