D-U87 Build

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ramshackles

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Dec 18, 2011
Messages
521
Location
Riorges, France
I wanted to document my first mic build and hopefully glean advice when I get stuck. So here goes :)

Of course, the pcb boards are from poctop, and there is a whole load of advice on the white market thread and the build thread here:
http://www.groupdiy.com/index.php?topic=48030.0

But of course it is, as ever with many people with questions on different things, a bit of a hodge podge of information. I wanted to have some kind of resource where we can go from A to B. Of course it is only going to apply to the particular configuration I'm making...

So lets go on to all the parts I've got so far.

Parts

PCB boards from poctop (these are the original tapered variety, so not easily compatible with the mic bodies chunger is importing - although I will hopefully get one of those (whenever they arrive) to do the next 'poctop/neumann mic (67 or 47..)

All electronics parts from the very helpful mouser cart on the white market page. I believe the transistor that was originally on the BOM has been discontinued, so I went with this:
http://gb.mouser.com/Search/ProductDetail.aspx?R=2N3819virtualkey61000000virtualkey610-2N3819

And the only other thing that was not on the BOM (at the time I used it) was the 560p capacitor. There is the alternative from just-radios, but as this is an american company, I dont fancy paying huge postage for 1 little capacitor. So I'm hoping this will be suitable:
http://gb.mouser.com/Search/ProductDetail.aspx?R=23PS156virtualkey21980000virtualkey23PS156

As for the options in the BOM, I just ordered the whole thing (plus my amendments) as I wanted to get stuck in soldering :). The more attentive and less care-free builders should be a bit more careful, I suppose.

I went for the cinemag 2480 transformer, for no other reason than price. At £73 it was cheaper than the other options I could find.

PS - I still bought the BOM from mouser though I'm in UK (rather than making an alternative on e.g Farnell) as it wasn't that much more expensive for postage, or even waiting for it to arrive (about a week) and, I just wanted to get moving and feel like something was happening :D (I've been battling for a while to get a shopping list together for the EQ69 project by ij research :D)

Mic Body:
Behringer B2. Many reasons why I chose this:
1. It has all the switches
2. It is about the same size as a U87 (some cheap chinese copies are deceptively small)
3. It seems to go for less on ebay than the MXL 2010

As it turns out, the B2 is surprisingly well constructed, in terms of metalwork, and very similar to the U87 in that respect.

I basing that info on what I've seen of the U87 in this video:
http://recordinghacks.com/2009/01/22/how-its-made-neumann-u87/

And my own dismantling of the B2:
th_IMG_1437.jpg


The only major differences that I can see are:
1. 2 mesh layers in the headbasket instead of the 3 used by the neumann
2. The headbasket is slightly domed on top and tapered more than the neumann.

Of course, the capsule looks much more inferior (I can pick out imperfections on the surface with my naked eye) and I'm quite sure it wouldn't have been made in the same 'clean room' conditions Neumann insists upon.

Anyway, the final thing to choose is the capsule. I'm undecided in going for microphone-parts RK-87 or the much more expensive Peluso. This is only after reading how the conditions of the room it is made in (i.e dustiness) is very critical....is the RK-87 guaranteed to to be imperfection/dust free like that?

 

ramshackles

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Joined
Dec 18, 2011
Messages
521
Location
Riorges, France
Build

Well, I decided to just go in gung-ho and start soldering. The PCB boards are exceptionally well marked so it is not too difficult. For the choice of 68 or 60MOhm resistors (R4, R5) I just went with whats on the PCB board (60MOhm).
I'm not a big fan of huge build threads detailing each component being soldered on. It's fairly easy to do this :).
There was just a couple of things to take note of
Two resistors need to be closely matched (R18 and R19 I believe). No problem; out comes the VU meter. The BOM has about 10 of these resistors (2K2), so that, along with about 5 I had lying around was enough to find 2 very closely matched ones.
R6 should be reversed in direction to what the silk screen says, for biasing the FET (I think this must be for easier access with your crocodile clips..not sure yet)

Anyway, here is an almost finished pair of PCB boards:

th_IMG_1439.jpg




I need to solder on the transistor and C15.

Then next I suppose will be the biasing of the FET. I going to be using a oscillioscope on my PC so I guess I'm going to have to rig up some crocodile clip to 3/4" jack cables :D.
I'm not sure I got that potentiometer (R11) soldered in too well (it was a bit of a stretch for it!), so once I've found a good value, I think I'll swap that out.

There seems to be some fairly fine links from the build thread about biasing the FET (Ive never done anythign like that before), so I hope I'll be Ok.

After that I need to figure out how to wire in the trafo and the various switches.

One thing I did notice is that the PCB is about 2-3mm to wide on either side for the screw holes on the Behringer chassis. I could just screw in one side (there will be plenty of space to still slide in the body), but will that be Ok? Hmmm...

And a final thing that will be tricky is figuring how to wire in the switches to the B2 switch thingy....

 

wave

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Joined
Mar 29, 2005
Messages
609
Location
Nashville
Hi ramshackles,
You should get one of tskguy's HK-87 capsules. They sound great and are less money than the Peluso. His capsules have
silky highs and the mids are ultra sweet. Add that with the nice open low end response and it equals one fabulous capsule.

I originally had an RK-87 in my DU87 and while it sounded pretty good (especially for the price point) it had the typical Chinese sound in the high mids (4K-7K). Too much response up there

For the cost, you can't beat Eric's capsule and it's 100% made in the USA (even the mylar is sputtered here in Chicago)

http://www.groupdiy.com/index.php?topic=49859.0

Something to consider,
Dave
 

ramshackles

Well-known member
Joined
Dec 18, 2011
Messages
521
Location
Riorges, France
wave said:
Hi ramshackles,
You should get one of tskguy's HK-87 capsules. They sound great and are less money than the Peluso. His capsules have
silky highs and the mids are ultra sweet. Add that with the nice open low end response and it equals one fabulous capsule.

I originally had an RK-87 in my DU87 and while it sounded pretty good (especially for the price point) it had the typical Chinese sound in the high mids (4K-7K). Too much response up there

For the cost, you can't beat Eric's capsule and it's 100% made in the USA (even the mylar is sputtered here in Chicago)

http://www.groupdiy.com/index.php?topic=49859.0

Something to consider,
Dave

Hi yeah, he actually messaged me. I've thrown it on the table. I'll be getting the capsule when I'm happy that the electronics are working....hopefully I'll get this thing done in under a month :D
 

kante1603

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Joined
Dec 2, 2009
Messages
1,942
Location
Munich,Germany
ramshackles said:
And a final thing that will be tricky is figuring how to wire in the switches to the B2 switch thingy....
Hello,

I did a little guide for exactly that a while ago in the original Vintage U87 thread.Please see my reply #189,there's a pdf attached that can be overseen easily,sorry for that.
Here we go:

http://www.groupdiy.com/index.php?action=dlattach;topic=48030.0;attach=12800

Have fun with your build and keep us posted,

Udo ;)

Edit:Concerning pattern switch,be aware that cardioid mode must be pattern switch in middle position ( open condition),so you must re-label the mic!
 
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