Neumann Vintage U87 Clone : Build Thread.

[Hank Dussen]

New Scoop

just receive an email from Tabfunkenwerk they are just to realese the new T13 wich is designed as a direct replacement of the u87 transfo,  email i received below ;D

Awesome!

 

[wthrelfall]

Dany,

I'm trying to wire the Aurycle transformer to the board.  I have Black, Green, Red, White cables coming from the transformer, how do they connect to the board?  I don't understand what the TRFO abbreviations are (1 RT, 2 SW, 3 BL, 4 WS).
Hope you can help.

cheers.

 

[poctop]

Dany,

I'm trying to wire the Aurycle transformer to the board.  I have Black, Green, Red, White cables coming from the transformer, how do they connect to the board?  I don't understand what the TRFO abbreviations are (1 RT, 2 SW, 3 BL, 4 WS).
Hope you can help.

cheers.

Aurycle Transformer lead connection to the U1621

RT = red from aurycle Transfo
SW = White from aurycle TRansfo
WS = Black from aurycle Transfo
BL = green from aurycle Transfo,

Just note that the Aurycle transformer is ultimately need to be replaced to get the full potential of the mike,

here is for the cinemag 2480 to u1621 if it can help anyone,
RT = red from cinemag 2480 Transfo
SW = brown from cinemag 2480 TRansfo
WS = yellow from cinemag 2480 Transfo
BL =  orange fromcinemag 2480 Transfo,

 

[wthrelfall]

thanks dany.

Dany,

I'm trying to wire the Aurycle transformer to the board.  I have Black, Green, Red, White cables coming from the transformer, how do they connect to the board?  I don't understand what the TRFO abbreviations are (1 RT, 2 SW, 3 BL, 4 WS).
Hope you can help.

cheers.

Aurycle Transformer lead connection to the U1621

RT = red from aurycle Transfo
SW = White from aurycle TRansfo
WS = Black from aurycle Transfo
BL = green from aurycle Transfo,

Just note that the Aurycle transformer is ultimately need to be replaced to get the full potential of the mike,

here is for the cinemag 2480 to u1621 if it can help anyone,
RT = red from cinemag 2480 Transfo
SW = brown from cinemag 2480 TRansfo
WS = yellow from cinemag 2480 Transfo
BL =  orange fromcinemag 2480 Transfo,

 

[0dbfs]

New Scoop

just receive an email from Tabfunkenwerk they are just to realese the new T13 wich is designed as a direct replacement of the u87 transfo,  email i received below ;D ;D

Hi Dany,

Thanks for enquiring about BV13’s!  We are about to add a new item to our website which is our T13 transformer.  It is built on the same platform as our T14 transformer but with the ratio and impedance necessary as a drop in replacement for U87’s and U87 DIY projects.  I don’t have a picture of it yet but I will be adding it to the site soon. 
The price will be the same as our T14 transformer, $95 plus shipping.  I think Oliver has a few available from the first production run that he made but I will check with him to see.

Cant wait to try this one out,

That's awesome. I can use those for some KM54 style mic's that I'm working up

Cheers,
j

 

[wthrelfall]

So, my first test reveals a very dark, quiet and bassy signal.  definately something not right.
I calibrated R11 without a 'scope as described, looking for 10.5v at the drain.  just to clarify, of the transistors legs, the drain is the closest to the side of the board, nearest R11?  I calibrate without the capsule connected (or the 50pf rear jumper cap)?  Anyway, with 10.5v i'm getting 4.46k across R11 (measured with one leg lifted), pretty far away from the expected 7k - 10k..
any thoughts?

 

[poctop]

So, my first test reveals a very dark, quiet and bassy signal.  definately something not right.
I calibrated R11 without a 'scope as described, looking for 10.5v at the drain.  just to clarify, of the transistors legs, the drain is the closest to the side of the board, nearest R11?  I calibrate without the capsule connected (or the 50pf rear jumper cap)?  Anyway, with 10.5v i'm getting 4.46k across R11 (measured with one leg lifted), pretty far away from the expected 7k - 10k..
any thoughts?

