Carvin CTM100 Mods
The Carvin CTM100 is a clone of the Apex 460; like the 460, it is a wonderful platform for DIY modification. We have several mod options for this mic -- enough to transform the mic into a virtual AKG C12 clone.
#1: Capsule Replacement
The stock capsule in the CTM100 is an undersized K67 type, just as is found in nearly every inexpensive large-diaphragm condenser. Quality varies from one to the next, but all of them sound peaky and bright. This capsule is the biggest problem with the CTM100 -- or, said another way, the best and most effective mod for this mic is to replace this capsule.
Our best-selling replacement capsule for LDC tube mic mods is the RK-12, which is our version of the capsule in the vintage AKG C12 and Telefunken ElaM 251. It will make your mic sound bigger and more present, and will present fewer sonic anomalies at mix time due to its smoother frequency response.
Another great choice is our RK-47, which gives the mic a U47-ish vibe.
Click to see all of our large-diaphragm microphone capsule choices.
#2: Grille / Headbasket Replacement
Our C12-style grille for the CTM100 looks great and sounds great too; the 2-layer mesh is more acoustically transparent than the stock 3-layer tight-weave mesh.
#3: Circuit Replacement
We make two distinct circuit replacements for the Carvin CTM100. Both offer user-controllable high-frequency EQ, so that you can adjust the high frequency response at build time. Both include custom circuit boards, best-in-class components, and custom transformers.
The Fox 460 circuit mod kit is a cathode follower design; it offers low noise and high output. The transformer is a custom-wound 6.5:1 ratio. We have sold hundreds of these kits, with many positive reviews.
The new V-251 circuit kit is a single-stage triode design, more closely modeled on the original Telefunken ElaM 251. It uses a US-made T/14 transformer (11.5:1 ratio). It has approximately 6dB lower output than the Fox 460 circuit, but at least 6dB more headroom. It also offers an internal high-pass filter switch, and your choice of HPF behavior (rumble filter vs. high pass).
Both circuits offer excellent performance. When combined with our RK-series capsules, both will allow your CTM-100 to compete with, if not beat, commercial tube microphones in the $1500-$2500 range.
The Fox 460 has higher output, which means you'll have less preamp noise in your vocal tracks. It benefits from 3 years' worth of refinements and hundreds of customer installations. The V-251 has more headroom, switchable HPF, socketed high-frequency EQ cap, is easier to build, and has a nicer output capacitor, but it costs more, and it needs more preamp gain on quiet sources.
Both these circuits will significantly outperform "capacitor swap" and "tube swap" and "transformer swap" DIY upgrades. Only by designing the entire circuit, end to end, can the performance of any microphone be truly optimized.
#4: Case Upgrade
Have the latches broken on your CTM100's cheap plastic suitcase? Or maybe you're just tired of the fact that you can't stand it up without it falling over?
We've commissioned a short production run of custom suitcases for the Carvin CTM-100 and similar mics. These are made of aluminum, with locking latches, and CNC-milled internal foam. The case is more durable than the stock design, and provides better protection for your tube microphone.