Category Archives: mic mods

The Austin Ribbon Mic

I recently received an Austin Ribbon mic kit from Rick Wilkinson (Rickshaw Records) out in California. Unfortunately, I can’t say I’m the proud owner… this mic is going to be built and given away as a door prize at the DIY panel at the Producers and Engineers Summit at Welcome To 1979 in November.

I haven’t finished the build yet, so I can’t give a complete review of the mic, but I can make some comments about the kit and the resources that come with it. Building a ribbon mic is not that complex- IN THEORY. It’s just a thin metal ribbon suspended between two magnets. There isn’t much electronic inside the mic, just a transformer. The design has been around since the 30’s.

The theory is simple. But like most things, it’s the Devil in the details. You can find articles and instruction on the web for free. And that’s what I started to do years ago. I got halfway through the project and shelved it… there wasn’t enough detail for me to be successful.

Or you can spend some money and increase your chances. Rick sells plans for ten bucks, or his ribbon kit for $275 with a Cinemag transformer. (There is a less expensive version with a stock transformer, and I understand the stock transformer is exceptionally high quality. It’s sold out right now, but should be available again shortly) Rick sent me a kit with a Cinemag transformer, so that’s the version I’m reviewing here.

The kit itself is extremely well done. The mic tube is powder coated brass, 1 1/2″ diameter, and exactly machined. All the holes are already drilled, so you don’t need a drill press. The motor frame (a critical part) is a machined piece of plastic. The fit was perfect. I especially liked his design… I designed my own once, and it was a cumbersome mess. Ricks is elegant, simple, strong, and works well. (some folks claim that metal frames are superior. Perhaps they are… I’m not sure… but I think that at least part of the reason behind this claim is that’s what is available from China.)

The greatest value for me, though, is Rick’s instructional materials. When you buy a kit (or his plans), he sends you a link where you can download  PDF instruction manual and several videos where he goes through the process of building a mic. These videos are really helpful, especially when it comes to corrugating and installing the ribbon.

Commercial mics use ribbons that are anywhere from 5 microns to 1.8 microns thick. The ribbon material that Rick supplies is about 0.8 microns. (Thinner ribbons increase high-freq sensitivity.) This is similar to “imitation silver” guilding leaf, it’s readily available on the internet. I’ve bought some from Hobby Lobby before and tried to cut a ribbon from it. I can say without hesitation that it ain’t easy. But that’s the beauty of these videos. Once you see someone doing it, you understand the method better… much better than just reading about it. And you can see that it is possible to make a well-functioning ribbon from scratch, but understand that it’ll take some practice. Even breathing can cause a cut ribbon to fly off your bench. So be ready to make several practice ribbons before you get one correctly made and mounted in your mic frame. And if you just can’t get it, there is an internet source for commercial ribbon foil now. A company called Lebow sells pure aluminum foil in a variety of thicknesses, including 1.8 and 2.5 microns. This would be vastly easier to handle, but it’s also vastly more expensive at $25/sheet. (There may be other sources as well, but this was the only one that I could find. I ordered two sheets to use in my own mics, but they aren’t in yet.)

Ribbon-making details is a big advantage of his instructions, but it isn’t the only one. For example, I learned that you can use a brass footrail cap on the bottom of your mic to hold the XLR connector. These things are nice, solid castings, and if you shop around, you can find them at about $5 apiece. (I wish I’d thought of that.) Circular Switchcraft connectors fit well in these caps.  This would be a good solution for any tubular-bodied homebuilt mic.

The videos do have a slight downside. You have to remember that Rick has built a lot of mics, so some of the things he does in the videos look easier than they will be to folks like you or I. It’s really difficult to explain the things that practice teaches you. But I’m pretty sure that I’ll have a working ribbon mic once the dust settles… I’ll keep you posted.

UPDATE: I finally got up the nerve to install the ribbon today. It worked on the second try, which really isn’t bad. I’m pretty sure that my success with this is pretty much due to Rick’s instruction. Like I said previously, I’ve tried this before and failed miserably. Seeing it done (in a video) makes all the difference.

A just-placed ribbon in the motor frame. This job requires lots of patience, but it can be done.

That is not to say, however, that it was easy. The foil is the definition of flimsy… if it were any thinner I think it’d fly off my bench because of the rotation of the earth. Using the more expensive 2.5 micron foil should be easier (though I expect still no picnic), and that’s what I’m planning for my own ribbon motor frames. (I figured this one should be made as a stock kit, in order to give a fair review.) There will be some slight differences, like slightly thicker magnets… I’m still in the design and prototype phase. But if they work, it’ll be fun to try some design variations like waffle plates (resonators) and silks.

More Mic Mods- the ADK SC-2

Because of my posts about modifying microphones, I recently received an invitation to visit a proper mic designer. Les Watts is an engineer who worked  for some VERY prominent microphone companies… I’m fairly certain that at least one of them is in your locker right now.

Les lives about a three-hour drive from me, so I went by for a short visit recently. It was, of course, extremely educational. I brought along a pair of mics that I had doctored, and we tested them using his calibrated setup.

The ADK SC-2 small-diaphragm condenser microphone. The stock mic is on top, the modified capsule is shown on the bottom.

One of the things that I learned… or rather confirmed… on my trip is that real microphone design is a very slippery fish. A microphone is a true “complex system…” one small change affects a whole host of other factors. The mod that I did (not so much a design as a “I-wonder-what-will-happen-if-I-do-this” sort of affair) was to cut away the area in front of the mic diaphragm, leaving the area more open and less restricted by the grille and metal in front of the diaphragm. It turns out that the “cup” shape that is created by the area that I cut away forms a high-frequency resonator, which I’ve essentially removed. Sometimes this  is a good thing, sometimes not.