I would say start with the basics,  the transistor drain is indeed the nearest from r11 , check the cap polarity check for cold solder on gnd plane connection to electrolytic capacitor, double check value and components with the meter when possibe , check for the voltage up to zener you should have 24V there , double check C7 polarity, wich side of the legs have you been lifting out the gnd side ?. measure R11 unconnected . is it possible for you to inject a sine tone in the mik to check on how you FET Bias pot is behaving . what is your setup transfo for now, have you double checked your transfo connection ? check all connection A-AA B-BB G-GG C-CC , i never attempted anything with the Aurycle aurycle traffo yet it is not intended here. ,. is the capsule intact any abnormality on he capsule if you look very closely those cheap chinese capsule sometimes arrives DOA (dead on arrival ) that is why i dont use them at all, hope this helps, also Check the capsule connection at FC    Cap= capsule and Bdy= Backplate  check for solder bridge look at schemo and check all connection in the circuit. last time i checked the Backplate Voltage it was arround 40V wich is not a really accurate reading because of impedance
D

 

[wtmnmf]

New Scoop

just receive an email from Tabfunkenwerk they are just to realese the new T13 wich is designed as a direct replacement of the u87 transfo,  email i received below ;D ;D

Hi Dany,

Thanks for enquiring about BV13’s!  We are about to add a new item to our website which is our T13 transformer.  It is built on the same platform as our T14 transformer but with the ratio and impedance necessary as a drop in replacement for U87’s and U87 DIY projects.  I don’t have a picture of it yet but I will be adding it to the site soon. 
The price will be the same as our T14 transformer, $95 plus shipping.  I think Oliver has a few available from the first production run that he made but I will check with him to see.

Cant wait to try this one out,

Got an email today :  "We will have the T13’s in full stock around Wednesday of next week.  They will be $95 plus shipping." 

 

[wthrelfall]

ok, had the capsule connections the wrong way around.  It's working so I made a comparison with my cheap valve mic and my Rode NT2, recording side by side..  This clone is way darker in tone to the others..  I like that.  when I compare them A/B it's quite shocking how much emphasis I can hear on the other mics.  I can't imagine a scenario when I wouldn't use the 100hz cut on the this clone, so much bottom end already there.  It's quieter than the valve mic, forgot to measure against the Rode.  I find it needs alot of gain to get a decent level, I mean alot.  is that normal dany?

on a technical note, the mic seems to be running nicely despite my R11 value of 4.4k, and I checked the voltage at the zener, it's around 15v.  Do you think this is maybe down to the different transformer I'm using? (the stock Aurycle transformer).

So, my first test reveals a very dark, quiet and bassy signal.  definately something not right.
I calibrated R11 without a 'scope as described, looking for 10.5v at the drain.  just to clarify, of the transistors legs, the drain is the closest to the side of the board, nearest R11?  I calibrate without the capsule connected (or the 50pf rear jumper cap)?  Anyway, with 10.5v i'm getting 4.46k across R11 (measured with one leg lifted), pretty far away from the expected 7k - 10k..
any thoughts?

I would say start with the basics,  the transistor drain is indeed the nearest from r11 , check the cap polarity check for cold solder on gnd plane connection to electrolytic capacitor, double check value and components with the meter when possibe , check for the voltage up to zener you should have 24V there , double check C7 polarity, wich side of the legs have you been lifting out the gnd side ?. measure R11 unconnected . is it possible for you to inject a sine tone in the mik to check on how you FET Bias pot is behaving . what is your setup transfo for now, have you double checked your transfo connection ? check all connection A-AA B-BB G-GG C-CC , i never attempted anything with the Aurycle aurycle traffo yet it is not intended here. ,. is the capsule intact any abnormality on he capsule if you look very closely those cheap chinese capsule sometimes arrives DOA (dead on arrival ) that is why i dont use them at all, hope this helps, also Check the capsule connection at FC    Cap= capsule and Bdy= Backplate  check for solder bridge look at schemo and check all connection in the circuit. last time i checked the Backplate Voltage it was arround 40V wich is not a really accurate reading because of impedance
D

