Neumann Vintage U87 Clone : Build Thread.

[0dbfs]

E6000 hobby glue has worked well for me for long-term solid connections. Comes off nicely and cleans up with a razor too.

Hot glue seems to age and crack and not be all that strong of an adhesive..

Cheers,
jb

 

[HellfireStudios]

I've used hot glue on two mics to hold a larger transformer in place (Nady TCM1050, Carvin CM-87S). I look out for the cracking that 0dbfs mentioned, but I haven't had a problem yet.

-James-

 

[poctop]

I just wanted to thank Poctop and everyone else who has contributed and made this project possible.

I built 5 of these using Styrenes/Tantalums, the AMI transformer and Tskguy's capsules (thanks Eric) which i chose after listening to Wave's samples.
I used ISK BM600's for the doner bodies with all 3 switches working. Also I set the bias using a scope.

Recently I started tracking some drums with the drummer from my band and used the clones for overheads and room mics.
I had two on overheads in an ORTF setup in cardioid pattern, one on either side of the kit in omni, and the last one about 2 inches away from and pointed toward the doorjam in cardioid pattern at the entrance to the room. The room only measures around 10 by 20 foot and is heavily insulated.

I haven't used a real u87 so i don't know how they compare to the original but the amount of detail these mics add to my mix compared to previous recordings i've done is amazing.

Here's a sample i recorded when we were setting up. It's a mix of all five mic's together, all tracked through jlm audio baby animal preamps into an apogee ensemble. I haven't added any eq or compression.

https://cdn.groupbuilder.com/groupdiy/u/39511/58d02819938cb.wav

thanks Mukole for this great post ,  it always nice to hear feedback like these i am super glad you are happy with your news toys, definitively sounds great.  thank for taking the time to do this , 
Best,
Dany,

 

[wave]

I just finiched another U87 clone with the same specs as Mukole. I gave it to Eric to bias it on the scope for me and behold my FET was dead.
I replaced it with a 2SK170. I pretrimmed the biasing resistor to 5.5K and the mic def has more gain than the 2N3819 version.

I was wondering if anyone else had used a 2SK170 and what the drain voltage range should be with the different FET?
I haven't biased it whether by listen or scope method but it's already sounding good.

Dany & Matador, would you care to weigh in on this question?

Thanks,
Dave

Oh-my DU67 AMI version is on the build menu for tonight (I'm gonna take plenty of pics Dany!)

 

[atticmike]

I just finiched another U87 clone with the same specs as Mukole. I gave it to Eric to bias it on the scope for me and behold my FET was dead.
I replaced it with a 2SK170. I pretrimmed the biasing resistor to 5.5K and the mic def has more gain than the 2N3819 version.

I was wondering if anyone else had used a 2SK170 and what the drain voltage range should be with the different FET?
I haven't biased it whether by listen or scope method but it's already sounding good.

Dany & Matador, would you care to weigh in on this question?

Thanks,
Dave

Oh-my DU67 AMI version is on the build menu for tonight (I'm gonna take plenty of pics Dany!)

Wave, was it obvious that with the RK-87 you could hear it was not built in the US or is this again some fancy way of expressing one's fortune with homemade membranes?

I remember that using the RK-87 gave you the impression to be equal, if not better sounding than the 87i?

 

[wave]

The RK-87 is not a bad capsule at all. It sounds great - it has a very nice low end and high end. It is a fine capsule in the mic and will yield great sounding results (when paired with certain components.)

I can tell you're having some trouble making a decision about which capsule to buy. There are sound samples from my first mic with the RK-87 and samples with Eric's K87. I used the same exact mic and just swapped the capsules so if you troll through the thread and find them you will be able to hear the difference and make a decision I guess.

I have a feeling that the $100 price difference is a big factor for you, and if you really only want to spend $110, then buy the RK87. It will sound great. I would use styrenes, tantalums and the AMI T-13 if you go with that capsule tho.

