Crawls Backward (When Alarmed)

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Oktava MK-219 Microphone Modifications Part Two: Electronic and Wiring Mods

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.

On the right you can see an image I created which identifies the (stock) components. We'll be replacing 2 resistors and most of the stock capacitors.

I changed out the original small value caps for silver mica caps with increased values. The holes in the PCB had to be opened up a bit to allow the thicker leads on the new caps to pass through.

An easy job with my trusty Dremel tool and some small bits.

Here's the PCB after changing out the selected components. You can see the input cap near the top - that was upped in value from 680pf to a 820pf silver mica cap. That was changed along with changing R1 and R2 to 1G resistors.

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.

This is the stock ground from the capsule. You probably know the capsule is fragile and if it gets punctured, it will be useless.

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.

The hot lead is on a tab at the bottom of the capsule - much less scary to unsolder and resolder.

You can see both new leads on the capsule at the right.

The screws that hold the capsule to the chassis are small. I magnetized them with my magical Wima magnetizer tool so they'd stay on my screwdriver.

Sort of like the 'peas with honey' poem, no?

And, in the interest of absorbing vibration, I put a piece of closed-cell foam (again leftover from the c900 sound deadening project) on either side of the capsule mount. You can see it in the picture on the right I took while remounting the capsule.

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!

Here's the new capsule wiring.

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.

This is the completed PCB. Note I took the plastic cover things off the capsule as well. This supposedly makes the mic less peaky in the above 10K frequency range.

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.

The last thing I did with the PCB is to put acrylic conformal coating on the input joints to protect them from corrosion. These high-impedance connections are sensitive and it's suggested to coat them.

Here's the reassembled mic on the bench.

I really like the look of that new mesh!

Closeup of the new headshell - you can see the capsule now!

Here's the mic in action. It sounds good.

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.

 
 

Oktava MK-219 Microphone Modifications Part One: Body Improvements

After reading a lot about the semi-famous Oktava MK-219 and MK-319 microphones online, and the various mods to improve them, I took the plunge and procured some used ones.

Here's the first victim, an MK-219 from 2001. This mic is a large diaphram condenser mic which sounds pretty decent unmodified. But there are a lot of popular mods to improve...or change it.

The microphones are made in Oktava's factory in Tula, the adminstrative center of the Tula Oblast in Russia.

I used Scott Dorsey's article as a reference point, as well as other references on the interwebs. If you do a search, you'll find a lot of information about these mics.

The most basic mod is to cut away the bars on the headshell around the capsule to open it up, and to add deadening material to the body to cut down on the 'ringing' produced when the mic is vibrated, which affects the tone.

First we'll take on the mods to the body.

It's easy to open up; take off the ring around the XLR socket, then remove the screw that holds the body halves together.

Some of these pop right apart, but this one was really tight. There are two brass shims between the XLR connector and the inside of the body to tighten it up.

I used a wood wedge to drive the body halves apart. I didn't want to scratch the paint off, so I didn't use something metal to do this.

Here's the body, now separated. You can see the two shims I mentioned which came out when I opened it up.

The pc board is held into place with a threaded rod which also accepts the screw we took out earlier.

Just unscrew the rod. And don't lose it!

The body halves with the chassis removed.

Be careful around the microphone capsule at the top! If it gets punctured it will cease to work.

I put the whole chassis safely aside while I worked on the body.

If you tap one of the body halves, you can hear it ring instead of 'thunk.' We're going to remedy that.

But first, we're going to cut the bars out of the top of the body and put new mesh in.

The stock mesh comes out easy - just pry it out. It's not glued in.

The bars at the top around the capsule limit the amount of sound that can get picked up. We cut them off with snips.

They're close together, so I used small snips to start cutting in one area, then I used larger snips to cut the remainder away.

I left little nubs of material on the body rather than try and cut the whole thing level with the frame.

While I was cutting, I had the occasional 'ping!' when a chunk of material flew off and went into never-never land.

Then I ground down the nubs as far as I dared with my trusty Dremel tool and a grinding attachment.

Then I filed the nubs down flat.

Bars are all gone and the area where they were is flat. I sanded the bare metal with 220 grit paper, then primed it and painted it with Rustoleum 'Textured Surface' black paint.

Some folks take one of the two layers of factory mesh out and leave one. The mesh is there to make a Faraday cage to cut out RF.

The stock mesh as seen on the left has about 22 or so openings per inch. The nice Microphone-Parts.com headbasket I put on my modified MXL 990 has about 10 or so openings per inch.

