U87 Inards, what to do with them?

I brought the InnerTube Audio mod for my Neumann U87 last year and love it. With that mod you totally remove the whole insides and replace with their electronics.

So I have the solid state insides of a U87 doing nothing. Incidently from the serial number it was made in August 1970.

Is there a cheap chinese mic that has the exact same body shape as a U87 so I could remove the insides and replace with the Neumann ones I have? I could also replace the capsule and have a second Neumann on the cheap. Is the Peluso CEK89 U87'ish?

My electronics is very limited, but I can do simple jobs.

Alternatively is it not worth the hassle and whack it on eBay!!! Any idea what it may be worth?





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...Or I could use it to go with that old U87 head assembly that I have...

:shock:

Keef

Useless piece of junk. I'll take it off your hands for $5.

:razz:

JC

From the pictures is that a 2sk107 and a 2.2K source resistor? It is sometimes hard to tell the colors bands on a CRT.

Anyone have a good spec sheet with curves for the 2sk107? I have not found more than the basic specs .9ma to 14.3ma IDSS Vgsoff -.45VDC to -4.95VDC etc.

FWIW the u87 with K107 I have seen did have a 2.2K source.

[quote author="SSLtech"]...Or I could use it to go with that old U87 head assembly that I have...

:shock:

Keef[/quote]

Don't suppose you fancy getting rid of it :grin:

I have been looking for a 'broken U87' for quite a while, there was one on eBay recently but it was withdrawn with a few days still to go.

Understandably with a mic of this cost people get them fixed!

Surely all those thousands of mics that ripped off the design of the U87 one of them must fit these electronics.

[quote author="Gus"]From the pictures is that a 2sk107 and a 2.2K source resistor? It is sometimes hard to tell the colors bands on a CRT.

Anyone have a good spec sheet with curves for the 2sk107? I have not found more than the basic specs .9ma to 14.3ma IDSS Vgsoff -.45VDC to -4.95VDC etc.

FWIW the u87 with K107 I have seen did have a 2.2K source.[/quote]

You'll have to excuse my ignorance, which parts are they ie R13 etc

I am a major electronics novice.

Gus,

Neumann sells a replacement 2SK170 part for the U87, but it comes with a pre-selected resistor, sealed in the plastic pack. The FET is never sold without the resistor, and the values that I've seen have ranged from 1k2 to about 3.9, from dim-n-dusty memory.

Ted,
About half of the mics that MXL and other manufacturers sell are based on the U87/KK67 model. However, the thing that's easiest to do is the electronics, and the thing that they still haven't got right is the capsule!

What differentiates the U87 design is the fact that the capsule has an inbuilt mechanical pre-emphasis (treble-boost) and the electronics roll off afterwards. The U67 did this also, but with a rather more pronounced roll-off.

There are both transformer and transformerless versions of the U87 schematic made and marketed by MXL and numerous other (Alctel capsule based) chinese manufacturers... however, the single biggest upgrade that you can do is to get one of these mics and slap in a REAL U87 capsule...

Bang! -IMMEDIATE improvement, bigger than ANYTHING else that you can do... transformer, anything. 'Reversing' the swap is partuicularly illuminating: Suddenly, the U87 stops sounding like a clear, bright mic, and sounds thin and brittle... What does that tell us?

Well, putting an 87 with an Alctel capsule inside next to an MXL mic with a K67 inside, I prefer the MXL... My simple conclusion is that there may be some small gains to be had by putting better transformers into the MXLs, but you'll NEVER make it great until you get rid of that capsule...
[quote author="TornadoTed"]Surely all those thousands of mics that ripped off the design of the U87 one of them must fit these electronics.[/quote]
Mechanically, no. They invariably have a rather smaller diameter 'taper-tube'... at least the only ones I've seen/owned have all been like that.

Keith

You could just keep it and have it as another sonic flavor in your arsenal. Just because it is a tube and sounds great does not render the solid state electronics useless. Yes changing it out takes a minute but you now potentially have 2 different sounds one can use.

Or if your so set on it being tube only, sell the electronics as is...

2nd picture bottom right resistor with the green body. It looks like red red red (2.2K) on my CRT.

What color dot on the microphone??

Now it looks like you also have the 50 ohm version R21 and R20 (the 47 ohm resistors). I would guess the transformer is strapped for 50 ohm output. Pivot the battery metal plate, note the stop tabs at the bottom. One or two wire jumpers soldered on the transformer taps?
If wired 50 ohm you might want to change it to 200 ohms and try it again not hard to do.


Keith I have seen up to 11K on early 87s with 2n3819s that looked factory.

It appears to be from left to right red, red, purple, red.

The dot by the serial number is red.

There is only 1 jumper on the transformer taps, the middle 2 of the 4 legs.

As a complete sideways step could I restore the original U87 with it's electronics.

And then for a 2nd mic buy a K87 capsule and put it and the InnerTube Audio electronics in a new body?

Would this be possible (for a novice) to do as the pattern selector on the U87 becomes obsolete with the InnerTube Audio mod as the polar pattern is selected from the power supply.

It seems a shame to have a large portion of a good mic doing nothing.

[quote author="Gus"]Keith I have seen up to 11K on early 87s with 2n3819s that looked factory.[/quote]
Yes, factory-fit.

I'm thinking about the 'Ersatzrteile' kit that Neumann used to sell... (perhaps still does. -I must search for a part number)

Keith

Tornado Ted,

Just to compare U87's and mods

If you or anybody post detailed pictures of your Innertube audio conversion or any other conversion for that matter.

I'll post some detailed photo's of my Steven Paul U87 conversion.
Obviously, My mic was modified before he passed away. RIP

Hmmm I personally I wouldn't feel right about doing that. InnerTube Audio are a small company who are still very much going strong. If they were no longer around or selling the mod then possibly.

In fact it may not be possibe as there aren't any electronics on view anyway. All you can see is the valve and the very top of the transformer.

I've owned a couple of those over the years and both of mine were "potted", couldn't see a thing.......

that being said, i also wanted to "make use" of the original electronics.
Neumann used to sell the mount and head electronics, but stopped making the part available. Now you could go to Peluso and get a mount and capsule and have a go at it. the parts in the head are nominal(in number)

have someone here with metalwork knowledge and equipment make you a body and grill, Doesn't need to look like the old one, just needs to work.....

All you can see is the valve and the very top of the transformer

Click to expand...

I understand your ethics , but If you can't see much , then what's the worry. DIY and political correctness don't mix very well.