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Employing only discrete circuitry and conventional components, the 73 JR II is a faithful 3 stage all Class A 73 preamp. Styroflex and tantalum capacitors have been used throughout. No corners were cut.
The useful all discrete Class A hi pass filter has been updated, making it sweepable from 20 to 220 Hz. Now it is even easier to make your low end tighter without affecting desired frequencies.
The Line mode allows for reamping of prerecorded tracks and it´s perfect for adding some Class A color to lifeless recordings.
The smart switched DI (automatically switches from MIC to DI mode when inserting a MONO ¼” jack) is an all discrete Class A JFET circuit ahead of the MIC transformer, so all the juice is there. Since its introduction in 2013, it has become a classic DI for bass.
Finally, special care has been taken with power handling, implementing internal +24 V slow turn on regulation (about 20 seconds to reach full voltage).This makes your 500 series enclosure´s power supply healthier and makes the 73JR independent of the rest of the slots.
WHAT TO LOOK FOR IN A 500 SERIES 73 PREAMP:
There are several compromises usually made when adapting a 73 preamp for the 500 Series, especially the following 3. You won´t find any of these in the 73 JR II:
Eliminates one gain stage and runs only up to 70 dB of gain. A “real deal” 73 mic pre must have 3 gain stages for a total of 80 dB of gain. Taking the first gain stage out and maxing out the other 2 will allow for up to 70 dB of gain, but the noise figure and the low end at high gain are seriously compromised. The 73 JR II uses the full 3 gain stage circuit for up to 80 dB of gain with a noise figure of -125 dBu EIN at all the gain positions.
Uses the readily available ±16 V power from the 500 Series protocol. By doing this, the magic distortion of a 73 amp is compromised. The 73 JR II uses a true 24 V on board power supply for identical performance and distortion.
Uses of surface mount technology. Although there is no actual drawback in using SMD components, it should be reflected in the price, not merely to enlarge the manufacturer´s profit. No 500 Series 73 mic pre using SMD should cost more than $500. The 73 JR II uses only discrete, through hole traditional components and hand labor for that great 70s vibe.
When looking for the ultimate 73 `500 Series preamp´, always do this fact check.
THE 73 JR II TRANSFORMERS:
No 73 preamp is such without the correct transformers. For the 73 JR II (and its predecessor the 73 JR), Heritage Audio went a step further than the competition. The output transformer, the same used all along the Heritage´s line of products, is a Carnhill gapped one made exclusively for us at the St Ives factory. The input transformer, again exclusive to our company, is made in Carnhill´s Oxord factory, and has a huge impact on the extra mojo of the unit. It is the same one found in our top-of-the-line end 80 Series modules and is responsible for one of the main sonic differences between the 73 JR II and the competitors.
When looking for an exclusive sound, do not settle for non-exclusive transformers.
Microphone input impedance: HI=1200 Ω minimum, LO=300 Ω minimum. Higher gain positions gradually have greater impedances, perfect for lo gain ribbon mics. Input is transformer balanced and floating.
Line input impedance: 10 kΩ bridging, transformer balanced and floating.
DI input impedance: Greater than 2 MΩ, unbalanced.
Output impedance: Less than 75 Ω, transformer balanced and floating, to drive a load of 600 Ω (factory terminated).
Maximum output: Greater than +26 dBu into 600 Ω.
THD: Less than 0.025 % at 1 kHz, less than 0.05 % at 100 Hz.
Frequency response: 20 Hz (+0.3 dB) to 20 kHz (-0.2 dB).
Maximum gain: Slightly greater than 80 dB.
Noise: Less than -125 dBu EIN.
Power consumption: 86 mA per rail ±16 V DC.