500 Series Modules

  • JM-530 Mic Pre
  • JM-130 Mic Pre
  • JM-115C Compressor
  • JM-120 Direct Instrument Input
  • JM-C30 (info. coming soon)

JMK Audio are now using the SonicImageryLabs 990Enh Op Amp.

JM-530 Mic Pre

Very high Input headroom: for a very wide Dynamic range, ov er 131dB for the JM-130, >128dB for the JM-530.

The Pad is on the output: this has several advantages; One it does not affect the loading and sound on the mic, Two; Since No DC voltage goes thru the switch (Phantom) like most Mic pre pad circuits on other mic pres there is NO pop when the switch is engaged. Third; being on the output allows the output transformer to be driven harder for a warmer sound.

All switches on both the JM-130 & JM-530 are the large Gold plated switch, to provide very long life and improve the clarity of the signal path, and greatly reduce the probability of noise and static.

The Phantom switch: the phantom voltage ramps up to reduce the pop when powering a Condenser mic.


  • Jensen JT-16B Input Transformer
  • Very high headroom & Wide Dynamic Range
  • Input Impedance: 1.6K @ 1Khz
  • Output Transformer Option: Nickel or Steel
  • Hand wired point to point
  • THD+N:   .006% @50dB Gain @ 1Khz
  • .025% @-5dB In @ 50Hz
  • .044% @ +5dB In @ 50Hz
  • .0125% @ 0dB Input @ 100 Hz
  • .025% @ +10dB Input @100Hz
  • .007% @-10dB Input @15Khz
  • 990 Op Amp Slew Rate: 18Vus @ 150 Ohm Load
  • Frequency response: +- 1dB 10hz to 170khz ; +-.25dB 10 to 50Khz
  • Max Gain: -3dB @174Khz.
  • 990 Op Amp Only: +-1dB 5Hz to 500Khz
  • Output clips at +32dBu
  • CMRR: 117dB @ 60Hz, 85dB @ 3Khz
  • E.I.N. Noise: -128.5dB w/ 20 to 20kHz filter w/150 ohm load @62dB Gain
  • -127dB W/20 to 20KHz Filter W/300 ohm load @62dB Gain
  • Dynamic Range: >128dB; 20 to 20KHz filter w/150 ohm load @ min gain
  • > 105dB; 20 to 20KHz filter w/150 ohm load max gain
  • Maximum Input: +8dBu
  • Gain: 62dB
  • Hand selected .1% Phantom Resistors
  • Pad: 8dB on output, enabling the output transformer to be driven harder.
  • Phantom switching: voltage ramps up to reduce popping with condenser mics.
  • Laser Engraved lettering, letters will not wear off.
  • Note: 20 to 20 kHz filter used; -10dB @ 38 Hz & 32 KHz, -20dB @ 90 KHz
    Far wider than the typical Brick wall filter, which is -20dB @36Khz

JM-115C Compressor

The JM-115C is a Transformer coupled In/Out VCA based compressor using true RMS detecting similar to the DBX 160VU. Compression ratio starts at a very low 1.25:1, for a very small amount of compression, preventing clipping the recorder input but not over compressing.

Like the 160VU the JM-115C is very easy to set up, simply start at a low ratio, set the threshold around +4 to +10dB and output where needed to get the level to tape you need.!

The JM-115C has a very short and direct signal path allowing for very low distortion and very low noise, it’s a very clean transparent compressor. It does not pad the input (reduce level) before compression, allowing maximum dynamic range from your mic pres ect.

Available in either the 500 Series module or the stand alone that will run off the same supply as the JM-130 mic pre.. Each JM-115C is hand wired and tested. 

“The JM 115C is one of the very best compressors I’ve ever used. It helps control the level of the source without changing the sound. Even at more severe compression the sound is the same, very smooth and natural. I really like it on vocals, sounds good on acoustic and electric guitars as well. Now I need a rack full of them!” Johnny Sandlin


  • Maximum Input: @100Hz +32dB With Reduction.
  • Noise:  -98.2dB Below 0dB(.775V) @ unity gain, 20 to 20KHz filter.
  • Distortion:  @15KHz +15dB Out  .015%
                     @ 1.5KHz +15dB out .007%
                     @ 1.5KHz  @10dB reduction  .012%
  • Dynamic range:  >120dB
  • Maximum Output:  +22dB
  • Jensen Input/Output Transformers
  • Current requirements:  +16.5V less than 75mA, -16.5V less than 35mA 
    The JM-115C meets VPR requirements.

JM-120: 500 Series Direct Instrument Pre-amp

Dual Hi-Z input DI Pre Amp, One common Output.
Transformer Balanced Out:  Jensen Transformer            
The Guitar input is specifically designed for Guitar; the input impedance, gain structure and bandwidth are optimum for guitar producing a very clean and quiet signal that is excellent for a DI track and/or for Re-amping.

The Bass/Keyboard input is designed for the higher output of a Bass Guitar or Keyboard and optimized for Bass Guitar.

The JM-120 meets the VPR requirements.
Current draw:  Less than 25 mA

“I’ve played my Modulus Quantum Bass in a lot of rooms through a lot of equipment, but have never been this satisfied with the sound. The clarity and warmth of the JM-120 is there in every pitch and really brought the bass to life!  Thanks and keep up the good work!”  Adam Holton, Memphis

JM-C30: information coming soon