Just a note on the tone of the U87 vs. other mikes: I've A/B'd this Aurycle mike with the K67-type capsule in this circuit against others like the C12 tube design and various other Schoeps-like designs.
What I find is that if you go head-to-head against mikes that do not de-emphasize the upper frequencies (like everything above 6kHz), the U87 tends to sound "dull" in comparison. However in a mix (especially mixes that are denser than just singer/songwriter and acoustic guitar), I find that the U87 just "drops right in" with very little tweaking. In fact, I've found that the U87 in cardioid just puts the vocal in the exact right spot for a modern rock mix, where the meat of the midrange is where the vocal sits, but the air is removed to not interfere with the cymbals and other high-transient material. For an every more laser-focused midrange sound (like heavy rock with 4 doubled guitar parts), the SM7 works even better, but the U87 is very close.
Every time I've tried to use my C12 in this situation I've always had to low pass filter it to get it to sit just right, whereas I know with the U87 is probably will "just work" with minimal tweaking during the mix. The high end is there, it's just not pronounced enough to get in the way of anything else.
Of course the magic of recording is capturing the essence of each part that will work well when mixed together, given the restrictions of the frequency content that each part is occupying. This is why I pull out the C12 when I need to capture the air, and the U87 when I don't. It's one less plugin and one less hassle for me later.
However when set up head to head on a single source I've almost always preferred the C12 because it seems to be the best "DC to microwaves" kind of sound (to steal Ethan Winer's line) that works on every single isolated source you can possibly find.
It just doesn't always work best in the mix....
sr1200 said:
If someone wanted to bring the mic level up say 6db or more, what would have to change in the circuit/transformer?
I've been thinking about this too. The three main areas are:
1) Increase gain in the JFET front end: if you pull more current through the JFET, we can theoretically swing more output signal for a given delta input signal (e.g. the slope of the load line increases). However the only way to pull more current through the JFET is to pull that current from the phantom supply, which drops the polarization voltage available to the capsule (because the increased current drops more voltage across the 2K21 resistors). Less polarization means less sensitivity which means less apparent gain, so it's ultimately self defeating.
The only way to combat this is to use a charge-pump-like circuit to increase the polarization voltage (which decouples the polarization voltage from the current being used in the rest of the circuit), which requires a whole new circuit. This is exactly what Neumann did with the U87AI.
2) A far easier way to is add a PNP follower after the JFET. This reduces the output impedance of the JFET stage from 40k-ish down to several hundred ohms. This means you can use a transformer with a much smaller ratio, which means less voltage loss. Even moving down to a 5:1 BV11P-type would give you back the 6dB of signal you are looking for. Ideally you could use a 2:1 transformer which would give you back 14dB.
This is how the stock Aurycle circuit works (although they use an NPN follower and cap couple it for some reason), but it sounds slightly different. The highs are more present, and the mike responds much more to sharp transients like pick attacks on acoustic guitar: the mike sounds less U87-like, if that makes any sense. I think part of the mellow U87 sound comes from the high output impedance driving the high-ratio transformer. It's subtle, but it's definitely different.
3) Reduce negative feedback: as I hinted at earlier in the thread, you can decrease the value of C6 (or remove it entirely) and it will give you back 3dB to 6dB, however the sound also changes as well. If you like the "EQ-ed" sound, lowering C6 will take that away, however the mike will be hotter. If you like/want the "air" it's a very simple mod to do and doesn't require any expensive or complicated circuit changes. The sound change is FAR more drastic than #2 above (removing C6 can make it sound like a completely different mike).
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