Neumann Vintage U87 Clone : Build Thread.

[Krumlee]

Hi again
I just finished this build and been doing some tests. I dont have any audible noise and i get a signal through which sound fine but very low. I have read in several posts that it is supposed to be a quite low signal from this circuit, but compared to an sm57 it is a very low signal and i am pretty certain it is lower than it is supposed to. I am using the Sowter 1303f transformer which is 9:1. As far as i could tell it is a replica of the original transformer, so i just assumed it would be fine, but I dont  see anyone else in this thread using this specifik transformer, and i am wondering if it may not be suited for this project after all? Any thoughts on this?

The Sowter should work fine. Did you measure the resistance of the primary and secondary before installing it? If so, what readings did you see? As Dany said above, the high side connects to rt and sw.

 

[jakobz]

Hey Krumlee
I get around 1k Ohm between the Blue and Green on the transformer , which according to the datasheet is primary and around 22ohm between brown and grey (secondary).
If i understand you all correct Blue and green on the sowter goes to RT and SW and Brown and Grey to BL and WS.

 

[Matt55]

Hello,

Firstly a big "Thank You" to everyone who has made this kit possible, I have enjoyed building it and look forward to using it I have completed the pcb build including transformer wiring and for the moment I have left the capsule disconnected.

Kit details; Chunger body, Dany Green PCB + Styrenes, Eric (TSKGUY) 87 capsule and Cinemag 2480 transformer.

I have a a few questions before I connect it up to 48v for testing if someone could help me out that would be awesome

1) Does the orientation of the Pot matter? And do all 3 legs need to be connected?

2) My FET's measured between 7.2 and 8.90, I chose one at 7.6 from reading it seems on the low side is it ok?

3) Do the GNDLINK or CGND need to be connected to anything?

4) I do not have a scope or sine wave generator. When I connect to 48V how do I test the voltages? Do I refer to B1 and B2 scematics and measure across the components with DMM or do I measure at the component and then to Ground somewhere? Sorry I did search the thread but still couldnt quite understand how people were measuring these voltages.

I followed chungers build guide and the schematics.

Thank you so much for taking the time to help aswell I really appreciate it

Regards,

Matt

 

[Krumlee]

Hi Matt,
1) It'll work either way. If you trace the pcb, I think that one of the end pins is just a pad with no connection to the circuit. Strictly that one doesn't need to be soldered, which makes it easier to remove it if you intend to replace it with a fixed resistor later. In practice I think most people just leave the pot in place. So do whichever you like.
2) That's perfect.
3) No.
4) To Bias: Power up with phantom power. Set a dc range on your dmm. Connect neg probe to a convenient ground (eg the mic chassis). Pos probe to the fet drain. Adjust pot till you see about 10.5V - anywhere in that region should get you a working mic. To measure other voltages (eg to test dc levels against values shown on the schematic) just move your pos probe to the point you want to measure.

 

[Krumlee]

I get around 1k Ohm between the Blue and Green on the transformer , which according to the datasheet is primary and around 22ohm between brown and grey (secondary).
If i understand you all correct Blue and green on the sowter goes to RT and SW and Brown and Grey to BL and WS.

Yes, that's right. I can't think why the transformer would be a cause of your problem.
Are you hearing any distortion, or is it just a case of low output? Did you measure the fet before installing it? How did you bias it?

 

[jakobz]

I get around 1k Ohm between the Blue and Green on the transformer , which according to the datasheet is primary and around 22ohm between brown and grey (secondary).
If i understand you all correct Blue and green on the sowter goes to RT and SW and Brown and Grey to BL and WS.

Yes, that's right. I can't think why the transformer would be a cause of your problem.
Are you hearing any distortion, or is it just a case of low output? Did you measure the fet before installing it? How did you bias it?

I do not experience any distortion or noise issues at all, only low output. I biased the fet using my dmm (11,5v) i did not measure the fet though, how do i do that?

 

[jakobz]

Just found out how to measure the fet http://studio939.blogspot.com.au/2012/12/vintage-u87-circuit-clone-microphone.html It reads 7.90 mA.
I think i will, check up on all the components one more time and see if i messed up somewhere :-\

 

[Matt55]

Krumlee thank you for answering my questions it all makes sense I will report back once I have tested!

Thanks,

  Matt

 

[Krumlee]

Just found out how to measure the fet http://studio939.blogspot.com.au/2012/12/vintage-u87-circuit-clone-microphone.html It reads 7.90 mA.
I think i will, check up on all the components one more time and see if i messed up somewhere :-\

Are your dc levels good? 24V across the zener and about 21V on the top of R14.
Get a magnifier and inspect all your solder joints - rework any that you're not totally sure about - be careful with the styrene caps though.

