Archive for the ‘diy’ Category

let’s listen to an rk-47 microphone!

Build reports are nice enough. (I wrote up a little errata post yesterday, by the by.) But the real question, of course, is how does the RK-47/990B kit mic sound?

Early impressions are surprisingly good. Even with only the single microphone, there’s a sense of presence and space – even with a purely mono signal path – that I normally have to dual-mic to attain. Also, it has tremendous precision – this is a mic capable of great subtlety. And the amount of gain built into the microphone itself is crazy – this is one spicy meatball of a microphone. That’s something you won’t hear in recordings, but it results in a lower noise floor, which is always good.

Let’s start with some unsubtle differences, ones that’ll show up on laptop speakers. Because while I’ve never liked the MXL-990, they sell a zillion of ’em, and we should make a couple of direct comparisons.

Here’s a snippet of chords from “Lukey,” alternating between the MXL-990 (unaltered factory) and the RK-47/990B. It starts with the MXL-990, then transitions in-song to the RK-47, then back and forth. It ends with the RK-47. It’s a pure mono signal path until prepped for uploading to Soundcloud.

And here’s a short melody, on zouk – again, starting on MXL-990 (factory stock), then RK-47, then back to MXL-990. The last phrase is repeated to allow us to end on the RK-47; also, I wanted that ending bit to be presented on both microphones. The glissando really highlights some of the differences.

But that’s shooting fish in a barrel, as it were. The MXL-990, while popular, is not a good microphone. We should do comparisons to microphones I actually like – let’s say, the M-Audio Nova. At about twice the price of the MXL-990, it’s still a cheap microphone, just one I consider entry-level competent. But it has issues – not the least of which being it’s kind of a noisy beast as these categories of microphones go.

So let’s take the easy swing – here’s a sharply boosted noise level comparison of the RK-47 to the M-Audio Nova, at equivalent gain levels. This is not the noise you’d actually hear; I recorded a silent room at gain appropriate on each microphone for instrument recording, then cranked that recording up 32db for easy noise levels comparison.

Unfortunately, this really requires headphones, because it’s RK-47 on left, Nova on right:

NOT SUBTLE. But also, an easy shot. The Nova is noisy and everybody knows it. There are some mods out there to improve that, but they change the sound a bit in ways I don’t like, so I work with it.

comparison of waveformsSo let’s dig down a bit. Pictured here is a snippet of waveform from a bit of music played, in mono, over my studio monitors, into identically positioned microphones relative to those speakers. These two recordings were made simultaneously.

You’ll note in this highly-zoomed-in render how the RK47 waveform remains clear and unmuddled in these extremely rapid changes, while the Nova’s blurs into a bit of a mush. That’s the sort of thing I’m talking about, and also, the sort of thing you can hear in these very short snippets of horns from a jazz track. This comparison requires headphones, possibly good ones:

They’re short because they must be uncompressed for best comparison – sorry about that – but listen to them a few times and compare. Note how the edges of detail – bits which add flavour – are blurred in the Nova, but retained in the RK-47. Neat, eh?

That out of the way, let’s step up a level in comparator microphones. Oktava 012s are considered very good affordable microphones, particularly strong in their price ranges, and street for a new 012 and one pickup is comparable to the cost of this kit. With a second head (to add a second pickup pattern, as this mic has), it’s a bit more. They’re small-can capacitor instrument mics, rather than large-can, but we’re doing instrument recording, so that’s fair. The components inside – particularly older ones picked up used – can be a bit dodgy, but the design is great and the pickups are great, and you can upgrade the iffy capacitors and the suspect transistor if necessary. I have, of course, done this with mine.

Here’s the intro to “King of Elfland’s Daughter,” on the Oktava 012 (upgraded components) and the RK-47/990B kit. This recording repeats phrases, with the Oktava 012 first, then the RK-47/990B. Pure mono signal path, identical recording setup made within a few minutes of each other, but not simultaneously, as you can’t put two microphones in exactly the same place and I wanted the most equal comparison I could, modulo performance limitations. This probably also requires headphones, as the 012 is a pretty darned precise microphone itself:

44.1khz/16-bit uncompressed WAV file version here.

Once again, I’m finding that the RK-47 has a real staging advantage. There’s a sense of in-the-room presence with the RK-47 that I can make happen by dual-miking with my other microphones and mixing down, but not directly in mono.

Now, I don’t want to leave the impression that it is BEST AT ALL THINGS, because it’s not. These aren’t the only recordings I made – they’re just ones that show differences best. The first example I found was mandolin – the Nova likes my mandolin better than the RK-47 does. The specific response behaviour and foibles of the Nova work in its favour; a single RK-47 may have more presence and precision than a single Nova, but the Nova recording sounded more musical just the same. I’m sure there will be other examples as well.

