Klaus Heyne on modification of the Neumann u87


New member
Got this email from him today. Very interesting to me.


There is more than one approach to modifying and improving the overall
performance of a U87.

The ³Innertube² approach of replacing the complete impedance converter
and mic amp with a new, tube driven unit that readily connects to the
original capsule head was already mentioned. Another approach would be
to stay in the solid-state domain and optimize the mic from there.

A short bit of background info may be in order, to better understand
the ³why?² of modifying a mic that sells very well and generally seems
well-enough liked in its stock configuration.

During the 1970s and still to date, the U87 and other German and
Austrian condenser mics were tailored to a highly specialized but very
lucrative market- the German Broadcast System.
The broadcasters¹ ³brown book² (spec book) mandated design elements any
bidder for a purchase contract for many thousands of mics needed to
fulfill (and eagerly fulfilled them), sonic consequences to all other
applications be damned.

Some of the U87¹s design parameters were actual quite reasonable in the
broadcast environment, even if they were detrimental to other
applications, like studio recording:

High-end shelving of -4dB @16khz, (the pilot tone of stereo broadcasts
was transmitted at 19k, so any interference by a mic transmitting
beyond 16k needed to be avoided). stark low end attenuation, overall gain
suppression (to conform to the gain chain established many years earlier)
heavy RF-choking (self evident in broadcast environments) and so on,
all needed to be addressed, so that Neumann was able to sell this and
other models to its biggest customer.

The modifier¹s job then would be to eliminate these curtailments,
rebalance the frequency response, avoid excessive headroom limitations after
removing the global and frequency specific feedback loops (which are
responsible for the infamous mid range ³honk² of the mic), and fine tune
a capsule which, as good as it is, has a wide enough manufacturing
tolerance resulting in a wide variety of timbres.

This kind of work costs according to the modifier¹s ultimate success to
transform the mic into an object of sexual desire, his reputation,
warranty, servide-friendliness.

The modifications can be applied equally successful to the old (U87i)
and new (U87Ai) model.
Best regards,

Klaus Heyne



Would you be able to tell us what modifications are available for an
87, and what the pros/cons of each are?


I am interested in what is done when what I would think is a perfectly
good mic (the 87) is modded? I am not meaning debate who is doing the
mod, or why, or whatever, but what would one change and why?


I know very little about what modifications are available from others
for the U87.

I know the route that Stephen Paul, my late, long time, and respected
competitor took: he concentrated on diaphragm design and replacement.

I also understand, (though never personally tried) the Innertube
philosophy of replacing the FET guts of the impedance converter's
(solid-state) electronic processor with a tube, while leaving the capsule alone

My fundamental approach to modifying a U87 is this:

I want to hear as much of the brilliant, ingenius K67/87 capsule
design's sex appeal with the least amount of loss or artifacts from the
electronic processing.

For those unfamiliar with the history of the U87:
This model used to be the bread and butter mic of the Neumann company-
more than 90,000 of these were made so far, and counting.
Unfortunately, anything and everything the German Broadcasting system
asked for, Neumann incorporated in the electronic processing of this
model - the good, the bad and the ugly. But then- who would argue with the
sales department?

In the non-broadcasting environment of today, (and these days even in
the broadcasting environment!) few of the Broadcast Brown Book specs of
the 1960s are useful:

High amount of negative feedback, both, for overall gain and for eq,
severe roll-off in the bass, 4dB down at 16k, and so on, all attribute to
the (in)famous "honk" of the mic when the same capsule used in the much
gentler processing of the SM69 and M269, or U67 tube models sounds so
much more musical and engaging.

So what do I do?
I gut the existing audio processing, connect the capsule with the
fewest necessary components in the simplest, most elegant way to the output
of the mic, replace the remaining components necessary with those of
the highest audio quality, regardless of cost, my ears can discriminate,
fine tune the capsule's parameters to the intended use, and enjoy the
ensuing musicality and sex appeal out of a mic that is not particularly
known for its musical sensuality.

On occasion, I will specialize the U87 for certain applications-
Scoring, ADR, foley, voice talent, specific vocalists, instruments or
ensembles, but overall the same philosophy is always applied.

This work is only successful if I have good capsule material to start
with- either a well selected new K67/87, or a used one, where at least
one of the sides has musical balance and somewhat of a personality that
draws me in.

These are the (to me) obvious advantages of modifying further a mic
that is hugely successful in the first place. There is one downside: I
lose a bit of head room when I remove global negative feedback from the
system- in the order of 6dB; however, I regain 3-4dB by using FETs with a
very high headroom. (Not that U87s are known for their huge head room
in the first place)

If all of this sounds rather unscientific- it is. I am not fond of
quoting specs or using measuring equipment to monitor my progress (when was
the last time an ELA M251 has changed hands for $18k with a frequency
plot attached?)

Instead, I listen, judge, adjust, listen, judge, adjust, sometimes all
day long, sometimes for days.

May God grant me a few more years of good hearing.

Kind regards,

Klaus Heyne


gimmi your mic!
Great post!

Does Klaus know that you publicly post his emails?? (not sure how many laws you just broke) :p


New member
Giganova said:
Great post!

Does Klaus know that you publicly post his emails?? (not sure how many laws you just broke) :p
It wasnt actually an email that he created just for me, but rather a compilation of several posts of his on prosoundweb, compiled in email format. prosoundweb is a public forum. ;)