Variable Input Impedance Transformer Coupled Discrete Mic Pre, EQ and Program Dependent Compressor



  • Lightly Colored Sound That Perfectly Complements a Wide Range of Mic Types
  • Discrete Mic Pre-amplifier
  • Equalizer with Broad Frequency Response Shaping
  • Soft-Knee Variable Ratio Compressor with Program Dependent Attack/Release
  • Dedicated Compressor Sidechain Filter
  • Low Cut Filter, Continuously Variable Between 30 Hz and 400 Hz
  • User Selectable Input Impedance for Shaping Audio Tones
  • Transformer Coupled Input / Output
  • 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
  • Combined Input Attenuator / Gain Adjustment for Optimal Noise Performance and Dynamic Range (No Separate Input Pad)
  • Buffered Output for Optimum Load Isolation and Current Drive Capability
  • Variable Output Level Control Using Long Life Noiseless Level Control Pot
  • Overload Indicator Accurately Detects Distortion to Ultrasonic Frequencies
  • Highest Quality, Audiophile Grade Components

The MPA575 is Ingram Engineering's foray into the 500-series format. It features a lightly colored mic pre-amp, compressor, and a unique EQ with combined low and high frequency control that allows broad tone adjustments with a single control knob. Together, they form a mini channel strip that performs all essential analog signal processing functions needed before committing audio to a recording medium. The MPA575 is ideal to use as a standalone mic interface or in combination with full featured hardware or plug-in compressors and EQs for more surgical audio processing.

Audio samples showcasing the Ingram Engineering MPA575 are linked below.

The MPA575 uses the same reference quality mic pre-amp circuits and architecture of the Ingram Engineering MPA685 rack mount preamplifier. The no-compromise design is superbly engineered for maximum usability and excellent tone quality. A transformer input with variable mic load impedance is provided to allow shaping of tones. The 600 Ohm impedance setting shows darker, more Neve-like tones, while the 2.4k Ohm settings increase the brightness and neutrality, providing tones more like GML or John Hardy type pre-amps. When switching between the impedance settings, the MPA575 automatically adjusts the gain so the two impedance settings are level matched. Noise matching and damping are carefully optimized for the widest range of microphone output impedances. Outstanding results are realized using any mic, from the low output impedance Neumann KM184 to the high output impedance Audio-Technica AE2500 (dynamic capsule), with ribbon mics like the Royer 121 (see Royer's comments about the MPA685 they auditioned by clicking here) and with condensers like the AKG C414. Proper gain distribution and the input attenuator design give the most possible headroom. This mic pre-amp, like the others in Ingram Engineering's lineup, provides the smoothest, most accurate sound with just the right amount of color.

Equalization consists of two controls: 1) a high pass (low cut) filter with continuously variable cutoff frequency, and 2) a combined low/high frequency EQ that acts much like a frequency response see-saw, with the pivot point set at 1.2 kHz. The HPF and EQ can be bypassed when not in use.

The compressor is a program dependent feed forward design with a simple user interface for controlling dynamics. The front panel Threshold (THR) knob not only controls the compressor threshold, but also controls compression ratio and make-up gain. Attack and release times are program dependent and automatically configured. The compressor has a soft-knee characteristic and compression ratios of 1.2:1 to greater than 20:1, depending on how far above compressor threshold the audio is driven. When working the compressor threshold in combination with the pre-amp gain adjustments, a very wide range of dynamic control can be implemented, from subtle and light compression to nearly limited response. Makeup gain is automatically increased for lower compressor thresholds so that a relatively constant average program level is realized as Threshold is varied and the audio material is auditioned. A second MPA575 combined low/high frequency EQ is dedicated to the compressor path and is used as a side chain filter. For more extreme side chain possibilities, the side chain path is also routed to the 500-series API "Option" or Radial Engineering "Omniport" output so that an external filter may be used instead of the internal EQ. The entire compressor path and side chain can be bypassed when not in use.

A high current buffer provides electronic balancing, isolation and capability to drive capacitive loads. An optional output transformer is available.

The MPA575 is engineered to take care of all complicated switching functions and gain adjustments behind the scenes so that the recording Engineer can concentrate on the music. As the mic load impedance setting, EQ and compressor are switched in and out, the gain stages are automatically adjusted so that the MPA575 gain is constant, within just a few tenths of a dB. Therefore, A-B audio quality comparisons when changing settings is extremely easy and more informative.

