WA-CX12 full upgrade

This upgrade allows you to send in your Warm Audio CX-12 to be optimized to its absolute fullest potential, and deliver a bigger, smoother, cleaner, clearer, richer, warmer, fuller and more well balanced sound. The microphone is optimized from end to end, in a truly holistic fashion. Every single aspect (including cable, PSU, and mic) is broken down and rebuilt to last a lifetime.

In addition, you may choose your pick of output capacitor! NOS PIO (paper in oil) for a smoother, more relaxed, slightly more rolled off and three dimensional sound, or JB audiophile grade film cap for a more forward, focused, and slightly more articulated (particularly in the top end) sound. The differences are not huge and we love both options; but worth considering and we are happy to let you make the choice! Both are a massive improvement over the basic 'box style' stock radial film capacitor.

From an electrical perspective, the CX12 is the mic that most desperately needs our upgrade. There are three distinct voltage rails which come out of the power supply to drive the CX12: bias voltage, filament voltage, and B+ (high voltage) for the tube amplifier and capsule polarization. Then there is grounding. All basically have issues which we need to correct. The filament voltage is too hot (6.7v when 6.2 to 6.3 is nominal), reducing tube life and increasing heat... We 'over-correct' this down to about 6.1 to extend tube life. The bias voltage (normally about 2.2v) is shorted to ground via the cable pin configuration, causing the bias voltage to essentially be 0v, due to the cable shorting pin 7 (bias) to grounding lug rather than pin 3 (circuit gnd). We correct this to give the tube proper bias. Lastly, the B+ voltage is dropped down to approximately 75v due to a bleeder resistor tied to the end of the B+ voltage rail on the PSU. We correct this by replacing this resistor with a precision multi-turn trim pot that allows us to calibrate the B+ voltage right under +120v based on the voltage of your territory. 75v is near brown-out levels and causes the capsule polarization to be even far far lower, resulting in a dull, cold, low headroom/high noise signal. This affects different units differently, a few being OK and many being un-usable in our estimation. Lastly, grounding is augmented through and through by correcting the cable, adding dedicated grounding wires for both the PSU's power supply board and the microphone's chassis. This alone is worth the price of admission; but this is just where we get started! Then we address SOUND!

Here's what we do:

Power supply:

Fully rebuild, re-wire, re-solder all solder joints and clean/trim all boards.

Steel washers added to reinforce the channel frame of the mains transformer.

All capacitors replaced with top shelf components, including four custom made electrolytic capacitors made to our specifications by Supertech Taiwan (47uF, 450v, 10,000 hour rating) that are exclusive to us, all power supply capacitors fitted with parallel ‘bypass’ film capacitors.

6v voltage regulator is reinstalled with high performance thermal paste added to the heatsink, and the ‘corrective’ diode which raises the voltage is removed and replaced with a solidcore wire jumper.  This brings the heater voltage down from 6.7 to about 6.1v in real-world measurements, which is much easier on the tube and closer to the 6.3v target, extending tube life and reducing heat stress both on the regulator and the PSU.

Installation of a trim pot circuit on the B+ voltage output stage to allow precise calibration of B+ voltage.  Each mic is calibrated to its host supply, both the B+ voltage and P+ voltages are fine-tuned.

Everything tightened down, loctite used on every screw, silicon based lubricant used on every internal contact, inside and outside cleaned, thermal paste added to regulator heatsink + better screw for better heat transfer.

Power supply lamp housing is reinforced with thick adhesive heat shrink tubing to reduce chance of breakage in the field (happens often).

Cable:

Cable is rebuilt on both ends for higher quality control and then labeled, and configured to ensure the two heavy gauge leads are placed on the highest current rails, filament voltage and ground, respectively. 

manufacturing flaw corrected with pinout issue, isolating pin 7 to properly conduct tube bias voltage and shorting grounding lug to pin 3 instead, as called for by mic and PSU wire orientation. Once this is done, the mic can now achieve proper bias; but it is important to ensure this cable is never used on any other microphone.

Contacts sprayed with DeOxit, cable jacket cleaned with Armor-All.

Microphone:

Tube replaced with a third-party selected low noise/low microphonics tube and re-seated, with contact enhancer on the pins and 2 Sandy Levy tube damper rings installed on the glass. aerospace silicon buffer strip added beneath tube area.

Tube is replaced with a 12AY7 tube of our choice, based on current availability, typically either a NOS JAN GE/JAN Sylvania 12AY7 or a new production TAD Highgrade or EH low noise tube.  In the case of NOS tubes, we personally clean, de-scale, and select the tube for low noise.  In the case of new production tubes, they are always third-party tested for low noise/low microphonics.  Tube pins are lubricated using DeOxit Red and tube is dampened using an aerospace silicon ring or pad.

Stock tube is included in return packaging as a working spare.

Capsule cleaned and re-seated, re-terminated, capsule saddle replaced or augmented to prevent future breakage, capsule mount cleaned with anhydrous alcohol.

Capsule mount and saddle are replaced as needed with higher grade/low resonance parts (as needed, because some units are OK and others need these parts to be replaced).  

Output capacitor(s) replaced with JB (Taiwan) Audiophile grade film+foil .47uF bipolar cylindrical capacitor or tested/cleaned NOS PIO military surplus capacitors that are burned in, de-scaled, and wrapped in Kapton tape. additional layer of Kapton tape added to board to reflect back tube heat.

Output transformer daughterboard taken out and cleaned/reflowed, transformer wrapped in Kapton tape, with a 1/32 strip of foam neoprene tape affixed to either side of the internal frame structure to acoustically dampen the mic and keep the transformer laminations from making contact with the endoskeletal frame. A Cu foil shield wiht drain wire is added between two kapton tape layers to add additional RF protection.

Dedicated ground wire installed to XLR ground lug and ran to the frame of the microphone to eliminate buzz and/or handling noises.

Boards cleaned, partially solder re-flowed.

RF suppressor ferrites added to all capsule terminations and tube grid. Polystyrene capacitors are shielded with Cu foil shield layer with drain wire then wrapped in Kapton tape, adhered with PerfectGlue to reduce microphonics.

Screws for base/bottom bell of microphone replaced with longer, high strength screws for improved structural durability.

XLR pins sprayed with DeOxit Gold.

Special adhesive added to all polystyrene capacitors in the high-z section to reduce 

microphonics/resonance/handling noise in the microphone.

All parts tightened down, loctite added where appropriate.

Microphone interior cleaned with anhydrous alcohol and lint free swab, mic exterior cleaned with microfiber cloth.

System:

The entire system is given a 24 hour burn in period to break in the tube and capacitors, and then re-calibrated via trim pot with a precision Fluke Meter one final time, re-tested, cleaned, and packed back up.