Neumann Vintage U87 Clone : Build Thread.

[fsalter]

The 2N3819 orientation on the PCB is fine. I built many of these.

 

[mhelin]

The 2N3819 orientation on the PCB is fine. I built many of these.

In theory the drain and source of JFET are interchangeable (correct me if I'm wrong), but usually the substrate is connected to "source" terminal identified by manufacturer and therefore the capacitance etc. may vary. In fact the capacitance between gate and drain might be smaller than that of gate and source so it might be better to intentionally swap the pins in high impedance circuits. I think I've seen that suggested by someone as a mod.

2N3819 seems to be symmetric device (at least the current parts):
http://theradioboard.com/rb/viewtopic.php?f=1&t=7496

 

[gyraf]

Aegonrero,

You're a bot, arent you..?

;D

Jakob E.

 

[PG_Sax]

Hi there,

Just planning a build using D87 pcb by Dany.

Just wanted to check something, is it fine to leave the variable resistor in place once you've set the bias? Or should you replace it with the correct constant resistor?

Also in setting the bias is the multimeter method (11-11.5v) enough, or should the 1k test tone method be done afterwards to optimise for headroom / thd?

Many thanks!

Cheers,

 

[Aleguitarpro]

Hi there,

Just planning a build using D87 pcb by Dany.

Just wanted to check something, is it fine to leave the variable resistor in place once you've set the bias? Or should you replace it with the correct constant resistor?

Also in setting the bias is the multimeter method (11-11.5v) enough, or should the 1k test tone method be done afterwards to optimise for headroom / thd?

Many thanks!

Cheers,

In mine (about 5/6 u87 made) I leaved the trimmers inside.
No problem about space and in this way you can double check with the 2method you describe (multimeter/1k tone)

 

[PG_Sax]

Thanks a lot for your reply!

Also just trying to source some jfet transistors for the build. Dany has already given me an option from the states - https://www.newark.com/nte-electronics/nte312/n-channel-jfet-30v-to-92/dp/29C5294?st=nte312

But I saw these also and wanted to check whether they are suitable, didn't want to ask Dany again as I've already bombarded him with a fair few emails.

These are Fairchild 2N3819 am I right in thinking these were used in the original U87i?

https://www.ebay.co.uk/itm/2N3819-FAIRCHILD-N-CHANNEL-JFET-TRANSISTOR-x5PCS/273131663608?epid=1017213417&hash=item3f97ea70f8:g:guMAAOSw4vJau3gR

 

[RuudNL]

My Neumann U87 microphones use Texas Intruments 2N3819's.

 

[PG_Sax]

My Neumann U87 microphones use Texas Intruments 2N3819's.

Ah ok, thanks for the clarification.

Cheers Piers

 

[gyraf]

..the last two batches of 2N3819 I bought turned out fake, just some rebranded generic NPN transistor..

They were branded, with laser marking:

(Fairchild-Logo-F)
BJ12
2N3819

 

[roger.unc]

..the last two batches of 2N3819 I bought turned out fake, just some rebranded generic NPN transistor..

They were branded, with laser marking:

(Fairchild-Logo-F)
BJ12
2N3819

How did you know they were fake? They've been hard to find and the ones I purchased off of Ebay have the Fairchild logo as well. I am, to say the least, suspicious. Thanks.

 

[fsalter]

The same thing happened to me. Using a transistor tester shows Base, Collector and Emitter pins and not Gate, Source, and Drain

 

[poctop]

How did you know they were fake? They've been hard to find and the ones I purchased off of Ebay have the Fairchild logo as well. I am, to say the least, suspicious. Thanks.

There is Copy ,    ok this is a vintage project LOL
Best,
Dan,

 

[roger.unc]

There is Copy ,    ok this is a vintage project LOL
Best,
Dan,

Ha Dan - I get it. There are always fakes out there. I was just curious if the transistors were wildly out of spec or something else that could clue me in that the parts were not genuine...

 

[gyraf]

The fakes I got tested as standard si-npn with hfe and all.

I have not yet seen genuine fairchild 2N3819's that were laser-marked (engraved)

Jakob E.

 

[Eitan25]

But I saw these also and wanted to check whether they are suitable, didn't want to ask Dany again as I've already bombarded him with a fair few emails.

These are Fairchild 2N3819 am I right in thinking these were used in the original U87i?

https://www.ebay.co.uk/itm/2N3819-FAIRCHILD-N-CHANNEL-JFET-TRANSISTOR-x5PCS/273131663608?epid=1017213417&hash=item3f97ea70f8:g:guMAAOSw4vJau3gR

The first batch of JFETs I bought from eBay came from China and were indeed fakes and not up to spec. Then I bought the JFETs from this exact seller in the UK you linked to and they worked great! 

 

[TillM]

there must be a fault in your build.
The voltage at the Zener is way to low.
Also the voltages at L1 and L2.
You should definitely go over the pcb.

 

[HosaMogami]

Got it figured out, It was actually my joint at G -> GG between the two main boards. biased up and sounding great!

Now to build the other 4...

 

[guisquil]

Hello,

I built this Mic a couple years ago and it works, I just got my firs oscilloscope and want to bias it using it, do I have to disconnect the capsule to do it?

Thanks

 

[TillM]

Yes you have to

 

[guisquil]

Thanks!

Yes you have to