Neumann Vintage U87 Clone : Build Thread.

[poctop]

Hello All,

I'm having some issues here. I'm not able to see the 1k tone coming out of the mic into my DAW. I can see the 1k at the FET drain and I've checked my signal chain coming out of the mic into my DAW and all is in order. Additionally, my FET bias resulted in symmetrical distortion, but there is clearly something wrong (see attached pic).

Info:

-My scope is connected at the FET drain.
-I have no transformer connected (waiting for a T13)
-I'm injecting the 1k tone at R6 (installed backwards)
-I have no capsule connected and I do not have anything in place of the capsule (i.e. 51 pF caps)

Source V: 48.0V
L1 & L2: 46.6V
Zener: 22.88V
R18: 46.6V
R19: 46.1V
Top of R17: 22.89V
FET Drain: 10.53V
FET Source: 2.62V
R12: 10.54V
R13: 43.4V
R14: 20.73V
R8: 39.7V

According to MagnetoSound, I may have a problem with my secondary. As a total noob, I'm not exactly sure what the secondary is (a second gain stage?) nor do have any idea where to start troubleshooting.

Any help with this would be much appreciated. Thanks very much everyone!!!

-DUDE GUY

Si if you have been able to have symetrical clipping adjusting the Pot and measure the signal at the drain then this is good,
probalby the reason why you dont see anything in your daw from the mic it is because you have no output trnsformer you need that in order for the mic to generate is output , let me know if that make sense,

hope this helps,

Dany,

 

[kante1603]

Hello Dude guy,

Secondary means the second or output winding of your transformer.
There must be two wires going to pins 2 & 3 on the xlr connector.
Measure them for a short,this is what  member magneto meant.

Good luck,

Udo.

 

[DUDE GUY]

Thanks very much Dany and Udo. So with no transformer installed, I have no output to my DAW. I get that. But why does my scope show that strange distortion? Is this also due to the fact that I have no transformer installed? Thanks for your help.

-DUDE GUY

 

[wave]

So what about the little black wire that connects to both switches in the stock Aurycle donor mic? Does it need to be connected anywhere?

Also when I inject a 1K sine into the RT and SW pads I use the "+" and "-" from a balanced line with a floating ground on that side?

Dave

 

[kante1603]

Thanks very much Dany and Udo. So with no transformer installed, I have no output to my DAW. I get that. But why does my scope show that strange distortion? Is this also due to the fact that I have no transformer installed? Thanks for your help.

-DUDE GUY

No trafo=no output,correct.
Have you checked the original output of your signal generator directly connected to your scope?
This way you can proof a) your generator puts out a sine wave and b) if your scope is working properly.

Cheers,

Udo.

 

[kante1603]

So what about the little black wire that connects to both switches in the stock Aurycle donor mic?

Hi Dave,

Don't know the aurycle mic,but if the switches are connected this could(!) be a ground connection.
Measure for continuity to the mic housing or pin 1 on the xlr.
I'm building a B2 so I'm not 100% sure,maybe Dan can chime in?

Udo.

 

[poctop]

So what about the little black wire that connects to both switches in the stock Aurycle donor mic?

Hi Dave,

Don't know the aurycle mic,but if the switches are connected this could(!) be a ground connection.
Measure for continuity to the mic housing or pin 1 on the xlr.
I'm building a B2 so I'm not 100% sure,maybe Dan can chime in?

Udo.

The black wire is an extension of the ground for both switch body to the basket and mic body ,
i did solder mine to the (gndlink pad) so everyone is happy,
Dan,

 

[poctop]

Thanks very much Dany and Udo. So with no transformer installed, I have no output to my DAW. I get that. But why does my scope show that strange distortion? Is this also due to the fact that I have no transformer installed? Thanks for your help.

-DUDE GUY

can you make sure that is signal from your tone generator is not just way too hot.. can you actually reduce the level and see a proper sine wave to the Drain pin with the scope also make sure you use a probe with a 10X divider in it ,
Hope this helps,
DAn,

 

[DUDE GUY]

can you make sure that is signal from your tone generator is not just way too hot.. can you actually reduce the level and see a proper sine wave to the Drain pin with the scope also make sure you use a probe with a 10X divider in it ,
Hope this helps,
DAn,

Hey Dan, I am able to see a clean sine wave with my scope with my signal generator at a low level. And yes, I do have a 10x probe. I can see symmetrical distortion that's similar to what I've seen in other people's posts, except the flattening of my 1k sine occurs at an angle (see pic on post #516). Then if I increase the 1k tone level, I see really strange distortion (see pic on post #517). Thoughts? Thanks.

-DUDE GUY

 

[poctop]

can you make sure that is signal from your tone generator is not just way too hot.. can you actually reduce the level and see a proper sine wave to the Drain pin with the scope also make sure you use a probe with a 10X divider in it ,
Hope this helps,
DAn,

Hey Dan, I am able to see a clean sine wave with my scope with my signal generator at a low level. And yes, I do have a 10x probe. I can see symmetrical distortion that's similar to what I've seen in other people's posts, except the flattening of my 1k sine occurs at an angle (see pic on post #516). Then if I increase the 1k tone level, I see really strange distortion (see pic on post #517). Thoughts? Thanks.

-DUDE GUY

So if i understand well you obtain symetry at
FET Drain: 10.53V
FET Source: 2.62V
This looks pretty good , the pad and nor the Lcut is not jumpered ,  have your signal probe ground connected to the mic body ,

since you are pretty much in the right condition, i would not be too much worried about the shape of your distorsion at the point that they behave symetrically and this is what is the most important , is your scope set to AC coupling or dC coupling , just a tought.
Keep on the good work, you almost there ,
Dan,

 

[wave]

SO.......
I dont have a scope. I did the listen method. To me I thought it sounded kinda distorted the whole time. I could hear the tone come up in volume then some of the "fizz" go away and come back.

