Neumann Vintage U87 Clone : Build Thread.

[eastwinds]

hi Fripholm
i finished one of these also. i had some problems with the low cut (should be pin 2 and 3) and pattern selector (should be pins 1,2 and 4) switches being wired the wrong way, so you may want to check that first. The M87 capsule appears to be a K67 design. you can do a continuity check across the backplates to make sure. it will work ok with this mic, you just won't be able to get fig8. i've been recording this week on this mic in cardiod mode, it sounds good to me. levels are about 10dB lower than a modern mic because this is a vintage circuit.
hope that helps 

Ian

 

[fripholm]

Thanks Ian. Maybe I'm just lucky because the switches on my mic body seem to be wired correctly. The lo cut - err - cuts the lows and the pattern selector sets the mic to cardioid in the middle position. Omni works fine as well. When switching to figure 8 the output is pretty low, but I can't use it at the moment anyway due to the wrong capsule (yes, there's continuity across the backplates).

Yay, it's finished (for now) and sounds pretty good! ;D

I'll wait until the 87-type capsule is available or I order it from microphone-parts.com. This K67 will then replace the stock capsule in my MXL tube mic which is cardioid only.

 

[eastwinds]

'When switching to figure 8 the output is pretty low'

this may suggest there's incorrect wiring.....with the pattern selector switch wired fig8 to pin 3 you will get a very low cardioid response instead of fig8. this will also mess with the cardioid setting from my experience and give you very low output on cardioid. the solution is to solder the fig8 wire to pin 4.i think this is a generic problem with these switch boards...maybe I'm wrong and it was just mine. either way you need omni to pin 1, cardioid to pin2 and fig8 to pin 4 with this kit.

btw, my low cut worked ok it was just wired back to front (on was off and visa versa)

cheers, Ian

 

[kante1603]

'When switching to figure 8 the output is pretty low'

this may suggest there's incorrect wiring.....with the pattern selector switch wired fig8 to pin 3 you will get a very low cardioid response instead of omni. this will also mess with the cardioid setting from my experience and give you very low output on cardioid. the solution is to solder the fig8 wire to pin 4.i think this is a generic problem with these switch boards...maybe I'm wrong and it was just mine. either way you need omni to pin 1, cardioid to pin2 and fig8 to pin 4 with

No.
If you have Dan's board(?) the figure eight will not work with a KK67 style capsule.
This is the old U87 design,an isolated (KK87-style) capsule is needed.

For the switches,ohm them out or do a continuity test refering to the switch pole.
Cardioid is an open condition while the others must have contact to their dedicated pins,nowhere else.

Mic&Mod clearly states on their homepage that figure eight will not work and the included capsule is a K67 style,that's why.They don't have a K87 yet.

I can tell you more about the switch board (or give a proof if it is working o.k. or not) when I have the body kit which is on the way to me atm.

Best,

Udo.

 

[eastwinds]

Hi Udo

my apologies i wrote omni..i meant fig8 :-[
i'll be interested to see what you discover. everything else I stated above is exactly what i experienced - cardioid pattern with very low output on both cardioid and fig8 settings (about 14dBs too low). this was with fig8 wired to pin 3 (i notice on the mic and mod website pictures that the selector switch is wired this way also, so i suspect this is generic). when i rewired the switch i got cardioid output at it's correct level. still won't get fig8 though for love nor money. 

best regards Ian

 

[kante1603]

Hello Ian,

no apologies needed,hahaha......
But what levels are your reference when you say e.g. it is too low or it is correct?
What do these pin numbers mean,is it the switch pins on the mic&mod build or those on the pcb?
And still the question if you're talking about Dan's (poctop) pcb or a different one....
I'm a bit confused.......

Best,

Udo.

 

[irfrench]

Hi,

This is a great project!  I've had mine running biased at 11.5v and all is working OK.  Am just going through the biasing-with-a-scope routine, just to see what happens, and was wondering what 'limits' there are on bias voltages?  For example - I seem to be getting widest waveform/symmetrical shape/clipping when biased to around 6.3v?  Am I way off?

