Now it's on to the electronic modifications for the Oktava MK-219.
I followed the suggestions for component changes in the original Scott Dorsey article, with the exception of changing the stock JFET to a Toshiba 2SK170BL. The Toshiba transistor is quieter, or so the article implies.
But after reading a lot on the interwebs about that change, I decided to do all of the other upgrades and then see if the stock JFET was noticeably noisy and warranted a change. I did procure a handful of the Toshiba transistors in case I decided to change later.
An easy job with my trusty Dremel tool and some small bits.
You read that right - one gigohms! The only place that stocked that value that I found was Digi-Key, and they cost $3.20 a pop. My Fluke DMM doesn't even read to that value.
You can also see two other silver mica caps, as well as the electrolytics. The most important change to the electrolytics is changing the output cap, C5, from 1uF to 4.7uF - and using a better quality cap. I put an Elna Silmic II 4.7uF/50v cap here.
The Dorsey article calls for changing the original aluminum electrolytics to tantalum caps (which are also a type of electrolytic capacitor). I have never read anything good about the tone of tantalum capacitors, so I decided to just go with high-quality Nichicon and Elna aluminum electrolytics as I did with my Altec mixer and preamp rebuilds.
One daring - you might say crazy - change I made that was not suggested was changing the wiring that runs from the capsule to the circuit board.
The stock wiring is super thin - maybe 32 gauge - and seems cheap. I decided to change it for known high quality wire.
I cut apart a short hunk (maybe 5cm) of Mogami quad microphone cable and used some wire from that to replace the stock wire. I also did a silly academic exercise in which I measured the capacitance of the stock wire and compared it to the same length of Mogami wire. The Mogami wire measured maybe 1pf less. Since capacitance is critical here, I felt better.
But that didn't stop me from using a piece of index card to protect it while I desoldered the wire from the tab on the center of the capsule and soldered a new lead on.
You can see both new leads on the capsule at the right.
Sort of like the 'peas with honey' poem, no?
The stock routing for the hot lead took a relatively long path to the board, so I drilled a new pass-though hole right near the tab on the capsule and ran the lead through that. That path saves almost 15mm of lead length, not a bad thing. The less capacitance in the capsule leads, the better.
Wait until you see how long the leads are on a stock Oktava MK-319!
When I finished the mic and tested it, it produced nothing but static. I discovered the hot lead was touching the metal capsule mounting and shorting it to ground. Be sure you have clearance at that point.
Is this worth doing? It's your call. If you're confident working around the fragile capsule, why the heck not? If in doubt, leave the stock wiring. I probably saved less than 4pf in doing this. Maybe 5.
Now to test and see how well it works.
I had done a test recording with acoustic guitar and the stock mic. Then I did a second track with the modded mic. It sounds cleaner, smoother and more defined and detailed to my ear. Most noticeably, the bass is a lot 'tighter' and less flabby.
I really like the look of that new mesh!
I need to do more recordings with it, but I think the stock JFET sounds just fine to my ears.
I'm planning on modding my MK-319 next and I will be changing the transistor on that one, so we'll see if it's worth it.