Neumann Vintage U87 Clone : Build Thread.

[storres1]

Hi Guys! finishing up my build and im having trouble getting the correct voltage on the drain. i originally had the 3rd pin of the bias resistor connected but i disconnected that. Still am barely getting a reading. Any tips or pointers?

 

[lboschini]

          Many people here were recommending the 2sk170 as a replacement FET for the 2N3819,
but Jim Williams considers this to be a "cloudy" sounding FET, and replaced it with the
faster J305.  How about using the J305 in the Neumann U87 circuit?  Has anyone tried this?

You can't directly replace the 2N3819 with the 2SK170 for several reasons:

1) the 2SK170 has about 20dB of more gain, so you will get at the drain a signal 10 times higher. First of all, you will reduce the dynamics of the microphone by the same amount and moreover, since the common source FET is a quite non-linear configuration, with a larger signal its distortion becomes more audible.
2)  the 2SK170 has about 20 times more input capacitance than  2N3819 (and the Miller effect increases it to more than 100pf). This has a double effect: it becomes a partition with C4 and decreases the signal at the gate (but this is not so bad, since it partially compensates the higher gain of the transistor) and the FET capacitance is strongly not-linear with the input signal, so it generates a further audible distortion.

As a consequence, you will get a quiet microphone, but with reduced dynamic and a more coloured sound.

If you wanted to replace the transistor with a 2SK170 to reduce the noise of the microphone (which is actually, I agree, a bit high) without big side-effects,  you should at least also increase C4 to a 2-3 nF to reduce the partition effect, and also decrease a bit R12 (for instance 22k or 15k) to reduce the gain of the FET.

 

[mixinmono]

Hi all,

I seem to have a problem with the polar patterns on my u87 build, particularly the figure 8 pattern. When I measure voltage at the front and rear backplate, I get around 40V when set to cardioid or omni and measure around 6V when set to figure 8. I double checked all the wires from the switch pcb and seems to check out. Has anyone else had this problem? Cardioid sounds fine, Omni sounds like it's not fully utilizing the rear diaphragm and figure 8 just gives a very low signal, also not really utilizing the rear diaphragm.

Thanks in advance for any help!

 

[hugo]

Hi all,
I finished the mic and it works, but it works bad... I have no gain, an audible self noise, and no highs on recording... Could you please give me some process to follow.?? I am lost since it is my first U87 build, and i do not know how to start. I calibrated the mic with voltmeter, 11.5v..
Thank you

 

[3nity]

I have a small question.
Im thinking to get a apex-415 with low cut, pad and pattern swithc.
now the question is can i use those switches to build a D87?

Thanks

 

[ln76d]

Yes, you can

 

[TijuanaKez]

Hey guys, sorry if this has been asked a million times, but no 'search topic' feature.
The boards in the photos have the trimmer hard wired... seems like a sensible idea, those multi-turns aren't likely to change.
So what's the big deal about swapping in a fixed resistors anyway?

 

[Colorblind]

Not sure about the trimmer, but the smart search bar at the top will search this thread only. 

C

 

[dchang0]

BTW, for anyone using the oldest Gen 1 SYT-5 bodies, one way to get the headbasket screw under the pattern switch to fit is by buying "wafer head" M2x4mm machine screws (non-self-threading). These are typically used in electronics like laptops and are better made than the screws that come with the body (cleaner threads, more precise Philips screw cuts = less chance of stripping the threads). You can build the whole mic using the same wafer-head machine screws.

For the hex standoffs for the switch PCB on the Gen 1 SYT-5 body, I used brass 8mm tall female-female hex spacers and cut and ground them down to 6.8mm to max of 7mm. This keeps the switch toggles right in the middle of the cutout meant for them. Chunger used 1/4in spacers and added washers of unknown thickness to achieve the same thing.

 

[lyricalgeek]

Bump

Help, I finished a U87 build, and the mic has a problem.

Voltage at Drain, is always 23.2v. Adjustments to potentiometer have no effect on drain voltage. It just sits to 23.2v.

Most voltage readings  look normal, with the exception of voltage at 10K resistor (after Zener). It reads 23.32. Voltage at zener is 23.45.

Also, if I check continuity between orange and yellow wires of transformer, DMM rings indicating 35ohm resistance on these two wires. Is this normal?

Thank you very much for you help, and best regards!

HL

 

[Neutrino]

Hi guys,

a quick question: I want to use the SYT-5 (gen 3) body for the build. Will the Sowter 1303 output transformer fit in there?
The transformer is cylindrical and dimensions are 34 mm (1,339") diameter and 24 mm (0.945") height:

http://www.sowter.co.uk/cgi-bin/ss000001.pl?page=search&SS=1303&PR=-1&TB=O&ACTION=Go%21

I would appreciate if somebody could check. Thanks!

Best,

 

[micaddict]

http://stamaudio.com/sa87.html

 

[Neutrino]

http://stamaudio.com/sa87.html

Thanks! Does the SA-87 use the SYT-5 body as well? It's hard to tell just from the pictures.

 

[micaddict]

Looks like it.

In any case it's big enough to harbor Dany's PCB.

 

[Neutrino]

I also see on the pictures that the SA-87 apparently uses the D-87M (blue) PCB from poctop, which is larger than the green one (D-87L). If with that the Sowter still fits into the body, that's great since one retains  the flexibility to easily swap out e.g. for a AMI T13 transformer for comparison. Can anybody confirm that?

Sorry for these questions guys. I just need to decide what to order 

 

[poctop]

With Sowter , D87L
Best,
Dan,

 

[Neutrino]

With Sowter , D87L
Best,
Dan,

Thank you! Order placed 

 

[micaddict]

Samples are only samples, but I really liked what I heard from the Stam with the Sowter.
I preferred it over an original (vintage) Neumann
And I was not alone.
To my ears it has some U67 mojo.

 

[Neutrino]

Samples are only samples, but I really liked what I heard from the Stam with the Sowter.
I preferred it over an original (vintage) Neumann
And I was not alone.
To my ears it has some U67 mojo.

Yes, I listened to the samples on gearslutz and came to the same conclusion (blind testing). Really smooth high end. I wonder how much of the sound is really due to the transformer, because I guess the capsule determines 80% of the characteristic already (I will be using the HK87 capsule as well). I would be tempted to compare the Sowter with the AMI T13 transformer, but not sure I would spend the extra 100 bucks for the T13 just for the test...

 

[micaddict]

You're right in that there are more variables.
But the kind of "mojo" I mean is not what typically comes from a capsule.