I followed that lead and procured some mesh from McMaster-Carr with more openings to use instead of the stock mesh.

Traced the stock mesh onto the new screen and cut it with snips. It took a couple of tries to get ones that fit nicely.

This is stainless steel mesh screen - I bought a sheet with 10 spaces per inch and one with 12. I wound up using the one with 12 spaces for this project.

I found that the mesh with more spaces is a lot easier to bend to shape. The screen with less spaces (such as the screen I used) is a lot stiffer and harder to work.

The mesh/screen must be grounded to act as a Faraday cage, so you need to scrape some paint off the area where the screen mounts. After you put the screen in, just test it for continuity to the body.
Here's a test fitting. There are small screens at the top of the opening, so I did those with the new screen as well.

One of the issues with the MK-219 body is that it rings when you tap it. That ringing can be picked up by the mic when you're recording. So the body needs to be damped.

Scott Dorsey and others have used RTV silicone to damp the body. That looked like a real mess to work with, so I decided to simply use some CLD (Constrained Layer Damper) tiles left over from my SAAB c900 sound deadening project. I put one large piece and one small piece on each half.

I probably used more than I needed, but I figured I'd put a big hunk in there for good measure.

Works amazingly well and it's a more elegant solution than the silicone I think. And nowhere near as messy.

Next time we'll work on the electronics.

 
 

2016 Strathmore Guitar and Ukulele Summit

I just got back from the wonderful eighth annual Guitar and Uke Summit at the Strathmore arts center in North Bethesda, Maryland. Four days of outstanding guitar and ukulele seminars, concerts, and jams culminating in a great show by the super talented instructors.

You may recall my post about the Summit a few years back. I've been there every year!

This year was the first time the final, free concert was held in the Music Hall. I love, love, love that building. I'm not a perfeshinul moosician, just a hack, so I was thrilled to get the chance to be on the stage there.

Crazy, right? This is the view you'd have if you were in the BSO.

In this instance, it's the Ukulele Orchestra of Washington, aka a group of us students. We had the pleasure of playing three four tunes led by our great instructors: Lil' Rev, Jeff Peterson and Tobias Elof.

We were the opening act. Don't have much of a following yet - note all the empty seats. The place filled up for the main acts - the whole orchestra level and the first balcony tier were full.

We had actual scores to play from.

Made us look like we knew what we were doing.

The Orchestra in between numbers.

Dress code is...casual. Need to be comfortable when you're wailing on the uku.

One of the balconies viewed from the stage.

In addition to being simply beautiful, the acoustics are amazing. What a place.

My buddy David Geyer opened up the main bill with the classic Gershwin brothers' "Our Love is Here to Stay."  He was accompanied by the incredible Tobias Elof (on the right).

Cathy Fink later described David's voice as "made for Broadway," and I agree. He's a first-class vocalist, and a heck of a uku player to boot.

The brains behind the whole Summit are the fabulous, wonderful, terrific, Cathy Fink and Marcy Marxer. If it has strings, they play it - incredibly well.

I am honored to be pals with these two ambassadors of music.

Cathy's playing her gorgeous tangerine burst Collings tenor uku, while Marcy is holding down the bottom end on her signature model Gold Tone cello banjo.

We also had the great pleasure of hearing the astounding Tobias Elof, who came in from his native Denmark to teach and perform.

Tobias taught advanced classes on traditional Scandanavian dance music, harmonics, scales. He also taught one of his own compositions - and conducted us ala Esa-Pekka Salonen.

He's a fantastic composer and performer. It was a privilege to hear him.

For the second year in a row, we had the great opportunity to study with, and hear, the incredible Jeff Peterson.

Jeff hails from the island of Maui, and is one of the finest guitarists on the planet. He's a master of the slack key style, but also plays jazz and classical styles with aplomb. He's jaw dropping and spellbinding - I don't know enough superlatives to describe him.

He's also extraordinarily knowledgeable about Hawaii - it's cultural, political and musical history. And a super nice, unassuming guy too.

Here's another shot of the audience - the place got quite full.

Did I say I love it there?

For the finale, everyone joined in to jam on a fiddle tune, including the fabulous Lil' Rev on harmonica. (He told us in a harmonica workshop that 'you suck' is a compliment to harmonica players!)

Here we see Cathy Fink channeling her inner Stephane Grapelli on violin while directing the band.

The Summit is great fun. I encourage you to come next year!

 
 

Cleaning Dell Laptop Fan for Improved Performance

This is my Dell Studio 1735 laptop.

