Neumann Vintage U87 Clone : Build Thread.

[kante1603]

Congrats!
On top of the pcb,is that residual solder flux or tears ;D

Cheers,

Udo.

 

[dissonantstring]

hello all,
i've recently built up two U87 from dany's original tapered pcb design.  the build and biasing went well, but my issue is that i have omni and cardiod modes, but no fig.8.  after reading through the thread there was at least one person (wthrelfall) who had this issue, but it was difficult to determine his actual issue and it looks like it was never resolved.  udo (kante1603) offered some good suggestions as to where fault might lie and i have looked at the schematic and tested the parts which are associated with the pattern (esp. fig8).  no luck so far.

i do see that in fig.8 the backplates on each side of the capsule are getting 6.8VDC, while in other modes there is about 38VDC on backplates (dependent on mode).  does anyone know what the backplate voltage should be in fig.8 mode?
any help would be greatly appreciated.
kindest regards,
grant

 

[kante1603]

Hello Grant,

I opened one of mine and measured 40,6vdc on the front backplate connection.
Seems you're loosing it somewhere.Is the switch o.k.?

Best,

Udo.

 

[dissonantstring]

hi udo, thanks for checking!  greatly appreciated!  i'll trace my voltages and see where this front backplate trace is loosing the voltage.
i never thought about the switch, but i did check it in all three positions and it does seem to be making proper contact in both the omni and fig.8 modes.
i'll report back when / if i find anything.
thanks so much udo!

 

[dissonantstring]

ok, this seems strange, checking voltages in my "fig.8 -less" mics:

In OMNI the FC BDY = 38VDC / RC BDY = 38VDC / 0VDC on FC CAP & RC CAP
In HyperC the FC = 38VDC & RC = 38VDC / 0VDC on FC CAP & RC CAP
in Fig8 the FC = 6.8VDC and RC = 6.8VDC / 0VDC on FC CAP & RC CAP

1) shouldn't there be some voltage on the diaphragm (either front or rear depending on mode)?    ???

2) should the FC backplate and RC backplate be continuous.  in my mic they are actually shorted when in circuit which explains equal voltages no matter what pattern is selected. 

edit: BTW the mic actually does deliver sound in fig.8 mode, but it sounds a lot softer and sounds more like Hypercardiod mode than a figure 8.

 

[JessJackson]

ok, this seems strange, checking voltages in my "fig.8 -less" mics:

In OMNI the FC BDY = 38VDC / RC BDY = 38VDC / 0VDC on FC CAP & RC CAP
In HyperC the FC = 38VDC & RC = 38VDC / 0VDC on FC CAP & RC CAP
in Fig8 the FC = 6.8VDC and RC = 6.8VDC / 0VDC on FC CAP & RC CAP

shouldn't there be some voltage on the diaphragm (either front or rear depending on mode)?    ???

edit: BTW the mic actually does delivery sound in fig.8 mode, but it sounds a lot softer and more like Hypercardiod mode.

I had the exact same problem

It was due to a bad connection from the eyelet to the rear screw connecting to the front backplate

Try continuity test between the screw head and the eyelet edge or circuit board. make sure you have 0 ohms everywhere on capsule connections

J

 

[dissonantstring]

hi jess, i think you're on the right track.  i just ohm'd out the backplate connection eyelet to the screws on each side.  on the working front side the eyelet ohms out to each of the screws on that side.  on the non-working rear side the eyelet and mounting screw does not ohm out to the other screws on that side, but it does make connection to the pad on the board.  this is the backplate light blue wire Peluso installs on delivery. 
would it make sense and can i remove the mounting screw to this backplate eyelet and remount it to one of the screw holes under the tape on the capsule edge of that backplate or will this retension the diaphragm in a bad way?
thanks all for your help, a big debt of gratitude to udo and jess!
best,
grant

 

[dissonantstring]

hello, thought i'd update....
i disconnected the light blue FC backplate pre-installed wire on the Peluso PK-87 as it seemed to not be actually connected to the backplate when checked with continuity with the other screws on that side of the capsule.  i then took a short screw (which i was fortunate enough to have) and connected a wire to it via looping it and using a washer (no spare eyelets) and then connecting it to FC backplate pad on pcb.....now all patterns are working. ;D
thank you very much jess for the suggestion of the backplate continuity though my issue is slightly different is amounts to the same solution.
much thanks to udo for checking the voltages for me as well, it really helped narrow things down.

i wonder if this is a common problem, i.e. should we let john peluso know his capsules have QA issues?

SO....now my issue now is to find another short screw that fits the backplate tapped hole and an eyelet to match.  can anyone tell me what size screw fits the tapped holes on the sides of the capsules backplates (same as the mounting screw holes).  i think they may be 2M, as the 2.5M do not fit, but they may be smaller.

thanks everyone!!
best regards,
grant

 

[JessJackson]

no problem mate, glad i could help. it wont retention because its not a tensioning screw. its one of the four screws that keeps the two backplates together.