Thanks,
Ian

 

[eastwinds]

hi udo

yes this is poctops pcb which is part of the kit supplied by mic'n'mod,
i made some comparisons between an AT4033 and the finished U87 kit before i realised the switches were wired incorrectly in the factory. on the cardioid setting (and fig8) i was getting a signal about 24dB lower than the AT4033. i'm factoring in the expected 10dB reduced gain for the poctop circuit, hence the '14dB lower' figure. once i'd rewired the selector switch (fig8 to pin 4 of the switch - reading left to right looking at the mic) the cardioid level was ok (about 10dB lower than the AT4033).
so yes I'm talking about the pins on the switch not the PCB (1 being to the left, 4 to the right). pin 1 is omni, pin2 cardioid and pin 4 fig8 (which should work if you have the correct capsule) according to Yannick.
i wonder if anyone else had this experience, i think there's quite a few of these sold now.....
i'm assuming that if this switch wiring is a generic problem, it will be an issue with isolated capsules aswell.  :-\

best Ian

 

[kante1603]

O.K.,got it now,thanks for clarifying Ian.
And yes,seems like others have the same issues,but some seem not to care at all.......sad.

Have fun,

Udo.

 

[fripholm]

I've just tested the volume of my U87 clone in cardioid mode against my Studio Projects C3 which I'd consider having a pretty healthy output. Both mics were connected to my Fireface UFX with a preamp gain of 54 dB. The U87 has only slightly lower volume - about 1.5 dB - which I'm totally fine with. Most of my dynamics and/or ribbons have much lower output.

BUT: When doing the test I discovered that the polarity on my clone's output is indeed reversed. I've double checked that the XLR wiring is correct. Where else should I start to look for wrong wiring?

 

[micandmod]

Hi fripholm,
can you send us pictures of the inside of your microphone ?
Regarding our U87 DIY kit, as I said to some of you, an exchange of the capsule MK-67 premium by the MK-87 (available in about a month) will be available and free.
Best.
Yannick

 

[poctop]

I've just tested the volume of my U87 clone in cardioid mode against my Studio Projects C3 which I'd consider having a pretty healthy output. Both mics were connected to my Fireface UFX with a preamp gain of 54 dB. The U87 has only slightly lower volume - about 1.5 dB - which I'm totally fine with. Most of my dynamics and/or ribbons have much lower output.

BUT: When doing the test I discovered that the polarity on my clone's output is indeed reversed. I've double checked that the XLR wiring is correct. Where else should I start to look for wrong wiring?

you  can simply reversed pin 2 and 3 on the xlr connector and you will be done.

Best,
Dan,

 

[poctop]

Hi,

This is a great project!  I've had mine running biased at 11.5v and all is working OK.  Am just going through the biasing-with-a-scope routine, just to see what happens, you dont need to fully clip them to see where it will happen, and was wondering what 'limits' there are on bias voltages?  For example - I seem to be getting widest waveform/symmetrical shape/clipping when biased to around 6.3v?  Am I way off?

Thanks,
Ian

the idea is to have them clipping at the same time on both phase i suggest you reduce the amplitude of the sinetone to really get a grasp on where they do that
the idea is to reduce and increase the sinetone amplitude to see this condition if you have too strong signal you wont see it ,

6.3V seems on the  low end you could also verify your idle current trough the source resistor to ground IIRC it should be around 0.25ma,
Hope this helps,
dan,

 

[kante1603]

I've just tested the volume of my U87 clone in cardioid mode against my Studio Projects C3 which I'd consider having a pretty healthy output. Both mics were connected to my Fireface UFX with a preamp gain of 54 dB. The U87 has only slightly lower volume - about 1.5 dB - which I'm totally fine with.

@fripholm

Yes,that's nearly spot-on.Have just checked back the technical specs of the C3 and compared to those of a vintage U87.Given that two fireface inputs set to the same level will be slightly off from each other I'd say it's perfect (I'm talking about just some tenth of a dB).

Have fun,

Udo.