 

[poctop]

ok, had the capsule connections the wrong way around.  It's working so I made a comparison with my cheap valve mic and my Rode NT2, recording side by side..  This clone is way darker in tone to the others..  I like that.  when I compare them A/B it's quite shocking how much emphasis I can hear on the other mics.  I can't imagine a scenario when I wouldn't use the 100hz cut on the this clone, so much bottom end already there.  It's quieter than the valve mic, forgot to measure against the Rode.  I find it needs alot of gain to get a decent level, I mean alot.  is that normal dany?

on a technical note, the mic seems to be running nicely despite my R11 value of 4.4k, and I checked the voltage at the zener, it's around 15v.  Do you think this is maybe down to the different transformer I'm using? (the stock Aurycle transformer).

i am glad your case in going forward but there is definitely something going wrong i made measurement just a minute ago without the transformer attached and no capsule attached no cap jumper just the circuit and the xlr connection to the mike and i have a 22.69VDC on the top off the Zener can you measure if you have the 48VDC from the 2K2 resistor my guess is that the problem is in that area or the microphone pcb GND is not firm to the chassis verify a 0 ohm from gnd pin from the PCB to the Mic body it self , check  the zener orientation , the R11 value will make sense only if you can get the proper inital voltage , double check also if you would by mistake confused some resistor with the L1 and L2 inductor, at this point if you dont have the proper initial voltage reading your R11 resistor will probably make no sense ,  Since your capsule if probably not polarized with the proper voltage try to measure the voltage coming trough the front backplate = bdy pad on the mik it should be arround 39V DC,  it looks that something is not in place correctly. So this way you rule out the ,capsule and transformer. you should be able to get those 3 voltages to start with, then go from there ,
any new builder should check those initial voltage before connecting transfo or capsule.

 

[Matador]

I find it needs alot of gain to get a decent level, I mean alot.  is that normal dany?

You have a low IDSS FET.  The higher the source resistance, the lower the gain.  Try another FET that gives you about 1V-1.5V on the source with 10V on the drain.

 

[wthrelfall]

i am glad your case in going forward but there is definitely something going wrong i made measurement just a minute ago without the transformer attached and no capsule attached no cap jumper just the circuit and the xlr connection to the mike and i have a 22.69VDC on the top off the Zener can you measure if you have the 48VDC from the 2K2 resistor my guess is that the problem is in that area or the microphone pcb GND is not firm to the chassis verify a 0 ohm from gnd pin from the PCB to the Mic body it self , check  the zener orientation , the R11 value will make sense only if you can get the proper inital voltage , double check also if you would by mistake confused some resistor with the L1 and L2 inductor, at this point if you dont have the proper initial voltage reading your R11 resistor will probably make no sense ,  Since your capsule if probably not polarized with the proper voltage try to measure the voltage coming trough the front backplate = bdy pad on the mik it should be arround 39V DC,  it looks that something is not in place correctly. So this way you rule out the ,capsule and transformer. you should be able to get those 3 voltages to start with, then go from there ,
any new builder should check those initial voltage before connecting transfo or capsule.

I have nearly 48v from the 2k2, 46.1v actually.  L1 & L2 are correct (46.7v both).  15.55v on the Zener diode, and here's a thing - I have 15.55v on the top of R17, but 46.1v on the bottom.  I have double checked the resistor and replaced with one of exactly 56k, still reading 15.55v.
Yes, i'm getting 39v from front body pad.

 

[wthrelfall]

I find it needs alot of gain to get a decent level, I mean alot.  is that normal dany?

