A possible way to convert U87Ai into U87Ii

I might buy myself a Neumann U87AI & was just thinking could it be hot rodded into the vintage 87i version my just lowering the polarization voltage from 60V back down to 46V ? maybe with resistors? & then make it switchable.....I have made a few 87i circuits from scratch on vero boards & it works well I like the lower output of the 87i so I can hear the pre amp more Im sure the 87ai would sound great but would be great to switch between the two circuits....

thanks

The U87Ai uses a DC/DC conveter with 1 M.ohm resistors at the output.
So I suppose that if you load the output(s) with 1 M.ohm, you will get half the output voltage. (Nominal= + or - 60 V.)
If you are aiming for 46 V. you should use a load resistor of approximately 3.3 M.ohm.
(No guarantees, measure and check the voltage yourself!)
Keep in mind that this will degrade the sinal to noise ratio by 3 dB.

Old thread, but I hope someone is interested.
It's my first post in this forum and probably this idea has been already posted.

What about buying a used U87AI and installing the vintage design PCBs?
I know it's a bit crazy to trash a 1500 U$S perfectely working mic for a DIY project, but still...
You get the capsule, the mounting, the headbasket, the tranny and the body. Cheaper than buying the spare parts from Sennheiser.

M

I'd be really curious what the results of a double-blind test would be, between a stock U87Ai and a reduced-voltage one would be ;D

That being said, though, perhaps the easiest way to drop the voltage would be to increase the value of one of the resistors on the input of the DC-DC converter (R20 and/or R21 on the schematic below)

http://recordinghacks.com/images/mic_extras/neumann/u87ai-schematic.gif

Perhaps add a 50k trimpot in series with one of them, or replace one with a 100k trimpot, at least during testing?

Khron said:

I'd be really curious what the results of a double-blind test would be, between a stock U87Ai and a reduced-voltage one would be ;D

Click to expand...

Good question. The consensus seems to be that the old one has more headroom and a sweeter/less harsh sound. People who ought to know and who have used them side by side have claimed this. I personally haven't done a double blind test.
Yes, a little more noise in the old one.

Me, if I were altering a U87ai, it would be into a U67.
Max (IOaudio) offers a drop-in, fully reversible kit.
Dany(Poctop)'s is not as quickly reversible, but is more flexible when it comes to tranny selection (which is an important part).
I'm not sure if Dany's kit fits the U87 body BTW. It was made for the SYT-5. His U87i kit comes in a small and large version.

Oh, some mic guru's (I believe Andreas Grosser is one of 'em) do alter U87ai mics into U87i.
Likely by modding the circuit rather than by completely gutting it.

Let's just say that, in audio, confirmation bias is a humongous obstacle in the way of objectivity, imho

I guess with the higher bias voltage, one could argue the diaphragm's "idle tension", for lack of a better term, would push its resonant frequency higher in the range, but then again, i'm no expert ;D

Let's just say that, in audio, confirmation bias is a humongous obstacle in the way of objectivity, imho

Click to expand...

I hear tou.
But "non-believers" are susceptible to confirmation bias, too. 

Maybe Klaus has something to say about  the U87ai versus the U87i.
He wasn't with us when this thread started.

I'm not claiming you definitely won't hear any difference Only that i'm highly skeptical of ones who declare they hear this and that, while in full knowledge of the DUT (device under test) ;D

I seem to recall watching some mic shootout, possibly from recordinghacks, with the performer doing a separate take for each mic, and i was just facepalming all the way...

*** end of rant *** and apologies for the hijacking...

dbrstudios said:

What about buying a used U87AI and installing the vintage design PCBs?

Click to expand...

Idea is little bit stupid
You don't have install any other PCB.
To make U87i you  have already almost everything inside U87Ai.
There are two ways!
- change D7 for 49V or 50V zener diode
- disconnect whole DC converter circuit

With both options there's need to change few components inside preamp!
Buy U87ai, put pics o the PCBs and i will write you what and where need to be changed.

Yup, makes sense to me.

As far as I know, the difference is not only in the electronics, but also in the capsule.
So changing the circuit won't make it a 'real old' U87.

(Offtopic) Last week I spoke with a very well known studio owner, who has been in buisiness for 40 years.
He said: "Everybody says the modern Chinese microphones are too bright, but that is exactly what I like! I don't have to add more treble now, I own a couple of relative cheap Chinese condenser microphones, and I like them better than the Neumann U87. The Neumanns are very dull sounding microphones." (/Offtopic)

Don't know if I can agree with that...

Old ears maybe?

And/or damaged?

ln76d said:

Idea is little bit stupid
You don't have install any other PCB.
To make U87i you  have already almost everything inside U87Ai.
There are two ways!
- change D7 for 49V or 50V zener diode
- disconnect whole DC converter circuit

With both options there's need to change few components inside preamp!
Buy U87ai, put pics o the PCBs and i will write you what and where need to be changed.

Click to expand...

Thank you In76d!!!
I see that there are several approaches. Full kits, mods kits and adaptations to the newer U87Ai.
What's the best option is hard to know. I just want a high-end big diaphragm all around condenser mic like the U87. I don't mind if it's purple or goldish.   
If anyone has an experience/opinion, audio comparaison I would love to hear your thoughts.

RuudNL said:

As far as I know, the difference is not only in the electronics, but also in the capsule.
So changing the circuit won't make it a 'real old' U87.

(Offtopic) Last week I spoke with a very well known studio owner, who has been in buisiness for 40 years.
He said: "Everybody says the modern Chinese microphones are too bright, but that is exactly what I like! I don't have to add more treble now, I own a couple of relative cheap Chinese condenser microphones, and I like them better than the Neumann U87. The Neumanns are very dull sounding microphones." (/Offtopic)

Don't know if I can agree with that...

Click to expand...

Capsule degradation is an issue. Maybe a boutique capsule would be best.
For me it depends with what are you recording, preamps, tape, Pro Tools. I heard around that digital has with high-end frequencies the same problem that analog with the low-end. If you overdrive it'll start to crush. I never worked on a proper analog setup, but I know that digital can do that. Anyway, it's all about where you want your instrument. I don't need a bass in 16kHz or a vocal in 60Hz. Give me a proper midrange and I'll be happy. Chinese mics can be useful, but not everwhere. At least to my taste.
Cheers,

M

dbrstudios said:

I see that there are several approaches. Full kits, mods kits and adaptations to the newer U87Ai.

Click to expand...

And evertyhing mentioned you really don't need
Grab U87Ai and use original PCB.
Not much to work with