Wunder Audio CM7 – The Tape Op Review

TapeOp Issue #59/May, 2007 | by

When Wunder Audio owner and CM7 creator Mike Castoro was asked to describe his mic, he said it was similar to a Neumann U 47 but better. I would agree. The Wunder Audio CM7 is the best vocal mic I’ve ever sung through in my life. Period. And the “better” part is in the sound, especially at the high end of the spectrum, with air and clarity that’s missing from the original U 47. Oh, and please don’t confuse this crystalline high end with the annoyingly bright 3–5 kHz bump you hear so much on cheaper tube mics. I’ve listened to both, and the difference is huge.

I preferred the CM7 on both guitar and voice

My first tests were done at Wunder’s own Stardog Studio using my Collings D1A and my own smoky vocals on a song I’ve sung and played a thousand times. We did a shootout between the CM7 and one of Castoro’s select U 47s. He had seven of his elderly beauties ready for us, culled from nearly 150 U 47s he had bought and sold over the years as a vintage mic dealer. We tried a few U 47s and then selected the one we thought sounded best for my vocals and ran it alongside the CM7. It was undeniable; I preferred the CM7 on both guitar and voice, in both omni and cardioid modes. Later in the week, I blindly re-listened to the CD of that session and again picked out the CM7 as having the sweetest sound.

It’s the best vocal mic I’ve ever sung through, period. Did I mention that yet?

A few weeks later, Castoro agreed to bring his CM7 to 5 a.m. Studios in downtown Austin for yet another shootout. This time, his CM7 would compete against some worthy adversaries: Pearlman TM 1; ØDE NTV; Soundelux U99 and U95s; Mojave Audio MA-200; and a vintage Neumann CMV 563 with the lollipop capsule. (For some reason never fully explained, Castoro did not bring one of his vintage U 47s to the shootout.) The test was done using two vocals: my lower-toned Jim Morrison–ish vox, and Steve Hudson’s higher-toned, John Fogarty–ish pipes. Only the ØDE NTV sounded truly bad to my ears, and unfortunately, I owned that mic. The others held their own, but the Neumann CMV 563 and the Wunder CM7 stood above the rest. Some at the shootout preferred the Neumann, but I absolutely preferred the CM7 on both my voice and Hudson’s. It’s the best vocal mic I’ve ever sung through, period. Did I mention that yet?

Castoro says there are three primary elements used to create the U 47–plus sound: the capsule, the transformer, and the tube… in that order. With the capsule, Wunder is shooting for a copy of what Castoro calls the “Berlin” M 7, as opposed to the Gefell M 7 capsule. The Berlin M 7 is machined differently from the Gefell, with three isolator rims instead of two. The 1'' diaphragm is glued on with precise tension to a very thin rim, much the way skins are stretched over a snare drum. The rims are milled onto a piece of brass that contains 90 holes per side and then super polished in a process called lapping. Unlike the original M 7s, which were 8-10 microns thick and made of PVC, the Wunder M7 is made of a six-micron Mylar substrate because it ages better. If authenticity is a must, PVC capsules are available upon request at a higher price. You can also get the capsules set at different biases, with one emphasizing the high-end tones, another emphasizing the low end.

The second key to the CM7 sound is the larger transformer based on the one used in the earlier Telefunken U 47 design, the so-called “large badge” U 47. Wound old-school style on vintage tool machines, these transformers allow for more saturation and a bigger low end, rolling off at 20 Hz instead of 40.

Finally, the third component is the tube. Yes, Wunder can make a microphone with the famous VF14 tube, but it’ll cost one arm and leg more to buy. Fortunately, the lower-priced EF14 tube comes standard and owner Castoro calls it the “savior of the mic.” The interior tooling in the EF14 is identical to the VF14, but the difference lies in how the filament wire is attached. To make the EF14 behave like the VF14, a capacitor and resistor — called a “dummy load” — is added to the back of the tube socket.

Although the capsule, the transformer, and the tube are the most important elements to the sound, there are other factors. The U 47’s unique grille provides a 1.5 dB boost at 5 kHz for presence but then a cut at 8 kHz to mitigate sibilance. Another 1 dB at 10 kHz allows for air, while a roll-off at 11 kHz prevents brittleness. Castoro says the grille design gives the U 47 its legendary aggressive sound and a natural EQ, so they’ve gone to great pains to ensure the grille is an exact replica of the original. But some improvements in the mic’s sound are due to innovations in the original design. For example, Wunder uses no PVC in the wiring, since wires sheathed with PVC tend to deteriorate and crack over time. Also, the mic uses high-end, metalized polypropylene capacitors instead of the now crumbling ones used when the U 47 was originally made. And although it has nothing to do with the sound, the power supply used for the CM7 features better wiring overall and a voltage regulator that wasn’t available in the original.

The entire package includes the CM7 in an oak box, a shockmount, the power supply, and an original, large Tuchel-connected mic cable. For those who can’t spend $5K+ on a microphone, Wunder will be coming out with a GT version of the CM7 priced under $3000. It will still have the signature Wunder large-style transformer and the U 47 look and feel, but the capsule will be a K47 (M7 available as an upgrade), the tube will be the Telefunken glass tube (hence the name GT) and other historical details adhered to in the CM7 will be adjusted in the GT version to keep costs down. And just in case you forgot how this review opened, let me remind you one more time; the CM7 is the best vocal mic I’ve ever sung through. Ever. ($5495 MSRP; Wunder Audio)

Read more about the Wunder Audio CM7 tube mic.

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