Neumann Vintage U87 Clone : Build Thread.

[Edward]

Hi all!

I would need some help with the calibration process, I apologize in advance if this is a dumb question or if it has discussed before and I missed it.

Boards are fully stuffed, AMI T13 transformer, no capsule yet. My problem is that I can't hear the 1KHz sinus tone through the microphone in my DAW. I am feeding the tone to RT + ,SW -, but all that comes out at the XLR is a big buzz. When I turn R11 all the way to one side the buzz goes away. If i turn it the other way nothing changes.

I made some measurments:

47.52V Phantom in. At the zener i measured 23.6V. R18 47.69V, R19 47.24V. At C10 I got 20.85V and when measuring at FC I have 40.78V.




What am I missing, are the measurments good enough? Any help would be highly appreciated!

Do you have a scope to bias ? your voltage looks goods, the behavior of the FET seems to be proper execpt for the buzz,  could you try setting your drain voltage at 11.5V and then connect the capsule and try the mic with the body installed and everything. that will tell us if there is an underlying problem with your buzz ,  make sure the pcb is properly grounded to the mic body so in this manner you take a step forward to come back with more answer.  please visit the first page of the white market thread as there is a ton of info for troublshooting and hint on capsule connection as well.

Thank you for your answer!

Unfortunately I do not have access to a scope, I was planning to do a THD / Tone calibration. I'm gonna make the ground connection better to the microphone body because I made it poorly just so I could start testing. I don't have a capsule yet but will order one soon, or actually I have the one I pulled out from my donor microphone... would that work for testing? It is a single sided capsule, the micophone was a TSL U87.

 

[kante1603]

I guess i could, but i think the way my mount is the capsul would be backwards from the way I want to orient it with the switches.  I guessi could reverse the mount entirely too... ugh lol.

Yes!

 

[Matador]

Thank you for your answer!

Unfortunately I do not have access to a scope, I was planning to do a THD / Tone calibration. I'm gonna make the ground connection better to the microphone body because I made it poorly just so I could start testing. I don't have a capsule yet but will order one soon, or actually I have the one I pulled out from my donor microphone... would that work for testing? It is a single sided capsule, the micophone was a TSL U87.

If you don't inject a signal, do you hear anything?  With no signal, the gate should be grounded through R7 and the mike should be (relatively) silent.

How about if you place your finger on the teflon standoff connected to the JFET gate connection?  Your body will act as a nice antenna for 60Hz radiation, so you should hear a nice 60Hz hum coming through the speakers (of course replace 60Hz with 50Hz if you live in Europe) .

You can also try working backwards:  disconnect the primary transformer lead that comes from the coupling cap (leaving the other side connected to circuit ground), and directly inject your unbalanced test signal there.  If you can hear the tone then you need to work 'backwards' through the circuit until you can find the problem.

 

[DUDE GUY]

Ah ya, back in business!!!

Got my replacement T13 (and another AMI sticker!!!) ha. This one looks like the pic in the spec sheet, which is nice. I'm going to install tonight and I'll post the results.

Happy building to everyone.

-DUDE GUY

 

[kante1603]

How about if you place your finger on the teflon standoff connected to the JFET gate connection?  Your body will act as a nice antenna for 60Hz radiation, so you should hear a nice 60Hz hum coming through the speakers (of course replace 60Hz with 50Hz if you live in Europe) .

I have 10 fingers-which one should I use? ;D ;D ;D

(Sorry,couldn´t resist....)
Udo

 

[Matador]

How about if you place your finger on the teflon standoff connected to the JFET gate connection?  Your body will act as a nice antenna for 60Hz radiation, so you should hear a nice 60Hz hum coming through the speakers (of course replace 60Hz with 50Hz if you live in Europe) .

I have 10 fingers-which one should I use? ;D ;D ;D

(Sorry,couldn´t resist....)
Udo

After all my years of soldering, I only have one finger left....so it's redundant to me.

 

[poctop]

I have the one I pulled out from my donor microphone... would that work for testing? It is a single sided capsule, the micophone was a TSL U87.

you can sure use the only side you have just connect it to FC section,
Cheers,
Dan,

 

[DUDE GUY]

GREAT SUCCESS!!!  8)

New T13 installed and all is well. I heard some glorious 1k going through the mic, music to my ears.

Thanks again Wave for the T13 reference pic, very handy.

-DUDE GUY

 

[poctop]

GREAT SUCCESS!!!  8)

New T13 installed and all is well. I heard some glorious 1k going through the mic, music to my ears.

Thanks again Wave for the T13 reference pic, very handy.

-DUDE GUY

Where will you put the AMI sticker Then  8)
Excellent
D

 

[Edward]

Thank you Matador an Dan for your excellent help!

I noticed the buzz went away as soon as I put the PCBs inside the microphone body, so that problem is solved. This just proves what a complete noob I am. Placing a finger on the teflon standoff made the exact same type of 50Hz buzz. By the way I used my right hand little finger for this task Udo

I also set the drain voltage to 11.5V and connected the capsule that was in my donor microphone, and man I have to say the microphone sounded really good already. I was truly amazed by that.

So back to trying the THD / Tone calibration method then...


I also need to make a decision on either the Peluso P-K87i or the Microphone Parts RK-87 capsule... which one do you recommend?

 

[kante1603]

By the way I used my right hand little finger for this task Udo

O.K.,I´m going to try it with my nose (imagine that funny picture) ;D

Have fun with your build,seems you are very very close to get a cool microphone (while I´m still stuck...... ).

