Neumann Vintage U87 Clone : Build Thread.

[newmod]

So I built the u87 and I am very pleased with the sound.
Just one thing I noticed is that I have been at my friends who was using a focusrite ISA One preamp and it was humming. I am no sound engineer but after a while he adjusted some levels (not sure what) an the hum was gone. Another friend had the gain set at 80db on the preamp. My question is this....for this circuit, is there a recommended db setting for gain? Is the problem here that my friends were cranking the gain too high. They mentioned that with other mics they have, they never get hum. Hum usually indicates poor grounding or shielding? Not sure if its a problem with the circuit .....Would it help if I ran an extra wire from the XLR pin and solder it to the chassis frame of the mic?

 

[Ricardus]

So I built the u87 and I am very pleased with the sound. Another friend had the gain set at 80db on the preamp.

This seems excessive for pretty much ANY recording situation.

My question is this....for this circuit, is there a recommended db setting for gain?

Every situation is different. Watch your meters?

Is the problem here that my friends were cranking the gain too high. They mentioned that with other mics they have, they never get hum. Hum usually indicates poor grounding or shielding? Not sure if its a problem with the circuit .....Would it help if I ran an extra wire from the XLR pin and solder it to the chassis frame of the mic?

The body should be grounded to pin 1 already through the PCB.

I just tested mine and it is.

 

[ostrol]

Hi Guys,

I have all the parts ready to build my u87... except for the fact that... well. The Behr*** B2 Pro is too small for the PCB i bought by about 5mm.

Would I be okay in filing away this amount off both edges of the PCB? Particularly the B1 side of the PCB worries me, as I would have to sever a part that is not transparent- I'm wondering if this would sever any connections at all? It doesnt look like it, but I am a 100% beginner at this so I'd rather ask....!

Pic related, would need to chop off both sides after the screwholes

 

[burbela]

Works perfect, only have a little noise and signal is a little lower then usual microphones in studio.
Transformer is 7:1, will try 10:1 - maybe will be better.

 

[simensez]

Id love to buy 2 u87 kits!

 

[geekmacdaddy]

Greetings, and respect.
U87i build, Dany's boards. Could only dial in 1.7v bias and had no output. Upon further inspection, I had C12 in backwards (gagggghhh!). I now have output and a nice ground style hum. Did I blow something up? 2.7v max bias now.

Thanks very much in advance.

 

[TillM]

Did you already change c12 ? What is the voltage at the reference points ?

 

[geekmacdaddy]

Did you already change c12 ? What is the voltage at the reference points ?

I used the same cap, as I don't have any "audio" quality 10uf's. I could just try another (sprague atom is all I have). Forgive, what are those test points?

 

[mrgrooves666]

Greetings, and respect.
U87i build, Dany's boards. Could only dial in 1.7v bias and had no output. Upon further inspection, I had C12 in backwards (gagggghhh!). I now have output and a nice ground style hum. Did I blow something up? 2.7v max bias now.

Thanks very much in advance.

Was this with the complete body and basket assembled? Just checking, because without them, the circuit will be suceptible to all sorts of interference..

 

[geekmacdaddy]

Was this with the complete body and basket assembled? Just checking, because without them, the circuit will be suceptible to all sorts of interference..

Yes on all accounts.

 

[TillM]

B1 Reference Voltage and Schematic https://cdn.groupbuilder.com/groupdiy/u/39511/58d1402a02050.pdf

B2 Reference Voltage and Schematic https://cdn.groupbuilder.com/groupdiy/u/39511/58d1402a02062.pdf

look at the first page, there are the references. On the original Neumann schematic, you can also see the voltages. At C12 the reference voltage is 33vdc. After R14 it’s 29vdc and so on.
You don’t need “audio” quality condenser, any 10uf will do it for your test.

 

[Drosselmeier]

At C12 the reference voltage is 33vdc.

In the scheme is Zener 24 volts not 33 volts

 

[Drosselmeier]

Break the connection at these points. At the connection point P13-R15-C11 should be >40 volts. At the connection point P14-C10 should be >20 volts.

 

[geekmacdaddy]

In the scheme is Zener 24 volts not 33 volts

Thank you, Drosselmeir. 5am here and I'll get right on it.

look at the first page, there are the references. On the original Neumann schematic, you can also see the voltages. At C12 the reference voltage is 33vdc. After R14 it’s 29vdc and so on.
You don’t need “audio” quality condenser, any 10uf will do it for your test.

Thank you Tillm, as well!

 

[geekmacdaddy]

46v on C11 and 21v on C10! dialed in and the mic sounds terrific and quiet! I'd pulled up the trace for the ground side of C11. Once that was sorted, my problems were solved, except one. What are the exact points (meter) for dialing in the trimpot? That's still reading 2.7v maxed out. Thank you for all the help! Here's a short clip. The 50hZ rumble is me holding the mic in my hand. iCloud

 

[Greenie]

I have finally managed to get sound from my U87 vintagemicrophonepcbkit, blue version. Only trouble is that it is sound there, very low and there is a fair share of loud hiss/whitish noise. Any hints on what to look for?

 

[Ricardus]

I have finally managed to get sound from my U87 vintagemicrophonepcbkit, blue version. Only trouble is that it is sound there, very low and there is a fair share of loud hiss/whitish noise. Any hints on what to look for?

Make sure the back Hi-Z board is super clean. The smaller board with fewer components. Clean that with the best alcohol you have many times (I use 99% or better) and then try listening again.

 

[Greenie]

That helped a bit, but the recording is still very low. It's a Maiku K87, and I wonder if there should be a differen cap at c6, Maiku sent a 150p instead of the 220pf?

 

[Drosselmeier]

Maiku sent a 150p instead of the 220pf?

It's OK.

 

[Greenie]

So I wonder if tyhere is a part of the D87 that decides the most when it comes to output amplitube? I seem to have the voltages on the different parts. the fet has 11.5v and the diode has 22.4v. Any other crucial parts?