QP5 Mic Pre




The Iron Age 500 series mic preamp was designed as a utility front end solution. The mic preamp is the most important part of your signal chain, and this preamp gives the detail and depth your signal deserves.

Each QP5 features an all-discrete, transformer balanced input and output mic pre with a flexible and powerful topology that offers up to 80 dB of gain! The QP5 uses the same preamplifier as our QPP rack mount units, packed with additional useful features. The unit uses a Jensen input transformer and a custom-wound steel core Cinemag output transformer, selectable for 1:2 or 1:3 ratio. The first op amp works as a preamplifier, with adjustable gain of up to 40 dB. We took the rumble filter from our CS1 channel strip, followed by the same discrete transistor buffer we use in the CS1 and the V2 equalizer. A second op amp is fed by a trim control, and a “high gain” switch adds 12 dB more if needed. A bank of -20 dB pad, polarity, and 48V phantom power switches round out the feature set.

As with all Iron Age products, the QPP uses the M2 discrete operational amplifier, designed and built by us.

Block Diagram

Technical Specifications

Gain Range                                               28 - 80 dB

Maximum Input Level                               -3.5 dBu

Maximum Output Level                            +29 dBu 

Input Impedance                                      2300 Ohms, transformer balanced

Output Impedance                                   <75 Ohms, transformer balanced

Frequency Response                               +0.1, -0.75 dB 20Hz-20kHz

Actual Measured Noise                            -107 dBA typical

THD @ +15 dBu output                            0.002% typical

Power Consumption                                 <120 mA

User's Manual


The GAIN knob adjusts the gain of the operational amplifier.

The OUT knob attenuates the signal before the output stage. For maximum headroom the OUT should be set fully clockwise.

The OUT HI/LO switch increases the gain provided by the output amplifier by 12 dB.

The POL button inverts the signal being set to the primary side of the output transformer, changing the polarity of the output signal by 180 degrees.

The RATIO button changes the ratio of the output transformer from 1:2 to 1:3 when depressed. This increases the overall gain by 3.5 dB and decreases the output impedance seen by the op amp, causing a pleasant change in tone.

The FILTER button engages a 50 Hz, 12 dB per octave slope high pass filter. This is followed by a discrete three-transistor buffer.

The +48 button provides phantom power to the microphone.

The PAD button engages a -20 dB pad with a characteristic impedance of approximately 2300 ohms.


The input uses a Jensen mic input transformer to receive a nominal -80 dBu balanced input via the 500 series pinout.

The output is a nominal +4 dBu transformer balanced line output using a Cinemag output transformer via the 500 series pinout.

If you are interested in owning one, please contact us at: contact@ironageaudioworks.com

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