Neumann Vintage U87 Clone : Build Thread.

[kante1603]

My combination is peluso pk87 and T13 for trafo.

Udo.

 

[poctop]

My combination is peluso pk87 and T13 for trafo.

Udo.

I really hope your capsule is not responsible for that and also i would really hope we get in the bottom of this ,

Best,
Dan,

 

[kante1603]

I really hope your capsule is not responsible for that and also i would really hope we get in the bottom of this ,

Best,
Dan,

Oh.......  ?.......you mean the pk87 in general or especially the one in my build?
As said it is really great soundwise,very close to a U87Ai.
That would be very bad financially,I have two from the group buy.....
And I measured the capacitance of it prior to mounting,it was close to 50pF,so spot on to the specs....

 

[poctop]

I really hope your capsule is not responsible for that and also i would really hope we get in the bottom of this ,

Best,
Dan,

Oh.......  ?.......you mean the pk87 in general or especially the one in my build?
As said it is really great soundwise,very close to a U87Ai.
That would be very bad financially,I have two from the group buy.....
And I measured the capacitance of it prior to mounting,it was close to 50pF,so spot on to the specs....

Udo,
no to scrare you Sorry  ,this was just a tought i had bad capsule from the best provider ,  but we still can't exclude it from the deal ,
measuring capacitance at rest in something but once polarized if the capsule has lost his tension equilibrium or too loose and get suck to the back plate when polarized then there will be a output loss,  but most proably covered with a rumbly mic , is your pair of mic behaving the same?

I really hope you can solve  the issue and enjoy the mic  after all,
if anyone would like to comments on the output level of their mic are very welcome as do So as an evolving point of view.
Anyone Suffering from very low output ?

 

[wave]

Well I guess I'm stupid.
I removed the body and did some visual inspection and I noticed I had the leads reversed on the front of the capsule.
I switched them and I'm not getting any issues so far. Plus it still sounds awesome.

Dave

 

[sr1200]

Mine is about on par with my SM7B which is ridiculously LOW output. 

 

[0dbfs]

Arrggh! I've just placed my mouser and justradios order for parts to finish four of these buttery morsels.
Already have PCB's, Aurycle bodies, T13 trafo's, and peluso capsules. He he he...
Looking forward to putting these babies together, playing with a hot iron, and slinging some solder so watch out!...
Been very busy with sessions and some studio commissioning so haven't had time to get my DIY on... But I figure no time like the present.

And hey, I personally think most mic's have way too much output anyway. Looking forward to a handful of lower output mic's so I can crank up the gain on my pre's and have less NFB and more FUN!

Ciao!
-jb

 

[kante1603]

Udo,
no to scrare you Sorry  ,this was just a tought i had bad capsule from the best provider ,  but we still can't exclude it from the deal ,
measuring capacitance at rest in something but once polarized if the capsule has lost his tension equilibrium or too loose and get suck to the back plate when polarized then there will be a output loss,  but most proably covered with a rumbly mic , is your pair of mic behaving the same?

Hi Dan,

No,I don't have a pair of clones yet.But I have two capsules,so there are at least two ways to shoot things out:
Building a second microphone and compare to my first build.Will take some time.
Or exchanging parts on my existing mic which as faster to do,especially changing the fet and re- bias.
I don't believe in a capsule issue at the moment,the sound it excellent.If say tension was low it would have resulted in a bad sound I think.This one is nearly identical compared to our U87Ais.

Udo.

 

[kante1603]

Mine is about on par with my SM7B which is ridiculously LOW output.

Yes,the sm7b is spec'd for -59,0 dBV/Pa / 1,12 mV/Pa,it is a dynamic mic.Seems to be too low too.

Udo.

 

[sr1200]

Dumb question, but does the calibration process effect the output at all?  I left the pot IN my mic and I "THINK" i calibrated it correctly.