 

[irfrench]

the idea is to have them clipping at the same time on both phase i suggest you reduce the amplitude of the sinetone to really get a grasp on where they do that
the idea is to reduce and increase the sinetone amplitude to see this condition if you have too strong signal you wont see it ,

6.3V seems on the  low end you could also verify your idle current trough the source resistor to ground IIRC it should be around 0.25ma,
Hope this helps,
dan,

Dan,

Thanks for this.  I suspected it was on the low side. 

I've tried the Scope program from a laptop headphone output as the source - volume turned right down - but that may still be causing the problem?  I've got a Minirator MR1 kicking around here so I'll give that a go instead and see how I get on.

I assume that the idle current will need to be measured in the calibration state (no capsule, no transformer)? And please excuse the GCSE-esq question, but would the best way to measure the idle current be to measure the voltage across the resistor (R11) and use V=IR?  :-[

Thanks,
Ian

 

[poctop]

the idea is to have them clipping at the same time on both phase i suggest you reduce the amplitude of the sinetone to really get a grasp on where they do that
the idea is to reduce and increase the sinetone amplitude to see this condition if you have too strong signal you wont see it ,

6.3V seems on the  low end you could also verify your idle current trough the source resistor to ground IIRC it should be around 0.25ma,
Hope this helps,
dan,

yes Take the (source) voltage and divide by the value of R11 that you have found , it should ballpark arround 0.25ma

Dan,

Thanks for this.  I suspected it was on the low side. 

I've tried the Scope program from a laptop headphone output as the source - volume turned right down - but that may still be causing the problem?  I've got a Minirator MR1 kicking around here so I'll give that a go instead and see how I get on.

I assume that the idle current will need to be measured in the calibration state (no capsule, no transformer)? And please excuse the GCSE-esq question, but would the best way to measure the idle current be to measure the voltage across the resistor (R11) and use V=IR?  :-[

Thanks,
Ian

 

[kante1603]

so yes I'm talking about the pins on the switch not the PCB (1 being to the left, 4 to the right). pin 1 is omni, pin2 cardioid and pin 4 fig8 (which should work if you have the correct capsule) according to Yannick.

Hi Ian,

received the body kit today and can now confirm that your pinout investigations are correct:

Pin 1 connects to omni
Pin 2 connects to cardioid and is the switch pole (open condition to the other pins when selected)
Pin 4 connects to figure eight

Cheers,

Udo.

 

[Deepdark]

Hi guys.

I was thinking about finishing the mic body. I have a Behringer B2 (not the pro). I plan to clean it with some alcool, fill the engraved labels with some epoxy filler, sand it and then, I would like to know about the paint and sealer. I plan to buy a spray can from probably NAPA and some sealerm but I saw some guys that Powdercoated their mic body. I approached some places about powdercoating but it's really expensive. Are the spray can and sealer a good and durable option? I'll post some photo of my build asap.  :

 

[Deepdark]

I did a test tonight to compare the output of my D87 and a AKG P220. The effective output level of teh akg is rating at -35 dbm, I don't find the rating of the U87i but the U87AI is rated -31dbm. So put a 1khz sine wave through my monitor, set the preamp and record first with the U87 and then with the AKG. Same setup, same adjustement, etc. I got -33db with the U87 and -22db with the AKG. Which means around 10db hoter than the U87, as specified across the thread. Is anyone can confirm my test, just to know if everything is alright. Thanks guys your awesome  ;D

 

[kante1603]

@Deepdark

You can derive infos from calculating the microphone sensitivity in Volt/Pascal to db at a reference vltage (normally 1V/Pa),given the same circumstances of course.But roughly to see it is in the ballpark:

AKG P220:18mV/Pa equals -34,89 dB re 1V/Pa
U87 (original):8mV/Pa equals -41,94 dB re 1V/Pa

So yes,looks like yours is o.k.,just a bit off,but no biggie.
If it is biased already and it sounds good then leave it as it is.The slight differences are caused by factors like transformer and capsule choice.

Udo.

Edited typo.