Neumann Vintage U87 Clone : Build Thread.

[Upacesky]

Just wanted to share that I finished my U87 and everything is working. I'm using Dan's PCBs (blue version), chunger's SYT5 body, cinemag 13113 and Maiku capsule. I'll have to do real world tests but so far everything seems fine on spoken words. Noise figure is good, even on spoken words with roughly 60dB gain (PMV70X) and normalized.

 

[rockinrob86]

I finished mine, and it sounds wonderful for the quick demo I made.  However, I am noticing some hissing (sounds basically like tape hiss) - my first thought is noisy FET - does this sound like a good place to start?

I biased it with my scope and a 1K tone.  Switched between square and sine waves and kept tweaking until they both were in the best balance of tall but straight.  Ended up at around 10 volts on the drain (I think)

I have a handful of those FETs - if I go through some troubleshooting and nothing else checks out, should I just sub one in and then inject signal and rebias?  Do I have to unsolder the capsule?  Is there another way to test the fets for noise without taking apart the mic?

 

[rockinrob86]

I finished mine, and it sounds wonderful for the quick demo I made.  However, I am noticing some hissing (sounds basically like tape hiss) - my first thought is noisy FET - does this sound like a good place to start?

I biased it with my scope and a 1K tone.  Switched between square and sine waves and kept tweaking until they both were in the best balance of tall but straight.  Ended up at around 10 volts on the drain (I think)

I have a handful of those FETs - if I go through some troubleshooting and nothing else checks out, should I just sub one in and then inject signal and rebias?  Do I have to unsolder the capsule?  Is there another way to test the fets for noise without taking apart the mic?

I figured it out.  I had wired the backplates incorrectly.  Hissing/white noise/crackling = backplate connectivity, pcb not clean enough, etc.

 

[TillM]

You don't have to do biassing again.
For the sounds, just try it and tell what you think.

 

[nyok]

Hi !

i've got a problem with the BOM :
Do you know something else to replace it ?
Thks a lot !

Mouser No: 70-IR2-47
Mfr. No: IR02BH470K
Manufacturer: Vishay
Desc.: Fixed Inductors 47uH 10%
RoHS No
Lifecycle: End of Life: Scheduled for obsolescence and will be discontinued by the manufacturer.

 

[poctop]

use the FIND simillar  button from mouser and use the filter to find and alternative part
they are many available.
just make sure you keep an eye on the size of the part.

Best,
Dan,

 

[nyok]

Thks ,
Is this one good ?
http://www.mouser.fr/ProductDetail/API-Delevan/1025-60K/?qs=sGAEpiMZZMsg%252by3WlYCkU5R0OkR2KpnrsbUxp%2f6LwXY%3d

It says RF inductors instead of power inductor

 

[gearhunter]

I have the same doubt

 

[TLRT]

I have the same doubt

Just bought this:
542-78F470-RC
MFG Part No: 78F470J-RC
Bourns 47uH 5% / Fixed Inductors

 

[Mrosso]

Quick question regarding the AMI T13 transformer. I measured the resistance between the yellow wires and got 21.8 R, but when I measured the resistance between the black wires the meter didn't read anything. It seems like infinity R. Do I have a bad xfrmr?

 

[gearhunter]

Just bought this:
542-78F470-RC
MFG Part No: 78F470J-RC
Bourns 47uH 5% / Fixed Inductors

Thanks!

 

[Neutrino]

Hi,

A quick question:
I had biased my U87 clone for symmetric clipping, but measured a drain voltage of only about 8.7 Volts. Since it sounded fine, I didn't worry too much about it. But in a recent vocal session I had the feeling that the microphone started distorting a bit when the vocal became really loud. Can somebody comment on whether both issues could be related and whether it is an indication that something is wrong in my built?

Best regards,
Waldemar

 

[ln76d]

Hi,

A quick question:
I had biased my U87 clone for symmetric clipping, but measured a drain voltage of only about 8.7 Volts. Since it sounded fine, I didn't worry too much about it. But in a recent vocal session I had the feeling that the microphone started distorting a bit when the vocal became really loud. Can somebody comment on whether both issues could be related and whether it is an indication that something is wrong in my built?

Best regards,
Waldemar

What's the value of phantom voltage, measured without microphone connected?
What's the value of potentiometer  inside your build?

 

[Neutrino]

The phantom voltage is 49.3 Volts. The value of the potentiometer is 7.29 kOhms measured inside the circuit. Do I need to de-solder the pot for this measurement?

 

[ln76d]

The phantom voltage is 49.3 Volts. The value of the potentiometer is 7.29 kOhms measured inside the circuit. Do I need to de-solder the pot for this measurement?

If you are using 2N3819 and 10k potentiometer, then replace pot for 15-20K and setup bias again.

 

[Neutrino]

Actually, I am using a 2N3819 and a 25k pot (small footprint) already.

 

[ln76d]

If you are sure that your microphone is properly grounded, and FET is properly biased -  then try new FET. Your readings are odd.
Potentially, you could paste pics of your build - this could be helpful, because for now it's tasseography

 

[Neutrino]

I've attached a few pictures of my build. Let me know if you want to see something specific. Note that I've used the jumper for the PAD and abused the pad switch for disconnecting C6 for a brighter sound (i.e. C6 is on the switch PCB).

I had bought 10 FETs and I remember that all of them had rather low IDSS (below 10 mA). I chose the lowest one for my build.

 

[ln76d]

Jumpered? From the pics i see that you used jumper base connector - are these two points connected to eachother?
Measure voltage in these points:
-both sides of R14
-both sides of R2
-c9/c7 point
-R19/R18 point

 

[Neutrino]

Jumpered? From the pics i see that you used jumper base connector - are these two points connected to eachother?

No the two points are not connected (see attached picture)

Here are the voltages measured to ground:
-both sides of R14: 20,73 V and 23,27 V
-both sides of R2: 44,7 V and 44,0 V
-c9/c7 point: 8,69 V
-R19/R18 point: 47,4 V