A long, trouble-free lifetime is ensured by the use of highest quality, long life caps and pots. Audiophile grade components are used throughout. The MPA575 provides the best sound quality, most value and most features of any 500-series available today, and does so with a user interface that requires minimum of effort to optimize the audio path.

Key Specifications:


  • Input Transformer with Switched Turns Ratio for Either 600 or 2.4k Ohms Mic Load Impedance
  • Max Gain: 70 dB
  • Frequency Response, ±3 dB, Gain Setting = 0: 10 Hz to >100 kHz
  • High Pass Filter -3 dB Cutoff Frequency Variable Between 30 Hz and 400 Hz
  • THDMIN = 0.002% at +10dBu, 1kHz, 2.4k Ohm Pre-amp Impedance
  • Input Referred Noise = -124dBu Unweighted, EQ and Compressor Off, 150 Ohm Mic Output Impedance, 600 Ohm Mic Load
  • Dynamic Range = >130dB
  • Max Input Level = +15dBu
  • Max Output Level = +25 dBu with <1.0% THD, 1kHz, 100k Ohms Load Impedance


  • High Pass Filter Type: Single Pole Design
  • High Pass Filter Frequency Range: 30 Hz to 400 Hz Continuously Variable
  • EQ Boost/Cut Range:> +15 dB, < -4 dB
  • EQ Pivot Frequency: 1.2kHz


  • Threshold Characteristic: Soft Knee
  • Threshold Range: -30dBu to +12dBu with 1dB Compression
  • Compression Ratio: 1.2:1 to>20:1
  • Attack Time: Program Dependent; Typically 5mS to settle within 1dB of Final Value for 10dB Compression
  • Release Time: Program Dependent;Typically 15mS to settle within 1dB of Final Value for 10dB Compression


Product Literature

About the following Audio files

Audio samples were recorded using the MPA575 with a wide range of instruments and microphones to demonstrate the quality that can be achieved. Steaming files as well as downloadable files are linked below. For additional audio samples, we refer you to the MPA685 audio samples, as the MPA685 and MPA575 share the same design approaches and, in fact, share the same discrete audio amplifier design.

The first group of songs are by Jason Deutsch, recorded at Slack Key Studios by Randy Kohrs. The MPA575 was used for drums and percussion. Streamed and downloadable files are saved as WAV format.


Full song, "American Dream" by Jason Deutsch, mixed and mastered

"American Dream"

Full song, "At Any Cost" by Jason Deutsch, mixed and mastered

"At Any Cost"

Full song, "Goldrush" by Jason Deutsch, mixed and mastered


The next song is "Toyland" by Created Ruin, recorded by Jon Nix at Jeff Hewlett studios. Jon is also a band member. Both the MPA575 and MPA685 were used for drums, with Octavia overhead mics and Heil HM ProPlus close mics. To hear a preview at Apple Music click this link: Toyland.

Randy Kohrs hosted a listening session at his Slack Keys studios with the MPA575 and a variety of other gear. The following group of comparisons resulted. For these files, Joel Hamilton played acoustic guitar and tracks were recorded through the different pre-amps listed. A Peluso P-28s mic was used for all tracks. For the MPA575 tracks, high impedance mode was used, and EQ and Compressor were off during tracking in order that comparisons of just the pre-amp functions could be made. Subtle differences in especially the upper frequency articulation is apparent when comparing the MPA575 (with EQ off) to the tube-based pre-amps or the Neve-based RTZ Audio 9762A.

To demonstrate the versatility of the MPA575, the file was reprocessed through the MPA575 with the see-saw EQ on and adjusted to -3 for slight high frequency de-emphasis, HPF was engaged with frequency = 120Hz and the compressor was engaged with threshold at -9dBu and sidechain EQ flat. This file shows the ability of the MPA575 to take on a darker personality and more directly compare to a Neve-type sound. Streamed and downloadable files are saved as .wav format, 96kHz sampling rate.

MPA575 Acoustic Guitar

MPA575 pre-amp only, no EQ or compression
MPA575 with EQ and compressor engaged
Classic API VP-26
RTZ Audio 9762A
Telefunken V-72
Edwards Audio LE10 Mono
Heider FD312, High Impedance mode
Heider FD312, Low Impedance mode

This last song is by Nathan Dantzler and was recorded by Randy Kohrs at his Slack Keys Studios. Full song, "Let Me See Your Koozie" with MPA575 on toms and drum overheads.

"Let Me See Your Koozie"