U87 circuit, and HF roll-off curve

[garp]

This thread is obviously (at least before turning to a real fight) about the U87 (not the submarine) and i clearly mentioned the AI version, so if you are not able to read my mind maybe you can read my ... words !
PS: My volvo is not a volvo ! But it is as grey as my neumann, should i change the brakes anyway ? Does Ai means that my U87 is capable of thinking by it's own ?

 

[LevinGuitar]

There are different versions of AI, that's why Khron ask for a specific schematic that matches your particular mic

A pic of your PCB would help I guess

 

[LevinGuitar]

Coming a little back into this thread, about using a quite cheap mics (even it wasn't that cheap back then) for pro recordings, if someone didn't saw this doc, there you have one of the brightest mics ever used for such a beautiful recording and talented artist. You can clearly hear the later EQ difference in the official CD version

 

[garp]

As far as i have seen in all schematics i've found not a lot has changed in the different revisions

 

[garp]

Mixing this track i had to deal with three different takes in three different studios with different mic/preamp combinations (AKG C414 TLS / Brauner Phantom / Shure SM57) really not my number one choices (i am more a ribbon or tube mic guy regarding vocals) . The whole album was made this way and i spent more time on vocal matching eq than everything else !

 

[LevinGuitar]

What value is your C105?

 

[garp]

Hard to tell the writing is half underneath ... I read 160 i think

 

[LevinGuitar]

In that case that's what you were looking for

 

[garp]

Ok so the more capacitance the more HF roll, where should i stop ? 680 pf ?

 

[LevinGuitar]

The original 87 had 220pf, the 680pf you have read about is used in a different microphone with a different circuit, don't mix them.

Anyway I would try first a small cap (4-6pf) between drain and gate of the fet (if you want to try, don't solder to the fet legs, use other connecting points).

BTW I don't take any responsabilities for your experiments. Personally I wouldn't mess with expensive gear without having a lot of experience and knowing for sure what I'm doing instead of doing something that someone told.
Thinking of "modding" is fun, but if you suddently have to deal with a problem (noise or non working mic) all fun (as well as some money and a lot of time) goes away. Giving a look at the "help threads" helps to chill the modding mood.

 

[garp]

Another silly question, the only working U87 i have has the bad habit of loosing bass when switched to omni, and has better bass response and increased overall smoothness in figure 8 than in cardio, i suspect the capsule but i have no other valid 87 head at the moment to make a swap and be sure of that ... any idea ?

 

[garp]

Thanks a lot for your answers ! I really don't care messing a bit with them as i am planning soon or later to modify them as U67's but maybe if achieve something interesting with a U87 circuitry i'll keep a pair as is. I sometimes (barely) use 48v microphones like the gefell M692 with M71, the vintage 47 fet the C414 eb transformer version and of course a U87 will close the loop at least for my taste. 4-6 pf in COG film or poly ?

 

[Khron]

Another silly question, the only working U87 i have has the bad habit of loosing bass when switched to omni, and has better bass response and increased overall smoothness in figure 8 than in cardio, i suspect the capsule but i have no other valid 87 head at the moment to make a swap and be sure of that ... any idea ?

https://en.wikipedia.org/wiki/Proximity_effect_(audio)

Probably not a coincidence that omni sounds less bassy than cardioid; fig-8 has even more pronounced proximity effect than cardioid. "Increased smoothness", which i'm assuming deals with the high-midrange(?) may well be down to interactions within the capsule, and/or interactions between the capsule and headbasket. Even the painfully-doctored "official" frequency response plots show some differences in that area, between the various patterns.

https://www.neumann.com/en-gb/products/microphones/u-87-ai/

 

[Paul W]

From those dubious "official" frequency response plots, it seems like the biggest EQ differences between a U67 and U87Ai would be that the U67 tones down the 10KHz resonance of the capsule slightly more (so it's darker by a dB or two) but the u67 rolls off the bass more, with a MUCH higher corner frequency. (They show the U87ai as flat down to about 70 Hz, but the U67 bass rolloff starts well over an octave higher.)

If that's even roughly right, it seems like the biggest sonic difference between the two would very likely be the overall FR curve (assuming you're not driving either circuit really hard and getting into serious distortion). They use the same headbasket, right?

Has anyone ever seen a blind test where the two are EQ'd to match in those obvious ways and you can listen for the remaining differences?

(For that matter, has anyone ever seen a blind test or just a shootout of any two mics where the overall FR curve is controlled for? I haven't run into them. [Edited to add: aside from Julian Krause's YouTube videos EQing an SM57 and a Behringer XM8500 to sound more like an SM7b, but that wasn't much of a test.])

 

[garp]

I am not here to talk about myself, but at 60 after more than 40 years in the business and lot lot of albums, i feel so happy to finally discover the "proximity effect" ! Waouu ! Thank you Khron for the Neumann advertising showing curves and also showing that the bass roll off is LESS pronounced in omni than cardio ... We are here in the typical case when pointing at the moon everyone notice that i have uncut nails. My question was about the moon; as simple than that. Again thank you for your answers, they helped me a lot !

 

[garp]

I replaced C106 with 0,1 Wima and C105 with first 220pf (better but still quite sibilant) then 470pf styro and now it sounds closer to a decent microphone at least to my aged ears ! Thanks a lot to everybody

 

[LevinGuitar]

If you need that much deemphasis is it possible that your C110 or C107 are out of specs and have lower capacitance?

 

[garp]

Thank you I'll investigate this track or maybe the capsule has to be reskinned ? Can a damaged capsule show such lack of bass (or excess of sibilance) ? It shows obvious differences between front and back in omni or figure 8 patterns, quite usual for an old beaten capsule

 

[Migs 31]

@kingkorg : “one of those left vs right brain discussions“

This makes me feel like having a double Lobotomy (sic) !!!!
Can we go back to Rolling off the HF on a U87 as in the OP?

M

 

[garp]

@LevinGuitar you were absolutely right, i replaced C110 and C107 with fresh ones, and bingo ! C105 is now back at 270pf, i increased C106 to 170nf and tried 8pf silver mika between drain and gate, i am now much more pleased by the sound, much better low end and the overall harshness nearly disapeared. Thanks to everyone here