U87 HF rolloff...

From what I've read, the U67 and later the U87 had an HF lift built into the capsule, and a corresponding HF cut built into the electronics... a sort of HF pre-emphasis/de-emphasis. (specific reference to the late Stephen Paul's article here.)

Looking at the U87 Schematic, I'm wondering exactly how much of a cut there is, and where it cuts in. I think I need someone to explain which components are handling the cut; I'm not seeing it clearly.

Thanks in advance,

Keith

C105 has 50K impedance on 20 KHz frequency

Presumably that's NFB from the drain of the FET... but it's attenuated by R107/108 right? -And it's across a R101/R106 divider, is that just a straight 500k parallel equivalence?

-So what's the result...?

My brain hurts for some reason. My eyes can't untangle it!

Keith

It's all a NFB in series with the capsule.
However, gain of the single FET stage is not so much, but anyway this cap will roll off a bit.
The simplest way is to SPICE it substituting the capsule with an equivalent capacitance, otherwise some calculations on different frequencies are needed.

Yesterday I thought about roll offs for mics with thick capsules using selected transformers, like Altec Lansing plugins that have roll off on highs....

Did you let Scenaria breathe on the capsule before you tested it?

According to Spice:

at 3 kHz, about -2dB
at 10 kHz, about -7dB
at 20 kHz, about -20dB

[quote author="dale116dot7"]According to Spice:

at 3 kHz, about -2dB
at 10 kHz, about -7dB
at 20 kHz, about -20dB[/quote]

Thanks! It means, if the capsule has a 10 dB peak on 10 KHz it will be flat up to approx 16 KHz (+-3 dB)?

HPF switch on or off?

Bells obiously ring (no pun intended) regarding bright Chinese capsules who's design was influenced by the Neumann capsules. Does anyone know if the Chinese treble rise follows a similar law to the the Neumanns, or are we just stuck with a crap sounding high-end in the first place?

[quote author="rodabod"]Bells obiously ring (no pun intended) regarding bright Chinese capsules who's design was influenced by the Neumann capsules. Does anyone know if the Chinese treble rise follows a similar law to the the Neumanns, or are we just stuck with a crap sounding high-end in the first place?[/quote]

It is obvious that capsules thicker than zero or smaller than infinite square will have comb filter curve starting from some frequency. Wider/thinner means better frequency response, roughly speaking.
Same sizes from any manufacturer of any race/nationality means the same curves.

If capsules were designed for microphones used to broadcast AM they don't need to be flat up to 20 KHz. If to use such capsules for voice recording they have to be equalized anyway.

Crap sounding high end does not mean boost/ringing, it means specific distortions. I proved that for myself modifying my MXL 770'th.

[quote author="rodabod"]Bells obiously ring (no pun intended) regarding bright Chinese capsules who's design was influenced by the Neumann capsules. Does anyone know if the Chinese treble rise follows a similar law to the the Neumanns, or are we just stuck with a crap sounding high-end in the first place?[/quote]
Well, that's my entire line of reasoning... Roddy's on the same path.

I have a few Neumann capsules here, and when I wire them to MXL 2001 electronics (for example) they sound too bright. -Not necessarily exactly the same, but similarly bright none the less. Now, comparing a U67 and a U87 with some MXLs in a side-by-side multichannel recording last weekend, it's striking how much more comparable these mics are when a certain amount of HF rolloff is applied to the MXLs.

Even the Scott Dorsey mods don't address the 'de-emphasis' part of the equation, assuming that a comparable amount of 'pre-emphasis' is built in.

Anyone want to host some side-by-side WAV files? -I just set up the mics side-by-side next to each other, and pointed them at different parts of the Brass band during their rehearsal, so I could make multitrack recordings and get a feel for how they respond to different instrument groups. (Trombone, Euphonium, Cornets, horns, tuba etc.)

Interestingly, the '67 capsules sound no less irritatingly bright with Scott Dorsey electronics, OR with the MXL original circuit. Play with a little 1-band EQ in Pro-Tools, and they become rather more like the Neumann 'control' comparisons...

Now of course, close-up vocals will have a proximity effect, and -coupled with the HF rise- that gives you a bright-yet-warm sound. -the "smiley-face-graphic-EQ" type of sound. Recording members of a brass ensemble from 6 feet away (as 'section' spot mics) and there's no proximity effect. The MXLs just sound bright and grating compared to the Neumanns. -Some judicious redress with a single-band HF EQ and things are more readily comparable.

Keith

Yes flat circuits with a stock 67/87 capsule can hurt your ears.

The 2001 and v67m have a filter circuit like the 87 there is a .47uf off the drain to the same kind of network: However the 100pf, 200pf, .47uf and .01 are ceramic still causing some harshness.
Flatpicker has a nice schematic of the china circuit like this.

You can see the lift at the MXL site look at the graph for say the 1006(china schoeps without a filter) and the V69m then compare them to the 2001 or v67


The 160pf was 220pf in the past in older 87s IIRC.

I have redone some of the 2001 v67 circuit and upgraded some parts.

The easy part is the caps in the filter .47uf and..........

I believe the U67's EQ (or de-emphasis, if you like) was more drastic than the U87's.

Peace,
Paul

Yes, now that I see the 2001 schematic, it's MUCH easier for me to see how the feedback works. -It's the same as the U87 schematic at the front end, but I don't have to twist my eyes so much to read it!

Becoming much clearer now.

Keith

Much nicer schematic to read---I confess I lost interest in the topic upon seeing the first one.

...that makes me feel better. I feel like I'm in good company aboutnot being able to see what the heck was going on!

Perhaps Neumann were trying to put off the cloners by way of obfuscation! ;-)

Keef

Mine is better, though it needs a tranny with more ratio.

[quote author="SSLtech"]...

Perhaps Neumann were trying to put off the cloners by way of obfuscation! ;-)

Keef[/quote]

It's just Ye Olde Style Deutsch drafting, which doesn't reproduce well, I think. Gives me a little frisson d' deja vu, as if a lifetime doing duty at Bletchley is being pinged :roll:

Here you go gentlemen, I'm revealing one more of my secrets...

[quote author="SSLtech"]
Anyone want to host some side-by-side WAV files? -I just set up the mics side-by-side next to each other, and pointed them at different parts of the Brass band during their rehearsal, so I could make multitrack recordings and get a feel for how they respond to different instrument groups. (Trombone, Euphonium, Cornets, horns, tuba etc.)
[/quote]

Come on lads! Give the man some webspace!

I'd be interested in hearing these.

[quote author="rodabod"][quote author="SSLtech"]
Anyone want to host some side-by-side WAV files? -I just set up the mics side-by-side next to each other, and pointed them at different parts of the Brass band during their rehearsal, so I could make multitrack recordings and get a feel for how they respond to different instrument groups. (Trombone, Euphonium, Cornets, horns, tuba etc.)
[/quote]

Come on lads! Give the man some webspace!

[/quote]

I have some.