Microphone Mod: Carvin’s CTM100 via Microphone-Parts.com

Carvin CTM100 Tube Mic

“Like butter in a black silk cocktail dress.”

I have been interested in microphone modification for years and I went so far as to purchase a Oktava-Mod mic and modification a few years back. While Michael Joly’s mod did sound great, I wasn’t satisfied because I hadn’t done the work myself. I have been short a tube microphone so I decided to get a cheap Chinese mic and put some time and effort into improving the sound.

I ended up getting a Carvin CTM100 tube microphone which is actually the same mic as the Apex 460. At the time of this post the mic is selling for $179 + $12 shipping, which is quite a bargain. The package comes with a large plastic foam lined case, a mic bag, a decent shock mount, a multipin XLR and a power supply. Out of the box the mic didn’t sound bad actually. Certainly better than I was expected for $200. Some high frequency boost made the mic sound sibilant and too bright. While the high frequency boost gave the impression of detail, the mid range wasn’t terribly clear. The was a pronounced proximity effect similar to most large diameter cardioids, but a little boomier than normal. I was thinking that the boost was more in the low mids than in the bass frequencies.

The modification kit that I bought was from Microphone-Parts.com. I chose the Apex 460 Mod Kit (not the SG version) and for a new capsule, I chose the RK7 which is a darker, more-colored U-47 style capsule. I like my mics darker. Most people choose the RK-12 which is based on AKG’s CK-12 which is much brighter and airy.

The kit including the new capsule is only $209, which seems like a great deal. The service at Microphone-Parts was great. Email questions were responded to quickly and completely. When I placed my order I received a bunch of updates and then the kit arrived in maybe 2 days tops. I was really impressed.

Everything was in order and the mod came with a really nice full-color booklet with directions. The directions are probably the best part of the mod kit. They are clear, specific, they have great suggestions and great advice. There are detailed instructions for desoldering and for how to properly use a solder-sucker pump. There were no weird tools required. A precision screwdriver (size 0 Phillips) was the most exotic tools required, but there are included in every $3 jewelers screwdriver kit. In the directions, emphasis is made on cleaning the flux off the board and connections afterwards which I admit I rarely do for cables or patchbay soldering. Still I had the solvent and QTips.

There are links on the website and in the text that point you to helpful videos and suggestions for tools and supplies to buy. I was able to do the complete mod and test in a leisurely morning. I was careful and I read the directions several times. I was fortunate to not have any missteps along the way and the mic sounds great!

All of the high frequency yuck is gone, the response seems very smooth and very detailed. The upper mid range is accurate and flattering for my voice and gave it the quality of a late 70’s radio personality mic, but with more detail and depth. A former professor of mine, Dr. William Moylan, was always very adamant about using objective, descriptive and accurate language to describe sound and timbre. Unfortunately, the word that seems the most descriptive to me is ‘silky.’ There is a slight bump around 4k and a slight dip at 8-9k. There seems to be a very slight natural compression to the microphone now. Before the mod, transient detail seemed too obvious, maybe even expanded. By constant the microphone seems to have a bit of natural compression. This might be due to the tube or to the slightly thicker and slower moving membrane. The RK7 is a 6 micron. I can’t say that I know for sure what the original in the CTM100 is. I did take some photos of the original diaphragm to compare it to the new one:

Original CTM100 Capsule

This is the original CTM100 capsule and diaphragm. You can easily see that the diaphragm is NOT flat.

Original CTM100 Capsule

In this angle of the original capsule you can see how much dust is on the surface of the diaphragm. This is a brand new mic, so I am pretty sure that the dust is from the manufacturing process.

Effectively all the sibilant frequencies were diminished to the point that I wouldn’t think about reaching for a de-esser. The proximity response seems more gradual and nuanced. The effect could be easily controlled for some reason and there seemed to be more gradations in the boost compared to distance. Overall, I think that the modded microphone sounds fantastic. It will certainly replace my other vocal mics for my own voice and I suspect that I will reach for this mic when I need to tone down an overly bright female or a sibilant/whistle-prone male vocal.


5 Responses to “Microphone Mod: Carvin’s CTM100 via Microphone-Parts.com”

  1. matt Says:

    where did u order the mike from ?


  2. admin Says:

    I ordered it from Carvin.

  3. Brian Says:

    Hello Modder,

    I am looking at this same mod but I am undecided at which capsule to get with the kit. I want the warmest capsule that would not be described as dark but warm and thick. Its for a female vocalist with an alto voice that can get alittle then in its upper register. Would you recommend the RK7, or the more neutral RK47?


  4. admin Says:

    I would go for the RK47. If the vocalist is quiet I would suggest a FET mic. I have found that this mood tube mic is too noisy for really quiet sources. HDGXIX

  5. Brian Says:

    Thanks for the quick response. It there a FET mic and mod that you have experience that my work good for this application?

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