Aurycle FET Mikes

[Rybow]

Cool thread! Looks like things are coming along nicely so far. Can't wait to see more!

 

[Matador]

hey matador nice work man!! im also keen to know where u got those nice looking capsules???

mick

I got them from Dave Thomas at Advanced Audio Microphones in Canada.  I was blown away by the C12 capsule he sold me to retrofit my Apex 460, so I thought I'd give the other capsule types a try.

 

[ricardo]

True:  it mainly depends on the individual capsule response.  I'd like to try two different capsules:  one with a K67 response, and another with a K47 response.  The de-emphasis will have to be tailored for each one.

Do you have any info or links on K67 & K47 responses?  ie measured curves?

I'm also not sure what the circuit is doing but it will be quite noisy.  R1 & R2 put 6k81 + 560R noise resistance in series with the capsule. 

You can short out C2 and remove R4 as they only introduce noise.  In the U87 with KK87 capsule, they are for the second backplate.

I'm also not sure I'd be happy driving that transformer directly from a single FET.

[edit] I see this is an attempt to copy the U87 circuit so I'll just shut up.  However, my comments on noise stand.

 

[Rybow]

hey matador nice work man!! im also keen to know where u got those nice looking capsules???

mick

I got them from Dave Thomas at Advanced Audio Microphones in Canada.  I was blown away by the C12 capsule he sold me to retrofit my Apex 460, so I thought I'd give the other capsule types a try.

Nice. I had looked at those capsules before, but I couldn't find any info about them on the web. Might give it a shot for my next mic build.

 

[Matador]

Do you have any info or links on K67 & K47 responses?  ie measured curves?

I'm also not sure what the circuit is doing but it will be quite noisy.  R1 & R2 put 6k81 + 560R noise resistance in series with the capsule. 

You can short out C2 and remove R4 as they only introduce noise.

I'm also not sure I'd be happy driving that transformer directly from a single FET.

Yes I'm going to leave in the PNP follower.

In general, the K67 capsule has a high frequency emphasis in the 7kHz-8kHz region.  For K47, this bump is down in the 4kHz to 8kHz range.  The action of C3 is to add a step in the amount of negative feedback that is coupled to the backplate of the capsule (out of phase).  C3 controls where the deemphasis occurs in the frequency domain.  Removing it removes the deemphasis completely.

On the U87 schematic, it looks like the 560R resistor was used as an easy way to inject a calibration signal for setting the FET bias (the Neuman schematic actually says "Messeng. Cal. Input"), as it is coupled directly in series with the capsule (as you say).

 

[poctop]

Hi Guys,  Need info Here , Got the a PTP protoboard with neumann u87 version 16 and 21 hybrid with peluso K87 clone (Picture Coming) and it seems to be working great but i wandered how to bias the FET in all the details so except from setting the FET to about 10V, what about the signal cal point and the capsule ?,  Do i have to input a signal there and tune for best THD or Best Swing Response? I did
replace the Tant by Electro but i am trying to Evaluate wich Capcitor with be the most important to varies in the circuit,  most of em are Wima for now.

Read you later
Cheers,
D

 

[poctop]

OK This is the ugliest things i have ever done but it works ended up pushing up the 1 K tone , and tuned with thd analyser i had to crink up the volume to see the Regions in the Klaus Method but it works when you reach the minima point in the T?HD just passed the FET opening and then it goes backup Sweet..... ended at 12.80V for 2N3819 and peluso Cap K87 and original spule 09145, hope this make sens,  i am preparing a sample will be 1) the clone 2)the real u87 vintage and then3) tlm 127 neumann,

cheerso.
Dany,

 

[poctop]

Snuff I cant post any sample here ,

pretty impressed by the sound i have here compared to the real thing, i have the exact replica of neumann circuit in there,but wander wich caps would be worthed trying play with, the real U87 vintage still exhibit a bit deeper bottom,  would it be worthed putting those old styrene caps like in the orginal circuit
C6, C4, C1, and C2 to make it naughty !!!!!

Well fitting all of these in the Aurycle body was not a Smooth Ride but i did,

Well Let me know if you have any suggestions,

Cheers
Dan .,

 

[Matador]

If you have sound clips feel free to post here if you can.

Biasing by symmetrical signal swing on a scope is the best method.  This may be a different DC operating point than 10V as you found out.  10V is a reasonable starting point mostly because it's roughly half of the DC operating supply for the stage (about 20V at the top of the drain resistor).

 

[ricardo]

..  i had to crink up the volume to see the Regions in the Klaus Method ...

What is the Klaus Method?

 

[poctop]

Thanks Matador ,  Can you be more explicit on your signal swing on scope technique,

Let me know if you want the Clip on your FTP where your got the picture and all that . because i dont have one and i cant post a sound clip here too bad,

I am on continuing experimenting with the mike still,  i am willing to try changing the response curve of the preamp by changing capacitor colors......

REad yA Later,
D

 

[poctop]

Hey Ricardo ,

Here is the Klaus Method,

http://recforums.prosoundweb.com/index.php/m/435425/0/?srch=u87+schematic#msg_435425

 

[Matador]

Thanks Matador ,  Can you be more explicit on your signal swing on scope technique,

It's documented in the Micbuilders file archive by user Zapnspark (file is called BiasingFETScopeMethod.pdf).

Essentially, you place a signal generator to replace the capsule, and increase the peak amplitude until clipping of a peak is seen.  Then the drain resistor is adjusted until the clipping disappears.  Then, the amplitude is increased again.  This process is repeated until both the positive peak and negative peak are clipping equally on the waveforms.  This should be the optimum bias point of that particular FET with those particular source and drain resistors (and the particular VDD of the mike in question).

 

[Matador]

Still waiting for my CM-2480's!

When I get them and assemble the mikes, I'll take some scope shots of the biasing.

 

[poctop]

Hey thanks Matador for the precious info, , would you happen to know the user an password for the micbuilder account so i cant take a look a this file,

Let me know,

Waiting for CM2480 as well !!!!!!!!!!
Dan,
 

 

[poctop]

Hey Matador,  just finish a batch of my U87 prototype with peluso capsule and cm2480 brought them to a big studio and it sounds terrific transient a sharp focused and super tight , they decided to leave the u87 vintage on the bench !!! I also grabbed a k87 capsule on craiglist and tried with that and it sounds identi-ti-ti-ti-cal to my vintage u87 ,  i should release a feeler thread about this board soon ,  let me know how it is going !!!!!!!!!

Dan,

 

[abechap024]

Hey Matador,  just finish a batch of my U87 prototype with peluso capsule and cm2480 brought them to a big studio and it sounds terrific transient a sharp focused and super tight , they decided to leave the u87 vintage on the bench !!! I also grabbed a k87 capsule on craiglist and tried with that and it sounds identi-ti-ti-ti-cal to my vintage u87 ,  i should release a feeler thread about this board soon ,  let me know how it is going !!!!!!!!!

Dan,

Hmmmm intersting a PCB for the u87? is that what I'm smelling in the works!? Does it fit into the aurycle mics? I might be interested in a couple.... just saying could be a good match to the capsules I picked up from oceano99  ;D

 

[poctop]

will Do,  should be really soon,
Dany,

 

[poctop]

Forgot to mentionned that the aurycle will fit perfectly,  that was my template, and notice that almost all the cheap body mic came from the same place,
Dany,

 

[abechap024]

will Do,  should be really soon,
Dany,

Sweet!