Heritage Audio 73 JR II 500 Series Class A Mic Preamp and DI

Heritage Audio 73 JR II: A Full 73 Preamp in a Single Slot

The Heritage Audio 73 JR II is a single-slot 500 series microphone preamp and DI, delivering slightly more than 80 dB of gain from a faithful three-stage all Class A circuit. It is the 2021 update to the classic 73 JR, adding a sweepable filter and refined power handling. Where many compact 73 designs cut corners, this one keeps the full circuit and the correct transformers. It brings genuine British console tone to any 500 series rack.

How the 500 Series Format Works

The 500 series is a modular standard in which small modules slide into a powered rack, or lunchbox, that supplies power and connections. It lets you build a custom rack of preamps, EQs, and compressors one module at a time. A microphone preamp like the 73 JR II raises a mic signal to a usable level before it reaches your converter. Fitting a real 73 preamp into that compact slot is the whole point of this module.

The Full Three-Stage Class A Circuit

A true 73 preamp needs three gain stages to reach 80 dB with the right low-end weight, and the 73 JR II keeps all three. Compact designs that drop a stage top out near 70 dB and thin the sound at high gain, a compromise avoided here. Every stage runs Class A, staying fully conducting for smooth harmonics. Styroflex and tantalum capacitors are used throughout for the classic 1970s voice.

Exclusive Carnhill Transformers

The 73 JR II uses Carnhill transformers made exclusively for Heritage Audio, a gapped output transformer from the St Ives factory and an input transformer from the Oxford factory. That input transformer is the same one found in the top-of-the-line 80 Series modules and is central to the module's extra weight. A transformer couples the signal and adds harmonic color, heard as warmth and body. This exclusive iron is a key reason it sounds different from other compact 73 preamps.

A Sweepable High-Pass Filter

The discrete Class A high-pass filter sweeps continuously from 20 to 220 Hz, so you can set exactly where the low end rolls off. That makes it easy to tighten a boomy source without hollowing out the tone you want to keep. Because the filter is Class A, it stays in character with the rest of the signal path. It is one of the main upgrades over the original 73 JR.

Smart-Switched DI and Line Mode

Insert a mono quarter-inch jack and the module automatically switches from mic to a discrete Class A JFET DI placed ahead of the input transformer. That DI has been a classic choice for bass since it first appeared in 2013. A separate Line mode lets you reamp prerecorded tracks and add Class A color to flat or lifeless recordings. Both modes route through the same colorful transformer output.

Power Handling Built for the Rack

The 73 JR II carries an internal 24V slow turn-on regulation stage that reaches full voltage over about twenty seconds. This keeps its power independent of the other slots and eases the load on the enclosure's supply. Running a true onboard 24V rail also preserves the amp's characteristic distortion instead of relying on the rack's lower voltage. It is a design choice aimed at both sound and reliability.

Where the 73 JR II Fits Your Studio

Engineers use the 73 JR II as a go-to 500 series preamp for vocals, adding presence and vintage weight to the voice. Its DI is a mainstay for bass, and it is a favorite on kick and snare where beef and body matter. Because it slots into any 500 series rack, it scales from a single channel to a full custom console. As a full 73 preamp in one slot, it delivers the real sound without the shortcuts.