You have a low IDSS FET.  The higher the source resistance, the lower the gain.  Try another FET that gives you about 1V-1.5V on the source with 10V on the drain.

if by source you mean the voltage on the leg on the opposite side from the drain, this is reading 2.4v.

 

[poctop]

The big question is why on the Zener side you have 15V , is the Zener oriented properly is it a 15V zener ?
look in this net of Zener, C12, R14, R16, R12, C9 , and C7 connection to FET,  , this is the first thing to find out .

on the nod touching C10, R14, R12 you should have 20VDC, on the other hand of R12 drain Cal point at 11V,
Hope this helps, here attached a pic of the board for any visual pointer.
D

 

[wthrelfall]

The big question is why on the Zener side you have 15V , is the Zener oriented properly is it a 15V zener ?
look in this net of Zener, C12, R14, R16, R12, C9 , and C7 connection to FET,  why is the zener not doing the job ?
this is the first thing to find out .

on the nod touching C10, R14, R12 you should have 20VDC, on the other hand of R12 drain Cal point at 11V,
Hope this helps, here attached a pic of the board for any visual pointer.
D

all the components are from your BOM and therefore should be correct.
I'm finding it a little hard to understand you, but certainly those voltages are very different.

 

[poctop]

all the components are from your BOM and therefore should be correct.
I'm finding it a little hard to understand you, but certainly those voltages are very different.

Lets Try to put a 10K resistor for R11 and see what happens ?

Dan,

 

[Matador]

I have nearly 48v from the 2k2, 46.1v actually.  L1 & L2 are correct (46.7v both).  15.55v on the Zener diode, and here's a thing - I have 15.55v on the top of R17, but 46.1v on the bottom.  I have double checked the resistor and replaced with one of exactly 56k, still reading 15.55v.
Yes, i'm getting 39v from front body pad.

The top of R17 and the voltage across the 2K2 are the same.

Your source resistance is 4K4, and you have 2.4V on the source, which means you are idling 0.5mA through the FET.

The U87 schematic assumes a 0.25mA idle point:  you need to adjust your resistors to match your FET.  You are reading 15.5V at the Zener because the 0.5mA is dropping across R17.  In this case, the Zener is doing nothing.

Here's what you need to do:  lower R17 until the Zener voltage raises to 24V.  Then, lower R14 until you get about a 3V drop across it (or about 21V at the "top" of the drain resistor R12).  Ohms Law says R12 should be about 6K (down from 10K) in this case.

Don't lower R17 too much though, as the Zener will take over and start dumping the phantom current to ground to keep the voltage at 24V (and this extra current will start dropping across the 2V2 resistors, which will then lower the capsule bias....).

Until you get the voltage at R12 up to 21V then setting the bias point is meaningless.  The output signal is developed across R12, and until the "top" of this voltage is up near 21V you won't be able to get any appreciable signal swing out of the circuit.

And this is the weakness of this circuit:  the entire topology must be tweaked around the individual FET.

 

[wthrelfall]

excellent analysis Matador, I will be attempting this and shall come back here with good news I hope!

I have nearly 48v from the 2k2, 46.1v actually.  L1 & L2 are correct (46.7v both).  15.55v on the Zener diode, and here's a thing - I have 15.55v on the top of R17, but 46.1v on the bottom.  I have double checked the resistor and replaced with one of exactly 56k, still reading 15.55v.
Yes, i'm getting 39v from front body pad.

The top of R17 and the voltage across the 2K2 are the same.

Your source resistance is 4K4, and you have 2.4V on the source, which means you are idling 0.5mA through the FET.

The U87 schematic assumes a 0.25mA idle point:  you need to adjust your resistors to match your FET.  You are reading 15.5V at the Zener because the 0.5mA is dropping across R17.  In this case, the Zener is doing nothing.

Here's what you need to do:  lower R17 until the Zener voltage raises to 24V.  Then, lower R14 until you get about a 3V drop across it (or about 21V at the "top" of the drain resistor R12).  Ohms Law says R12 should be about 6K (down from 10K) in this case.

