BELOW
I noticed something surprising. The leg of the FET passing though the PCB to a 1G ohm resistor was touching the edge of the circuit board (fixed for the photo). This is a big no-no as touching the board increases circuit noise which defeats the point of isolating the connection in mid-air. I used a small screwdriver to carefully pry the leg away to center it in the hole. Behringer should pay more attention to this during production.

THE MOD
Swapping out the blue electrolytics was my first task but replacement choices were limited. Tantalum capacitors are classed as electrolytics and have been used in microphones for decades because of their tiny size. However despite their long history by modern standards they are considered sonically inferior and obsolete. Tantalum is also a conflict mineral, so I don't feel comfortable them using them even in a vintage restoration. Modern film caps are too large meaning the only choice for coupling caps are tiny audio-grade electrolytics. 21st century choices are the Elna Silmic and the Nichicon KZ which are specifically designed for sound quality. The Silmics have pages of forum comments describing their sound, yet the KZs have fewer despite being known to the audiophile community since the mid 1990s.

I didn't want obsess over which was better. But when dealing with microvolt input signals subtle differences between caps are going to appear. Bright vs tube-like, etched vs smooth, which is correct? To my ears the Silmics are dynamically correct with 'body' and realistic bass. The KZs had a clean, natural presentation but I found them slightly leaner tonally and a bit polite. I decided on a combo of the two. NOTE: the boards have plated-through holes and thin tracing on both sides, care must be taken when de-soldering so as not to pull the traces from the holes or board.

- I had to bend over one 22uf/50V Nichicon KZ to reach the solder joint. The lower pair were too tall so I relocated them to the bottom of the board.

- I changed the two 1000pf caps to Wima FKP2 1000pf/100V 2.5% (film/foil polypropylene). I replaced the Wima .015 with a .015 1% Wima FKP2

- The 220uf/25V electrolyic was a low impedance cap from the factory so I decided against an audio-grade electrolytic. I replaced it with a Nichicon PW (low impedance, high reliability, for switching power supplies). I also added a .22uf Russian K73-11 PETP bypass.

- I replaced the three 1G ohm resistors with Ohmite MOX-200001007JE 1G ohm 5% versions which are rated for "Avionics, medical electronics, high gain feedback applications, current pulse limiters, vacuum and space application". I also replaced the three 51M ohm resistors with 50M Ohmite MOX-200005005FE 1% versions (I installed them on the bottom of the board because of crowding).

- The factory had filled up the XLR connector with hot glue and put dabs in the wire solder joints on the board. I removed all the old hot glue and replaced the three wires from the XLR to the circuit board with stands of 21g Canare L-4E6S wire.

NOTE: The factory had wired XLR jack pin 1 and the ground tab together. Some cables ground this way but conventional wisdom is that a microphone circuit should always 'float' to prevent ground loops. So I clipped the jumper between ground and pin 1 to make the B2 fully floating.

When I first powered the B2 up after the mod I was surprised through headphones to hear a very low-level rumble across the noise floor. It sounded like distant bass notes pulsing through from a radio station. I've seen references to this calling it "ghost rumble". It was unrelated to the mic cable or preamp. So I took a close look in the mic and realized I had not defluxed the board properly, especially around the new 1G resistors. I had used Chemtronics flux-off and Q-tips but noticed several near-invisible fibers had remained stuck to the board, touching leads, etc. By squinting under a strong light I used tweezers to clean these fibers off which seemed to be everywhere. From now on I will use foam swabs rather than cotton ones that shed. The rumble was reduced but still present so I went through the circuit with my Fluke and found I had a bad solder joint on one of the 22uf electrolytics (which I then fixed).

SUCCESS! The modded B2 is clean and clear with a detailed, natural sound. Delicate and responsive with zero ghost rumble even with my Scarlett 2i2 cranked to max on sensitive headphones (MDR-V6). A pre-mod recording of my voice had been clean but had an audible layer of pink noise across the noise floor. In comparison the post-mod circuit is vanishingly silent and cranking the pre-amp gain to max only produces circuit noise from the pre-amp, the mic is so quiet it may as well be out of the circuit.

CONCLUSION: Behringer should double-check the FET leg/board clearance at the factory, remove the hot glue from the XLR and solder joints to prevent bleed-over, and float the circuit by not using the XLR ground lug. All cost nothing and increase performance.

A decade ago it was commented online that Chinese mics needed to EQ their circuits to tone down the slight brightness of the capsules they used. This new generation B2 is said to use a custom-made capsule, and taking into account the redesigned SMD circuit boards and gold-pin connectors it appears Behringer has consciously updated the older design. The final clarity and low noise of this sub $200 microphone with $20 of tweaks was beyond what I expected. I am very pleased and satisfied.

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Click on the links below to play my 44khz 24-bit tests

The noise floor between stock and modified circuits is audible and visible. NOTE: to hear the details use sensitive headphones.

PRE-MOD RECORDING



POST-MOD RECORDING with Silmics



POST-MOD RECORDING with new resistors, Silmics and KZs

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