In the end, I think this will probably become a heavy-use microphone in my kit. It may even become my go-to mic on the zouk – I need to do some stereo and multi-distance comparisons before I will know that for sure, but it’s looking very good. I also like what it does with piccolo and flute. I haven’t done any playing around with fiddle or drums, and one thing I want to play with is a two-mic setup with the ribbon kit mic I built, to see how those behave together – it’s a mic placement technique I’ve wanted to try for a while, but have never got round to testing. Now is probably the time.

I kind of wish I’d ordered the matched-pair version of this microphone kit. But it would’ve cost twice as much and I couldn’t know in advance I’d like it this much, so.

a bit of errata for the rk-47 build report

A bit of errata on the micparts rk-47/990B kit microphone build report yesterday:

First, I didn’t mention that the board kit includes extra capacitors, to be used either for different capsules than I chose, or to tailor the response curve of the microphone. I went for flattest response, but I could’ve had more or less high-end responsiveness by choosing which included tone capacitors to use.

Second, I said that the “omni” switch setting probably wasn’t really going to be actually “omni,” but was more likely to be figure-eight or the like. This was in response to both the capsule design, grille design, and older pictures of the circuit board which appeared to indicate that. In testing, I discovered that I was mistaken – as you can see here, levels as seen in waveforms made by holding a tone generator at the four cardinal directions remain constant. But read on, after the graphs, because there’s a catch:

rk-47 set to omni, against tone generator at 30cm, front, right, rear, left positions

And here’s the same test, with the mic set to cardioid:

rk-47 set to cardioid, against tone generator at 30cm, front, right, rear, left positions

And here’s an M-Audio Nova, same conditions, for comparison:

nova, cardioid, against tone generator at 30cm, front, right, rear, left positions

The total pickup is certainly omnidirectional. But this is not a true basket head on this thing, there are support brackets on the left and right sides, and that does affect tone! High-end harmonics definitely fall off on the left and right sides.

So while it does qualify as an omnidirectional microphone in “omni” mode, I’d have to call it flawed in that mode, and use something else – like an Oktava 012 with the omnidirectional head, which is built for true omnidirectional pickup and does not exhibit this behaviour.

Alternately, I suppose it might be usable in that mode if you’re recording someone who is a tad screechy – aim the wrong side at the performer and presto, fewer high harmonics. EVERYBODY WINS XD

let’s build an rk-47 kit microphone!

After a few suggestions that I do so, I finally went ahead and splurged for another kit microphone – the micparts RK-47 capsule and amplifier circuit board, both sized to use the dirt-common MXL-990 microphone case.

The MXL-990 is kind of a go-to microphone for people just starting at home recording. I don’t recommend it, even in that role; I think it’s a nasty piece of kit and sounds terrible. Even at $50 – the used price, roughly – you’re better off spending another $40 and getting a low-end AKG or Nova. But it is about the cheapest condenser microphone with XLR out that you could pretend to treat like a real mic, and that has meant a thriving mod community.

Here are the basic parts included with the kit. I didn’t have the capsule out – the actual thing that vibrates to sound – because it needed to stay in its protective box until installation.

This is technically an MXL-990 mod, one wherein nothing is kept but the case and socket. It’s also a nontrivial assembly, so I’m going to talk about building in this one, and have some sound samples in the next.

You can see the instruction booklet over on the right. It’s quite clear, and has some important commentary, about extra care being needed not to touch certain components any more than you have to, and which parts are particularly sensitive to heat. It does not say up front that about 25 pages in it will suggest that you use a couple of chemical products if you have them, so I ended up having to order some purple loctite and conformance coating.

If I had it to do again, I probably wouldn’t order the conformance coating, because the MDA sheet on that is not attractive. But now that I have it, I might as well use it. If anyone local needs some, let me know.

As you can see, the board is clearly labelled:

For the most part, this is one of those insert-and-solder projects. The tolerances are reasonable, though they were emphatic about working at a meaningfully lower iron temperature than I prefer. If you use 60/40 lead solder, their temperature would be fine.

(I ran at 350°C, which is a little hotter than they recommend, but I use silver solder, and it seemed to work out. In these cases, I solder only one leg from each component, then cycle back to the start, and do the second leg, then cycle around again for the third if necessary. This lets the heat that is building up in the component itself dissipate, reducing peak temperature inside the component. This is most important with semiconductors, usually – particularly transistors.)