Dave

 

[kevinkace]

How would I test my build with a DMM?
I have all components in (test capacitors in place of capsule, headers in place of switches), I plugged it into a preamp +48v,  surprisingly no smoke nor strange sounds (about -70 with the output on the pre cranked to max).

I don't have a scope/signal generator (other than what can be simulated with an audio interface/computer).

Thanks!

 

[tskguy]

Hey attic,

I will make this as easy as I can,,, The first clips are Dave and I comparing my capsule against the RK87. The details of the mic differences are in the clips. The other two clips are one of a real vintage u87 (not an AI) and the other is a poctop 87 with a cinemag transformer and my capsule and was built by Geekmcdaddy. Keep in mind the first two and second clips are done through different pres and are built with different components. 

http://dl.dropbox.com/u/55530129/test87_ericmic3.wav
http://dl.dropbox.com/u/55530129/test87_Davemic.wav
real U87a
https://dl.dropbox.com/u/87086401/U87.aif

Geeks clone
https://dl.dropbox.com/u/87086401/Capsule%202%20U87%20Clone.wav

 

[Volume11]

Can someone please explain the p/r, bias, and r11 section on the new boards to me please? Do I put a jumper there to use either the trim pot or fixed resistor? Couldn't tell by looking at the trace.
Thanks

 

[Dylan W]

Hey attic,

I will make this as easy as I can,,, The first clips are Dave and I comparing my capsule against the RK87. The details of the mic differences are in the clips. The other two clips are one of a real vintage u87 (not an AI) and the other is a poctop 87 with a cinemag transformer and my capsule and was built by Geekmcdaddy. Keep in mind the first two and second clips are done through different pres and are built with different components. 

http://dl.dropbox.com/u/55530129/test87_ericmic3.wav
http://dl.dropbox.com/u/55530129/test87_Davemic.wav
real U87a
https://dl.dropbox.com/u/87086401/U87.aif

Geeks clone
https://dl.dropbox.com/u/87086401/Capsule%202%20U87%20Clone.wav

Eric, your capsule sounds awesome. Tough to say without a back to back comparison, but I hear a similar sense of detail and space as in my 87. Much closer than the RK87!

 

[wave]

I'm bumping this question

"I just finished another U87 clone with the same specs as Mukole. I gave it to Eric to bias it on the scope for me and behold my FET was dead.
I replaced it with a 2SK170. I pretrimmed the biasing resistor to 5.5K and the mic def has more gain than the 2N3819 version.

I was wondering if anyone else had used a 2SK170 and what the drain voltage range should be with the different FET?"

Thanks
Dave

 

[Matador]

I'm bumping this question

"I just finished another U87 clone with the same specs as Mukole. I gave it to Eric to bias it on the scope for me and behold my FET was dead.
I replaced it with a 2SK170. I pretrimmed the biasing resistor to 5.5K and the mic def has more gain than the 2N3819 version.

I was wondering if anyone else had used a 2SK170 and what the drain voltage range should be with the different FET?"

Thanks
Dave

The calculator I posted previously will give a good clue what the drain voltage will be:  but the math only works if you know the IDSS and VGSoff of your particular FET.  A reasonable typical range will be 10mA for IDSS and -1.5V for VGSoff (at least if you believe the data sheet).

 

[Volume11]

Can someone please explain the p/r, bias, and r11 section on the new boards to me please? Do I put a jumper there to use either the trim pot or fixed resistor? Couldn't tell by looking at the trace.
Thanks

I hope that this makes sense. I am referencing the pictures in the first post of the tapered boards. I don't see the p/r on the tapered board, and the new board has the bias and r11 separated. So, what does p/r stand for, and does this mean that I can just put a trim resistor in the bias spot and leave r11 empty? P/r turns up no results in the search, but I'll keep digging for info anyhow. Thanks

 

[poctop]

I'm bumping this question

"I just finished another U87 clone with the same specs as Mukole. I gave it to Eric to bias it on the scope for me and behold my FET was dead.
I replaced it with a 2SK170. I pretrimmed the biasing resistor to 5.5K and the mic def has more gain than the 2N3819 version.