 

[Joekkel]

i just finished my u1621 first impressions are great, listen to them here.

pics here.

it is certainly not the most beautiful build ever. the behringer b2-body has it's faults and i'm not really talented in metal-works neither do i have any instruments. i just left one of the straight metal-connections between the headbasket and bottom away, so i had enough space for the boards.

the trafo is just iso-taped to the bottom, will build a metal-shield some time soon, but for now, this is entirely sufficient. don't forget, this is my first diy-build ever (beside some trial/error-circuit-bending some years ago...). i am proud of me and all of you who have built this mic

thanks a lot dan!! feels like christmas

 

[Joekkel]

hi there, so...my previous post was a little too enthusiastic. the mic sounds great, but output ist low, so i measured voltage from ground to aa: 28.5v and ground to cc: 17.8v (same as front-backplate) c6 is sharing these voltages. how to find the mistake?

fet-voltage-drain is 10.3v
zener 23.6v
top of r14 21.2v
c13 40.4v
c11 35.8v
top of r13 28.6v
top of r12 11.6v

compared to this measurements:

Dany

I removed the transformer connections, and the connections to the capsule, and also removed the fet and R11.  original bom components elsewhere.  Here are my voltages:

Phantom power is 48.6v

top of L1 - 48.6v
top of L2 - 45.9v
top of R18 - 48.6v
top of R19 - 45v
bottom of R17 - 45v
top of R17 - 23.18v
Zener 23.17v
FET drain pad 23.15v
FET source pad 0.089v
top of R12 23.15v
top of R13 42.4v
top of R14 23.14v
top of R8 41.8v


What is R9 & R10 doing?  I got 0v there..

i think the fault is either on r13, r12 or c9, as the measurments begin there, to drift apart. what do you think?

thanks, joachim

 

[Joekkel]

forget everything i just wrote!! don't know about the measurments...they stink. i just compared my u1621 to a lineaudio cm3 which specs as -44dB sensitivity. i positioned both mics close to each other, amplified both with exactly the same amount and played a sinewave. guess what? the u1621 is about 2 dB hotter, which means about -42dB sensitivity!

merry x-mas again!

 

[Matador]

Polarization voltages cannot be measured with a regular DMM at the capsule as the impedance is too high by several orders of magnitude.  About the only place is the last decoupling cap before the 60M resistors.

Here are some sims of the circuit with some various changes:

The green line is the stock circuit with a 10:1 transformer.  Gain is roughly 27dB in the passband of 40Hz to about 9kHz (or an overall voltage gain of roughly 22 times, so a 1mV signal looks like a 22mV signal to the preamp's inputs).  The red line is what happens if you try to use a 5:1 transformer with no other circuit changes.  The transformer loads down the front end below 500Hz, and the bass response basically disappears.  This effect will become more pronounced the lower the primary L of the transformer (or the smaller the coupling cap).

The yellow line is the response after adding two resistors and another active device:  a PNP follower.  Here is the circuit:

The follower reduces the output impedance of the front end from 47kohms to about 270ohms.  This means that the lower ratio doesn't effect the pass band:  you can see the yellow line is identical to the green line, just 6dB higher everywhere.  In fact, this circuit can happily drive a 2:1 transformer which will give back 13dB over the stock circuit.

This new circuit pulls an additional 0.5mA from the phantom supply which will drop the polarization voltage slightly.  One needs to adjust the values of the 56K and 10K drain supply resistors as well to keep the Zener regulating.

Dany:  you might consider adding a provision to a future version of the circuit board for those who need more gain:  the extra components can be easily left off and jumpered across for those that want to stick with the original topology.

 

[HellfireStudios]

A U-87a PCB might make the people who need more gain happy. I would be in for one. If the pnp follower works, and sounds correct, let us know. Maybe a cheap (but great-sounding) fixed-gain inline preamp might fix the problem. It could also be used for other lower output mics as well. Just a thought.

 

[Gus]

Matador did you see this thread?
http://www.groupdiy.com/index.php?topic=47569.0

 

[HellfireStudios]

My earlier post suggested an inline preamp might help the gain situation. While reading other unrelated material, I stumbled upon Naiant mics, and they now have an inline preamp.

http://www.naiant.com/naiant/inlinedevices.html

It's the ITP. At $89, it is hard to tell whether it is a good value or crap product. Any experience with the brand?
Is the Cloudlifter a viable product (w/ standalone P48 box placed prior to Cloudlifter) to rectify the situation?

 

[tskguy]

So how many of you guys used a scope to bias your fet? I did the headphone method first and the output of the mic seemed a bit low. After scope biasing my mic it had more gain, I didnt really measure the difference but it for sure had more gain. When Dave and I did our shootout it was clear baising with the scope had a impact,  Im also a bit blown away by everyones need to try and get more gain, I just did a session with my u87 and had zero problems getting a nice level.

E

 

[sr1200]

E, If your mic has any more gain than mine does it's no wonder you didnt have a problem.  When you have to crank a 70 db pre up to 9 or 10 to get a decent input level, its an issue.  The mic sounds awesome, theres no argument there, just could use a little LESS head room lol.

 

[tskguy]

How did you bias the fet???