Neumann Vintage U87 Clone : Build Thread.

[Cardinen]

I forgot to say: if I use the switch to change the plot or the filter I got close to 20V at drain for 2-3 seconds. then falls again.

new photo added.

 

[kante1603]

Hello,

sadly I'm on holidays at the moment,so I don't have all the info with me.
I can vaguely guess,not more.
At first these giant Dale resistors,they don't touch anything I hope (exept their solder pads of course).
Second thing: Are you sure the trim pot is soldered in at the correct places?You should compare to the schematics,one leg must connect to ground,the other to the fet source.
As said,just a guess,but maybe worth to check this first.

The voltage at top of zener looks very good btw..,so it can't be too hard to find.

If nothing works you should bring the mic to some kind of very basic performance.That means you must lift all the switch wires.The mic will work then without any pad or filter and is in cardioid mode meaning that only one capsule side is active,should be the front.
Start from there then.
It's a nice wiring you have done,but sadly not too service-friendly.That's why we often use headers from top of the pcb to easy lift connections,hahahaha........sorry........

Let us know here please,

Good luck,

Udo

 

[Cardinen]

Thanks Udo for the reply!

Yes, the giant Dale resistors are not touching anything except their pads, i've checked everything with a tester and seem all good, all the components are fine, i've triple checked everything.

Again, the trim pot is soldered in the right pads, at first i thought it was a faulty trimmer (never happened to me)
so i changed it 3 times. the one in the photo is 50K and work exactly as the previous ones (10K-25K) it change the voltage between 0V and 0.5V not so good bias point  ;D

Usually i love to have problems with the stuff i build, because is so funny to discover errors or mistakes but this time i can't find anything wrong!

Meanwhile, thanks to the great advices, i will try to disconnect the switches and try just with the cardioid,
if someone have some ideas will be appreciated.

And yes, i'm always obsessed with the shortest wiring, sometimes you have to pay for it... 

Cardinen

 

[poctop]

Hi All,

I've my U87 clone sitting on the workbench from a long time now, so i hope you can help me.
The main problem is: i'm not able to bias the FET, the voltages seems Ok everywhere but not on the Drain.
I'm using Peluso transformer and RK-87 capsule by M. Parts.

I've swapped 3-4 different FET, now i have the one with the lowest IDSS installed (5mA) and i have just 0.4V on the Drain. Tried to change the trimmer from 10K to 25K/50K don't help.

my voltages (with capsule and transformer, same without):

Phantom:  47.86V

Top of R18: 47.8
Bot of R19: 47.8
Node R18/R19: 46.68V
Zener : 23.83V
node R12/R14: 19.71
FET Drain :  0.42V    (23.3V on the pad without FET and trimmer)
FET Source: 0.32V

I'm using 68M resistors instead of 60M, could be a problem ?

Below you can see two photo, any help will be appreciated.

Thanks 

I am wandering where did you solder you FET Gate the middle pin of the feT should be solder in the air or on an isolation pin  and goes to the ther board labeled G ,  if you have  (FET Drain :    (23.3V on the pad without FET and trimmer)) happening then you should be all set on board number one unless there is somthing simple that is preventing it to work, you can try for now to put a 10K resistor in place of the pot and troubleshoot from there ,

hope it helps,
D 

 

[poctop]

Hi All,

I've my U87 clone sitting on the workbench from a long time now, so i hope you can help me.
The main problem is: i'm not able to bias the FET, the voltages seems Ok everywhere but not on the Drain.
I'm using Peluso transformer and RK-87 capsule by M. Parts.

I've swapped 3-4 different FET, now i have the one with the lowest IDSS installed (5mA) and i have just 0.4V on the Drain. Tried to change the trimmer from 10K to 25K/50K don't help.

my voltages (with capsule and transformer, same without):

Phantom:  47.86V

Top of R18: 47.8
Bot of R19: 47.8
Node R18/R19: 46.68V
Zener : 23.83V
node R12/R14: 19.71
FET Drain :  0.42V    (23.3V on the pad without FET and trimmer)
FET Source: 0.32V

I'm using 68M resistors instead of 60M, could be a problem ?

Below you can see two photo, any help will be appreciated.

Thanks 

I think I know what your problem is ,

if you look on the picture U87-2 the pin of the pot do not even attach to the pad of the FET source ,

in short you need to have the pot solder on the ( if you look at the picture )
on the 2 lefmost pin of the (3 insidepad) these are for the pot the 2 outmost are for a resistor,

one of those pin will be continuity with the FET source and the other one to GND, 
make sure you also connect the wiper of the pot also not the 2 sides

Hope this helps,
Dan

 

[kante1603]

That's what I meant 4 posts ago...the pot doesn't seem to be in the right place,but Cardinen states it is......so..............

Udo.