Fine. I put the RK-87 in. Lots of hum until I put the body on. Now there's some capacitor noise (like low thunder) and the signal will drop quieter every now and then but come back.

Besides that the mic sounds pretty good. I have all styrenes in the positions that could use them (10, 220, 470, 560 pF)
Could the noise be coming from one of those? Both the cap noise and the volume drops are intermittent.

Bias pot is still in as I'm not sure I got that right yet.

Dave

 

[poctop]

SO.......
I dont have a scope. I did the listen method. To me I thought it sounded kinda distorted the whole time. I could hear the tone come up in volume then some of the "fizz" go away and come back.

Fine. I put the RK-87 in. Lots of hum until I put the body on. Now there's some capacitor noise (like low thunder) and the signal will drop quieter every now and then but come back.

Besides that the mic sounds pretty good. I have all styrenes in the positions that could use them (10, 220, 470, 560 pF)
Could the noise be coming from one of those? Both the cap noise and the volume drops are intermittent.

Bias pot is still in as I'm not sure I got that right yet.

Dave

I put the RK-87 in. Lots of hum until I put the body on

this  perfectly normal as there is no shield for the mic,

Now there's some capacitor noise (like low thunder) and the signal will drop quieter every now and then but come back.

what is your final Drain voltage ?

could you be more precise on the thunder sounds and capcitor noise i am not sure of those meanings,

can you try setting the pot such as you have arround 11.5V at the drain and try it again to see what happens.

hope this will help,

Dan,

 

[wave]

Hi Dan
interestingly enough when I was doing the fet bias my final drain voltage was around 12.2
i manually dialed it back to 10.5 then put the capsule in and listened. dont ask me why I did that.
Could this be the reason that the mic is a bit on the quiet side too?
I will adjust the drain voltage and report back.

 

[saxmonster]

Ok so I flipped the front with the back capsule and I still have the noise.  I am going to switch some of the caps with the others that came with the the BOM as optional.  Is there an order I should start it or just take a guess and maybe get lucky.  I will keep track of what I do though.

Dave,
This thunder sound that you have, is it very low on the mic.  Like you need to turn the gain up and headphone vol up to really hear it.  This is sorta what my mic is doing too.  Almost sounds like bad electricity or like a capacitor is expanding or when you first sit on a leather sofa.  But in the background or the sound of the mic.

-Scott

 

[saxmonster]

Ok Guess who has a clean mic sound now!!!!!!!!!!!


OH YEA ITS ME HAHAHAHAHAHAH!!!!!!!!

C1 was the culprit!!!!!!!!!!!!!!!!  Something must have happen to it.  So I will order a new styrene for it but the wima is working very quiet now, hahahaha.

Only 4 components had to be swapped before I found, not to bad.  It could have been a lot worse. HHAHAHAHAH

Thanks again Udo and Dan and everyone else, this is a great mic build.  I must have fried the styrene at some point.

-Scott

 

[wave]

Sax,
What kind of noise did you have? My "thunder" noise is very quiet.

Dany,
I changed the drain voltage to 11.5V as you suggested and the mic seems to be better. I haven't heard any of the weird volume drops since and overall I think it's nice and as my friend said - "vintagey"

Here is a link to a clip of me doing an extremely rough vocal for a song I'm working on

http://soundcloud.com/waveaudio/u87-clone-11-5-drain/s-jdZvb

Let me know what you think.

Dave

 

[Matador]

can you make sure that is signal from your tone generator is not just way too hot.. can you actually reduce the level and see a proper sine wave to the Drain pin with the scope also make sure you use a probe with a 10X divider in it ,
Hope this helps,
DAn,

Hey Dan, I am able to see a clean sine wave with my scope with my signal generator at a low level. And yes, I do have a 10x probe. I can see symmetrical distortion that's similar to what I've seen in other people's posts, except the flattening of my 1k sine occurs at an angle (see pic on post #516). Then if I increase the 1k tone level, I see really strange distortion (see pic on post #517). Thoughts? Thanks.

-DUDE GUY

Can we see what the peak-to-peak amplitude is of your input signal (or just show us a scope picture and tell us what the volts/division is set to)?

 

[saxmonster]

Dave,

I hear is a sound file of the issue.  You might have to crank it a bit and use headphones. It turn out to be C1 a bad styrene cap

http://www.ehornstudios.com/media/little%20pops.mp3

I hope this helps.
-Scott

 

[DUDE GUY]

can you make sure that is signal from your tone generator is not just way too hot.. can you actually reduce the level and see a proper sine wave to the Drain pin with the scope also make sure you use a probe with a 10X divider in it ,
Hope this helps,
DAn,

Hey Dan, I am able to see a clean sine wave with my scope with my signal generator at a low level. And yes, I do have a 10x probe. I can see symmetrical distortion that's similar to what I've seen in other people's posts, except the flattening of my 1k sine occurs at an angle (see pic on post #516). Then if I increase the 1k tone level, I see really strange distortion (see pic on post #517). Thoughts? Thanks.

-DUDE GUY

Can we see what the peak-to-peak amplitude is of your input signal (or just show us a scope picture and tell us what the volts/division is set to)?

In the pic attached to this post, I'm sending -22.6 dB (Peak-to-Peak) and my volts/division is set to .5. Thanks for your help.

-DUDE GUY

 

[kante1603]

Congrats Scott,well done.
Styrenes don't like too much heat,just very short solder times.Maybe that's what it was.
Just for future refence,do you have c1 still laying around,can you measure it for dead short?
Would be nice because we can trace errors better then.

Thank you,

Udo.