They also have you cleaning the board with isopropyl alcohol regularly, and suggest cleaning your iron between each solder point. I don’t know if they just meant wiping the tip or actually using the sal ammoniac, so I kind of compromised. (Though for the most sensitive components, I did do a complete sal ammoniac cleaning between each point.)

This is the board essentially complete:

The process is a bit fiddly, I have to say. They’re quite strict in the manual about flux cleanup and so on, so you’ll end up using tweezers and foam swabs and lint-free cloth and and and. Still, with kits this expensive, it’s best not to take chances.

You might note that the connections on the switch are not made yet; that’s because you’re wiring two of the leads from the pickup to the circuit at these points directly. Those connections are where they’re most persnickety about how things are to be done – but I followed their directions precisely and it worked out.

Here’s the new RK-47 pickup canister in its mount:

I’m liking this canister already, at this point. I know, I know, “good feel” is silly, but this capacitor pickup has a good materials feel to it. The mounting system you see in use is also partly a replacement – the original was a ring mount system; this is a saddle, larger, and is also where you need the threadlocker. I’m not convinced MXL used a threadlocker on that post, but I see how the larger, heavier pickup does kind of call for it.

Once the board is mounted back into the bracket and grille, you end up with this:

And once you’ve wired the three leads from the pickup and the three from the XLR connector, you’re pretty much ready to test.

I did have an initially-worrying test result: voltage at the primary test point – the one you conduct before any audio checks – was running high. The manual had a lot to say about what you’ve probably done wrong if it runs low, and further tests to isolate your mistake, and spends a couple of pages going on making sure you’ve got a bare minimum of 45V going to the exciter, with a preferred minimum of 50v, and an “operating range” of 50-62v, where 60v is optimal.

The range on mine ran from a low of 62.45v to a high of around 68v, so I was concerned. But it turns out the actual operating range is 50v-70v – they just don’t expect anybody to be able to get to the upper end. Support even said that if I was mostly recording quiet material I could safely crank it up to 65v full-time for an even hotter pickup, but, heh, that’s not what I generally do, so I’ll leave it where it is. XD

As for the sticker – I put “MP-SVS” over the “MXL” logo because at this point, it’s not an MXL microphone in any way, so why would I keep that? It’s just silly. MP-SVS is MicParts-Supervillain Studios, naturally. I also changed the model number to RK-47, after the canister number.

I did not mention before that this is a switch-selectable dual-pickup-pattern microphone:

That will let me try an instrument miking style I’ve wanted to try for a while anyway. The only downside of using an existing microphone housing is that the switch has to live on the inside, and you have to unscrew the bottom of the housing to get to it. But it’s just twist-open, so not really an issue.

Regardless, as you can see, the switch says “cart” (for cartioid) and “omni” (for omnidirectional), but I think I’m pretty sure it’s really more figure-eight, given the construction of everything and what the switch does. And pictures in the manual actually agree with that – the printing on the board is different in the photos.

An optional modification to the case involves coating the lower half with silicate caulk (or a couple of other listed materials). I, of course, did that too:

The idea is that this reduces case resonance. Does it? I dunno, I just went ahead and did it because silicon caulk is dirt cheap – the local hardware store down the hill had a small tube for three dollars. The lack of silicon at the top is necessary – the upper part of the case scrapes into the lower half quite tightly, and any added material would be scraped off right away. As you can probably see, it’s even scraping off its own coating.

This is what it looks like all put together, and put in the standard MXL-990 shock mount:

As always, larger versions of the photos are at my Flickr account.

All in all, I’d call it a straightforward well-documented build. It’s far from the most difficult I’ve done. Not a good starter project, but if you’re reasonably good with a soldering iron, you’re going to be fine.

And this is already a long post, so I’ve decided to make it Part 1 of 2, and will talk about the important part – what the result sounds like – next time. Spoiler: a whole hell of a lot better than an MXL-990. But it also has audibly (and visibly, in the waveform) finer and more precise pickup than, say, my Novas.

I’m also going to see if I can’t do some comparisons to my Oktava 319 and possibly the (already-improved via mods) Oktava 012s as well before next time. That, too, might be interesting.

Have a good weekend, everybody!

wherein i thought i was going to be posting about a new microphone today

I thought I was going to be posting about a new microphone I built today! I was pretty sure I could get the kit construction finished and even make a couple of recordings.

And I could’ve, but no, I had to have one of these moments:

…wherein on page 24 of the assembly instructions it talks about connection sealing material and special kinds of thread-locking fluid which aren’t strictly necessary but are definitely good to use, if, you know, you just happen to have them around, and if you don’t, well, you can add them later but EVERYTHING WILL EXPLODE.

Particularly the connection sealing material. Apparently.

