The fine art of building a ribbon microphone - Pt.1

'The tool is half the master'... always true, whether you're a carpenter, a farmer, or a surgeon. In our case, the right tools are indispensable, and the ribbon microphone doesn't forgive.

We're working on a micrometric scale; the aluminum ribbon is 1.8 microns thick. To give you an idea of what we're talking about, here's a list from Wikipedia that illustrates the order of magnitude in question with some examples:

1-10 µm: Typical diameter of a bacterium

1.55 µm: Wavelength of light used in optical fibers

6-8 µm: Diameter of a human red blood cell

6 µm: Anthrax spore

7 µm: Thickness of a spider web thread

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Cutting a bacterium in half is already a difficult concept to visualize, let alone being careful not to damage its edges, crumple it, or make it fly away with a sigh, and so on.

For an easy-to-imagine comparison, consider that household aluminum foil has a thickness ranging from 40 to 80 microns, which is almost 50 times greater than our microphone ribbon.

But cutting is just the beginning of the work. Once the ribbons are cut correctly (4 mm wide and 100 mm long), the next phase is corrugation. This system allows the ribbon to expose more surface to the sound field than a flat ribbon. It also increases its elasticity and resistance.

We proudly present our super vintage (and, above all, artisanal) machine for corrugating the ribbon, built with used Meccano parts.

The next phase, once the ribbon is cut and corrugated, is its placement inside the structure, called the motor.

The ribbon motor is a simple mechanical system consisting of two permanent magnets glued to a metal structure.

We'll cover the housing and tuning phase in another post. For now, let's conclude our beloved scientific talk.

The ribbon microphone exploits the physical law of electromagnetic induction, the same wonder of physics that brings dynamic microphones and loudspeakers to life. In practice, the aluminum ribbon is suspended in a strong magnetic field and vibrated by the surrounding sound field. Due to this physical law, a tiny electrical current is generated at the ends of the ribbon, consistent with the incident pressure wave. This current is then extracted, converted through an output transformer, and made available on the microphone's balanced output.

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Tube 47 - Braingasm Custom

My Neumann U47 needed functional restoration, and once it returned back, shining like the sun, it gave us an idea: a Braingasm-branded valve U47.

Aware that we were stepping onto the field for the Champions League final, we got to work for many months, studying the original schematics and various "clone" projects, testing the Neumann in all its aspects to discover its versatility, and soldering away. Finally, we are ready to present it.

Like other handmade microphones born in the lab, this is not just another U47 clone or replica in circulation. We aim to create something innovative, inspired by the genius of our predecessors. Always keeping in mind that the Braingasm Lab’s mission is to offer high-quality sound at an affordable price for everyone. We seek to move forward, not sideways.

Before diving into the usual technical details, we are publishing the beta test of the finished microphone, compared to the original Neumann and a Braingasm Deluxe with a Gefell M7 capsule, the flagship model of our transistor series. The microphones are positioned as close as possible to each other, about 3 meters from the drum kit. The preamp used is a Tubetech. Check out the sound:

We have a long testing session planned where we aim to be as comprehensive and precise as possible, appreciating the performance of our new tube microphone on vocals, electric, and acoustic instruments. For now, we'll settle for these three tracks. Follow us to hear the rest.

After treating your ears with some snare and kick, let's finally move on to our beloved technical details:

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Let's start with the body, made in Europe with CNC machines. Like the original model, the grille has three levels of mesh, the basket is made of copper, and the body is anodized aluminum. We experimented with other models, shapes, colors, and materials, but the nuclear torpedo has always been the hands-down winner.

Braingasm Tube 47 - Long Body

Neumann U47 Short Body (1960)

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We've maintained the original layout and point-to-point wiring on the sides of the transformer, ensuring that the high-impedance area is as close as possible to the capsule and valve. Our electronic design differs from the original in many aspects, including the capsule biasing circuit and the tube’s power supply voltages. Among various options, we've chosen a Telefunken EF800, powered according to specifications.

NOS Telefunken EF800 tube, AMI BV8 transformer, MKP film capacitors

VF14 M tube, BV8 original transformer

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Finally, the capsule is a Thiersch STW7 transducer (M7 Red Line). Soon, we'll also test fitting a vintage M7 Gefell. The original Neumann U47 mounts a KK47.

Thiersch M7 Red Line capsule

Neumann K47 capsule

Decca Tree 47

Three identical microphones in cardioid/omni versions for Decca Tree recordings. With this matched trio of 47s, we've raised the bar even higher, implementing a subminiature switch on the circuit for polar pattern selection.

