Neumann U87 Clone D-87M Build Guide by Andrew Schaap

poctop · Feb 11, 2015

Hi All, Special Thanks To Andrew Schaap for this nice Presentation of the build of the D-87M in is final Format,

Feel Free to have a look,

http://www.vintagemicrophonepcbkit.com/Neumann%20U87%20Build.htm

Enjoy,
Best,
Dan,

hugo · Sep 10, 2016

Hi all,
I just finished a D-87 from vintagemicrophonepcbkit ,a nd i have this issue :
When i turn up the phantom 48v of my preamp, my mic do pass the sound of my voice, but it stops after 10sec. and it do not come back... if i switch to 8 mode, the sound comes back for 5/6sec...
Can somebody help me with that issue ?
Thank you

RuudNL · Sep 11, 2016

Is there any variation of the drain voltage of the FET, or is the drain voltage steady?

hugo · Sep 11, 2016

Thank you for your answer, can i check this without removing the capsule ?.. On every "build guide" i saw, the calibration is made before capsule installation..is it ok in this case ?... When the audio passes, it sounds really great, i really want to work with it ^^

RuudNL · Sep 11, 2016

Yes, measure it with the capsule in place.
From what I read, I get the impression that the bias of the FET is 'drifting'.
Remove the body tube of the microphone, connect a meter between the drain of the FET and ground and switch on the phantom power, while you observe the reading on the meter of the drain voltage.
I have the impression that the voltage will be all over the place...
(Be prepared to hear a loud hum, because the electronics are not screened after you removed the body tube!)

Gus · Sep 11, 2016

hugo said:
Hi all,
I just finished a D-87 from vintagemicrophonepcbkit ,a nd i have this issue :
When i turn up the phantom 48v of my preamp, my mic do pass the sound of my voice, but it stops after 10sec. and it do not come back... if i switch to 8 mode, the sound comes back for 5/6sec...
Can somebody help me with that issue ?
Thank you

Have you checked the microphone without your voice? I could be the moisture in your breath causes dust etc. on the capsule to conduct and discharge the voltage from the capsule

hugo · Sep 11, 2016

i speak far from the capsule...

hugo · Sep 11, 2016

Originaly, i calibrated the mic a 11.5v without capsule. It was stable

Now, it is like that : It starts at 16v, then it slowly fall..13v after 2min.

I have a doubt with the pattern switch.. When i closed the mic for the first time, i did not see that the screw of headbasket was at the same place, and that screw pushed the top of the switch, which started to be open..

RuudNL · Sep 12, 2016

This is what I would try:
Switch on the phantom power and wait for a couple of minutes.
Then adjust the drain voltage to the correct value and try again.

hugo · Sep 12, 2016

thank you, i check this today and i will let you know... Is it normal to have to wait with that type of mic ?...or is it just like DIY issue.?

You don't think the switch can be broken and is responsible of a voltage problem ?

hugo · Sep 12, 2016

I do not understand...the mic is working normaly now, even when i change the pattern BUT, sometime if i change the pattern the mic become silent and stay silent... I really think the pattern switch is broken and i ordered a new switch to replace it. Just one other thing : when i change the pattern, the mic makes a "shhh" for 3sec before being normal.. Is it a standard thing ? Or may i fix this too ?

RuudNL · Sep 13, 2016

The 'old' Neumann U87 microphones always muted for a couple of seconds (sometimes as long as 10 seconds!) after you changed the pattern selection. So this is not so strange. They didn't produce a 'shhh' however...
BTW: I would keep an eye on the drain voltage of the FET. If this keeps fluctuating, there may be something wrong in the high-impedance region of the input.

hugo · Sep 13, 2016

i had an old version of mouser cart so i remember the 68M resistors in my mic (R4 R5) are replaced with 60M...should i correct this ?
Again, i really big thank you from France for your support.

RuudNL · Sep 13, 2016

Personally I would prefer a higher value than 60 M, but this can't be the cause of your problem!

hugo · Sep 13, 2016

RuudNL said:
Personally I would prefer a higher value than 60 M, but this can't be the cause of your problem!

Ok i will change this at the same time. Could you please tell me which components can be involved in my Drain issue ? Which process can i follow to find the origin ?
Maybe this would help : when i switch off the 48v, i have a 5sec shhhh.

RuudNL · Sep 14, 2016

If the clone circuit follows the original circuit diagram, the only way to check is to remove one connection of C4 (I would suggest at the junction of C4 and R7) and check if the drain voltage stays stable over time.

EDIT: Looking at the schematic, the 60 / 68 M resistors are not critical. I would leave the 60 M resistors in.
Over C1 in series with C4 is a voltage of 47 V. If there is a very small leak current in those capacitors, this may influence the FET bias.

hugo · Sep 28, 2016

Thank you very much. I changed the switch, and it was not this (just as you said !). I checked all connections, and i made a mistake during the wiring : One resistor, one styroflex and one ground wire have to be soldered together. Because i started by populating the pcb, i remained the styroflex and resistor's legs in the pcb holes...That was my mistake : only one leg is soldered to the pcb, the other comes straight point to point. The current was splitted between this bridge and the pcb, so the drain was not good.
Thank you very much for your help Ruud !
Hugo

hugo · Nov 18, 2016

Hi again...
The mic is finished, it works, but i still have a substancial self noise, no gain and no high freq.... Which component can be involved in that issue ?..Can the 68M resistor be involved in that issue ? That the only component i see with other value (60M in my case). Does it look like a calibration problem ? since i do not have oscillo, i made 11.5v with MM.
Thank you

hugo · Nov 23, 2016

hugo said:
Hi again...
The mic is finished, it works, but i still have a substancial self noise, no gain and no high freq.... Which component can be involved in that issue ?..Can the 68M resistor be involved in that issue ? That the only component i see with other value (60M in my case). Does it look like a calibration problem ? since i do not have oscillo, i made 11.5v with MM.
Thank you

up

lukas · Nov 24, 2016

hugo said:
Hi again...
The mic is finished, it works, but i still have a substancial self noise, no gain and no high freq.... Which component can be involved in that issue ?..Can the 68M resistor be involved in that issue ? That the only component i see with other value (60M in my case). Does it look like a calibration problem ? since i do not have oscillo, i made 11.5v with MM.
Thank you

Take 20k Pot in place R14 and set voltage to 20,62v.

Neumann U87 Clone D-87M Build Guide by Andrew Schaap

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