Neumann Vintage U87 Clone : Build Thread.

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So I figured out what was wrong with the IDSS readings not working.....LONG STORY.
So here is another question....
What idss range would you guys recommend and why?
I am sitting on a stock pile of 2n3819 ranging from 3.24 up to 15.28 IDSS.
 
So I figured out what was wrong with the IDSS readings not working.....LONG STORY.
So here is another question....
What idss range would you guys recommend and why?
I am sitting on a stock pile of 2n3819 ranging from 3.24 up to 15.28 IDSS.
Someone recommended under 10.

The vintage NOS Motorola and Fairchild 3819's I've used clock in around 6.
 
So I figured out what was wrong with the IDSS readings not working.....LONG STORY.
So here is another question....
What idss range would you guys recommend and why?
I am sitting on a stock pile of 2n3819 ranging from 3.24 up to 15.28 IDSS.
I believe between 9 and 11 is ideal. Can’t remember well though
 
I'm just finishing up my U87 PCB's & have some questions.

The Polystyrene 10pf cap I got from Farnell measures 29pf, it's code is 2127, I had installed it before I noticed.
Is this going to make much difference in position C3?

I would like to know which wire size AWG to use for the PCB board to board connections, also as I might need to extend the capsule wire so need to know exactly what type of wire is used for the purpose.

I somehow forgot to order the zener diode 1N4749A so it will have to wait a few days.......!
 
Still don't quite know what using a 3 would do as opposed to a 10, and I've got plenty that I measured in the 3's. Some even in the 2's.
try one in the 2s you should end up with about 3.9k source resistor
 
try one in the 2s you should end up with about 3.9k source resistor
After a lot of research, I have have found that any JFET in the 5-6 idss range is actually ideal for the u87 circuit. 6-8 is ok too, but 5-6 idss is acutally ideal. I even contacted some guys who build u87 clones for a living and it seems the 5-6idss range is the best. Apparently, the higher IDSS JFETs will give higher dynamic range before distortion, however overall output will be a little less than the lower IDSS ones.
 
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I posted that as a nicety

Ones in the 2s bias like the Neumann circuit fragments you find in the Neumann PDF "Microphones".

I am aware of the differences in IDSS. I bought 1000 3819 because of the spread in specs years ago and measured them in circuit and tried them out in microphones
 
Cheers mrgrooves666,

I've got most of those I believe.

I couldn't get a 1N4749A locally so bought some BZX85C24, a 24V zener diode, only difference on the spec sheets is power dissipation @ 1.3W instead of 1N4749A @ 1W.

Transistor / diode number coding designation system is one of JEDEC, JIS or EECA, / USA, Japan or Europe. In this case just 24V zener diodes with different codes.
 
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The Polystyrene 10pf cap I got from Farnell measures 29pf,
How did you measure them? Cheap meters are known to be very unaccurate at measuring very small or very high values. And just holding the wires changes significantly teh measurement.
I would like to know which wire size AWG to use for the PCB board to board connections
Since currents are very small, you should not worry about gauge. Take the smallest gauge compatible with practicality.

, also as I might need to extend the capsule wire so need to know exactly what type of wire is used for the purpose.
You should use the most flexible wire there.
 
Hi guys, can anyone recommend a not too expensive oscilloscope for the build? (what spec should I look for?) Or it makes more sense to use an audio card and software? Thanks!
 
Hi guys, can anyone recommend a not too expensive oscilloscope for the build? (what spec should I look for?) Or it makes more sense to use an audio card and software? Thanks!
A scope will be more useful since it can visualize the combination of AC and DC levels.
You just need to make sure it's compatible with the high voltage in a tube mic.
Almost any scope in combination with a switchable X1/X10 probe can visualize up to about 500V.
 
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Hi guys,

Regarding R18 and R19 (2k2 resistors).
I understand they have to be matched but Dan's website build demonstration section under the u87 done by Andrew Schaap says the two resistors must be within 4% (link below).

http://www.vintagemicrophonepcbkit.com/Neumann%20U87%20Build.htm

Studio 939's blog post of the build states .4%
Link here .....> Vintage U87 Circuit Clone Microphone Build

So which is it.................. 4% OR .4%

???
I don't actually know the real answer to that, but the BOM includes more resistors than you need. 10 I think, and if you have a quality DMM you can match them very closely. I built two of these so I had a lot of resistors to choose from, and was able to make 5 or 6 pairs that matched within 1 or 2 ohms.

I plan to build two more of these sometime, so I won't need to order that line item next time since I already have them.
 
