R/E/P > Klaus Heyne's Mic Lab

U87i & U87ai....Differences?

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Working Musician:
I was able to purchase a u87i in great condition which after checking the seriel number, found out was made in 1974. Was curious to know what the major differences were between the "i" and the "ai" which took its place in 1987.

The battery for internal power and its meter in the "i" series was the only real physical difference I noticed. I heard through other sources that the "ai" had a raised output level.

Any information appreciated.

Mark Baker

Klaus Heyne:
I am sure David Satz could execute a precise, all encompassing narrative of the differences.
In the meantime I try a Klutz version:

The central difference between the U87 and its successor U87A was the introduction of a DC-DC converter in the new model (the 'i'-suffix identifies an XLR connector, which all U87A and most U87 have anyway.)

What is a DC-converter?  It is a circuitry ,situated in the space where the battery compartment of the old U87 was, that increases the phantom power's available 48VDC to 60 VDC, and thereby polarizes the capsule voltage with 12 more volts than in the U87.
The extra volts available at the capsule increase the output of the mic by about 10dB. The side effect of the output improvement is a slight reduction in headroom (distortion from very loud sound sources) by 5-6 dB.

All other audio and EQ parameters of the two mics remain the same.

One other advantage of the DC converter is that now the U67 capsules and the (identically constructed) U87A capsules, known as K870, are interchangeable.  

The old U87 capsule required an isolation washer between the capsule halves, to generate three patterns out of 48V, which made the U67 and U87 capsules not interchangeable.

Kind regards,

Henrik Vogel:
Klaus Heyne wrote on Sat, 22 May 2004 21:56

All other audio and EQ parameters of the two mics remain the same.

They do? I have never been in the position to compare a U87 and a U87ai side by side, but what I hear from others is that the ai is brighter which many people seem to dislike. Are you saying this isn't so?

Henrik Vogel

David Bock:
It's true the amount of HF rolloff is reduced in the more recent U87.

Klaus Heyne:
The Neumann frequency plots of U87 and U87A show a difference of high frequency peak in the 7-10k region of less than 1dB between the two models (facilitated by a change of the HF Eq cap from 220pf to 160pf.)

I am not sure whether less than one dB difference qualifies as "the same" or "brighter".  "Harder" may be a better term, caused by the significantly "stiffer" polarization voltage.


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