Mystery mic guts

[crazydoc]

Here's another mic I've got apart. The FET is marked K170 GR 1K - I'm hoping it's a 2SK170 GR. The two orange yellow resistors R8 and R9 are are marked 1KM which I assume is 1 gigohm.
I'm going to put one of the Oktava LDC capsules onto this board in its housing to see what she sounds like.

[crazydoc]

Reverse side.

[Marik]

Considering that the attachment has MXL990 file name, I would guess that it is a Marshall

[crazydoc]

Duh! Where can you see the filename?

[Marik]

Attachment: mxl990bsm.jpg

Anyway, I saw them inside

[crazydoc]

Where can you see the filename of an attachment someone posts? What browser do you use? I can't find the attachment name even in the pages source code in Netscape 6 or IE 5.

[Flatpicker]

Yes, the FET’s a 2SK170GR.

From what I can tell, it’s the same circuit as the 603s (on a different board, of course).

For improvements, replace the cap on the bottom with a 820-1000pF COG ceramic, polyester, or polystyrene – try all three and see which you like the most. Replace C3 and C9 with a 0.22uf metalized film (Panasonic “V” series) or polyester. A larger value like 0.33uF might be better if it will fit. A larger cap in these places will pass a little more low-end.

Lastly, I’d try removing C1 and C2. This is just personal preference, though. You may not “hear” a difference, but I just feel like it’s unnecessary clutter. If you start picking up radio stations in Moscow or something, I’d put some 0.01uF ceramic COGs or some type of polys in their place.

Q4, L1 and L2 form part of a DC-DC converter that boost the phantom power voltage to a higher value. This give the mic more headroom and can improve the sound. Other MXLs like the 2003/V93, and 1006/57/63 use this method. I’ve heard that SP does this with their mics too.

(edited to correct info)

[crazydoc]

Thanks, Flatpicker.
Those (C14 and C15) are marked 102 - does that mean 100pf (0.001uf)? C2 is 223 - 0.022uf? C3 224 - 0.22uf?
What does COG mean?
I didn't even notice the inductors in there - they just look like slightly fat resistors.
For starters I'm just going to leave the board the same and replace the capsule with the 219's, since it is a "darker" mic and the 990 is "harsh," and see what it sounds like.
The 219 and 319 capsules have plastic disks with holes in them screwed to the front and back of the diaphragms - I guess they're supposed to be some type of accoustic shaping element. I'll have to try it with these both on and off the capsule.
Thanks for your suggestions. BTW, nice review of the 319 over at mojopie - and it's a "most requested."

[Flatpicker]

Originally posted by crazydoc
Thanks, Flatpicker.

No problem, Doc. Glad to help.

Those (C14 and C15) are marked 102 - does that mean 100pf (0.001uf)?

"102" stands for "10" and 2 zeros, thus it is 1000pF or .001uF.

C2 is 223 - 0.022uf? C3 224 - 0.22uf?

Oops! I screwed those up. Go back and re-read my post since I edited it concerning this and the other caps I said to remove.

What does COG mean?

"COG" (also known as "NPO") is a type of dielectric used in ceramic capacitors that is very stable, much more so then the X7R and Z5U dielectrics used in lesser expensive caps (we're only talking a few cents here, but when using thousands of caps, it adds up). If you look in a Digi-Key or Mouser catalog you'll see them listed as COG, X7R, and Z5U.

For starters I'm just going to leave the board the same and replace the capsule with the 219's, since it is a "darker" mic and the 990 is "harsh," and see what it sounds like.

Those cheap capacitors are probably what's making it harsh instead of the capsule.

The 219 and 319 capsules have plastic disks with holes in them screwed to the front and back of the diaphragms - I guess they're supposed to be some type of acoustic shaping element. I'll have to try it with these both on and off the capsule.
Thanks for your suggestions.

Take them off and they’re even darker and less defined. I’d leave them on.

BTW, nice review of the 319 over at mojopie - and it's a "most requested."

Glad you liked the review - After reading soooooo many uninformative reviews in my lifetime, I was aiming to please!

[crazydoc]

Here's the first of the two chinese-russian bastards. Now to crank her up and see what she sounds like.

The second will be the 990 capsule with the 219 board and housing. That's going to be a tougher fit physically (sort of like the stallion with the donkey).

[Marik]

Crazydoc--this is good approach! Make a chart and give us report. Give a chance to the 319 body as well

[Flatpicker]

Originally posted by crazydoc
Here's the first of the two chinese-russian bastards. Now to crank her up and see what she sounds like.

The second will be the 990 capsule with the 219 board and housing. That's going to be a tougher fit physically (sort of like the stallion with the donkey).

Doc, that is just too cool!

[ausrock]

Just butting in and OT for a second.......

FP,

I just posted a pic in the Studio Design forum of our setup..........on the RH side you can see part of my rack and the lower section (with doors) is what was inspired by your PC cabinet. I haven't put the PC in yet, but it will happen.........lol.





Sorry for the interuption.

