Modding Neumann U87Ai to U87i voicing and headroom

[mean_street]

Hey guys,
I’ve been using my U87Ai for all things, it sounds great on some but good on almost all sources. Two things that bug me with that mic is the really low headroom and the high mid/treble bump. I already changed C105 to 220pf, to get a little bit less high end response which worked out flawless. For the headroom issue I plan to install a 50V zener at place of D7, to lower the polarisation voltage for additional headroom and installing a cap between drain and gate like A. Grosser did in his mods to further gain some headroom. I would leave the FET as is for the moment.
Anybody got some more ideas or remarks doing those mods?

 

[Khron]

Using the pad, and/or putting some more distance between the mic and the source, are not viable options?

 

[mean_street]

Using the pad, and/or putting some more distance between the mic and the source, are not viable options?

Already doing that, but I always feel that using the pad thins out lows and low mids.

 

[RuudNL]

Is that only a 'feeling', or can you measure a difference when injecting a signal to the test input?
(In this case the capsule is still in the circuit.)

 

[MagnetoSound]

Do the zener mod first. Report back

 

[mean_street]

Is that only a 'feeling', or can you measure a difference when injecting a signal to the test input?
(In this case the capsule is still in the circuit.)

I may have chosen the wrong words, I definitely can hear a reduction of low end. I’ll try to measure that.

Do the zener mod first. Report back

Will do

 

[living sounds]

https://groupdiy.com/threads/is-the...-that-sounds-as-good-as-a-vintage-u87i.80523/

 

[mean_street]

https://groupdiy.com/threads/is-the...-that-sounds-as-good-as-a-vintage-u87i.80523/

Read that thread already with great interest. Did you find out what transistor and cap Andreas Grosser was using on the mod?

 

[btyreman]

I wonder if there are any similar mods one could do to a TLM103?

 

[lampas]

I have in my collection U87, U87 ai, M269c, U67 and TLM 103 and did builds for the 1/10 of the price of the Neumann's mics, which are in the same or even better league... I would never mod any original Neumann in any case except in the case If I would not get original spare... but this is just my opinion...

 

[mean_street]

I don’t doubt that you can get a mic for 1/10 of a new U87Ai and tune/mod it to sound similar. But the Neumann capsules are still the best around and highly regarded clones like Stam and Serrano both didn’t to much for me. And if I factor in the costs for high quality parts like mic body, pcbs, transformer, components and capsule and factor in the time that I need to research, build, troubleshoot and tune, the total wouldn’t be far away from a used 87Ai, at least in Germany or Europe.

 

[RuudNL]

I would never mod any original Neumann in any case

I modded my last Neumann U87ai right out of the box!

 

[kingkorg]

Hey guys,
I’ve been using my U87Ai for all things, it sounds great on some but good on almost all sources. Two things that bug me with that mic is the really low headroom and the high mid/treble bump. I already changed C105 to 220pf, to get a little bit less high end response which worked out flawless. For the headroom issue I plan to install a 50V zener at place of D7, to lower the polarisation voltage for additional headroom and installing a cap between drain and gate like A. Grosser did in his mods to further gain some headroom. I would leave the FET as is for the moment.
Anybody got some more ideas or remarks doing those mods?View attachment 111444

What are you recording with it that leads to loss of headroom? Remember the specified max thd is just 1% for the named spl.

But the Neumann capsules are still the best around and highly regarded clones like Stam and Serrano both didn’t to much for me. And if I factor in the costs for high quality parts like mic body, pcbs, transformer, components and capsule and factor in the time that I need to research, build, troubleshoot and tune, the total wouldn’t be far away from a used 87Ai, at least in Germany or Europe.

I can see you've been following the wrong forums, i hope you will stick around here to gain some valuable info. Stam and such are nowhere near highly regarded here, and we have managed to find some more than good (maybe even better?) than Neumann's capsules. In any case more consistent than the originals.

 

[Khron]

Does Stam even make their own capsules?

 

[mean_street]

Does Stam even make their own capsules?

No, they don’t, they use italian-made capsules.

What are you recording with it that leads to loss of headroom? Remember the specified max thd is just 1% for the named spl.

I would want to use it as a drum overhead, but especially on snare hits the headroom limit is apparent. Maybe I get a second one later, I really like them on overheads and also on acoustic guitar (but no issue there, obviously).

 

[Андрій Чубака]

As my opinion totally Neumann is good mic. They have very good smoothest in sound with good balanced sound and it is good for post processing. Before i checked many videos on YouTube about comparing mics. And almost always in details i can find sound from pure Neumann 87. Other mics almost always has differences in smoothest of sound and balance. Difference can be very small but anyway. Totally Neumann 87 is a good product even if sound from it not like very spectacular directly. But price of course is not for me. And i no need this Neumann mic anyway. Some solutions here is also working very good about naturalization of sound. But best smoothest of sound with good natural sides in sound i can't reproduce at this moment maybe i will try some different circuits for it. In any case sound have different sides. Maybe for somebody Neumann is good value for a price, but for me it is not most important mic totally

 

[kingkorg]

I would want to use it as a drum overhead, but especially on snare hits the headroom limit is apparent. Maybe I get a second one later, I really like them on overheads and also on acoustic guitar (but no issue there, obviously).

Makes sense. There's a lot of space inside, maybe do internal switchable pad with several zener values in series. Reversable if you decide to sell it. 50v zener won't make a world of difference, i'd go lower.

 

[RuudNL]

The early U87i used a 3.3pF feedback capacitor, in fact between gate and drain.
Later this value was increased to 10 pF.
I suppose the value Andreas Grosser used in his modification will be in this range. (3...10 pF)
Of course this can also be done in the U87ai. And if you don't like it, it is easy to undo...

Edit: I just checked the effect of an added drain-gate capacitor in my own U87ai.
A 10 pF capacitor reduced the output in my case a little more than 9 dB. (So: 9 dB more headroom!)
Since we are dealing here with a very high impedance, a good leak free capacitor should be used!

 

[Khron]

For the headroom issue I plan to install a 50V zener at place of D7, to lower the polarisation voltage for additional headroom and installing a cap between drain and gate like A. Grosser did in his mods to further gain some headroom.

Makes sense. There's a lot of space inside, maybe do internal switchable pad with several zener values in series. Reversable if you decide to sell it. 50v zener won't make a world of difference, i'd go lower.

Indeed - going down to 30v(!) would give you "only" 6dB less sensitivity.

 

[kingkorg]

Indeed - going down to 30v(!) would give you "only" 6dB less sensitivity.

Last time i used ldc on snare i applied 15v to the capsule