Neumann Vintage U87 Clone : Build Thread.

[wave]

Hey,
This has been covered in depth in this thread. Go to the top right hand of this window and try searching for "scope bias" in the search bar that says Good for searching within topics.

Here is a quote from one of Dany's posts (found through searching)

"then if you have a scope you can tweak this adjusment by injecting a 1K sine tone trough r6 leg, do not add another probe to the fet gate.  then with the red scope probe on the drain pin of the fet and the black on the mic chassis , set the scope so you can see the sinus output from the scope and then increase the amplitude of the signal until the sine wave flat out,  the idea of this adjusment is to have the sine flat out equally on both phase at the same time so in short both top and bottom should flat out at the same time as you increase the amplitude of the signal . to see that happen you need to cycle the amplitude of the sine tone up and down while tweaking that drain value until this happens and then you have the optimized bias point."

Dave

 

[poctop]

Also Here :

Precious Info on how to use a scope to Bias a Fet (Thanks To Matador) http://www.groupdiy.com/index.php?topic=46109.40

DAn,

 

[kante1603]

Since I'm at this step already, can someone give me some instructions on how to better bias the FET?  I'm using a potentiometer at R11 to keep things adjustable, and I've done the basic task of adjusting that potentiometer so that the voltage to the FET drain is about 11.5 volts.  However, I know there's a better way that I think involves using an oscilloscope?  If someone could give me some step-by-step instructions on that process, I'd love to learn how to do this properly.  As I said, I'm pretty new to this.

http://groupdiy.com/index.php?topic=46109.msg600806#msg600806
Read through the thread please......

Udo.

Edit:Ooooppppsssss,double post,excuse me brother Dan! ;D

 

[Caiwyn]

Awesome, thank you, guys.  Sorry for being such a n00b.  I had done a search for "oscilloscope" and didn't find what I was looking for, didn't think to search for "scope" instead.  So thank you guys for pointing me to the info.

 

[Caiwyn]

I put together a makeshift oscilloscope with an iRig and an iPhone: http://www.youtube.com/watch?v=Y8C6ac7UrHI

I'm also using the test oscillator plugin in Logic Pro to generate a 1kHz tone and sending that from the headphone jack on my laptop to a pair of alligator clips.  The ground is connected to the mic chassis and the center conductor is connected to the bottom of R6.

Unfortunately, I am not seeing what I expect to see per Matador's instructions.  I'm still learning this stuff so I'm not sure if I'm using the app wrong or if I'm not connecting things right.

Does the mic need to be connected to phantom power when biasing with an oscilloscope?  I haven't done this out of fear that the voltage will be too much for the makeshift rig I'm using.

 

[wave]

Yes you need the power so the amplifier will work

Dave

 

[kante1603]

Does the mic need to be connected to phantom power when biasing with an oscilloscope?  I haven't done this out of fear that the voltage will be too much for the makeshift rig I'm using.

Yes.

 

[Caiwyn]

Thanks, guys.  I was afraid of that.  With 11.5 V at the FET drain right now I'm not sure what to do next.  The iPhone can only handle 1 V, and I'm worried about frying it.  I know the iRig will afford it some amount of protection against higher voltages, but I don't know how much.

 

[kante1603]

Thanks, guys.  I was afraid of that.  With 11.5 V at the FET drain right now I'm not sure what to do next.  The iPhone can only handle 1 V, and I'm worried about frying it.  I know the iRig will afford it some amount of protection against higher voltages, but I don't know how much.

During bias procedure you will measure ac,not dc.
Don't know this iRig thingy but from a first sight I wouldn't trust it.
And it's better to measure with a device having a high impedance input.
Can't you get a real scope from a friend or so?

Just my 2 ct,

Udo.

 

[wave]

I agree with Udo. I think I would go the listen test route before this way. Did that on my first DU87 and it sounds great.

Dave

 

[Caiwyn]

During bias procedure you will measure ac,not dc.
Don't know this iRig thingy but from a first sight I wouldn't trust it.

You mean you wouldn't trust it to get a good reading, or you wouldn't trust it to be safe for my phone?

The iRig being used in this youtube video really just provides a 1/4" connection to the microphone input on your phone or tablet.  It's meant to be used to input a guitar signal. There's a newer version that plugs into the dock connector or lightning port on iPhones and iPads, which is nicer since it uses its own higher-quality converter instead of the one built into the phone/tablet.  They should both be high-impedance inputs, since they're meant for instrument level connections, but only the dock-connector version is powered so I don't know how well the mic-jack version will work.  I own both, so I can go either way and they both will work with the oscilloscope app.

My only concern is whether it'll fry my phone when I turn the phantom power on.

Can't you get a real scope from a friend or so?

Unfortunately, the only friends I know who have one don't live near me.  And it's not worth the $150-if-not-$300 it would take for me to buy one just for this project.

 

[sr1200]

http://www.amazon.com/s/ref=bl_sr_industrial?field-brandtextbin=Seeedstudio&node=16310091

I got one of these over the holiday, its not as robust as a big scope but it actually works REALLY well and its awesome that i can just bring it into the studio and crawl behind a rack with it and see whats going on if need be.  And it can hook up USB to your computer for even more options.  (the one i got was about $100 and has a tone gen in it as well!)

 

[kante1603]

http://www.amazon.com/s/ref=bl_sr_industrial?field-brandtextbin=Seeedstudio&node=16310091

I got one of these over the holiday, its not as robust as a big scope but it actually works REALLY well and its awesome that i can just bring it into the studio and crawl behind a rack with it and see whats going on if need be.  And it can hook up USB to your computer for even more options.  (the one i got was about $100 and has a tone gen in it as well!)