Cheers,

Udo

 

[wave]

Thank you Matador an Dan for your excellent help!

I noticed the buzz went away as soon as I put the PCBs inside the microphone body, so that problem is solved. This just proves what a complete noob I am. Placing a finger on the teflon standoff made the exact same type of 50Hz buzz. By the way I used my right hand little finger for this task Udo

I also set the drain voltage to 11.5V and connected the capsule that was in my donor microphone, and man I have to say the microphone sounded really good already. I was truly amazed by that.

So back to trying the THD / Tone calibration method then...


I also need to make a decision on either the Peluso P-K87i or the Microphone Parts RK-87 capsule... which one do you recommend?

I can answer this one with a question...

What kind of capacitors did you use in the 10, 220, 470, and 560pF positions?

Dave

 

[saxmonster]

I took my grill off tonight  to look at my capsule because I wanted to double check the wiring on it for another project I am starting but I noticed that the front capsule has a few pieces of something on it.  Maybe loose particles from the head basket / grill.  I don't think its dust or dirt.  So how do you clean this off?

Can I use a very small soft tip artistic paint brush to gentle wipe or pick this off?  The pieces are on the gold plating too.


Errr, always something.  The mic sounds fantastic so maybe I will just leave it alone.

-Scott

edward

here is my sax through the Peluso P-K87i

http://www.ehornstudios.com/media/MRMEDIT.mp3

HTHS

 

[MagnetoSound]

The mic sounds fantastic so maybe I will just leave it alone.

Good call. 

 

[kante1603]

I took my grill off tonight  to look at my capsule because I wanted to double check the wiring on it for another project I am starting but I noticed that the front capsule has a few pieces of something on it.  Maybe loose particles from the head basket / grill.  I don't think its dust or dirt.  So how do you clean this off?

Can I use a very small soft tip artistic paint brush to gentle wipe or pick this off?  The pieces are on the gold plating too.

@Scott (and anybody who´s interested):

I have found a guide to clean a capsule,written by Neumann originally in april 1988.It´s in german language of course,so I tried to translate the last chapter about

cleaning the membrane:

"Each membrane should be cleaned with destilled water,applied using a very soft brush drenched with it.
The water containing now the loose dirt should be  picked up with a piece of soft and good absorbent blotting paper.
Repeat this step until final cleaninig.
Membranes that can not be cleaned this way must be exchanged.

It is not allowed to use solvent for this procedure.
Solvent has a low viscosity and is too volatile:There is no time to do a gentle cleaning,it will cause cords ("Schlieren") on the membrane:Solvents go under the membrane ring and take the dirt with them.
Solvents cool down the membrane-they will generate humidity under it which can badly evaporate then.
Additionally there is the danger to remvove the tension of the membrane."

And I can not repeat it often enough:
Never ever touch the membrane or the contact- and isolation elements with your fingers!No high impedance part likes it!
Even the smallest dirt or fat parts from your skin can definetely decrease the isolation and then cause interfering voltages!!!

Wear gloves!

Hope to have helped,

best regards from germany,

Udo.

 

[MagnetoSound]

Gotta say, capsule cleaning is a very risky procedure and should only be carried out in cases of serious contamination.

If there is no audible problem - that is, if the sound is not disappearing under the breath test, there is no problem.

... I noticed that the front capsule has a few pieces of something on it.

This is in no way a problem. Best to leave it alone.

 

[kante1603]

Gotta say, capsule cleaning is a very risky procedure and should only be carried out in cases of serious contamination.

If there is no audible problem - that is, if the sound is not disappearing under the breath test, there is no problem.

... I noticed that the front capsule has a few pieces of something on it.

This is in no way a problem. Best to leave it alone.

I absolutely agree with you Dan!
I just wanted to make people get aware of what this is about,I think it helps a bit to understand how sensitive this is,therefore taking special care on handling capsules.Have translated this from the original NEUMANN-INFORMATION "88 042".Thought it might help.
But you´re right:
Never change a running system!

Have a good day,

Udo.

 

[saxmonster]

Thanks guys it will stay in there and not be touched!!!!!!!!!!!

 

[Edward]

Thank you Matador an Dan for your excellent help!

I noticed the buzz went away as soon as I put the PCBs inside the microphone body, so that problem is solved. This just proves what a complete noob I am. Placing a finger on the teflon standoff made the exact same type of 50Hz buzz. By the way I used my right hand little finger for this task Udo

I also set the drain voltage to 11.5V and connected the capsule that was in my donor microphone, and man I have to say the microphone sounded really good already. I was truly amazed by that.

So back to trying the THD / Tone calibration method then...


I also need to make a decision on either the Peluso P-K87i or the Microphone Parts RK-87 capsule... which one do you recommend?

I can answer this one with a question...

What kind of capacitors did you use in the 10, 220, 470, and 560pF positions?

Dave

220, 470 and 560pF are Polystyrenes. The 10pF is a Mica, but I just found a 10pF Polystyrene at Farnell that maby would fit so I'm thinking about getting that.

 

[adeptusmajor]

I'm curious if anyone at this point has swapped the mica for a styrene and noticed any significant difference.

I have the micas as per the BOM in my mics, can't say there is anything I don't like about them. But better is always better...

Just wondering if it is worth the effort to hunt down and replace one cap.