u87Ai Experimentation

[poctop]

DU87A  The sequel ! same Footprints as u1621 i had that in the pipeline for a while but just needs some more polishing but i hope it is coming soon , Same transfo used but the K67 can be used in there with 3 leads ,  all orginal.  and it should have a lot more gain because the PCB is Pretty busy 
but again a lot of fun..  time go sleep now, 

cheers,

Dan,

 

[wave]

Dany,
So is this another U87? What are the differences from the previous one?

DAve

 

[poctop]

it is the AI  ,  ,

D

 

[Edward]

I'm in for two sets if the price is in the same range as the previous one.

Great work Dan!

 

[kante1603]

Woahhhhh....but what about us (p)k 87 capsule users......? ;D

 

[saxtim]

I'm definitely interested in this.  How are you implementing the DC-DC converter to get the +/- 60V?  Is it your own converter design?  The original AI has a auto transformer on the DC board.  I managed to clone the DC-DC part of U87ai circuit a few years ago, I wound my own simple autotransformer.  I had trouble getting the head amp to bias right, however, so I shelved the project.  I'd like to give it another crack though.

 

[MagnetoSound]

Woahhhhh....but what about us (p)k 87 capsule users......? ;D

You know the answer - it's fine, you just connect the two backplates together. 

 

[kante1603]

Woahhhhh....but what about us (p)k 87 capsule users......? ;D

You know the answer - it's fine, you just connect the two backplates together. 

Have you seen the smiley?
Cheers,

Udo

 

[poctop]

I'm definitely interested in this.  How are you implementing the DC-DC converter to get the +/- 60V?  Is it your own converter design?  The original AI has a auto transformer on the DC board.  I managed to clone the DC-DC part of U87ai circuit a few years ago, I wound my own simple autotransformer.  I had trouble getting the head amp to bias right, however, so I shelved the project.  I'd like to give it another crack though.
[/quote

Thanks Saxtim,
That is the only part i need to figure out for this autotramformer for now i am still cluless on its details ,  it seems this whole drawing might be good for the garbage at this point ?

 

[poctop]

is anyone would have any info on this autotranformer thing like a spare parts list for the neumann u87ai  or something similliar ,

Let me know if nothing is expectable then i will remove this post and throw this in the garbage  :-\ :'(

Cheers,
Dan,

 

[saxtim]

I had luck winding the auto transformer myself - check this thread, it has details of the original neumann one as well as Dale's suggestions as to how to wind one (which I did and I got the DC-DC converter working):

http://www.groupdiy.com/index.php?topic=1651.0

I think if I could manage it (I don't have a great deal of expertise) most people could manage to DIY one - all you need is a bit of ferrite rod and magnet wire.  I didn't seem to be too sensitive to the turns ratio (in order to get it in the ball park of +/- 60V).  I never actually got the whole project going (had problems with the head amp and FeT biasing but i'd like to have a go at it again).

 

[HellfireStudios]

Could a different DC-DC converter be used in place of Nuemann's design? Capsule polarization style shouldn't affect the sound. A clean 60V is a clean 60V, correct?

 

[zephyrmic]

Should be no problem to use a different converter. I would suggest you look at zapnspark's schematics in the Files section of micbuilders site. They follow a tried and true circuitry. That is the sort of DC converter I use and it is simple to build and works well. Main thing is to ensure that the two inductors in the circuit are as close as possible together. Hope that helps you.

Kindest regards,
zephyrmic

 

[sr1200]

i gotta send you a pic of the OPC mic board which is a 'copy' of the ai aswell, and has the transformer ON the board...

 

[poctop]

i gotta send you a pic of the OPC mic board which is a 'copy' of the ai aswell, and has the transformer ON the board...

mmm.... interesting,  let me me see that picture, any other info would be Excellent as well,

Dany,

 

[sr1200]

sorry it took so long, got caught at the office yesterday...huge application failure.... anywho... to the gear ****..

 

[sr1200]

Aaaaand the reverse side...  it should be noted that there was a third board that pluggedinto these two that held the switches and the 1g resistors which i used in my U87 build. (removed all those parts and just used the mounted switches)

 

[HellfireStudios]

i gotta send you a pic of the OPC mic board which is a 'copy' of the ai aswell, and has the transformer ON the board...

Have you had a chance to trace the circuit? If so, how close is it to the U-87Ai (i.e.-layout, component values, etc.)? Also, for curiosity's sake, my quick search on evilbay shows that the OSP STM-1300 is a back electret design. If this is the case, it could make for a very different circuit, but how often does evilbay get their info right? Thanks for any info you can come up with.

 

[sr1200]

Component wise is VERY VERY similar, from what ive seen... i can do a trace per component up to where the boards connect to teh switch PCB which i dont have assembled anymore.

 

[HellfireStudios]

Component wise is VERY VERY similar, from what ive seen... i can do a trace per component up to where the boards connect to teh switch PCB which i dont have assembled anymore.

Thanks. Does the switch PCB have other components (caps, resistors, etc.) on. it? If not, then their function would be easy to figure out without needing to take apart your U-87 clone.

Did you find out if the original capsule is a back electret or externally polarized? Thanks again.