The Black Lion Audio edition of the Avantone CV-12 is a really interesting microphone. It incorporates numerous changes to the stock CV-12, although it's not clear all of those changes actually make the mic better.

We propose replacing the mic's circuit, tube, and transformer. Those changes will significantly reduce distortion, reduce smearing of the audio signal, open up the top end of the mic, and restore bass response. We could either retain the stock capsule, or upgrade to one of the RK series capsules, depending on what you want for the microphone.

BLA CV-12 Analysis

Like the stock CV-12, the BLA edition uses a CCDA circuit, where both triodes of the tube are used in series. The capsule has a flatter response than the one found in most Chinese tube mics. But the mic's overall response is quite dark (-2dB @ 10kHz, -10dB @ 15kHz, -22dB @ 20kHz), due to an aggressive low-pass filter built into the mic's circuit that nukes the "air" band above 10kHz.

The BLA circuit's response dips to -10dB @ 13kHz, -17dB @ 20kHz; we measured this via injection. This is curious behavior because the capsule does not require such heavy-handed EQ. The circuit rolls off the low frequencies slightly too (-2dB @ 20Hz).

Here are a couple changes we would make to the BLA CV-12 to immediately upgrade the sound:

Trim the tape wrapped around the capsule. The narrow CV-12 headbasket risks contact with the capsule. If the capsule touches the inside of the grille, the mic will short-circuit. Taping the capsule edges is not a terrible idea, but the tape should not be so wide that it creates a tunnel around the diaphragms, as this could cause anomalies and smearing in the high frequency response as well as adversely affect the polar patterns at high frequencies.
Remove C9 and C10 (or clip the wires leading to those components). These caps appear to have been included in all the original Chinese tube mics for EMI/RFI protection, but the capacitors' value is far too high and the physical location is wrong. These components add significant distortion: 10-12dB of second harmonic across the spectrum, up to 30dB of 3rd harmonic (!) at high frequencies. They also interact with the transformer to exaggerate the 15kHz notch EQ effect; removing or disconnecting C9 and C10 gives the circuit a much smoother HF rolloff. To be clear, the mic would be improved if the circuit had a linear response, but that's not possible with this design. Removing or disconnecting C9 and C10 makes the problem less stark, but does not fix it.
If the tube is not a 12AY7/6072, install a microphone-grade 12AY7/6072.

Even with those changes, the mic has higher distortion than is ideal. It remains band-passed, with a slight rolloff in the lows and a fairly aggressive rolloff above 7kHz.

The mic's circuit has an overly complex signal path. For example, the high-pass filter implementation puts an unnecessary capacitor in the signal path, which arguably negates the value of the upgraded output capacitor. It is possible that the mild HPF behavior of the circuit originates with the capacitors used to couple the two triodes together.

And it is still a CCDA topology, which is not necessarily a bad thing, but is not what the vintage C12 or ElaM 251 used. A well-built CCDA mic has low distortion and high headroom, but this particular implementation -- at least the mic we tested -- squanders those benefits, delivering high distortion and low headroom.

About the V-251 circuit

Rather than upgrade a few components in the existing circuit, we would replace the entire thing with an alternate topology designed to outperform mics that cost 3x more. The MicParts V251 circuit design is a single-triode topology (not CCDA), like the vintage ElaM 251 and C12.

The new circuit includes a selected 6072 tube, and a hand-wound (US made) output transformer that is significantly more linear than the one in the BLA mic. The output capacitor is custom made in Europe, with polypropylene film and copper foil (which sounds better than aluminum-metallized polyester).

Compared to the BLA CV-12 circuit that we tested, the MicParts V-251 circuit has:

40dB less 3rd harmonic distortion @ 1kHz
30dB less 2nd harmonic distortion @ 1kHz
significantly more headroom for moderate to loud sources
significantly cleaner / simpler / more direct signal path

About the Mod

We would replace the BLA CV-12's entire circuit, tube, and transformer. The pad and HPF switches will still work after the mod (although we implement both features in ways that do less harm to the audio signal than the method used by the BLA circuit).

We modify the power supply, which typically has higher voltage than a 251 style circuit needs.

If your BLA CV-12's capsule exhibits a bright or peaky response, we would contact you to recommend upgrading to an RK-12; this option would be invoiced separately. Or if you already know you wish to upgrade the capsule, you can order that option using the menu above. Otherwise, we would retain the stock capsule, which is capable of good performance when paired with a high-quality circuit.

How it Works

After you buy this service, see our Service Policies page for instructions on packing and shipping your mic. Be sure to print the Service Request form linked from that page.

Send us the microphone and power supply. It is not necessary, nor recommended, to send us the shockmount, cables, or case. But it is critical to pack the mic and power supply carefully; both are heavy enough to damage themselves if the box is dropped. Pack both the PSU and the microphone in 3-4 inches of cushioning material, and use a sturdy shipping carton (not a used Amazon box) to avoid damage in transit.

The typical turnaround time is 5 business days. We can provide more detailed turnaround time estimates after you purchase the service.

Compatibility

This upgrade is compatible with the Black Lion edition of the Avantone CV-12.

Costs

The mod service includes the parts, installation, testing, and return shipping (domestic US only) from our shop back to you.

Availability

This mod service is open to US residents only, or to non-residents who are shipping the finished mic to a US address.

(Residents of other countries might find that it costs less to purchase a finished microphone.)

Optional Upgrades

We build custom tube mic cables with Gotham GAC7 wire and Neutrik connectors. This cable is superior to the thin, compromised stuff that claims to be Gotham brand sold on Amazon. We source the cable directly from Gotham in Switzerland.

If your budget allows for a superior power supply, see our VPS options.

We also have a superior clamp for the CV-12 shockmount.

Price

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