I have one too,bought last year.It even came with a switchable probe (1:10),a nice tool for simple measurements.Has delta functions,cool.
Thanks for the hint,I nearly forgot that I have it,it's so small,hahaha.......

Udo.

@ Caiwyn:

At least the dc must be blocked somehow.
I remember once having seen a diy probe with a capacitor inline in the the hot signal to probe the audio in a circuit using a guitar amp or a device having a guitar input.
Do a search for "audio probing", there are some suggestions to find in the net.
Might work,but please don't make me responsible for it or even frying your cell phone.
Personally I do have a real scope and that before mentioned "pocket- piece".
A scope is always a good investment once you got into diy.
And I swear that if you succeed with your build you will start to build more stuff.
Diy is highly infective! ;D

Your choice,maybe it works with a "special probe" like this:

http://diy-fever.com/misc/audio-probe/

Best regards,

Udo.

 

[Caiwyn]

http://www.amazon.com/s/ref=bl_sr_industrial?field-brandtextbin=Seeedstudio&node=16310091

I got one of these over the holiday, its not as robust as a big scope but it actually works REALLY well and its awesome that i can just bring it into the studio and crawl behind a rack with it and see whats going on if need be.  And it can hook up USB to your computer for even more options.  (the one i got was about $100 and has a tone gen in it as well!)

Thanks for the link! I bit the bullet and ordered one of these.

 

[Caiwyn]

Next question:

For my capsule, I chose a replica of the K-67 rather than the K-87, as it was cheaper and I don't really need the figure-8 pattern.

Interestingly, the specific capsule I received (http://micandmod.com/en/capsules/29-microphone-capsule-mk-67-premium.html) has four wires, like the K-87.  There's a white wire connected to each diaphragm, and two blue wires to be connected to the backplates.  I find this confusing since most K-67 replicas only come with three wires.

Is it recommended that I leave one of the blue wires out?  I'm worried about damaging the mic if all four wires are connected and the figure-8 pattern is switched on.

 

[duduac]

Sorry Guys just need to make a really stupid question...

Can`t work out the BOM for the project... Mine comes up costing $84.41 (AUD) bucks and the guy at the video said he only spent $19,22. I purchased the PCBs with the Styroflex Capacitor Kit and now I`m just really confused with the whole thing.

Sorry about the question again, but I just can`t get my head around it.

Cheers

 

[lkipod]

Sorry Guys just need to make a really stupid question...

Can`t work out the BOM for the project... Mine comes up costing $84.41 (AUD) bucks and the guy at the video said he only spent $19,22. I purchased the PCBs with the Styroflex Capacitor Kit and now I`m just really confused with the whole thing.

Sorry about the question again, but I just can`t get my head around it.

Cheers

Hi duduac,

all build options are included in the BOM. So if you bought the Styroflex caps you don't need the replacement caps for these. Also there are two options for the 60G resistor (60G or 68G) so you can delete one of them. Also two options for the 2.2k resistors, delete one from the order form.
Then there are Molex headers that are not essential for the build (at least to my understanding).
I don' know how he came up with 19$, but you can cut down the cost to like 40$ or something like that (I don't remember exactly).

Hope this helps,

Moshe

 

[poctop]

Sorry Guys just need to make a really stupid question...

Can`t work out the BOM for the project... Mine comes up costing $84.41 (AUD) bucks and the guy at the video said he only spent $19,22. I purchased the PCBs with the Styroflex Capacitor Kit and now I`m just really confused with the whole thing.

Sorry about the question again, but I just can`t get my head around it.

Cheers

if you cut even more on Vishay and Wima caps and resistor and replace them with cheap stuff , you will probably end up to 20.00 as well,
i am just using high quality parts on all my build, because once soldered you just cant change your mind ,
Best,
D.


Hi duduac,

all build options are included in the BOM. So if you bought the Styroflex caps you don't need the replacement caps for these. Also there are two options for the 60G resistor (60G or 68G) so you can delete one of them. Also two options for the 2.2k resistors, delete one from the order form.
Then there are Molex headers that are not essential for the build (at least to my understanding).
I don' know how he came up with 19$, but you can cut down the cost to like 40$ or something like that (I don't remember exactly).

Hope this helps,

Moshe

 

[lkipod]

Hi all,

so I'm at the FET biasing part now.

As I don't have an oscilloscope I'm trying to do it the Klaus Heyne way, as described here

My question is what should the signal amplitude be for biasing?
Klaus Heyne says there:"The trick is to feed enough 1k into the gate that at this ideal bias point the distortion is indeed barely audible or gone altogether, and clearly audible to each side of the ideal bias point."

How much is "enough"?

Is there something I missed?

Appreciate your help.

Cheers
Moshe

 

[lkipod]

Hi all,

so I'm at the FET biasing part now.

As I don't have an oscilloscope I'm trying to do it the Klaus Heyne way, as described here

My question is what should the signal amplitude be for biasing?
Klaus Heyne says there:"The trick is to feed enough 1k into the gate that at this ideal bias point the distortion is indeed barely audible or gone altogether, and clearly audible to each side of the ideal bias point."

How much is "enough"?

Is there something I missed?

Appreciate your help.

Cheers
Moshe

So I searched the web for an answer to my question and I think I found it here.

Dan maybe link to it from your first post?