V-251 Circuit Kit
The V-251 Circuit kit is a recreation of the circuit from the most famous female vocal microphone in history, the Telefunken ElaM 251.
We have implemented it with the best parts on the market: US-made, film-and-foil input and output capacitors from Reliable, a selected low-noise 6072 tube from Russia, and a custom T-14 transformer. The result, when combined with our premium RK-12 capsule, is a stunning single-triode tube mic that rivals the performance of multi-thousand dollar commercial microphones.
The circuit kit was designed to fit the Avantone CV-12, TnC ACM-1200, and similar donor microphones.
If you don't already have one of those donor microphones, see our complete V-251 microphone kit, which includes the microphone body, switches, PSU, shockmount, and case.
What's in the kit?
We provide everything you'll need to transform your Avantone CV-12 (or compatible mic) into a studio powerhouse:
- Custom circuit boards. We designed these in-house and manufacture them in the US with DIY in mind. We use high quality two-layer boards with clear silkscreen markings and reasonably sized solder pads.
- Fantastic components. The kit includes 100% of components needed to build the mic circuit. All these parts are selected from among the best available, including low-noise Dale metal film resistors, a polystyrene input cap from Reliable, a polypropylene film and foil output cap from Reliable, high-grade electrolytics from Panasonic and Elna, a NOS styrene tone capacitor, Wima film capacitors, and a US-made T-14 output transformer.
- Low-noise tube. The tube is a 6072a type, manufactured in Russia, then tested and selected in the US to conform to our specifications for noise and microphonics. We picked this 6072 over many other types because it has better distortion characteristics.
- Internal wiring. We've sourced pre-cut and tinned, color-coded, multistrand silver-plated OFC with Teflon insulation, made in the US specifically for this kit.
- Two HPF choices. We include two different capacitor values for the high-pass filter, so that you can choose at build time whether to build a "rumble" filter or a more traditional high-pass. Note: for donor mics without external switches, we include a miniature toggle switch on the PCB to support the HPF feature.
- Socketed HF EQ. Set the circuit's high-frequency rolloff via a socketed capacitor -- no soldering required for final tuning!
- PSU mod. The V-251 kit includes diodes to reset the output voltage of the donor mic's power supply. (Our custom VPS1 PSU circuit is sold separately.)
- Unparalleled documentation. Each kit comes with a full color, step-by-step instruction manual. Our installation guides are known throughout the DIY audio community, and have been widely praised as the best available.
Note: although the circuit can be used with (and can provide corrective EQ for) the stock K67-style capsule, we strongly recommend that you order one of our excellent large-diaphragm capsules to accompany this circuit upgrade kit. The RK-12 is the best-selling choice for tube mic upgrades, and is the obvious top choice for an ElaM 251 clone build.
Needless to say, this kit requires the customer to supply a compatible donor microphone, into which this circuit would be installed.
Our mod kit is designed as a drop-in replacement for the circuit in the Avantone CV-12 and TnC ACM-1200 (and other rebadged SYT-1200 / SYT-1201 microphones). The V-251 circuit supports the pad and filter switches on those models.
The circuit boards also fit the Apex 460 and other Alctron T11A clones (BadAax T11-A, Carvin CTM-100, etc). We include a microswitch to enable a HPF feature, switched from the circuit board, on these models that lack external switches.
If your donor mic is dead, this circuit can be used to revive it. The circuit replaces the entire circuit and transformer of the donor mic. (If your dead mic's problem is a bad capsule or bad power supply, we can provide replacements for those too.)
If your donor mic is NOT listed here, it is unlikely the V-251 circuit kit will fit. You can confirm by printing this PDF template. Measure to confirm that your printed template matches the indicated dimensions. Cut out the template and hold it up to your donor mic chassis. Does it fit? Do the mounting holes line up? If the answer to either question is "no," then this circuit will not work with your microphone.
We do not recommend hacking away pieces of PCB or chassis to force fit this circuit into microphones that fail the above compatibility tests. See also the V-251 microphone kit, which includes this same circuit and compatible metalwork.
Not ready for DIY?
No premium-grade tube mic should be stuck using a cheap XLR cable -- which can cause up to a half-volt in loss to the critical tube heater supply. Upgrade to our Gotham GAC-7, custom terminated in the USA with Neutrik connectors.
The Chinese-made PSU that accompanies most inexpensive tube microphones can be noisy, and its output voltage can drift. We recommend our VPS1 supply, which provides tightly regulated voltage, superior filtering, and slow ramp-up power to extend the life of the tube. It allows B+ and heater voltages to be set independently via internal trimpots. The VPS is available as a fully built, tested, and warrantied unit, and as a circuit kit to upgrade an existing compatible power supply.
V-251 vs Fox 460
How does this V-251 differ from our Fox 460 tube mic circuit?
Both are premium tube mic circuits based on vintage models. Both use the 6072 tube (selected for low noise and low microphonics). Both deliver exceptional performance, far above what the price point would suggest. But they differ in component selection, topology, features, and specifications:
- The V-251 has ~6dB lower output, and at least 6dB higher headroom.
- The V-251 is a single triode, whereas the Fox 460 uses a dual triode/CCDA topology. The V-251 is a more authentic copy of the original 251 circuit, and conveys harmonics in a subtly different way.
- The V-251 kit is easier to build, primarily because we've eliminated nearly 50% of the wire joints.
- The V-251 circuit requires a higher-ratio transformer than does the Fox 460 circuit. We use a custom T-14 here rather than our BV8-style 6.5:1. Both transformers provide excellent performance, but they sound slightly different.
- The high-frequency rolloff "EQ" capacitor in the V-251 is socketed, making high-frequency tuning much easier.
- The V-251 supports external pad and filter switches, and provides an internal HPF switch for mics that lack an external switch.
- The V-251 uses a film-and-foil output capacitor. We did not have room for such a capacitor in the Fox 460 kit; it uses a high-grade metallized output capacitor.
- The V-251 is available either as a standalone circuit kit (for customers who provide a compatible host microphone), or as an all-inclusive V-251 Tube Microphone kit. The Fox 460 kit is available as a standalone kit, or as part of the all-inclusive 12-251 tube microphone kit.
In practice, both circuits offer performance rivaling commercial mics priced above $2000. The V-251 is easier to build, supports external switches, and has higher headroom. The Fox 460 circuit has higher output, and therefore requires 6dB less preamp gain on quiet sources.
Which of these circuits best suits your needs depends on what you record, what features you need, and whether your donor mic has external switches.