I was wondering if anyone else had used a 2SK170 and what the drain voltage range should be with the different FET?"

Thanks
Dave

you will need a scope meter to find out where it sits at proper bias in term of Voltage to the drain,
I never use one of those ,
hope this helps,
Dany,

 

[poctop]

Can someone please explain the p/r, bias, and r11 section on the new boards to me please? Do I put a jumper there to use either the trim pot or fixed resistor? Couldn't tell by looking at the trace.
Thanks

Please Just ignore this P/R jumper ,  it is actually a pad to measure the Source Voltage in reference to ground to evaluate what the idle current is ,  if your are not sure about this pad just ignore it.
the principle of having the pot or the resistor is the same as the older revision , it is one or the other ,
but not both at the same time ,
dany,

 

[mrcase]

hey all!

I am having trouble biasing my u87. I tried the method explained by matador:
injecting a 1khz sine into R6 and measuring at the drain (the leg nearest to the trimmer, right?)
I increased the signal until I had clipping and then turned the resistor till the clipping was even on both sides. so far so good.(I had the capsule detached. But I also didn´t have th 51pf connected - does this ruin the measurement????)
but after the biasing the mic sounded very low in volume and also does some strange noises, like as the fet was shutting on and of or so...
I then measured the voltage at the drain and it was only 5V. Increasing this to 10-11V makes the mic usable again. enough gain and sounds good to me.
But I´m not sure how to do this the proper way. maybe its a language thing but I´m lost with properly biasing th fet. PLease help!!!  :'(

thanks!

 

[HellfireStudios]

Is your transformer hooked up? If so, disconnect the primaries and try to test it again with your oscilliscope. The 51pF cap(s) is for testing the head amp, and not used for biasing. Was R6 oriented backwards from the markings on the PCB? This is required to inject a sine wave at the right point in the circuit. I hope this helps.

-James-

 

[mateus]

Heya guys,

does anyone ever tried Marik's trafos in this build?

http://samaraudiodesign.com/BobbinTransformers.html

How do they sounded?

 

[geekmacdaddy]

Heya guys,

does anyone ever tried Marik's trafos in this build?

http://samaraudiodesign.com/BobbinTransformers.html

How do they sounded?

I was unaware of them. Do you know where they are located?

 

[Matador]

hey all!

I am having trouble biasing my u87. I tried the method explained by matador:
injecting a 1khz sine into R6 and measuring at the drain (the leg nearest to the trimmer, right?)
I increased the signal until I had clipping and then turned the resistor till the clipping was even on both sides. so far so good.(I had the capsule detached. But I also didn´t have th 51pf connected - does this ruin the measurement????)
but after the biasing the mic sounded very low in volume and also does some strange noises, like as the fet was shutting on and of or so...
I then measured the voltage at the drain and it was only 5V. Increasing this to 10-11V makes the mic usable again. enough gain and sounds good to me.
But I´m not sure how to do this the proper way. maybe its a language thing but I´m lost with properly biasing th fet. PLease help!!!  :'(

thanks!

After biased to symmetrical clipping, what was the final value of the source resistor (the resistor you adjusted)?  You have to pull it out of the circuit or lift one leg to measure this properly.  We can probably reverse engineer the FET parameters from that.

I suspect the IDSS value was too high on the FET you used.  Running it at lower current will indeed raise the drain voltage back up, however it will clip asymmetrically with a large enough input signal (e.g. close miking a drum set or something similar). 

If you don't mike loud transient sources then don't sweat it.  This is all fine tuning to squeeze every last bit of signal out of the circuit, but for 90% of cases 10.5V on the drain is good enough.