st55 mic kit

Coal to Diamond: Revamping a Sterling Audio ST55 into my new Go-To Mic

In my feed on Reverb.com I have several watches set up that alert me when certain items become available at a certain price. One of those watches was for a Sterling Audio ST55 Microphone for less than $80. One day, I had an email from reverb saying I had new items in my feed. And within a week, I had my latest microphone donor body for a rebuild.

I was particularly interested in rebuilding an ST55 because:

  • It has a Transformer Output
  • It has Low Cut and Pad Switches

The mic sat unused on my bench for a month or so until I got around to ordering the Microphone Parts.com T84-55 kit and transformer for it. I also ordered an RK47 Capsule.

To Paint or Not

So far, I’ve given all my modded microphones a common look: basically repainted the bodies with Rustoleum Spruce Green paint. The Sterling body is a little fancier than the MXL bodies I’ve been dealing with. The logo is engraved and there is a badge attached to it with a tiny mounting hole in the cylinder. Ultimately, I decided to go for it and refinish it. Because of the engraving, I would need some “bondo” to make the surface smooth.

st55 with bodo
The ST55 body with engraving and badge hole bondo-filled and sanded

Rebuilding the Mic

The ST55 is mechanically a very well constructed microphone. The cylinder has a good weight to it and the internal metal framework and capsule base is very sturdy. The first step is to gut all the serling parts so you have an empty shell to start with

st55 mic kit
The new mic-parts circuit board done (left) and the donor mic ready to gut
gutted sterlng st55
The Sterling Electronics and Transformer removed and I only stabbed myself in the thumb once!
sterling st55
New Electronics and Transformer. Still with original Sterling Capsule

Mechanical Difficulty

The one known issue with this particular microphone body is that a standard 35mm capsule does not quite fit through the opening to the headbasket. It requires a little grinding of the opening. I Tried a few different methods and finally found that a round grinding bit in my hand drill worked pretty well.

st55 headbasket
Two notches ground out of the headbasket opening so that the new capsule will fit through
st55 new guts
new Electronics, Capsule and Transformer. Ready for testing and final assembly

Final Assembly

While all this electronics stuff was going on, two coats of paint were drying on the body cylinder. I plugged it in and watched for smoke (none found) and proceeded to do final assembly and testing. Unlike other kits I have built by mic-parts.com there is no calibration step for this mic to adjust the capsule voltage.

The only thing I wish I did different was to NOT re-use any of the Sterling Capsule Pedestal. The instructions say to use the saddle from the new capsule screwed into the Sterling base, but that really doesn’t work so well. For one thing, there is nothing to lock the capsule in a perpendicular position to the axis of the mic. You just eyeball it and crank the screw down as hard as you can (I put blue locktite on all fasteners in these kits too). In my case, the other suboptimal thing is that the capsule actually “leans back” a bit in the mount. What I should have done I think, is to remove the whole capsule base plate assembly and drill a new mounting hole so that I could use the entire micparts.com shockmounting base and saddle assembly. If I did that, that whole white piece would be gone and the saddle would be sitting on a stiff rubber shockmount.

st55 mod finished
The finished Mic with Spruce green Body and awesome new guts

Happy Family

Below are my current array of DIY mics. Left to right are:

  • Matched Pair of MXL990s with micparts.com electronics and matched RK12 (akg-ish) Capsules
  • MXL910 with micparts.com electronics and Michael Joly’s K47 Capsule
  • Sterling Audio ST55 with micparts.com Electronics, Transformer and RK47 Capsule

diy mics

How Does It Sound?

After all that work, you don’t expect me to say it sounds awful do you? Actually it sounds wonderful. The RK47 capsule is well documented as a very very close approximation of the Neumann K47 Capsule. It has the character for sure. The Mic-parts transformer is about middle of the road in terms of harmonic distortion. There are cleaner and dirtier choices I could have gone with. I think it’s perfect. Just a nice amount of zing from those harmonics without the mic being overly bright or harsh. The Pad and Low Cut filter make this mic more versatile. It does not have a polar switch so it is always Cardioid pattern but as an up-close vocal mic, this is how it would be set all the time anyway.

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