 

[Matt55]

Hello,

I biased my JFET to 11.0v for drain, checked a few voltages according to the schematic and posts on here, and double checked my solders and component positions which seemed ok.

I then decided to solder up my capsule and connect the mic up to see if it sounded ok. Before I continue, the preamp/monitor/cables are confirmed ok with another condensor microphone using phantom power in exactly the same setup.

When I select 48v phantom on the Preamp with my D-U87 connected to a monitor for testing purposes, I just hear loud crackle and noise no real output from me speaking into the microphone at all.

The pad switch appears to work (thud through speaker as I switch and lowers noise/crackle), roll off I can't tell, and mic pattern switch appears to do nothing, not sure if thats a good or bad thing?

The capsule is a TSKGUY 87, I was very very careful when installing it and wore gloves as suggested (One thing I didnt do was test for continuity between front and back plate...). The capsule appears to be wired up correctly! The Transformer is Cinemag 2480 which I have checked seems to be wired correclty (although I havent tested the transformer with DMM, ill search the thread!!!). I used tantulums and Polystyrenes and was very careful installing and working around the styrenes, I didnt use IPA near or around the styrenes as I read they are sensitive but I cleaned everything else thoroughly as I went along! I checked all the resitors and they seemed to measure ok on my DMM.

My next question is I guess I shoud check the voltage on the board more throroughly? Is it best to do this with capsule still installed or disconnect the capsule to do this?

Any help would be greatly appreciated!

Regards,

  Matt

 

[Matt55]

Also as a note, I can put up some pictures if you think it may help

Thank you so much for taking the time to help, regards, Matt

 

[Matt55]

Hey,

I did some more tests on my D-U87 that is producing lots of crackles and noise.

1) It seems the capsule does not have continuity between the front and back plates so that seems ok.

2) Even with only 1 screw in each board the chassis is getting good ground everywhere (headbasket, mic body, etc...) 0.00 resistance on my DMM.

3) What I have noticed is that there is continuity between Pins 2+3 (Hot and cold) of the XLR cable which I guess should not be there?

4) I have the Cinemag CM-2480 transformer wired up as below;

RT - PIN 1 - Red from Transformer
SW - PIN 2 - Brown from Transformer
BL - PIN 3 - Orange from Transformer
WS - PIN 4 - Yellow from Transformer    (This set as per previous post in this topic)

There is continuity between Pin 3+4 with measured resistance of 0.033 Ohms.

There is resistance between pins 1+2 of 1.5K Ohms

There is resistance between pins 1+3 of 125K Ohms
There is resistance between pins 1+4 of 125K Ohms

There is resistance between pins 2+3 of 125K Ohms
There is resistance between pins 2+4 of 125K Ohms

I havent reconnected the mic to the 48v yet because I am wondering whether I should remove the capsule to do that?

Thanks for the help Matt

 

[MicDaddy]

Who makes a historically accurate BV13?  Same laminates/core geometry?

 

[Pip]

Who makes a historically accurate BV13?  Same laminates/core geometry?

Neumann?

 

[Krumlee]

Hi Matt,
Let's see if we can get you closer to a working mic.

First, the noise you heard. Whenever you're listening to the mic, you need to have the headbasket and body tube firmly in place, otherwise the mic just picks up RF - I'm not sure if you were running it 'open' on the desktop.

Also, if it's easier, you can safely leave all the switches disconnected for testing purposes. The mic defaults to cardioid, no-pad and no-low-cut which is fine for initial testing. Also, the mic will work fine with just the front diaphragm and front backplate connected - you can leave the back connections disconnected initially. Those points may save you a bit of soldering/unsoldering.

I think you've identified your most obvious problem - you shouldn't be seeing continuity between pins 2 & 3 on the xlr connector - something like 30 or 40 ohms would be closer to the mark. So... use your eyes and trace everything from the xlr connector to pins 3 & 4 on the transformer, by way of R18 and R19 etc. You've probably got a stray strand of wire from one of the XLR connector or transformer wires, or an inadvertant solder bridge.

Hope that helps...

 

[Matt55]

Hey Krumlee,

Thanks so much for the help I really apprciate it!

I have been over the mic with a fine tooth comb, cheecking for loose wire strands, solder bridges, cold solders or anything that could cause continuity between pins 2 + 3 but I cant find anything! I even checked every trace and they are all still joined as they should be!!!