[Marik]

BTW Crazydoc,

Is the brass ring on 990 capsule easily removable? If yes, cold you take it off and see how it changes the sound.

[Rossi]

Cool idea to swap capsules, Crazydoc. But do you really find the 990 harsh? The one I had was fairly neutral, almost mellow, laid back-ish.

[crazydoc]

Originally posted by Marik
BTW Crazydoc,

Is the brass ring on 990 capsule easily removable? If yes, cold you take it off and see how it changes the sound.

Well, it's certainly removable. One of the leads is screwed to it also. I'll try taking it off when I've tried the mic like it is.

Originally posted by Rossi
Cool idea to swap capsules, Crazydoc. But do you really find the 990 harsh? The one I had was fairly neutral, almost mellow, laid back-ish.

They all sound harsh to me - it's probably my sound card's AD/DA, or a brain defect.

Here, BTW, is little Guan-yin's tall, thin brother Piotr.

[Marik]

Hey Crazydoc, could you do me a favor and post a pic of the other side of the capsule.

[crazydoc]

Originally posted by Marik
Hey Crazydoc, could you do me a favor and post a pic of the other side of the capsule.

Here ya go. Ain't digital photography great!

[Marik]

Thank you. One more question. I don't see clearly--is there any mylar film in front of the backplate?

[crazydoc]

Originally posted by Marik
Thank you. One more question. I don't see clearly--is there any mylar film in front of the backplate?

No - that's a plastic plug that has 8 holes drilled in it.

[MichaelJoly]

Crazydoc -

too bad I don't have a dig cam. I've been doing similar swaps and mods...

1.) I put an Oktava MK-219 capsule in a lollipop head grille sitting on top of an MXL V63 Fet amp.

2.) Put the MXL V63 capsule / headgrille on top of an Oktava MK-012 head amp via the -10dB pad converted to 0 dB attenuation - ( just used as a electro-mechanical connection. Looks sort of like a Geffel UM70. I've also done a version of this with the MXL V63 capsule / headgrille driving Dave Royers 5840 cathode follower circuit installed in another MK-012 body.

re: Oktava LDC black plastic HF boost discs - I posted quite a bit of info about these on rec.audio.pro (do a search on my name and Oktava) The discs boost HF by 4dB at 10kHz but they smear the transient response. I prefer the lower HF but better time alignment when the discs are removed.

re: Piotr - you might want to cut out the grilles of the MK-219 body you're using. these mess up the clarity of the HF due to reflections and refractions.

My headgrille experiments have taken this path to greater claritiy - first I cut off the MK219 grille fins, then I pulled out the fine wire mesh of all my mics that use a double layer of wire mesh and just left the larger gauge wire mesh intact, next I removed the head grille of the MK319 (which also exhibits a ringing resonance when tapped) and replaced it with an ELA-M 251 style, single layer mesh. Much better transient response than the stock MK319 head grille.

My most recent experiments have been turning MK319's into lollipop bottle style mics. I seem to prefer the open sound of minimal reflective and refractive surfaces around the capsule.

oh...I've also been experimenting with conical-shaped foam inserts that cover the flat base capsule mounting area and rise to an apex just below the bottom of the capsule. Again, seems to minimize HF annomolies due to reflections in the capsule head.

[Marik]

<No - that's a plastic plug that has 8 holes drilled in it.>

Yeah, that's what I thought judging the depth of the capsule--it is one diaphragm one, and this plastic jobbie forms acoustical labirynth for backwaves. I know I wanted to say something, but I didn't find words, yet. I think the main difference between 603 and 990 sound is not in the grill construction, but the way the backwaves reach the rear of the capsule. In 603 the back chamber is tuned to higher frequencies, so the mic sounds brighter. In 990 there is actually no back chamber, and the brass ring forms kind of baffle, which most likely augments the low freq. response even further. Take the ring off and tell what do you hear.

[crazydoc]

I've used both mics - they work. Won't have time to do any comparisons for awhile.

Thanks for the note MichaelJ - I'll look your posts up when I get a chance.

And while I'm posting pics, here's a screw in the 219 before I ever touched it. Looks like Olga was having a bad day on the assembly line.

[Marik]

<then I pulled out the fine wire mesh of all my mics that use a double layer of wire mesh and just left the larger gauge wire mesh intact...>

Michael,

Yes, I also always remove the thinner mesh, and silk thing as well. It improves clarity, and reduces standing waves. However, the pop screen is a must, and no outdoor use (who cares?) Have a look at my coming projects--old astatic lolipop mic is gonna adopt a tube and K87 (above on the pic). Two strips of my new tube pre, I just stuffed tonight. All these on wire mesh, I use for grills:

[Flatpicker]

Originally posted by MichaelJoly
...I posted quite a bit of info about these on rec.audio.pro (do a search on my name and Oktava)

Michael,
Welcome to HR! I've seen your post over at r.a.p. and seems like I've seen you somewhere else - Tech Talk maybe?
Anyway, good to have you here.
BTW, did you make the ELA-M 251 style, single layer mesh grille?