Heiserman Audio Type-21

The Heiserman Type-21 is a large-diaphragm, phantom-powered condenser microphone featuring a hand-built Generation 5 HK12 dual-diaphragm capsule, transformerless JFET amplifier, tri-pattern operation, integrated pad and high-pass filter, and ultra-low 42-ohm output impedance engineered for modern studio capture with authentic 251 tonal architecture.

Classic 251 Heritage Meets Modern Circuit Design

The Heiserman Type-21 delivers the harmonic richness, forward midrange presence and extended air that engineers associate with classic ELA M 251 microphones while introducing a modern transformerless signal path optimised for high headroom, low noise and consistent performance. The hand-crafted Generation 5 HK12 capsule employs brass backplates and an acrylic chamber to shape a three-dimensional frequency contour that preserves transient realism and harmonic complexity while maintaining excellent off-axis behaviour.

The microphone utilises a low-noise JFET amplifier with precision resistors, tantalum capacitors and film capacitors that stabilise biasing, control harmonic behaviour and maintain clarity under dynamic conditions. This circuit architecture produces a fast transient response, a controlled low-frequency profile and an open high-frequency extension suitable for both close-mic and ambient recording techniques.

Compact Form for High-Pressure Recording Environments

The compact aluminium chassis allows the Type-21 to operate comfortably in confined acoustic spaces such as vocal booths, drum rooms, guitar cabinets and percussion arrays. The rigid metal enclosure resists mechanical resonance and electromagnetic interference while supporting consistent tonal integrity across varying SPL conditions.

A softly illuminated logo integrates into the circuit path and functions as a power-status indicator, enabling rapid visual confirmation during session setup.

Advanced Control at the Source

The microphone provides three switchable polar patterns including cardioid, omnidirectional and figure-eight. This allows engineers to shape room interaction, proximity effect and stereo imaging with precision.

A fixed 160-hertz high-pass filter reduces low-frequency accumulation from mechanical vibration, air handling systems and close-mic proximity. The integrated minus-15-decibel pad increases maximum sound pressure handling to 145 dB, enabling distortion-free recording of drum kits, brass sections and high-output guitar amplifiers.

Manufacturing Integrity and Component Standards

Heiserman designs, machines and assembles the Type-21 entirely in the United States to maintain tight component tolerances, long-term reliability and sonic consistency. The dual 6-micron 24-karat gold-sputtered Mylar diaphragms maintain stable capacitance and uniform mass distribution for consistent transient accuracy and long-term capsule stability.

The low 42-ohm output impedance ensures strong signal transmission across long cable runs and improved compatibility with transformer-based and transformerless preamplifiers.

Why Choose the Heiserman Type-21

• Captures vintage vocal and instrument tone while integrating seamlessly into modern recording workflows

• Delivers consistent results across sessions without reliance on external power supplies

• Maintains clarity when recording loud sources without sacrificing harmonic richness

• Simplifies setup in tight recording spaces without compromising sonic scale

• Provides long-term reliability backed by full USA manufacturing standards

• Hand-built Generation 5 HK12 capsule
• Dual 6-micron gold-sputtered Mylar diaphragms
• Transformerless low-noise JFET amplifier
• Cardioid, omnidirectional and figure-eight polar patterns
• Integrated 160-hertz high-pass filter
• Integrated minus-15-decibel pad
• Maximum SPL handling of 145 dB with pad
• Low 42-ohm output impedance
• Compact aluminium enclosure
• Softly illuminated functional logo
• Fully manufactured in the USA
• Phantom-powered XLR operation

This item, like everything we supply, comes with the complete support of our expert team. Our excellent technicians have been specifying, building and supporting studios for over twenty years. If you have any problems with installation, setup or everyday use, they’re never more than a click away, and always happy to help.

You can contact them here.