My new microphone

[rascalseven]

I wanted something FET 47-ish, so I decided to build something that could hopefully do similar jobs.  

For a few years I've had an Oktava MK319 with a bad capsule sitting on the shelf, and when I recently saw a non-functioning Studio Projects C1 for cheap on ebay, I snagged it for use as a donor body.  The circuit was bad, and I already have a pair of C3's, so I gutted it and made a new pcb using the MK319 circuit including the transformer from my bad MK319.  Used Scott Dorsey's mod as a basis for this circuit, but I chose film and polystyrene caps in place of the COG's he recommends in his mod.  Also, the extra room in the C1 body allowed me to use film caps in critical spots (especially the output) instead of tants.

The capsule I used is the RK-47 from www.microphone-parts.com.  This inexpensive capsule is based on Neumann's kk47, but is 3-micron instead of 6.  It is double sided, so I could have other patterns.

I reworked the C1's HPF and pad switch to provide selection of omni, cardioid, and cardioid with -10dB pad (for use with kick drums and cabinets).  For the pad function I used Marik's trick of a voltage divider to drop bias voltage to the capsule.  

I just fired it up for the first time today, and haven't put it through any tests at the studio, but with just my spoken word and singing (I'm quite familiar with my own voice) I can say that I very much like this mic.  It is very smooth, with a subtle airy quality, excellent midrange detail and a wonderful proximity effect.  Most mics just get boomy when worked up close, but this one just gets huge without ever losing detail.  Would be awesome for VO work ("in a world....").

I'm going to put it to work on drums, vocals and guitars next week, but I can already tell I'm going to like this mic quite a lot.  

Pics:

(Note the Oktava transformer and the large film caps).

BTW, as you can see I painted the body a cream/white to make it easy to differentiate from my C3's (which I only use on occasion any more), and I like the ELAM vibe the paint gives it.  I used automotive touch up spray paint and baked it to make it hard and shiny.

Cheers!

JC

 

[kato]

That's my kind of DIY. Nice job JC!

 

[tommypiper]

Great job!  Which Scott Dorsey mod is it?  Is it the design that he sold boards, based on the Schoeps?  I built that one and had some bad RFI issues.  When I told him about it he recommended ferrite beads all over the place.  That helped.  If you're using the same design you may want to check for RFI.  Move it around and listen.  In my location it changed from radically bad  -  to moderately noisey at high gain, within inches, just moving it around.  It even picked up AM radio at one point.  ;D  Still sounded / sounds great, though.

 

[rascalseven]

Great job!  Which Scott Dorsey mod is it? 

It's his Oktava MK319 mod.  Basically just replaces components with higher quality ones of more appropriate values for the circuit (and for the 2SK179BL fet that he suggests).  He recommended COG type caps for the small values, but I really like polystyrenes and films instead, so I went that route -- seems smoother/silkier to my ear, though in this mic I didn't A/B the two, just went with what I normally prefer in other circuits.

Also, having room for a good film cap on the output is a plus (not enough space to cram one into a 219/319 Oktava, but the C1 body is bigger, and doing my own pcb layout gave me ample space to fit a couple in).

JC

 

[Rybow]

Nice work! Looks great.  ;D