Neumann Vintage U87 Clone : Build Thread.

[Deepdark]

Cool. Thanks Udo. For now, I just calibrate it to 11.5v (and i think right now it's like 11.4v) so i'll give a check just to be sure of the voltage. I use the cinemag\mic parts combination. Curious to see if other combination are hoter I saw that Cinemag is 10:5:1 instead of the Peluso and AMI that are 9:5:1 so probably some gain lost there. But anyway, the mic is really silent in therm of noise, no hum, so I'm pretty happy with the results  8)

Here are some pics I did during the build. I'll put some more.

 

[Deepdark]

Interior

 

[Deepdark]

Tranny mounting with a water bottle cap That is DIY

 

[poctop]

Tranny mounting with a water bottle cap That is DIY

Refreshing 
Best,
dAN,

 

[Deepdark]

haha. It was a Dasani one It fitted so tightly, no need of any glue, shimming, etc.  ;D

 

[kante1603]

Hahaha.......and I thought mine was cool:

http://groupdiy.com/index.php?topic=48030.msg618227#msg618227

;D ;D ;D

Cheers,

Udo.

 

[Deepdark]

Hahaha. To be honest, i searched for those kind of tubing, but unfortunetly, never find a chair at home like that haha. Next time, coca cola cap

 

[kante1603]

...or banana peel to give the mic some taste (use flat end only,just dry it for some months).

;D

 

[irfrench]

the idea is to have them clipping at the same time on both phase i suggest you reduce the amplitude of the sinetone to really get a grasp on where they do that
the idea is to reduce and increase the sinetone amplitude to see this condition if you have too strong signal you wont see it ,

6.3V seems on the  low end you could also verify your idle current trough the source resistor to ground IIRC it should be around 0.25ma,
Hope this helps,
dan,

yes Take the (source) voltage and divide by the value of R11 that you have found , it should ballpark arround 0.25ma

Dan,

Thanks for this.  I suspected it was on the low side. 

I've tried the Scope program from a laptop headphone output as the source - volume turned right down - but that may still be causing the problem?  I've got a Minirator MR1 kicking around here so I'll give that a go instead and see how I get on.

I assume that the idle current will need to be measured in the calibration state (no capsule, no transformer)? And please excuse the GCSE-esq question, but would the best way to measure the idle current be to measure the voltage across the resistor (R11) and use V=IR?  :-[

Thanks,
Ian

Dan,

Thanks again for your help.  I've tried the scope procedure again but with using the other 1k source.  There seems to be a definite point where the waveform is replicated at its greatest amplitude and where both halves appear to begin clipping at the same time.

This time the drain voltage ended up at a similar 6.8v!?  Weird.

I then measured the voltage drop across R11 (.98v) and its resistance (3.5k) resulting in 0.28mA.

For my own sanity I checked the waveform when drain was set at approx 11.4v and it was definitely clipping on one side more than the other, when adjusting R11 to get a lower drain voltage the waveform 'opened up' increased in amplitude and started losing it's flattened form.

Could this just be a quirk, or is something definitely amiss?  In any case the mic works and sounds good to me, it'd just be nice to KNOW I'm not causing it to run sub-par.  ;D


Thanks,
Ian

 

[Deepdark]

Haha Udo!

You can try too a spray can paint cap to give it more color  ;D

 

[poctop]

the idea is to have them clipping at the same time on both phase i suggest you reduce the amplitude of the sinetone to really get a grasp on where they do that
the idea is to reduce and increase the sinetone amplitude to see this condition if you have too strong signal you wont see it ,

6.3V seems on the  low end you could also verify your idle current trough the source resistor to ground IIRC it should be around 0.25ma,
Hope this helps,
dan,

yes Take the (source) voltage and divide by the value of R11 that you have found , it should ballpark arround 0.25ma

Dan,

Thanks for this.  I suspected it was on the low side. 

I've tried the Scope program from a laptop headphone output as the source - volume turned right down - but that may still be causing the problem?  I've got a Minirator MR1 kicking around here so I'll give that a go instead and see how I get on.

I assume that the idle current will need to be measured in the calibration state (no capsule, no transformer)? And please excuse the GCSE-esq question, but would the best way to measure the idle current be to measure the voltage across the resistor (R11) and use V=IR?  :-[

Thanks,
Ian

Dan,

Thanks again for your help.  I've tried the scope procedure again but with using the other 1k source.  There seems to be a definite point where the waveform is replicated at its greatest amplitude and where both halves appear to begin clipping at the same time.

This time the drain voltage ended up at a similar 6.8v!?  Weird.

I then measured the voltage drop across R11 (.98v) and its resistance (3.5k) resulting in 0.28mA.

