Neumann Vintage U87 Clone : Build Thread.

[poctop]

i have been reliably informed that the 2sk170bl is much better for audio applications than the 2n3819

OK. ?

From Klaus Heyne:

The 2436 is similar to the 2N3819 for which you will find specs by Googling it.

Both transistors were used by Neumann interchangeably for at least 10 years, from the late 1960s to the late 1970s, and occasionally thereafter as well.

The two transistors mentioned above are also compatible with a couple of other ones Neumann used after the Texas Instrument 2N3819 became obsolete: K105 and SK107.

The specs are pretty close on all four of them, and you may liberally substitute them in any Neumann FET mic without negative consequences for the circuit or the sound of these mics, provided that you custom bias each FET, just as Neumann used to do, regardless of the brand of FET it used.

Trading for gain or headroom,  Matador nicely presented the topics , page 68
But most of all this is DIY 
Best,

 

[atticmike]

You guys have a diagram which legs I have to hook up and which I'd have to measure with the ddm? I'd mainly do that prior to the biasing just to have matched fets for both mics.

 

[poctop]

You guys have a diagram which legs I have to hook up and which I'd have to measure with the ddm? I'd mainly do that prior to the biasing just to have matched fets for both mics.

if you mean measuring the IDSS for each FET then have a look here , thanks to Matador for the procedure ,
https://cdn.groupbuilder.com/groupdiy/u/39511/58d02819939d1

 

[andyfromdenver]

Happy holidaze!
  Got my parts and started in earnest.
Wanted to confirm again the cad gxl2200 is a good fit.
I was worried that the parts might bump the body (esp. the resistors) but, no problems!
Wired in all the resistors and found 2.2k matches (within .4% a minuscule 8.8ohm diff!)

Maybe some help for new guys like me:
The pcb pads are soo small, continuity checks after each connection help paranoia.
Maybe starting on board 2 and/or doing the molex headers first is a good confidence booster.

Andy

ps. I am a pic whore and am suffering w the groupdiy site inability to
post straight from iPhone...er well

 

[sr1200]

First world problems... haha

 

[berkleystudios]

First world problems... haha

haha

 

[poctop]

First world problems... haha

Maybe we could assist the first problem resolution of the new world as well,
Dan 

 

[kante1603]

World-what world?
Am I missing something ;D

Udo.

 

[poctop]

World-what world?
Am I missing something ;D

Udo.

End of the world Today Only ,  ;D
D

 

[kante1603]

Oh,still on rehabilitation from the after-show-party......... ;D

Udo.

 

[andyfromdenver]

Dany, or any other kind souls,
(Yes iPhone pic problems are super 1st world-y btw )
One big 2 part question and i should be home free with all the previously posted info.
I feel like v1.1 has a slight newb repellant hazing ritual re: the xlr pinout, aka the 123 on the board (which is absent from v1.2) and the transformer terminology.
So, did I pass the hazing with the following?:

Per the peluso t87 (you can see the diagram in the pic)
Red to RT(1)
Black to SW(2)
Yellow to WS(4)
Green to BL(3)
This seems to make sense w/ the schematic

Also, on the boards
Gnd (3...the strange hazing part) to pin 1 of xlr (black wire in pic) which grounds to body too.
Cold (marked 2 for some esoteric reason) to pin 3 of xlr (white wire in pic).
Hot (1) to pin 2 of xlr (red wire)

Thank you in advance!!
And (if it doesn't violate any rules) to show that I'm not "all take and no give" whoever helps me is welcome to ten of the 2.2k resistors or anyone you'd like to have 'em.
I accidentally double ordered without deleting. 
US or afar, my treat

Andy

PS.  Hope my inquiry helps another too.

 

[wave]

As long as your T87 diagram is correct then your hookup looks right to me.

Dave

 

[andyfromdenver]

Thank you Dave!  I measured the resistances on the trans, so I believe the Peluso scheme is right (thankfully...that Tabfunk situation must have been very frustrating for many).  PM me if you'd like those resistors.
Smilie abuse  ;D : 8)

 

[kante1603]

Also, on the boards
Gnd (3...the strange hazing part) to pin 1 of xlr (black wire in pic) which grounds to body too.
Cold (marked 2 for some esoteric reason) to pin 3 of xlr (white wire in pic).
Hot (1) to pin 2 of xlr (red wire)

Hello Andy,

the numbering on the pads are not "esoteric".They refer to a header,e.g. molex etc. and are always numbered from left to right,so they are just "geographic or physical" (pardon me for not finding the right words,I'm still learning).That's why Dan was so kind and wrote the function (hot,cold,gnd) on the silkscreen too.It just looks a bit confusing on a first sight but isn't when you compare them to the schematics.

Have fun with your build,

Udo.

P.S.: No resistors please  ;D,and merry christmas,

Udo

 

[andyfromdenver]

Thank you Udo!
Merry C Monster

 

[atticmike]

hey guys, I've just stuffed the board and determined the FET idss for both mics (about 10,5 ma). But I can't really figure out what to do next? How am I supposed to calibrate the microphone now? Everytime I asked about that particular part of the proceedure, I was refered to matador's form? Though in the thread, it says that it could also be done with the trim pot? What about the trim pot actually? Is it just supposed to be for the calibration? Do I have to replace it later with a firm resistor? I mean, I've dug through this topic fairly thoroughly, though I have really trouble connecting the dots since the information is spread all over the place.