 

[Cardinen]

Hello Dan,

Thanks for the help!

I am wandering where did you solder you FET Gate the middle pin of the feT should be solder in the air or on an isolation pin  and goes to the ther board labeled G ,  if you have  (FET Drain :    (23.3V on the pad without FET and trimmer)) happening then you should be all set on board number one unless there is somthing simple that is preventing it to work, you can try for now to put a 10K resistor in place of the pot and troubleshoot from there ,

the Gate is connected on an isolation pad and goes to G in the other board, see the black wire in the photo below.

I think I know what your problem is ,

if you look on the picture U87-2 the pin of the pot do not even attach to the pad of the FET source ,

in short you need to have the pot solder on the ( if you look at the picture )
on the 2 lefmost pin of the (3 insidepad) these are for the pot the 2 outmost are for a resistor,

one of those pin will be continuity with the FET source and the other one to GND, 
make sure you also connect the wiper of the pot also not the 2 sides

i think the trim pot was connected right with wiper and one side, i've now swapped it with a 10K resistor, and still 0.43V at Drain.

tomorrow I will do a few more test i'm tired now, i don't know why but i suspect the problem could be in the board 2 (the one with big resistors).

I'll let you know!

 

[Cardinen]

added a new photo

 

[poctop]

Just a quick note,

The FET Gate Pin should not be soldered to the pcb directly.
Let me know how it goes ,
Best,
Dan,

 

[JessJackson]

I'm going to try and remove all switches from the circuit and disconnect rear capsule and rear backplate for cardioid only and see if it helps with noise and output slightly.


Has anyone messed with different flavours of coupling cap (C7) for this build.

U47 / u67 / C12 builds pay a lot of attention to this and in this build the coupling cap hasn't seen much attention here on the forums. Is it not as important to the circuit due to it being a FET mic?

What was the original type used in vintage u87?

A cap could be mount under the board such as the smaller TE1501 wet tantalum (elam251)

 

[poctop]

What was the original type used in vintage u87?

original is 470pf polystyrene,

Best,
Dan,

 

[JessJackson]

What was the original type used in vintage u87?

original is 470pf polystyrene,

Best,
Dan,

Hi Dan,

No its 1uf 35v

 

[poctop]

oupss sorry you are correct I had this on the top of my mind and my memory is playing on me ,
I was thinking of the FET Gate coupling Cap
the original is a Tantalum capacitor ,  some like the elctrolytics instead of tantalum tough.

Best,
Dan,
 

 

[JessJackson]

oupss sorry you are correct I had this on the top of my mind and my memory is playing on me ,
I was thinking of the FET Gate coupling Cap
the original is a Tantalum capacitor ,  some like the elctrolytics instead of tantalum tough.

Best,
Dan,

All good mate...

Actually about that 470pf cap (C4) , heres is an excerpt from Klaus on modding it.

Case in point: C4 in the original U87. 
Here, a 470pf cap is placed in series between the capsule's front diaphragm and the FET's gate. (I routinely remove it in the course of my U87 modifications- it does not contribute to anything audible or measurable; all it does is introduce phase shift at a crucial point in the circuitry. (Yes, David Satz: phase shift! Audible!)

 If it's not decoupling anything, if it does not eq, if its removal does not cause the collapse of the Roman Empire, what the hell is it for?
I still think that Neumann's answer to me makes the most sense: low frequencies, those close to and including DC, are curtailed. Maybe it serves as a safety valve in case there is any kind of DC (electrostatic?) charge left on the diaphragm. But if that's the case, 25 years of living without it has not got me in trouble yet.

More info on u87 mods and Gus speaks on this klaus mod here
http://www.groupdiy.com/index.php?topic=29958.0

And RRS modded one here
http://www.groupdiy.com/index.php?topic=35153.0

I just disconnected all switches and rear capsule connections and the mic sounds much better now, more output and less system hiss.

Just cut a monster of a record with it. It absolutely kills the top end of my sony c800g and makes that mic sound like a smeared soft wet sandpaper and it doesnt sound too FET yet still sounds immediate... if that means anything to anyone.

I'm gonna do some research on the original coupling caps.

 

[poctop]

oupss sorry you are correct I had this on the top of my mind and my memory is playing on me ,
I was thinking of the FET Gate coupling Cap
the original is a Tantalum capacitor ,  some like the elctrolytics instead of tantalum tough.

Best,
Dan,

All good mate...

Actually about that 470pf cap (C4) , heres is an excerpt from Klaus on modding it.

Case in point: C4 in the original U87. 
Here, a 470pf cap is placed in series between the capsule's front diaphragm and the FET's gate. (I routinely remove it in the course of my U87 modifications- it does not contribute to anything audible or measurable; all it does is introduce phase shift at a crucial point in the circuitry. (Yes, David Satz: phase shift! Audible!)

