Once again, this is a modification where the customer is responsible for shipping us their microphone, and we will ship it back to them on completion.
We're always keeping busy here at the lab and there's a few new things to go over. Firstly, we finally have developed an upgrade for the WA-67 tube microphone, after years of requests. I procrastinated about this particular model for a number of years because I just wasn't sure that I had anything to 'add' to this design, given certain immutable constraints that it has (Lundahl output stage, etc.) and the limited real estate on the board, etc. It turns out, I do have something to say about this mic after all and have come up with a best-case-scenario set of upgrades to make it, it my opinion, the best it can be.
There are a few things they did right, and I do want to give credit where due. The mic circuit for the most part follows the 67 schematic, and the power supply is built correctly as well. It has the some of the telltale 67 characteristics that a 67 must have, including a negative heater voltage that can be calibrated. They did that right. They used good polystyrenes for the most part, and WIMA film caps. The included Electro-Harmonix EF86 is a decent choice as well, although we 'do' retrofit the tube to a selected new old stock pentode anyway.
The output capacitor is a generic film capacitor; but in their defense, there really isn't enough real estate to put something a lot nicer in that position. They didn't put their customary 'Solen Fastcap' there (ala 251 and WA47); but I never liked those anyway. I'd honestly put a generic film cap there in place of those in most mics. What we did to get around the real estate problem is to move some Wima caps out of the way to the opposite side of the board, then split the larger 4.7uF cap up into four smaller value JB JFX Premium film caps that we can place around that position with one even on the backside, all in parallel to make a composite 4.7uF capacitor network. It was cumbersome, almost crazy, and also expensive to multiply the cost of an audiophile cap by 4x; but it was the only way to upgrade that section and make it fit.
I am puzzled over their choice of a custom Lundahl transformer for the output, as Lundahl have never made a conventional BV12 transformer (ala 67), and this certainly isn't one either (significantly smaller); but it is what it is. The part is PCB mounted and there is no room to do anything larger; therefore this is simply part of the baked in properties of this mic. This transformer, and the 10x larger value output cap needed to drive it, are deviations from a traditional 67 design and therefore will probably make this mic miss the mark a little bit in terms of sounding like a vintage 67; but they are quality parts and the slight difference from authentic tonality just has to be accepted. I feel that we can work around that design choice and improve it in every other way that we can.
What I do take greater issue with is their choice of capsule on this design, as this capsule appears to be a more generic Asian K67 import, something along the lines of the Alctron/Xingde Trading K67 often seen in more generic/cheap products or that pop up sometimes as affordable 'capsule upgrades' by some other vendor sites... This is a very budget capsule, one that sells for only a fraction of the more decent Asian capsules they typically use in their products. It almost certainly accounts for some lack of realistic sound or lack of 'heft' or weight that some listeners may perceive. I have evaluated these very capsules in the past, and always found them to sound thin, harsh, un-lifelike, and one dimensional. We never before replaced the capsule in our WA mic mods, hoping to keep things more budget consicous; but in this case we are making an exception. For not a completely unreasonable amount of money, we are able to put in a much better imported K67 capsule made to our specs. The better capsule is not cheap (runs us about $50); but unlike the other tube mic mods where we have to replace the regulator, in this case we do not, and so we save some money there and have simply decided to absorb the rest of the cost. The upgrade capsules gives it a slightly fuller and smoother sound.
Once again (as with the WA-CX12, WA-47, and WA-251), the cable is reconfigured to be optimal for this mic design, and we do our usual process of replacing all capacitors and wire in the PSU and rebuilding it more clean and tidy. On the mic, we replace the output capacitor, add a chassis ground wire, add more adhesive to the polystyrenes to reduce microphonics, replace the capsule with our own custom imported K67, and replace the stock tube with a selected New Old Stock EF86 pentode (typically 60's era Winged C or Tungsram, which is what we have the most of here). The stock tube makes a great spare, but I still find the vintage ones have better construction and a richer sound.
The stock capsule, stock tube, and stock output capacitor are returned in the return packaging. US shipping is included in the price, and due to the cost of some of this stuff (4x JB capacitors!, a new capsule and a vintage tube, in addition to all our usual process!) we don't make as much on this mod as with some of the others... but I strongly fought the urge to raise the price. We just won't make as much on this one; but I still wanted to add it to our portfolio because it definitely makes a difference.
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