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[Derek Samuel Reese]

Happy holidays everyone,
I was wondering if a knowledgable person can tell exactly what was modded on my u67, if i posted clear pictures here ?
If so, it would be great to also know how many components were replaced.

I love my mic but I know it was modded in the past, but the guy who performed the modifications will not tell me exactly what he did, (his secret sauce I suppose)
I can only tell that the S2 switch was removed, outside of that I have no clue.

If someone is kind enough to help me, I will post great quality photos,

Thank you, and I hope everyone has a safe and Happy Holiday.

[klaus]

I understand if someone does not want to share his "secret sauce".

Most if not all circuit alterations of condenser mics are straight-forward. With a schematic, a versed microphone technician could easily deduct what's different from a stock U67 circuit, and be able to tell you. If photos are not conclusive, a personal inspection certainly will.

[Derek Samuel Reese]

Hey Klaus, I should have asked you to check it out when it was in your presence.
Would it be ok if I uploaded a few photos here to see if you can tell visually ?

[klaus]

I'll make a (one-time) exception, but please consider that a forum cannot reliably authenticate mics.

[Derek Samuel Reese]

I appreciate this Klaus :-)

[RadarDoug2]

The yellow caps and the 15K 10% resistor. Thats a funny one. Also some caps down by the transformer?

[klaus]

Three filter caps and R10 (the 15kΩ resistor) were replaced.
Assuming you are concerned that these changes would negatively affect the performance of the mic, I can assure you they won't.

As audio only passes through these components indirectly, I would leave them alone.

 

[Derek Samuel Reese]

Just thinking out loud here, are all the components that were replaced still available if i ever wanted to buy them ?
I have no idea what an un-modded u67 sounds like as this is the only one i have tried.
It truly sounds fabulous on all sources thanks to Klaus.
I have no concern at all, the mic sounds insanely beautiful, i was simply curious and thank you for this guys.
I would like to wish everyone a safe and happy holiday and hope that 2021 will be much better for all of us

[RadarDoug2]

I find it strange in this day that someone would fit a 10% carbon resistor in a vintage mike.

(A precision DC volt meter applied to the junction of R10 and R11 could tell whether the replacement resistor is off enough so push the bias voltage outside the prescribed 1.6-1.8. VCD. But I doubt it. K.H.)

[Derek Samuel Reese]

Where exactly are you seeing this ?
Just trying to learn a little here :-)

I am seeing two yellow cylinders looking things closest to the head basket,
and one more on the left side of the ef86 tube,
then another one on the opposite side of the microphone (right side).

[klaus]

There are two yellow caps in the head, and one sideways next to the tube.

The resistor in question is next to the big metal shield (tube side of amp): it has color bands of brown, green, orange and silver.

first color = brown = 1
second color = green = 5
third color = orange = number of zeros = 00
fourth color =  silver = % of tolerance = 10%

[Derek Samuel Reese]

Brown green orange and silver? I thought that was an original. lol what is that??

[klaus]

Radardoug referred to a resistor that was changed. It's identified in one of your picture by the 4-color ring. I described where it is located in my previous post, where I mentioned that it's likely not relevant to the mic's performance.

[Derek Samuel Reese]

I appreciate this guys, I’m not touching anything, was just curious

[RadarDoug2]

Neumann used the best resistors they could find when they built these mikes, but they do fail. Replacement with a cheap carbon resistor I find insulting to the heritage.

[soapfoot]

Neumann used the best resistors they could find when they built these mikes, but they do fail. Replacement with a cheap carbon resistor I find insulting to the heritage.

Yes, I find that strange also.

The first mic I built, I used this style of resistor, because up until then the only tube electronics projects I had done involved guitar amps, where old Allen-Bradley carbon composition resistors were rumored to add "something special," so I thought the same would be true in tube microphones.

I now know that to have been mostly misguided. But if Klaus says this one isn't hurting anything, I'd trust his expertise.

[klaus]

(...)But if Klaus says this one isn't hurting anything, I'd trust his expertise.

Let me slightly rephrase that:
I think there are bigger fish to fry in a mic like that. You would first need to analyze the exact impact a given material or construction has on the sound of the (obsolete) component; then you would need to hunt for a replacement of similar material and construction; then you would need to undertake listening tests, and... good luck with that for a single-component exchange.

In the present case, the resistor in question regulates the heating voltage, nothing more, nothing less. So you choose you battles, given a limited time on this earth.