My DMM does measure 30 Ohms between pins 2+3 in resistande mode but it also measures continuity in continuity mode... Not sure if thats right or wrong?

The mic was tested with it fully assembled, I did also test it with the body off incase there was something grounding that should not have been across the body or something similar.

Its a neat build its not untidy or anything like that. I built 2 x EZ1073 with many more components and both worked perfect first go...

The Pad and Low cut switches are working I tested them with my multimeter! They are both currently set to NO continuity which I guess should equal, NO low cut and No Pad. They both work and I tested them at the pcb joints by switching the switches and checking continuity/no continuity!

I dont know how to test the the Cardiod/Onmi/Fig 8 siwtch, but its wired up as per the schematics, with no solder bridges or anything...

I removed the headbasket just to check I had wired up the capsule correctly and it seems I have. There is no continuity between the backplates and the FD+FBKP and RD+RBKP are soldered to the correct points on the PCB...

I checked all the resistors, but other components like the styrenes and capacitors my DMM is not good enough to check... Maybe I should invest in a better DMM?

I will keep probing away and checking everything I can but I just dont know where to look next, I have double and triple checked everything I can...

Thanks for the help though I do really, really appreciate it

Matt

 

[Krumlee]

Matt,
Thats fine - I was going by this statement:
>> There is continuity between Pin 3+4 with measured resistance of 0.033 Ohms.
Presumably you meant 0.033 kilohms (not ohms). Which is fine.

Are you hearing any output from the mic? Can you describe it.
Treble check your capacitor polarities. C7 would be a prime culprit.
If your dc levels are fine, then the next thing I'd do is unsolder the capsule and try injecting a signal in to the capsule side of C4. If you don't have a signal generator, you may have to improvise something eg using the headphone output on your sound card and a 1kHz sinewave. With the mic connected to a preamp you should hear the signal on the preamp output. That will tell you whether you've got a good audio path through the mic.

Alternatively you could post some pics (as clear as you can make them). Someone else may have some ideas to help...

 

[Matt55]

Hey Krumlee,

Thanks again for the help.

Basically when I plug the mic into a preamp and connect it to a speaker (Stage monitor I use for gigs) I hear loud pops and crackle like static effect permanently (I can record it if you think it will help). If I switch it out for another condensor I have (CAD M179) instantly no noise/crackle/pop just pure signal, me talking into the mic and sound coming out from the speaker.

I will trace back along from pins 2+3 from XLR to transformer pins 3+4 to see if I can see anything, but it seems unlikely because I have done it already.

Should there be 33 Ohms/0.033 KiloOhms (apologies) resistance between pins 3 & 4 on the Transformer? Is that normal?

I tested a few other mics and they dont have continuinty between pins 2 and 3 on the XLR according to my DMM.

C7 is the tantulum next to the Pot. Its hard to see but with a light i can see the small + and its definitely in the correct way round!!

I will just have to be much more thorough!! I have take some pictures, and will post tomorrow

Thanks for the help I really really appreciate it

Matt

 

[Krumlee]

Matt,
You haven't got a problem with pins 2 & 3 - I was assuming your "continuity" referred to the low resistance value you saw (but which was actually a units mixup!) I didn't realise you meant the 'continuity' setting on your dmm. Don't use 'continuity' - dc resistance tells you the same thing in a better way. The reading of 33 ohms is exactly as it should be. Your other mics likely don't use an output transformer which is why your meter sees them differently. To be clear - everything from the xlr back to the transformer seems to be exactly as it should be - we don't need to look there any further.

You could try putting a temporary connection between FD and ground, and see if the noise goes away.

And if you can post pics (both sides of the boards) that may help too...

 

[Matt55]

Hey,

Again thank you for the help, really appreciate it!

Here are some pictures i took of my D-U87 build of the mic, hope this works!

https://www.dropbox.com/s/wtcyibosnq210sc/Pic%201.jpg?dl=0?raw=1

https://www.dropbox.com/s/7j3v035r43rkidc/Pic%202.jpg?dl=0

https://www.dropbox.com/s/5hm23pkkd2khi2c/Pic%203.jpg?dl=0

https://www.dropbox.com/s/v86yzacz2w83tf7/Pic%204.jpg?dl=0

https://www.dropbox.com/s/acb3xxbkv11cvhs/Pic%205.jpg?dl=0


Okay I understand! It is defo 33Ohms resistance between pins 2 & 3 so I guess thats ok!

I have probably made a sill mistake somewhere, I hope the photos arent too bad!!!

Thanks,

  Matt