Crawls Backward (When Alarmed)

IconProjects, musings about guitar builds, guitar repairs, vintage tube amplifiers, old radios, travel, home renovation, and other stuff.

Apex 210 Ribbon Microphone Mods and Upgrades, Pt. 1

In recent years, there has been a resurgence of ribbon microphones for studio recording. Ribbons sound smooth and natural, and were commonplace during the golden age of radio in the 1930s through 1940s. Their high frequency response was not always great, but in a radio medium where 5kHz was the high end, ribbons were king.

But the development of dynamic and condenser microphones and a demand for higher fidelity quickly made ribbons a thing of the past. Ribbons are fragile, and generally bulky, making them hard to work with for remote recording, unlike a dynamic. And their frequency response isn't as great as a condenser.

However, with the development of powerful neodymium magnets for improved performance, there has been a glut of inexpensive Chinese-made ribbons on the market - as well as some fantastic high end models as well.

As you might expect, there are also a number of popular modifications for the cheaper mics - and the results are dramatic.

Which brings me to this post.

On the left you see my recently acquired Apex 210 ribbon mic. Apex offers a full line of inexpensive condensers as well as this ribbon. For a measly $80, I took the plunge and snagged one to play with.

Out of the box, it's not bad at all. Very smooth, a bit boomy, and a little closed-up sounding. But it would work reasonably well on vocals or acoustic guitar.

A ribbon mic is a very simple device - there's just a ribbon motor, consisting of the thin ribbon (foil) and two magnets, and an output transformer

It follows that the two most common mods for these mics are upgrading the ribbon, and upgrading the output transformer. I did both.

The ribbons in these mics are made of a thicker, less-than-optimum foil - generally about 4.5 microns thick. An improvement in sensitivity and frequency response can be had with a thinner ribbon - 2.5 microns or less.

Aside from the ribbon, the only other part in a ribbon mic is the output transformer. The voltage output from the ribbon motor is extremely low - as in microvolts - and the transformer steps this voltage up so it can be used with a preamp or console. A higher quality transformer will pay big dividends in terms of frequency response as well.

So let's get started!

First we need to remove the yoke from the microphone body. Just undo the two thumb screws and the yoke comes off.

This mic really resembles a classic RCA 44-BX, doesn't it? I'm not crazy about the blue body, but I love the shape and that huge headbasket.

Remove the three screws holding the headbasket to the body.

Then we remove the two 11mm yoke bolts that hold the mic chassis to the headbasket.

Slide the headbasket off and expose the whole chassis.

The ribbon is mounted under that mesh wind screen. We need to take the screen off to access the ribbon, and in the interest of higher fidelity, we won't be putting the screen back on.

The silver can houses the output transformer.
Two 5mm nuts hold the screen on one side of the ribbon.

Now one side of the ribbon motor is exposed.

There are two threaded rods on the other side holding the mesh on.

Now the ribbon motor assembly is freed from the main chassis.

Make a note or diagram or take a photo of the wiring on the little board on the back of the transformer can and then desolder the connections.

As it turns out, the red wires from the ribbon are the negative side, and the blue wire is positive. This will be important to know when we connect the new transformer.

Unsolder the microphone cable leads as well - you can check which connection is which against the XLR plug. Pin 2 is hot, Pin 3 is cold, and Pin 1 (the most obvious) is ground.

Really simple compared to the Oktavas I just worked on.

A couple of things to note on the ribbon.

First, it's not corrugated! Corrugations on the ribbon smooth out the frequency response. Amazingly enough, this one is smooth.

Second, it's visibly sagging - see the points at the blue arrows. I had read online that about 50 percent of these mics have ribbons that sag - this affects frequency response in a big way. Tension of the ribbon is critical to its performance.

Third, the plating on the magnets is peeling off and its touching the ribbon - see the white arrow.

None of this is good for performance.

Since we're going to make a new ribbon (!), let's take the old one off. There are bars at each end that hold the ribbon down - remove the two nuts on each.

I believe these are 3mm nuts, but I don't have a wrench or a socket that small - a 5/32 socket will work.

Here's the motor with the ribbon removed. Note the plating peeling off - I scraped as much off as possible, leaving the uncoated magnets.

Next we'll make a new ribbon and install a new transformer.

 
 
 
 

Post a Comment 0 comments:

Post a Comment