Lately it's been crashing - as in stopping dead with no warning - when I'm on the interwebs.  I did some fine tuning, like moving files off the desktop, taking some things out of the process tree, etc., but it still dies occasionally.

I got to reading on the interwebs about cleaning the cooling fan. Seems that they pick up a ton of dust and dirt and that affects its cooling. Then the CPU hits a temperature limit and shuts down.

So I took the laptop down to The Dungeon to take a look at it. I had armed myself with some disassembly instructions from some other blogs.

Turns out this particular machine doesn't need much disassembly to get at the fan.

First I took out the battery.

Note the two screws near the sliding lock for the battery.

There are a number of those screws on the back panel.

We take them out first.

They're pretty cool because they don't come all the way off the panel. Once you loosen them they stay in place. I show my driver here, but I actually just unscrewed them by hand.

Once all of the screws are loosened, the panel slides off.

Piece o' cake. (MMmmmmmm cake).

The fan is on the upper right - easily accessible.

Wow. I expected to take more pieces off this thing.

You can see the dust on the fan blades.  We'll get that off.  Not as bad as some pictures I've seen online.

One side note: the backup battery (a 2032 on this machine) is right near the bottom - easy to get to for replacement.  I probably should have changed it out, but I figured it's so easy to do, I'll wait until it needs to be replaced.

So, I've read these "warnings" about not using a vacuum to clean the dust off the fan, "because the vacuum might make the fan spin faster than it's designed for and it might damage it."

Seriously?

Clearly these folks don't know these puppies spin at several thousand RPM. No way your vacuum will spin a fan that fast.

I did use compressed air to get some of the dust out, along with a vacuum.  Turns out my vacuum didn't turn the fan much at all, nor did it remove all of the dust.  The compressed air got more off, mainly because the dust was sort of caked on.

After getting most of the dust off, I used q-tips to get the remaining dust off the fan blades.  I was also able to reach in past the ends of the blades and get the dust off the inside of the curved housing - there was a lot of dust there.

I also blasted the dust off the vents on the bottom panel.

Then I put the thing back together, and there is a major improvement. The fan is about 90% quieter.  And the machine is running much cooler overall - the top surface got very warm to the touch, and now it stays cooler as well.

When the laptop was working hard before, it would run at up to 80% usage.  Even at idle, it would be at 50%.  It's been running at about 13% while I wrote this post.  And it drops to 0% at idle.

It's probably worthwhile to open your laptop up and clean the fan - I'd guess you'll see an improvement as I did.

 
 

Custom P-90 Pickup Shim for Gibson Archtop Guitar

I did some fine tuning on my Gibson ES-225T over the weekend. One of the things that has bugged me is the location of the pickup is parallel to the top, but not to the strings.  I honestly don't have a lot of experience with archtop Gibbys with P-90 pickups, but I suspect this is a common issue.

Here's what I'm talking about. You can see the pickup is in a 'flat' plane, but the strings are not.

Since the pickup is also stuck in the center of the space between the end of the neck and the bridge, the tone is so-so.  I'm thinking it might help the tone if we get the pickup more parallel to the strings.

The way a P-90 adjusts is by shims. From the top in this view, you can see the pickup cover, a thicker plastic shim, then the one shim I have at the bottom to raise it up. When I got the pickup from Lollar, I bought a set of fiber P-90 shims, which helped raise it up closer to the strings.  But the tilted angle has been  bugging me for a while.

How to fix this? Here's what I came up with.

The set of shims I have contains shims in varying thicknesses. I used a straightedge to determine the distance the bridge side of the pickup needed to be raised. I selected a shim that was closest to that distance.

Since we don't want to raise the neck side, we want to create a wedge shape. So I cut the fiber shim with a razor saw just beyond the mounting holes.

I tried using an X-Acto, but boy is that fiber hard to cut.  Hence the razor saw.

Then I stuck the modified shim onto a piece of scrap wood using double-sided tape.

I put it near the edge thinking that I needed to be get the proper angle of approach to the shim.

I started to work on the shim with a file. It didn't go well, so I switched to some 60 grit sandpaper glued onto a paint stick with spray adhesive.

It worked perfectly.  I only needed to angle the two 'ears' on the shim, so I had good control with the sanding stick.

Here's what I wound up with.

You can see the wedge angle on the ears. I tried to get the edge just beyond the screw holes as thin as possible.  That's the edge that will be on the neck side of the pickup.

Wow.

It worked!

The arrow points to the new wedge shim in place on the guitar.

It seems to have made a difference in the tone of the pickup - seems to have more punch. And it looks much better to boot.