The directivity and slight emphasis on high frequencies (typical of pressure gradients in omni configuration) nod to the behavior of the M50s, absolute protagonists of the traditional Decca Tree setup.

Another special feature is the very strict matching (the capsules were selected from a stock of 20 transducers).

Microphones for singers and songwriters- In studio with Pino Marino

The 47 and 12 capsules are two complementary transducers, very different in character and intended use, and they adapt well to both vocals and instruments.

The first is a rather neutral capsule across the spectrum, with its natural emphasis on the high-mid range, displaying the typical mid-focused timbre of the 47. On the other hand, the second has a more 'loud' attitude, more pronounced at the extremes of the audio band thanks to a greater proximity effect and a bell curve shifted towards 8-10kHz.

When it comes to vocals, my advice is to choose the Deluxe 47 for rock vocals (vintage tone) and the Deluxe 12 for softer productions (modern tone).

This approach promotes the correct placement of the vocals in the mix without many artificial adjustments, as a rock song will naturally be very 'loud' due to the presence of distorted guitars and prominent drums, leaving the upper midrange open for our vocal track recorded with the 47 to comfortably sit without hindering or being hindered. On the other hand, in a pop production (or any softer genre), the vocal recorded with the Deluxe 12 will have its space within the spectrum and can be the reference instrument for the entire arrangement—full, present, and pleasant.

P.S. Pino chose the Deluxe 12.

The purchase of a studio microphone often relies on habit, sometimes on reading (controversial) technical specifications, and almost never as a result of an awareness derived from in-depth listening tests.

The opportunity to test a microphone on your own instrument (in this case, the voice) is a rare commodity in the global 'add to cart' market. However, it is an immense resource when dealing with the boutique market.

I met Pino Marino, an evergreen figure in Italian singer-songwriter music (as well as a keen ear), to record a song in the studio and conduct tests on our Braingasm Deluxe 12 and 47 large-diaphragm microphones.

ASCOLTA LE TRACCE VOCE:

Sud Sound System Signature

Four identical microphones, in the style of the Neumann U87, solid, customized, and colorful. In summary, the specifications that Paolo Panella, sound engineer for Sud Sound System and director of the Roman record label Altipiani, requested to develop a series of signature studio microphones for the masters of Salento's Raggamuffin, Sud Sound System. So far, so good, indeed, as they say in Rome, da paura (awesome).

The first knot to untie concerns the colors. My proposal for a Jamaica/Ethiopia-style pattern is a big hit with the band. These are the color samples I sent for approval. I suggested replacing the yellow color of the Ethiopian flag (in my opinion, not very suitable for a microphone) with an entirely golden headbasket, a touch of 'gangsta' class. Don RIco, Terron Fabio, and Papa Leu approved the proposed models in the photos, while Fernando 'Nandu Popu' preferred the classy look of Braingasm, with a chrome basket and matte black body.

The first step in obtaining four identical microphones (the real challenge of this job) is matching the capsules. Fortunately, the first great help comes from our Capsule Test Bridge, a high-impedance electrometer built by Calrec laboratories in the 1970s to measure the capacitance of a condenser electroacoustic transducer with extreme accuracy. The crown jewel of our laboratory, a priceless relic for a nerd of my caliber.

Knowing the capacitance of a capsule greatly facilitates calculating the microphone's sensitivity, but it is not enough to guarantee the maximum matching. Another step is to measure the frequency response of each individual capsule and choose those that are most similar to each other based on the tolerance one decides to respect. For my matched models, I consider differences of 1.5 dB on individual portions of the spectrum acceptable, considering that small inaccuracies can occur in the placement of the test capsule in relation to the source (pink noise).

Once this is done, we move on to the circuit. For the occasion, I decided to create a superior version of the usual Deluxe circuit, implementing a 2 Giga Ohm MOX resistor and selected Fairchild J305 JFETs.

Furthermore, the DC-DC converter section for capsule polarization has been modified for a voltage of 72 volts instead of the usual 62 volts. Additional improvements have been made to the ground plane and the capacitors on the signal path.

The film capacitors are all WIMA 5%, the TDK COG/NPO ceramics, and the ELNA low ESR electrolytics. All resistors are Vishay-Dale Military with a tolerance of 1%.

It's time to give the Phantom and have a beer.

Finally, the packaging, always handmade as Braingasm tradition dictates.

The interior of the box is made of neoprene and lined with black velvet.

The birch plywood boxes are painted with a water-based impregnator and engraved with a laser CNC.

For the occasion, we also had the band's logo engraved.