Neumann Vintage U87 Clone : Build Thread.

[PG_Sax]

Hi guys,

Just double checking, I don't need to make any changes to the D-87 circuit if I'm using the HK87 over the Peluso capsule do I?

Thanks,

P

 

[fsalter]

You can use any 87 capsule without any modification.

 

[PG_Sax]

You can use any 87 capsule without any modification.

Thanks Fred!

 

[doggy6812]

Hey Guys!! I am a total noob. I've built a couple of microphone parts mics in the past but I'm trying something different now. I'm trying to build a DIY u87. Im at the stage of  biasing the fet. I've connected the 48v to the mic. The meter is reading 21.3 v and will not move when I turn the variable  resistor. Can you guys help me? I am at a loss. Thank you so much.

 

[PG_Sax]

Hi guys,

Just looking for some help on checking the Idss of the FET.

Is this right the pin1/2 short together connect to negative side of 9v battery.
Pin 3 to multimeter probe, other probe of multimeter to positive 9v battery?

I have my multimeter in mA and I get no reading.

Using this multimeter https://www.amazon.co.uk/gp/product/B078JDL61X/ref=oh_aui_detailpage_o09_s00?ie=UTF8&psc=1

Probes are connected to mA and COM

 

[PG_Sax]

Hi everybody,

Just wanted to clarify when testing the initial voltage through the circuit, without the the capsule or transformer connected, does anything need to replace the capsule or transformer or can those pads just be left open?

 

[PG_Sax]

Do these voltages look acceptable?

Initial Mic Voltages (No transformer or Capsule Connected)

Phantom Measured at 48v-48.1v

BIAS Pot - shows 2.1v on 1 leg but the other two show 0v - could it be a bad pot or is it because its wide open?

Fet Drain - 11.4 but Bias is wide open and voltage seems to be getting lower
      Source - 2.1

I sent a 1k signal and the sine wave looked ok on the scope.

Zener 22.8
R18 - 46.7
R19 - 46.2
R12 - Top - 11.7 Bottom - 20. 4 Again looks like voltage is falling
R13 - 28.3
R14 - 20.7
R15 - 35.5
R16 - 40.01
R17 - 22.9
R8- 17.6
R9 - 0
No voltage R7 / R6

L1 - 46.7
L2 - 46.7

C6 28.3 - Slight variances
C11 35.5 - Slight variances
C13 40.1 - 40.03
C15 17.6

C1 / C4 - No voltage - Is this because know capsules are connected?

 

[PG_Sax]

Hey guys,

Is anyone able to help me?

Transformer attached, no capsule attached at the moment.

Fet seems to loose voltage and won't go above 8-9v it starts off at 12-13v then just falls down slowly. Bias is wide open

So far everything else is working, have transformer in and can hear sine wave. Thought I had a problem with ground noise but noise is gone as soon as the outside sleeve is attached.

Was Going to start by changing Fet and maybe bias pot?

Source voltage of Fet is at 2.1v

If anyone has any insight I would be really grateful!?

Cheers,

Piers

 

[ln76d]

Hey guys,

Is anyone able to help me?

Transformer attached, no capsule attached at the moment.

Fet seems to loose voltage and won't go above 8-9v it starts off at 12-13v then just falls down slowly. Bias is wide open

So far everything else is working, have transformer in and can hear sine wave. Thought I had a problem with ground noise but noise is gone as soon as the outside sleeve is attached.

Was Going to start by changing Fet and maybe bias pot?

Source voltage of Fet is at 2.1v

If anyone has any insight I would be really grateful!?

Cheers,

Piers

What value of pot you are using? If 10k, then go higher with pot resistance. 20k for example.

 

[PG_Sax]

What value of pot you are using? If 10k, then go higher with pot resistance. 20k for example.

Thanks for replying!

Its a 25k pot, I have another one but they both seem to be working when I hook up them up to the meter.

I forgot to mention I can also see the sine wave on scope and it looks normal. Ive also been able to hear it on headphones although the ground noise is quite bad without body.

Could it be FET?  Is the source voltage 2.1v ok?

When the mic is first supplied with phantom fet voltage is around 12-13v but it moves around a lot and gradually starts falling?

 

[PG_Sax]

Ok it looks like I have a current leak which is why the jfet won't stay still.

What is the most likely culprit, capacitors, or could it be anything on the board?

C1 is only showing 45mv?

Any advice on testing the polystyrene capacitors? Can I connect a 9v battery to them?

 

[ln76d]

If you hear "ground noise" even if you touch the metal body part, then definately check your ground wiring.
Last original U87 i worked on, had perfect bias with ca. 13.5V at the drain, source don't remember exactly but something around 3.5V.  I would rather start checking all the wiring, than molesting styroflex caps and yes, you can test it with 9V, but don't see the point. Danny's boards need a little too much wires for different parts of the circuit, some other diy-ers made mistakes with wiring - i would start from this point, especially if there's some potential ground wiring issue. Is it Fairchild 2n3819 from china? If so check, is it FET at all - this was also reported by some builders.

 

[PG_Sax]

I only hear ground noise when the sleeve is not screwed on. Wiring looks all good I have spent time to carefully clean everything with alcohol as I was stuffing the boards,

Is wiring likely to cause a voltage drain?

Any idea of how to find were the drain is coming from?

 

[PG_Sax]

Thanks to fsalter for sorting me out with jfets and also helping me fix the problem I had!

Turns out capacitor was wrong way round! :/

 

[PG_Sax]

Ok can anyone tell me what I've done. Mic is biased and sounding great so far in testing.

Buuuuuuuuut, am comparing to an old U87 and the waveform is inverted on my mic compared to the U87?

Anyone have any ideas what that could be?

I haven't got the polarity switched on the pre etc.

Its ok think I've got it solved transformed is wired wrong way round..doh

 

[PG_Sax]

Could anyone confirm this for me?

Green Wire - RT - Primary High +
Blue Wire - SW - Primary Low -
Brown Wire - Blau - Secondary Low -
Grey Wire - Weiss- Secondary High +

Wiring the Sowter 1303

 

[doggy6812]

Hey Guys! I am trying to build one of these microphones and I am having an issue. I have too much current at the drain. I can adjust the trimmer from 17v to about 22v. I have 23.21v at the zener. What can I do to fix this? Thank you guys for your help! Randy

 

[ln76d]

Change FET or use different potentiometer value.

 

[Haoxian]

I wonder, if I only use the heart - pointed capsules, what should I delete? Please help me, thank you

 

[PG_Sax]

Has anyone tried increasing C5 to a higher value and got any feedback on the results?

Going to experiment with increasing C6.