None of this was in the components and tools list up front. Of course. So thanks, now I get to order all that stuff, which I already have, and it’ll get here Wednesday. (No, it’s not at the local hardware. I did check!)

Anyway, this is how far I got, and where it’ll be until Wednesday:

truly excessive geekery ahead

All those posts I made about data cleanup and old hard drive data recovery got someone I know from my old SF club interested in his old Amiga hard drives, which he sent me, and which I imaged for him, and did as much file recovery as I could.

One of them was just fine – complete image, files pulled off separately as well, life is good. The other…

This is what’s actually in the disk’s partition table.

And for those who have no idea what that means: disks can be divided up into smaller disks, more or less. There are reasons to do this, mostly on servers, mostly not workstations, but whatever. These are called partitions.

This particular drive is cut up into six, count ’em, six partitions, sort of, except that two are completely broken and one is made up of parts that are also at the same time parts of two other partitions, and just kind of… overlayed atop each other.

Spoiler: this don’t work.

It’s like if you got to chapter two of a book, and midway through, chapter three appeared, overprinted and interleaved with the second half of chapter two. And after chapter two ended, chapter four picked up, printed underneath the rest of chapter three, making chapter four unreadable. But you can still make out chapter three if you squint.

There is no partition utility in the world which would let you do this.

The amazing thing is that I managed to recover the contents of both “TWork” partitions, which is a lot like getting chapters two and three from my analogy back and sorted out separately and readable. Couldn’t do anything for chapter four, though. And chapter six… I don’t know what happened there. It’s some kind of goddamn chainsaw murder scene with horror movie implications.

Sadly, both of these drives did the all-too-common very-old-drives-out-of-storage thing, where I managed to image them and pull contents, but after one last heat up/cool down, they just said “aaaaand we’re done here” ’cause that seems to be that. They’ll work long enough to come online, but the Viking won’t even stay up long enough to format it, and the Quantum ST will format, but will only let you write between 10 and 60 megs before taking itself offline and hiding from the controller until you reboot the machine. So no eBay listings for these.

Still, I’m happy. I made enough auctioning off all this old stuff to buy another microphone kit and I am closing in on another toy. Expect more DIY studio gear posts! It’ll be fun. 😀

so let’s say there’s an emergency

The new year is here, which means it’s time for the annual BIG CLEAN! But – living in earthquake territory and surrounded by active volcanoes – it’s also about emergency prep! Because it’s wise to have right the hell now, one-day, and two-or-three days plans for getting out.

(Some people also talk about having a month’s notice plan? But really, that’s a move, and I think it’s silly to think of that as ’emergency.’ Even one week isn’t a whole lot worse, even if you have a lot of junk – most of what people own that takes more than a week to sort out doesn’t really need to be sorted out.)

So! Let’s say you have one day, or worse, Mt. Rainier has just gone up and the Cascadia fault just tripped and everything is completely pear-shaped but a rescue boat is outside. For someone like me, who creates a lot of content, the key to getting out quickly without massive losses is already be ready.

What’s that mean? Well, you hear a lot about the three-day bag, of course. (At least, you do in Cascadia. It’s not really adequate, you should be prepared for at least a week, but three days is a start. Is this just us?) The three-day bag is one you can grab and take out the door as the building is falling down around you.

You should have data in that too. At very least, a recent backup of key data. For example: we back up our servers to USB flash drives. This sounds hilarious but it’s actually pretty good, because it means we can swap the flash drives monthly, and have a completely offline set of backups as well. And the monthly swap means they never have data-loss issues related to being unpowered for months.

Where do those offline backup flash drives live? The three-day pack.

If you have your creative works scattered across a bunch of formats – by which I mean other-than-digital formats – scan your stuff. And have your digital work collected – at least in backup form – in one place, and let that live in the three-day bag too. (But don’t use flash drives for this, they drop storage over time if left unpowered. They aren’t a good archive format.)

Alternatively, back your data up somewhere off-site. But that’s not always the best idea, for a lot of reasons – bandwidth being one of many, but there are many. If you can do it, great.

So as part of this year’s Big Clean, I’ve been getting my data situation together. I’ve made an image of my recording archives, and I’ve ripped all those old Commodore and Amiga floppies, and right now, and I’m scanning those old fanzines I put out back in the 90s, because why not? All that old stuff’s so small it can live in backed-up archive directories on my laptop, and the laptop is effectively part of the three-day kit anyway.

This is me, following my own advice, and being generally ready, like y’should. I was hoping to be done with all of this by the end of the 2nd, New Year’s Day Observed Bank Holiday Whatever, but I’m not quite done. But I’m close.