So which is it.................. 4% OR .4%
4% is actually a large tolerance. Statistically, if you take a dozen of 10% resistors from the same batch, you'll probably find they are within 1% of each other, so, although the average value may be quite different than nominal, matching will probably be very good.
Now, why do these resistors need to be matched?
There are two factors there:
One is the presence of DC current in the secondary. Supposing 1% tolerance* on the phantom-feed resistors (6.8k) and 4% for the 2.2k, the maximum DC current flowing through the secondary is less than 10uA. This is not enough to skew significantly the BH curve in the magnetic core.
The other is the loss of CMRR. With the same 1% tolerance for the 6.8k and 4% for the 2.2k, worst-case CMRR is 49dB.
With 0.4% tolerance for the 2.2k, worst-case CMRR goes up to 64dB.
None of these figures can be deemed good or bad, because it depends on many factors. In a clean environment with little EMI/RFI, proximity micing a decent spl source, there should be no problem with 49dB , when 64dB in a heavily EMI/RFI polluted environment, trying to record fly farts from a distance may prove unworkable.
Resistors are so cheap and matching them by hand is not a difficult task. I bet you take only 10 resistors, you can find pairs that match better than 0.4%.
I don't know where these figures (0.4 or 4%) come from, but I think the person who offers them should also provide an explanation of the basis for this assertion.

*The 1% figure I have retained for the 6.8k is 10 times the P48 standard (0.1%). Since the 2.2k are dominant over the 6.8k, it makes sense that, in oder to protect CMRR, the tolerance on the 2.2k should be about 3 times better than the standard (0.03%), which is quite difficult to achieve in practice because of component aging and temperature gradients.

Finally, remember that CMRR is pertinent to a connection, i.e. to a combination of a source and a receiver.
It is perfectly possible to achieve excellent CMRR with significantly unbalanced legs, as long as the unbalance in the source is compensated by a complementary unbalance in the receiver.
Specifying CMRR for a source or a receiver separately is a way of achieving some kind of standard that guarantees a minimum level of performance and interchangeability.
Bill (CMRR here) may chime on it, as he is the one that helped defining the standard measurement, based on assuming an imperfectly balanced source.

For TMI, there are units that include a CMRR adjustment, quite often limited to HF, in the guise of a trimmer capacitor, but there are a few that also have an adjustment of wide band CMRR. Crown had that on their Micro/Macrotech series. It was not a user-adjustable control. I guess had it been user adjustable, some idiot would have cranked it all the way up and claimed it sounded better.
 
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4% is actually a large tolerance. Statistically, if you take a dozen of 10% resistors from the same batch, you'll probably find they are within 1% of each other, so, although the average value may be quite different than nominal, matching will probably be very good.
Now, why do these resistors need to be matched?
There are two factors there:
One is the presence of DC current in the secondary. Supposing 1% tolerance* on the phantom-feed resistors (6.8k) and 4% for the 2.2k, the maximum DC current flowing through the secondary is less than 10uA. This is not enough to skew significantly the BH curve in the magnetic core.
The other is the loss of CMRR. With the same 1% tolerance for the 6.8k and 4% for the 2.2k, worst-case CMRR is 49dB.
With 0.4% tolerance for the 2.2k, worst-case CMRR goes up to 64dB.
None of these figures can be deemed good or bad, because it depends on many factors. In a clean environment with little EMI/RFI, proximity micing a decent spl source, there should be no problem with 49dB , when 64dB in a heavily EMI/RFI polluted environment, trying to record fly farts from a distance may prove unworkable.
Resistors are so cheap and matching them by hand is not a difficult task. I bet you take only 10 resistors, you can find pairs that match better than 0.4%.
I don't know where these figures (0.4 or 4%) come from, but I think the person who offers them should also provide an explanation of the basis for this assertion.

*The 1% figure I have retained for the 6.8k is 10 times the P48 standard (0.1%). Since the 2.2k are dominant over the 6.8k, it makes sense that, in oder to protect CMRR, the tolerance on the 2.2k should be about 3 times better than the standard (0.03%), which is quite difficult to achieve in practice because of component aging and temperature gradients.

Finally, remember that CMRR is pertinent to a connection, i.e. to a combination of a source and a receiver.
It is perfectly possible to achieve excellent CMRR with significantly unbalanced legs, as long as the unbalance in the source is compensated by a complementary unbalance in the receiver.
Specifying CMRR for a source or a receiver separately is a way of achieving some kind of standard that guarantees a minimum level of performance and interchangeability.
Bill (CMRR here) may chime on it, as he is the one that helped defining the standard measurement, based on assuming an imperfectly balanced source.

For TMI, there are units that include a CMRR adjustment, quite often limited to HF, in the guise of a trimmer capacitor, but there are a few that also have an adjustment of wide band CMRR. Crown had that on their Micro/Macrotech series. It was not a user-adjustable control. I guess had it been user adjustable, some idiot would have cranked it all the way up and claimed it sounded better.
Great information!
Thanks so much!
 
Eh guys, I assume the switch used in this design for the pattern is ON-OFF-ON correct? If that is the case, then is one to assume and the circuitry always provides a cardiod pattern to the capsule when the switch in its "off" position? This changes when you toggle to the left or right for 8 or onmi?

Thanks
 
Eh guys, I assume the switch used in this design for the pattern is ON-OFF-ON correct? If that is the case, then is one to assume and the circuitry always provides a cardiod pattern to the capsule when the switch in its "off" position? This changes when you toggle to the left or right for 8 or onmi?
The pattern switch acts only on the rear capsule. The front capsule is biased the same in all positions.
 
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