Don't lower R17 too much though, as the Zener will take over and start dumping the phantom current to ground to keep the voltage at 24V (and this extra current will start dropping across the 2V2 resistors, which will then lower the capsule bias....).

Until you get the voltage at R12 up to 21V then setting the bias point is meaningless.  The output signal is developed across R12, and until the "top" of this voltage is up near 21V you won't be able to get any appreciable signal swing out of the circuit.

And this is the weakness of this circuit:  the entire topology must be tweaked around the individual FET.

 

[poctop]

Hi Matador,

I have been initially using this FET here 512-2N3819
http://ca.mouser.com/ProductDetail/Fairchild-Semiconductor/2N3819/?qs=sGAEpiMZZMutXGli8Ay4kAuOt55Alb1HdgBfgvzEKeQ%3d

this is what i get from reading on the 3 mikes i have built so far,
Across R12  47K  i get about 10V wich would be arround 0.22ma ,
and accross R11 the 2.4 V from the Source of the FET so about .25ma.

i had to put replace the FET in the orginal BOM because the 512-2N3819 cam obsolete ,
the new FET in the BOM is http://ca.mouser.com/ProductDetail/Fairchild-Semiconductor/2N3819_D74Z/?qs=sGAEpiMZZMutXGli8Ay4kHKRdIvtrnJvJrjALq5IAXw%3d

do you think the problem would be The FET itself,  i had checked all the spec and they are the same, i will order a bunchof those and try it out by myself then. i would like to catch anything before it is too late.

anyone has completed their build so far with any comments on this FET used,
any finished build out there ?

so i am really confused as why the idling current of whtrelfall is beeing 0.54ma hence calibration value so low, should be more like 10K  for 0.25ma . there is must be a simple reason for this to happen ?
just trying to help here.

 

[wthrelfall]

Matador

I dropped R17 so I now have 23.5 volts at the zener (i can't get it exactly to 24v as I don't have a large range of resistors).  doesn't the voltage at R12 depend on the R11 value?  I mean as soon as I adjust R11 to bias the fet then R12 just tracks this voltage from the fet drain.  so I don't understand how I can get R12 to produce 21v if I'm going to then adjust R11 to bring the fet drain (and therefore R12) back to 10.5v.?
I'm clearly no expert when it comes to electronics but it seems for such a simple small circuit this is proving to be very difficult!

I have nearly 48v from the 2k2, 46.1v actually.  L1 & L2 are correct (46.7v both).  15.55v on the Zener diode, and here's a thing - I have 15.55v on the top of R17, but 46.1v on the bottom.  I have double checked the resistor and replaced with one of exactly 56k, still reading 15.55v.
Yes, i'm getting 39v from front body pad.

The top of R17 and the voltage across the 2K2 are the same.

Your source resistance is 4K4, and you have 2.4V on the source, which means you are idling 0.5mA through the FET.

The U87 schematic assumes a 0.25mA idle point:  you need to adjust your resistors to match your FET.  You are reading 15.5V at the Zener because the 0.5mA is dropping across R17.  In this case, the Zener is doing nothing.

Here's what you need to do:  lower R17 until the Zener voltage raises to 24V.  Then, lower R14 until you get about a 3V drop across it (or about 21V at the "top" of the drain resistor R12).  Ohms Law says R12 should be about 6K (down from 10K) in this case.

Don't lower R17 too much though, as the Zener will take over and start dumping the phantom current to ground to keep the voltage at 24V (and this extra current will start dropping across the 2V2 resistors, which will then lower the capsule bias....).

Until you get the voltage at R12 up to 21V then setting the bias point is meaningless.  The output signal is developed across R12, and until the "top" of this voltage is up near 21V you won't be able to get any appreciable signal swing out of the circuit.

And this is the weakness of this circuit:  the entire topology must be tweaked around the individual FET.