For my own sanity I checked the waveform when drain was set at approx 11.4v and it was definitely clipping on one side more than the other, when adjusting R11 to get a lower drain voltage the waveform 'opened up' increased in amplitude and started losing it's flattened form.

Could this just be a quirk, or is something definitely amiss?  In any case the mic works and sounds good to me, it'd just be nice to KNOW I'm not causing it to run sub-par.  ;D


Thanks,
Ian

Did you actually measure the IDSS of the FET before installing it to make sure it was in the range of 10ma IDSS or lower,
that might explain the low voltage settings.
the idle current seems fine and in the range is the gain of the mic as expected.
Best,
Dan

 

[irfrench]

Did you actually measure the IDSS of the FET before installing it to make sure it was in the range of 10ma IDSS or lower,
that might explain the low voltage settings.
the idle current seems fine and in the range is the gain of the mic as expected.
Best,
Dan

Hi,

In all honesty no I didn't but this was one of the Mic and Mod kits where the JFET is chosen so that the IDSS is supposed to be less than 8mA.

As I said before, the mic sounds really good so far (vocals so probs not really pushing it) so if the JFET can be biased correctly in this state I'm happy enough to leave it.

Thanks for making this and these mic projects available.

Ian. 

Woohoo 101 posts!  8)

 

[kante1603]

Haha Udo!

You can try too a spray can paint cap to give it more color  ;D

Yep,I already have a "Blue87".

 

[Deepdark]

Hey Dan and Udo, Great news. I re-check my drain voltage and Saw that it was 11,3V instead of 11,5V. I re-adjusted it and now, I think I'm in the right track Udo, I made the same  test with the AKG P220. Now, the AKG is around -17db and the D87 is -23db. So around 6db different. Sound in the ballpark, isn't it?  8) Now I got a great microphone fully workable. Thanks again guys for your help and the great project

 

[kante1603]

Hey Dan and Udo, Great news. I re-check my drain voltage and Saw that it was 11,3V instead of 11,5V. I re-adjusted it and now, I think I'm in the right track Udo, I made the same  test with the AKG P220. Now, the AKG is around -17db and the D87 is -23db. So around 6db different. Sound in the ballpark, isn't it?  8) Now I got a great microphone fully workable. Thanks again guys for your help and the great project

Athough this comparison is not a really scientifically correct method it still looks very good.
As said it depends and some different factors.So roughly -35 to -41,xxxdB difference after the math is.....?
The only way to get it to the equal clipping point is the scope method.If you care for those tenth of a dB do it to confirm.Personally I don't think it is necessary in your case.
"If it sounds good it is good".

Best,

Udo.

 

[Deepdark]

Allright. Thank you. Next step, record some vocal hehe.  8)

 

[micandmod]

Hi,

In all honesty no I didn't but this was one of the Mic and Mod kits where the JFET is chosen so that the IDSS is supposed to be less than 8mA.

As I said before, the mic sounds really good so far (vocals so probs not really pushing it) so if the JFET can be biased correctly in this state I'm happy enough to leave it.

Thanks for making this and these mic projects available.

Ian. 

Woohoo 101 posts!  8)

Yes Ian, the JFET is selected to be less than 8mA IDSS
Do you use hardware scope or software scope ?
Best

 

[irfrench]

Yes Ian, the JFET is selected to be less than 8mA IDSS
Do you use hardware scope or software scope ?
Best

Hi,

I used the software scope linked to on the first page.  I've tried a couple of source-methods and it seems to come out at about the same setting so it's either the soundcard/scope or that it just happens to need to be like this!?

All I know is that I like the sound of this mic!  I've done direct comparisons to an SE z5600a II and they are like polar opposites, the 87-build is very warm, detailed and 'mid-forward' whilst the 5600 is hyped at the top and generally scooped sounding in comparison.  Definitely a useful tool in the arsenal.

Thanks again to all who have made this project available.

Ian
8)

 

[LG]

HI everyone,

First of i'd like to thank Dan, Udo and Matador for making this build possible for me.

Now my question... I'm stuck on my second U87 build, the first one i did was kinda hassle free made in a Behringer B2 donor.

The second one is in the same donor but with another version af the switc pcb. I've calibrated the drain voltage with the dmm, but as soon as i connect my transformer (t13) to pcb the drain voltage drops from 10.5v to 0.1 o-(or something like that). I desoldered the pcb switch bord just to make shure that wasn't the problem.

I'm quiet shure the transformer is connected the proper way (the yellow 21r side to xlr or 3 and 4 points on pcb as described in the newbie build thread). I've tripple checked all solder points. Any sugestions what to do next?

all the best from Copenhagen
-Leifur

 

[LG]

Now i found out that i have some continuity between the primary and secondary winding. Is this normal? my other t13 doesn't have that. Is my transformer bad?

-Leifur