The ADK capsule shell disassembled for modification. As you can see, a small-diaphragm capsule is a fairly simple affair with just a few parts. An important part that you can’t see is the spacer ring that lies between the diaphragm and the backplate. It’s a simple washer made from thin mylar film that looks much like diaphragm material… about 6 microns thick.

Assembling the modified SC-2 capsule. Any dust trapped between the diaphragm and backplate will ruin the capsule. It took a few tries.

Consider the following two mic capsules. These are for some ADK SC-2 small-diaphragm condensers that I have. I had an extra pair of dead capsules, so I figured I could play around with these without much risk. (I did get them working again) The only change was removing the cage at the front of the diaphragm, lowering the height of the sides to about 2mm, giving the edges a gentle radius, and using a finer brass screen in front.

I did a quick recording of both modified and unmodified capsules. On guitar, I really couldn’t tell much difference at all. But Les’ test rig tells a different story. Take a look at the following response curves:

First off, you should ignore the huge rise below 200 Hz, which is due to proximity effect of the test setup. What I found interesting was the rise in response of the stock capsule centered around 8kHz. Les told me this is a pretty typical Chinese mic response. Looking at the lower of the two curves, we see that modifying the headshell does even out this rise, and gets us a slightly extended high end response…  but it also introduces a pretty deep notch at around 6kHz. This notch is present in the unmodified capsule too, but to a lesser degree. This could be why the capsule shell was designed the way it was.

Another take-home lesson from my trip is the need for a better testing setup at my studio. Remember, on guitar I could make out very little difference in the two mics. (I don’t have golden ears, but I have done a lot of listening.) Perhaps another recording of something with more transients, like a snare, might be more revealing. Again, according to Les, notches in a response of this sort are very difficult for the average person to identify in listening tests. What I could really use is a setup that’s similar to his.

Les uses ARTA software, which is available as a download. His calibration mic is an extremely expensive calibrated B&K, and his loudspeaker (for generating the test tones) is custom-built. It might be possible to get a similar setup at my studio using some equipment that I already have. It won’t have the accuracy that Les’ system does, but I believe I can get something put together that will show the relative changes of a modified vs unmodified capsule. I’ll need a few things, like a Windows computer… I’ve been a Mac guy for many, many years. (Our first Mac II at the recording studio gave us a HUGE advantage, enabling us to design several cassette and CD releases in-house. Back then, graphics ability was a big deal that only Mac folks could do… nowadays, not so much!)

So I’m currently on the hunt for another inexpensive computer (this will be #4) that I can use with ARTA as a dedicated test machine. My son’s old Dell doesn’t seem to want to generate any video, but I may yet be able to get that one going. If not, it’s off to the thrift store for some computer shopping.

I’ll also need a calibration mic and a speaker. The mic might not be too bad, and I may be able to borrow or beg this one. The speaker will be a little harder, though I do have a pair of KRK5s that might at least get me started.

Lots more to come… stay tuned!

Small diaphragm Condenser Modification Results

Last week I sent the small-diaphragm condenser mics from the post below to a friend in Nashville, John Billings. John’s been working in Nashville for years as a session bass player, and  has a very nice studio. I only wanted his general impression, but he went the extra mile and set up a quick A/B test during a recent session. Here’s what he had to say:

First off WOW, thanks for some toys to play with! Here’s what I’ve got so far:Did a session the other day. One song was just these mics out in the room, capsules aligned and secured. You can hear a distict but subtle difference. The mod is much smoother, whereas the stock mic seems to have a significant rise. The other song was a drum corp type of thing, just snare rudaments. Mics placed a few inches over the head, inch or two inside the hoop. I much prefer the mod, though if you need something hyped for top end, the stock mic might be the better one to go to. The mod is smoother, not brassy. Preamps were Yamaha, very neutral. No compression, straight to my SSL AD, 44k 24bit.

The snare mic setup at John’s studio. John Billings photo

I’ve been meaning to upgrade my WordPress account for quite awhile now, but John’s efforts gave me the final push. Now I can post these files here so you can hear the results and judge for yourself. First, the snare drum solo using the stock, unmodified CM90:

drum corp- Snare 1 N Stock

And next is the modified mic:

drum corp – Snare 1 N Mod

Now the same two mics placed further back as a room mic on a full drum kit. Again the stock mic is the first sample:

Drums Room Nady STOCK

And now the modified mic:

Drums Room Nady MOD

John’s studio is equipped with Genelec monitors, so he’s able to hear things very accurately. I listened to these samples on the best headphones that I have, a pair of  AKG 271s, and on my KRK Rokit 6 studio monitors as well. I noticed a slight drop in level on the modified track, and raising this a touch in Mixbus gives more closely-matched tracks in terms of level. (As you probably know, you’ve got to have levels very close when doing A/B comparisons. In blind tests, people always select a source that’s slightly louder as the better track. )

I tend to agree with John. I’m hearing an overall improvement in freq range, with a touch less upper-midrange and an increase in overall smoothness. It’s a subtle improvement… but when comparing them side-by-side, it’s noticeable.

But something that I always find surprising is the fact that really, these mics aren’t all that horrible right out of the box. I’m showing my age here, but in my studio days you couldn’t even approach this kind of signal for less than three or four C-notes. Sure, the quality control isn’t there… for example, the tiny screws that hold the mic body in place are chewed up and look like they were forced together at the factory… but I can’t really complain given the list price.

In order to make some proper mic comparisons, I’m going to have to buy a proper reference mic, so I’m currently selling some excess gear to buy a Neumann KM184. I’d rather have a vintage KM84, but they’re just much for my current budget to bear…maybe someday. And I’m also on the hunt for an affordable BV107 (or perhaps a suitable equivalent) mic transformer… I want to experiment with a transformer-balanced version of the above mod.