Neumann Vintage U87 Clone : Build Thread.

[dmp]

U67 doesn't need isolated backplates. Check the schematics

 

[newmod]

Eh gang,
I was wondering if you could answer a question I have.
How does one go about measuring/checking on a k87 style capsule if the front and back plates are matched?
What instruments and tools are used and how can one adjust if even possible?

Thanks

 

[dmp]

A easy test I have done is to set the mic in Fig8 and use a test tone that you can move from front to side and see the dB rejection. If the front and back are well matched, the side rejection in Fig8 will be high. When I compared several different capsules, the cheap Chinese capsules had poor rejection, while the high end (Thiersch, Tim Campbell) had high rejection.

 

[newmod]

A easy test I have done is to set the mic in Fig8 and use a test tone that you can move from front to side and see the dB rejection. If the front and back are well matched, the side rejection in Fig8 will be high. When I compared several different capsules, the cheap Chinese capsules had poor rejection, while the high end (Thiersch, Tim Campbell) had high rejection.

Interesting
What do you use to set off the test tone and how are you measuring it?
Sorry, new territory for me
Thanks

 

[dmp]

I used a cheap guitar tuner that had a A 440 test tone. Anything with constant volume. You can get into more detail by doing it at different pitches if you want.
Just record the mic as you move from front to side. Subtract the front level from the side level by reading the levels in the daw to get the dB rejection.

I think it is a really cool simple test because it is assessing the off axis response a LDC mic will have, which is what sets apart really great mics, imo

 

[newmod]

Eh gang,

Does anyone know if the styroflex capacitors Dany sells on his site are 1% or 5% tolerance.
Styroflex/630V - 1x 10pf/630V , 2x 470pf/630V , 1x 560pf/630V ,1x 220pf/630V

I assume these are the 1% ones?

 

[Purplenoise]

Eh gang,

Does anyone know if the styroflex capacitors Dany sells on his site are 1% or 5% tolerance.
Styroflex/630V - 1x 10pf/630V , 2x 470pf/630V , 1x 560pf/630V ,1x 220pf/630V

I assume these are the 1% ones?

I believe it’s the 5%

 

[ostrol]

Anyone know of suitable replacements or somewhere to find the now obsolete

1- Metal Oxide Resistors 60Mohmns 1% 750V 100ppm

2-Aluminium Electrolytic Capacitors - Axial Leaded 63volts 10uF 5x12 20%

Help much appreciated!

 

[Ricardus]

Anyone know of suitable replacements or somewhere to find the now obsolete

1- Metal Oxide Resistors 60Mohmns 1% 750V 100ppm

2-Aluminium Electrolytic Capacitors - Axial Leaded 63volts 10uF 5x12 20%

Help much appreciated!

If you search further down the BOM on Dany's site, you will see two 68 megohm resistors in the list. They are alternatives to the 60 megohm ones that are unavailable. Apparently the circuit will function fine with either.

https://www.mouser.com/ProductDetail/660-GS1-4LC686J
And any good quality Axial lytic will work for that cap. A quick search shows 2 choices. This one will be fine.

https://www.mouser.com/ProductDetai...2128109E3?qs=sGAEpiMZZMua3V2yDfsb6UJiwAUSVOjf

 

[newmod]

Eh gang,
I am a complete noob in electronics so just a warning.
I am trying to measure the idss of the 2n3819 JFETs but I am not getting any reading on the mulitmeter.
I am so confused.
I have tried all three meters I own all of which can measure mA

I understand about shorting the source and gate and the rest of the connections.......I think I got that part.
But maybe I got my meters settings wrong?
Can someone please provide me with a detailed step by step including proper meter settings?
I am so lost here.

 

[Purplenoise]

Eh gang,
I am a complete noob in electronics so just a warning.
I am trying to measure the idss of the 2n3819 JFETs but I am not getting any reading on the mulitmeter.
I am so confused.
I have tried all three meters I own all of which can measure mA

I understand about shorting the source and gate and the rest of the connections.......I think I got that part.
But maybe I got my meters settings wrong?
Can someone please provide me with a detailed step by step including proper meter settings?
I am so lost here.

Try the 9v battery method. Watch polarity or you’ll burn the fet.

 

[newmod]

Try the 9v battery method. Watch polarity or you’ll burn the fet.

I am using this method but the meter is not responding which is very weird.
My settings on the meter are
mA
Auto ranging active
DC
Not sure what is going on.

I have tired two other meters and both the same.
I don't know if I have the wiring wrong but I checked it over many times as per Matadors recommendations on page 3 of this thread.
I also tired to follow Chungers directions on his blog.

 

[Purplenoise]

I am using this method but the meter is not responding which is very weird.
My settings on the meter are
mA
Auto ranging active
DC
Not sure what is going on.

I have tired two other meters and both the same.
I don't know if I have the wiring wrong but I checked it over many times as per Matadors recommendations on page 3 of this thread.
I also tired to follow Chungers directions on his blog.

You have n channel fets right? Some fets on eBay are counterfeits and they are not what they say. You are probably aware of this but…Just making sure

 

[newmod]

You have n channel fets right? Some fets on eBay are counterfeits and they are not what they say. You are probably aware of this but…Just making sure

Oh that is a good point. I did get these off of flea bay!
I think I will go to the local electronics store tomorrow and buy some NTE-312s just for measuring (will not use these).
I will report back as to what I discover.

I wonder what other JFETS can you use to replace the obsolete 3819?

 

[Purplenoise]

Oh that is a good point. I did get these off of flea bay!
I think I will go to the local electronics store tomorrow and buy some NTE-312s just for measuring (will not use these).
I will report back as to what I discover.

I wonder what other JFETS can you use to replace the obsolete 3819?

You can still find plenty 3819. You just have to buy from a reputable source…but make sure first what yours are.

 

[newmod]

You can still find plenty 3819. You just have to buy from a reputable source…but make sure first what yours are.

Is it possible my multimeters cannot measure that low??
I tried this method from diyaudiostore.com and it seems to make sense when I do the math...
https://diyaudiostore.com/pages/jfet-matching-information
They use a 100ohm resistor and I am able to get numbers that make sense.
The first of the 3819 I put to it gave me a reading of 1.28volts when measuring across the 100ohm resister, and when solving for X, I get a number which makes sense to be an idss value as shown in the picture.

Therefore, I wonder if my multimeters are not up to the task?
Their all cheap meters.

 

[Purplenoise]

Is it possible my multimeters cannot measure that low??
I tried a this method from diyaudiostore.com and it seems to make sense when I do the math...
https://diyaudiostore.com/pages/jfet-matching-information
They use a 100ohm resistor and I am able to get numbers that make sense.

Therefore, I wonder if my multimeters are not up to the task?
Their all cheap meters.

Not sure. I was able to measure with mine but never tried with more affordable meters.

 

[Ricardus]

Mouser has 2N3819 in stock right now. 2 different SKUs:

https://www.mouser.com/ProductDetai...=sGAEpiMZZMutXGli8Ay4kEZjWkX4Fjl5vYFq8NqDduo=
I have no idea what the idss is on these, but they're available.

 

[Ivan K.]

Try the 9v battery method. Watch polarity or you’ll burn the fet.

Also, check the web for an article by Nelson Pass "Matching Devices" PassDiy & a more extensive thread on DIAAudio: Nelson Pass' Easy Peasy MOSFET Vgs Measurement

 

[Ivan K.]

Try the 9v battery method. Watch polarity or you’ll burn the fet.

Check this out--pretty complete: Nelson Pass' Easy Peasy MOSFET Vgs Measurement