Chunger wrote in the thread of his build: "I adjusted R14 for a 3V drop across R14 according to the thread." Where f**k did he get that information?

Also, where am I supposed to install the troubleshooting cap within the circuit? No information on that on the first page at all.

 

[andyfromdenver]

Hi guys.
  About to put it all together and give it a go.
wanted to share my beyond crude method for biasing.
1. I made the little gimpy trim pot (with a crazy leg attachment and shaved edge) a permanent part of circuit (i'll attach the pic shortly as it looks funny...).
2. Of the 3 jfets I chose the one with Idss of 9.17 (one was 13ish, one was 10 something)
3.  I didn't understand how to measure the Vgs (though I am reading feverishly) so here was my crude deduction:
    Matador's post #1032 has a pic of some Idss and Vgs I did a relative amount to his 9 something Idss jfet
  and plugged -2.38 into Matador's wicked calculator program and derived a resistor value of ~10k.
4.  I set my trim pot resistor to 10k and am going to go for it.  The plan is to try and fine tune by ear, or as I learn more fine tune with a (sadly unavailable to me now) scope.
I'll do some voltage checks per the scheme when it's all finished. 
If this is just horribly flawed lemme know

Matador, thanks so much for those killer posts etc.

Andy


(off to RadiopoopShack to get some switches :-\)

*edit: in the end I set the drain voltage to 11.25 and it sounds fantastic.*

 

[poctop]

hey guys, I've just stuffed the board and determined the FET idss for both mics (about 10,5 ma). But I can't really figure out what to do next? How am I supposed to calibrate the microphone now? Everytime I asked about that particular part of the proceedure, I was refered to matador's form? Though in the thread, it says that it could also be done with the trim pot? What about the trim pot actually? Is it just supposed to be for the calibration? Do I have to replace it later with a firm resistor? I mean, I've dug through this topic fairly thoroughly, though I have really trouble connecting the dots since the information is spread all over the place.

Chunger wrote in the thread of his build: "I adjusted R14 for a 3V drop across R14 according to the thread." Where f**k did he get that information?

Also, where am I supposed to install the troubleshooting cap within the circuit? No information on that on the first page at all.

you dont need to fiddle with R14 at all, the pot is to take place at R11 , if you dont have a scope you can set the drain voltage to about 11-11.5V and you should be very near the sweet spot to start with ,
hope this helps,
Dan,

 

[3nity]

Dany i want to thank you, once again, for this project man!
I completed mine just a few minutes ago and it sounds sweet.
Used tskguy capsule, cinemag 2510 (i had it) .

Used a MXL 2001 you supplied too!! it works and sounds perfectly.
i had a xlr badly wired but thats all.

Now i want another 2 as a matched pair!
Thanks.

 

[atticmike]

hey guys, I've just stuffed the board and determined the FET idss for both mics (about 10,5 ma). But I can't really figure out what to do next? How am I supposed to calibrate the microphone now? Everytime I asked about that particular part of the proceedure, I was refered to matador's form? Though in the thread, it says that it could also be done with the trim pot? What about the trim pot actually? Is it just supposed to be for the calibration? Do I have to replace it later with a firm resistor? I mean, I've dug through this topic fairly thoroughly, though I have really trouble connecting the dots since the information is spread all over the place.

Chunger wrote in the thread of his build: "I adjusted R14 for a 3V drop across R14 according to the thread." Where f**k did he get that information?

Also, where am I supposed to install the troubleshooting cap within the circuit? No information on that on the first page at all.

you dont need to fiddle with R14 at all, the pot is to take place at R11 , if you dont have a scope you can set the drain voltage to about 11-11.5V and you should be very near the sweet spot to start with ,
hope this helps,
Dan,

Thanks a lot Dan, though I still got a few questions left:

1. Now that I've matched the fets at 10.5 mA, which is hopefully okay, the next step would be to calibrate it?

2. For the calibration, I have to connect the xlrs to the respective holes at the bottom of the pcb and feed it with a pre's +48v over the xlr jack?

3. The trimpot has to be at maximum capacitance at the point of calibration? To which lead would the maximum capacitance have to go (positioning of the trim pot on the board)?

4. Where am I supposed to install the caps that substitute the capsule during calibration? BC and FC?

5. I suppose that fixed resistor is now not needed since I'm using the trimpot for R11, unless I want to replace that determined value after calibration with a fixed one?

Also an information for everybody approaching / encroaching that build :

After having stuffed the boards, it is smart to clean them throughly, because the 1 G ohm resistor changes its capacitance just by your fingerprint after touching them drastically.

Dany i want to thank you, once again, for this project man!
I completed mine just a few minutes ago and it sounds sweet.
Used tskguy capsule, cinemag 2510 (i had it) .

Used a MXL 2001 you supplied too!! it works and sounds perfectly.
i had a xlr badly wired but thats all.

Now i want another 2 as a matched pair!
Thanks.

Good stuff mate, can't wait to put eric's capsules into action myself! Have you had any chance to compare them yet? How's the excitement?