Hold a credit card across the diaphragm so if your screw driver slips it doesn't hit the membrane.

 

[kante1603]

i wonder if this is a common problem, i.e. should we let john peluso know his capsules have QA issues?

Hi Grant,

glad you got it solved,congrats!
As said I have built 4 of those microphones,all using John's capsule,orders were split over a long time as two years or so. No issues here.I always mounted the fourth wire through the saddle by removing some of the tape at the corresponding hole with an eyelet and a washer.
I posted some some pics a while ago,maybe that helps for future reference.
Sadly I don't know the screw size either,you should contact John,or does anybody here know it since it was asked before?

Best,

Udo.

 

[dissonantstring]

hi udo,
i took a look at your posted pics of the capsule and it seems that you are using the provided / already attached light blue FC backplate wire which was giving me the short to the RC backplate which defeats the isolated backplate situation in a U87 circuit.  i certainly don't want to suggest that there are continuing issues with mr. peluso's capsules, but i believe there is something wrong with the one's i received...or maybe i'm just not understanding the intricacies of this particular capsule.

another update on my situation...the two U87s were built exactly alike at the same time and i managed to solve my fig.8 problem by connecting another wire to the perimeter screw hole on the backplate under the tape on one of them.  NOW i thought this would also solve my second mics fig.8 problem so i did the same mod, but this time it did not work.  all my voltages are exactly alike on each mic at every pad point.  the quest continues to get this one up and running fully...or the worst is this mic will just not have fig.8 pattern as an option. 
thanks again udo for follwing this issue.  hopefully i get this issue solved.
best,
grant

 

[kante1603]

Hi Grant,

yes,I used the thin blue ones on my first two capsules.On the next two there wasn't a wire attached but an eyelet at the very same position.
So for your second mic you must start again.I'd say measure if there is any continuity between the backplates first.If yes then the capsule seems not to be assembled correct and I would contact Mr.Peluso for an exchange.
If no then there's a good chance to get it up and running.
Grant,do you have an lcr meter or access to one?It's helpful to figure out the capacitance of both capsule sides.This way you can find out which diaphragm connection belongs to which backplate.
The higher displayed values will be the correct ones.

Keep us posted,best,

Udo.

 

[dissonantstring]

udo you are brilliant!  i had checked continuity between backplates before and i was certain that there was no short there and the differences in backplate voltages in different patterns supports this.  so, when you mentioned looking which backplate belonged to which capsule side i thought i'd test this idea even without an LC meter handy.  so i simply switched the backplate wires and all patterns work now! ;D ;D

simple fix, but still a QA issue with these peluso capsules.  oh well, simple fix and it took some debugging time, but nothing extra-ordinary by DIY standards.

i thank you kind udo for all your help and also jess jackson for the help with the other mic.  together you both helped with toubleshooting both my new U87 mics!  thank you dany for making the project available to us and chunger for the bodies.  thank you also to mr. peluso for the fine capsules at groupbuy rates...even though both had some issues, i was at least able to make them work.  success!!  viva la DIY!

now for some burn in time and then off to the studio they go!
kindest regards,
grant

 

[kante1603]

Excellent Grant!

I swear you'll have a lot of fun with them (I really love them).

All the best from munich,germany,

Udo

 

[EEMO1]

any ideas on how I could use a transformer from oktava 219 in this?

 

[Mr.GrinchSD]

Ok so Im trying to set my mic to exactly 11.05 but the voltages keep jumpin around. Like from 11.05 to 11.13 to 11.20 then it will go down to like 10.55 ????? Any Ideas

 

[kante1603]

Ok so Im trying to set my mic to exactly 11.05 but the voltages keep jumpin around. Like from 11.05 to 11.13 to 11.20 then it will go down to like 10.55 ????? Any Ideas

Are you probing correct and hold them really steady?
Is it a good DMM you're using?
Is the capsule connected?

Cheers,

Udo.

 

[Mr.GrinchSD]

CApsule is connected Fluke DMM and ya Im pretty sure im doing it right.

 

[kante1603]

CApsule is connected Fluke DMM and ya Im pretty sure im doing it right.

Hmmmm....o.k........drifting voltages over time normally is something related to parts like capacitors.
Let's see if it changes if you do the easy to reach things first.Can you try to lift the capsule connections (one wire per capsule side is o.k.,you mustn't lift them all)?Look if there is a change meaning if the voltage doesn't move anymore.
For biasing,you don't have a scope,no?

Best,

Udo.

 

[Mr.GrinchSD]

No No scope so remove one of the capsule wires???