Anyway, here’s my RIGHT THE HELL NOW list:

  • three-day pack (yours should have a solid week of meds, if any)
  • laptop
  • instruments (at least the zouk)
  • phone
  • purse (which includes passport)

That gets me almost all of my creative output, food, meds, srs bsns ID, and so on. If you don’t have a passport – or passport card – you should have one if you can afford it. It’s better ID than a driver’s license or ID card, and doesn’t get questioned.

My ONE DAY’S NOTICE list – basically like going on tour with less gear but more paperwork. All of the above plus:

  • one suitcase of clothes
  • all hard drives
  • the One Day Warning box (important legal papers, pretty much)
  • studio tablet and custom studio hardware (one box max)

Anything more starts getting into “well, now, it’s just a move,” but with 2-3 days, I’d start with more general lab and studio gear, and favourite books and art.

For an emergency, doesn’t that sound luxurious? I’d have that luxury – all that time – because my Right the Hell Now and One Day plans are together. If you live anywhere that can get Abruptly Dangerous? Yours should be too.

oh look, the feet… ran. and computer case feet should not do that.

This is what’s left of the rubber feet of my 1994 Commodore Amiga 4000/040.

Yep. That’s a viscous tar-like residue that ran along the bottom of the case and into the gap between the bottom case and the cover. It’s very sticky and resistant to detergent, but, fortunately, not to citrus-based sticky tape removers. Isn’t it gross? I mean, seriously, doesn’t this look like some sort of OOZE OF SATAN special effect?

Oddly, the stickytape used to hold the rubber feet on was intact! And, as far as I can tell, fine. This actually saved me a lot of cleanup, because the cores of the old feet were pretty solid? The further I removed down, the more like rubber it became. The thickest material had an actual rubber-like consistency.

Fortunately, all the rubber that ran could be cleaned up pretty easily with an old spudger and a lot of orange oil. But goddamn.

I’ve repaired tube equipment from the second world war and this is the most bizarre materials degradation I’ve ever encountered.

and some days things don’t work

I wanted to post about the cool second-generation crystal microphone today BUT NO IT’S ALL STUPID AND NOISY AND I DON’T KNOW WHY but it sounds like either a really bad cold solder joint (please be that) or a bad transistor (@&*$&!!! special orders please don’t be that) and I don’t know which.

It’s too bad because I came up with a nice little jury-rig jig (say that five times fast) and so the backplate of the housing came out really well and I was looking forward to showing that off. Fingers crossed this is some sort of Surprise It’s Easy! fix – that would indeed be a surprise, to be honest about it, but a pleasant one.

In the meantime, enjoy this video of Overwatch players in custom game mode making some genuinely gorgeous Genji Beams. These are effects created by lining up opposing teams of Genji players opposite each other, in continuous-shot-deflection mode, and hitting them with various weapons. The shots bounce back and forth between the teams, and you get some really neat graphics interactions. It’s pretty cool and occasionally hilarious. Enjoy:

cyberrrrrrrr mondaaaaaaaay

It’s Cyber Monday, apparently, which means LET’S PUT EVERYTHING ON SALE. I’m doing my part – I’ve put out four singles this year, so I’m putting all of them on pay-what-you-like.

It’s funny, but the most recent one – We’re Not Friends (The Future Has a Place) – has really changed on me since the election. Particularly with Mr. Pence involved, it’s stopped being a celebration, and has turned into a declaration of defiance.

Fortunately, I’m real good at defiance.

Here’s the 2016 tracks. I think they’re real good. Pay what you like – and thanks.

orycon this weekend, with show and tell

I’ll be at Orycon this weekend! I have panels and workshops and a concert on Sunday afternoon, so please come out for it!

They’ve actually given me a panel on building old-technology microphones, which is pretty cool, and I’ll let people record themselves on a 1920s-ish carbon mic and a 1940s-ish crystal mic, so hopefully that will be fun. People really seemed to enjoy it when I had the setup running at my dealer table at CBCC.

I need to find time – somehow – to wedge in building a new amp board for the microphone panel, because I don’t want to take apart the existing crystal microphone for show-and-tell, and I think it’ll be neat to show that off. Later today. Hopefully. Assuming nothing else explodes.

Like, Monday, right? Things Happened, and then I got to spend the afternoon pulling unimaginably gross material out of a fluid pump system while going, “oh gods, oh gods, I hope this is only cat litter, please let this just be cat litter,” and when that’s happening, you have officially reached what one might call a BAD SCENE.

Not “darkest timeline” bad scene, but: bad.

so disgusting

Anyway. Thank the gods that’s over. See you this weekend!

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