 If it's not decoupling anything, if it does not eq, if its removal does not cause the collapse of the Roman Empire, what the hell is it for?
I still think that Neumann's answer to me makes the most sense: low frequencies, those close to and including DC, are curtailed. Maybe it serves as a safety valve in case there is any kind of DC (electrostatic?) charge left on the diaphragm. But if that's the case, 25 years of living without it has not got me in trouble yet.

More info on u87 mods and Gus speaks on this klaus mod here
http://www.groupdiy.com/index.php?topic=29958.0

And RRS modded one here
http://www.groupdiy.com/index.php?topic=35153.0

I just disconnected all switches and rear capsule connections and the mic sounds much better now, more output and less system hiss.

Just cut a monster of a record with it. It absolutely kills the top end of my sony c800g and makes that mic sound like a smeared soft wet sandpaper and it doesnt sound too FET yet still sounds immediate... if that means anything to anyone.

I'm gonna do some research on the original coupling caps.

Thanks For the Post ,  Just wandering how could the wiring and switches could affect the sound as they are just switches as when they are disconnected (off) there are not part of the circuit anymore , but well i am glad you made a monster recording with it and that you are happy with it
this is DIY after all,
Best, 
Dan,

 

[Cardinen]

Just a quick note,

The FET Gate Pin should not be soldered to the pcb directly.
Let me know how it goes ,
Best,
Dan,

Hi Dan,

unfortunately I have not yet solved the problem, now the Gate is connected just with a wire.
I've disconnected pad and filter just to be sure as Udo said, i don't know what else i could try.
i noticed if i touch one of the 60M resistors (68M in my case) with tester the voltage rise at the drain then it fall again. I did tried to lower the value of one of the 68M res. with a 22M in parallel just to see what happen, and is still the same.

maybe is time to swap some components ??

 

[kante1603]

Cardinen,

have you lifted the pattern switch too (3 wires)?
As said it is best to start troubleshooting with the mic in its' basic function,so no switches connected.

Udo.

 

[poctop]

What is the FET you are using ,

i would start by removing the FET and capsule and check you transformer wiring if you are using the T13 make sure the lower resistance pair is on the xlr side as it can trow off everything  and remove all wiring as Udo said  and check all the basic voltage trough the circuit ,
when this is all done start by adding adding the FET (install a 10K resistor like you did to start with.
Hope this helps,
Dan,

 

[Cardinen]

Hello,

Sorry for the late reply, i was on holiday these days.

have you lifted the pattern switch too (3 wires)?
As said it is best to start troubleshooting with the mic in its' basic function,so no switches connected.

Yes, the pattern switch is now disconnected (just left the central wire to the switch)

What is the FET you are using ,

i would start by removing the FET and capsule and check you transformer wiring if you are using the T13 make sure the lower resistance pair is on the xlr side as it can trow off everything  and remove all wiring as Udo said  and check all the basic voltage trough the circuit ,
when this is all done start by adding adding the FET (install a 10K resistor like you did to start with.

Ok, the situation i'm now: (photo below)
All switches are disconnected, i've removed the FET (don't know what the brand is ?? anyone have ever used ?) and let the 10K resistor in place.
I think i'll try some new FET, at the moment i've 10 of the CEN brand and 2 Fairchild with high IDSS (11 and 12mA).

The transformer wiring i'm sure is correct, i've followed the peluso wiring sheet in this thread and checked with tester.

Wich brand of FET are you using ? (bought mine from musikding some time ago)

Thanks 

 

[HellfireStudios]

Well, I finally got my studio built, and have started tracking the local talent. I was tracking a female vocalist with the U-87 clone, and a problem arose. I'm getting a high-pitched whine off of the mic (seems to be around 12-13kHz). It also seems to swell in and out of the track (maybe a faulty capacitor?). Unfortunately, I was unable to discern this cricket-like and intermittent noise during tracking, and may be doing a free session or two to make up for the problem (EQ and noise reduction have been unsatisfactory tone-wise).

Other than an ungrounded polar pattern switch acting as an antenna, what else should I check out? I appreciate any help that can keep this from happening to someone else.

BTW, the mic sounds amazing otherwise. I'm using the Peluso K-87 capsule and BV8P-S transformer wired for 11:1. Styrenes and tantalums except for a couple of silver micas replacing the styrenes that were unavailable at the time. Fairchild 2N3849 FET biased with a oscilliscope. Full 48v phantom power from the included standalone P/S that comes with the Carvin CM-87S. I also added the polar pattern switch because the mic only had low cut and pad switches stock. Which is why I hope it is just the switch case leaking RFI into the circuit, but the sound swelling in and out sounds like a capacitor issue to me... Let me know, if I need to post an audio example. Thanks again.

-James-