AMA - Vanguard V14 Variable-Voltage Tube Condenser

stream of consciousness incoming

C12 runs on a fixed bias while the C24 is a cathode bias (same as a 251). The C24 is a sort of amalgamation of a 251 and C12 circuit in some ways. The V24 starts with the C24 circuit. The V14 is essentially one half of the V24 circuit and is cathode-biased.

I was able to remove the crosstalk filters from V24 when we started designing the V14, because there's not a second capsule/signal path for it to talk to. I do have some extra power filtering in place that the C12/251 didn't have. The 2nd gen of the C24 implemented some of this, but not all of it.

transformer size increase in the Cinemag means you can increase the low end extension without fear, unlike the old AKG T14/1s which were tee-tiny. You get quite a bit more low end extension when you raise a few component values from the C12/251/C24 schems. In the earliest C24s the transformer coupling caps were 0.5uF, and the LF rolloff was significant!

Most tube mics out there in the CCDA vein are actually 6-pin, even though they use a 7 pin connector. This includes the APEX460, Vanguard V13, Avantone CV12, and plenty of others. Having that extra pin, I was able to use a separate line for the tube voltage control without needing any sort of fancy-pants connector like the V24 needed…just a good old Neutrik 7-pin XLR.

The biggest connection back to the C12/251/C24 remains the single-triode transformer-coupled design centered around a really high-spec 6072 (triple mica GE 5-star tubes in the case of the V14 and V24), and of course Ben's excellent BeesNeez CK12, the true beating heart of the entire operation.

The PSU is probably the biggest component-for-component change from a C12 or 251 PSU. The nice thing about high-ripple low-ESR electrolytic caps you can get these days is they are oodles better than anything AKG had access to. We do muuuch more filtering than they did, as well, particularly on the B+/capsule voltage leg of the transformer. I tried paralleling smaller SM caps along the big filter caps during V24 testing, and was surprised to find that I couldn't detect a difference in the B+ noise level on my O-scope. I'm guessing the extra filtering we already have in place has something to do with it.

Ultimately though it's the ears that matter here. I was never trying to sound "exactly like" a 251, 12, C24, or anything else - just sound fantastic. (this is beside that quest being a fool's errand, given how different the C24s we've tested against the V24 sound…)

Ben is far more knowledgeable about mics than I may ever be. And i don't know if i'll ever summon the courage to try building or even re-skinng capsules. I drink too much coffee to have hands of ice like that!

I could come over next time I'm in the Ranch, and bring coffee and Bailey's and watch and/or assist!

Baileys AND coffee for sure!

Alright, a serious final design question. I'm usually function > fashion kind of person, so initially wanted to have the tube voltage knob be a different color than the pattern knob.

However, they look really slick with just the red knobs.

As an engineer, does this matter to you? Which one do you prefer?

Def all red or all black. I vote red with the red screws.

I don’t think it would bother me (being the same color)…but it does kind've make sense for them to be different colors.

Voltage control does a number of things sonically.

1/ FR - sagging the tube in particular will start a slight "frown" curve - highs and lows start to sag off.
2/ THD - this is the big one. It will increase/decrease THD depending on the setting. There's a handy-dandy reference guide we engrave into the bottom of the PSU. See below image. If you start to push the tube beyond its stock voltage, this actually increases the THD a bit as well, but on the 3rd-order harmonic rather than the 2nd-order. It's hitting the xformer harder. I'm going to try to make a video of the various states with a signal injection approximating 1 Pascal. We did something similar to it in Matt's video using his monitors and a 1kHz injected signal, but that's not quite the same as a sine sweep.
3/ OUTPUT - this is the part we put on the front knob after much debate - it tells you how much makeup gain/trim you'll need for the various tube voltage states.
4/ the sag will also change transient response to high-volume sources.

We might just ship it with a spare black knob so people can choose and have the reds attached standard. I already have them in the shop, doesn't make sense to just let them molder!

Just no Brown ones😁

and red is just about the hardest color to match, unfortunately...