Advanced Audio: CM 48T Large-Diaphragm Tube Mic

It seems like the market has never been more saturated with various types of new recording equipment attempting to emulate vintage gear. Vintage microphone recreations are hot right now — especially modern takes on the Neumann U 47. Not true clones, but adaptations. Really, adaptations are the only possibilities these days, rather than clones. Why? The original VF 14 metal-cased vacuum tube has not been in production since 1960. This is the tube that the original U 47 circuit was designed around. So, since then, alternatives and compromises have been developed. None of them are absolutely true to the sonic character of an original U 47 with an original VF 14 tube. Additionally, let me reiterate (from my previous Advanced Audio microphone reviews) that Dave Thomas of Advanced Audio does not claim to make clones. He does, however, make microphones that, in my experience, respond in the sonic direction of the mic being emulated. They not only perform well, but exceptionally well, considering the price. With all of that aside, what mic am I talking about today? Well, not a U 47. Rather, a U 48, or in Advanced Audio terms, the CM 48T. So, what’s a U 48? In the original Neumann version, the U 47 had only cardioid and omni patterns. They later developed the U 48 to add a figure-8 pattern. In fact, most U 47s that we think we see in old films of Abbey Road Studios (EMI Studios) were actually U 48s that had been modded from their U 47 beginnings.

So, this is where the Neumann designations and the Advanced Audio designations deviate a bit. Advanced Audio makes the previously reviewed CM 47 [Tape Op #71], which in my opinion, is a fantastic mic. Unlike the original Neumann U 47, the Advanced Audio CM 47 comes with a nine-position polar-pattern selector that includes figure-8. So then, why make the CM 48T? It is a similar mic, but specifically designed to be offered at a lower price point. While the CM 47 lists at $735, the CM 48T has a price of $595. That is a reasonable savings. This is accomplished, first of all, by using a mic body that is already in use with a few of his other mics. Second, the pattern selection has been changed from a nine-position rotary switch on the power supply, to a three-position switch on the mic body itself, saving some cost in parts and assembly. This does mean, however, that you have just the three patterns (cardioid, omni, figure-8) without the flexibility of “in between” settings such as wide cardioid. Next, the tube has been changed from the 6072A tube (in the CM 47) to a capable and lower-cost GE/JAN 5654W subminiature 7-pin tube. Since the original VF 14 has long since been impossible to obtain, tube choice will always be a deviation from the vintage original. Dave feels that he can get very acceptable performance out of the 5654W in comparison to a VF 14. Also, the CM 48T uses a different capsule and transformer from the CM 47. Ironically, this lower-cost version adds a −10 dB pad and a high-pass filter that the more expensive CM 47 lacks, and the capsule is the one used in the even more expensive CM 47VE! The mic comes with a briefcase, shockmount, power supply, and 7-pin cable like all Advanced Audio tube mics do.

This review is going to be a little bit different in how I evaluate this mic. I’m actually going to be comparing it directly to the higher-priced Advanced Audio CM 47. In my review of that mic, I already established that the CM 47 sounds fantastic, and it compared very well to the much more expensive Wunder Audio CM7 [Tape Op #59]. Now we will see how the lower-cost CM 48T compares to that.

Everything I’ve tried from Advanced Audio is very balanced in its sonic character. Depending upon the mic model, there are certainly appropriate tonal differences, but never a feeling of excessive non-linearity or overly hyped high end. The same is certainly true for the CM 48T, although its sonic signature was not identical to the CM 47 (at least in the case of the review mics I was using).

I used both the CM 47 and CM 48T on several sessions, on a variety of instruments, for comparison. In most cases, there was a slight character difference that seemed to be fairly consistent regardless of the source. I tracked a live studio session that required a reed player to continually switch between flute, clarinet, and alto sax multiple times, even during the same song. Tracking with a Rupert Neve Designs Portico 517 preamp [Tape Op #90], both mics did a great job capturing the constantly changing instruments. There was a slight difference in the contour of the mid to high frequency response. The CM 47 displayed a slight rise in the higher, airier frequencies, while the CM 48T had a presence boost that seemed a bit lower, more in the upper midrange area. Depending upon the instrument, I had a slight difference in preference. The CM 48T faired a bit better on the flute, while the inherent aggressiveness of the sax’s sonic character worked slightly better on the CM 47, since it has a bit smoother upper mids. Let me say again, this is a slight difference. With the smallest amount of EQ, either mic would do a fabulous job. Again, while very close, to me the CM 48T slightly won out on clarinet. I thought it captured the body of the lower midrange a bit more favorably than the CM 47. This is likely due to the small increase in proximity effect from the capsule in the CM 48T as compared to the CM 47. Both mics displayed terrific headroom without a hint of distortion, even when met with sudden dynamic transients.

My findings stayed pretty consistent when recording other instruments. When placed about a foot away from a screamin’ ‘57 Bassman amp, the overdriven electric guitar was again captured wonderfully, without any signs of overload. Again, the CM 48T showed a slight contour towards the upper mids, while the CM 47 had a presence peak at a slightly higher frequency. Both mics were great, but had slightly different responses. Without EQ in this instance, the CM 48T was awesome on clean electric, while the CM 47 smoothed out a somewhat harsh overdriven rhythm track.

I love Advanced Audio mics on vocals. Vocals can be tricky. The mic has to be able to capture a very wide dynamic range without any distortion. Our brains are very good at picking up on anomalies in the human voice. The CM 48T handled a whisper to a scream quite well. The presence peak and proximity effect meant that little or no EQ was required, depending, of course, on the type of voice. The addition of the −10 dB pad and the high-pass filter makes this mic virtually bulletproof for vocal recording. For most singers, I found the CM 48T to be almost more forgiving of sibilance than the CM 47, partially due to the slight response difference. In recording a delicate female jazz vocal, I slightly preferred the CM 47 due to the somewhat airier top end, but again, the mics were really close.

Everything else followed this pattern. Acoustic piano was captured with great nuance. Depending upon the piano, the upper midrange presence of the CM 48T could be a good or a bad thing. In my case, I was recording a somewhat dark Steinway, and the response lift helped out the character of the instrument. An overly bright piano might not be the best fit for this mic.

In all cases, the CM 48T performed very well. When using Advanced Audio mics, I never think that I’m compromising, just because the mic is affordable. I have access to some seriously expensive mics, and often choose the Advanced Audio versions anyway because they just sound great. $595 buys you an excellent-sounding large-diaphragm tube mic with a custom-wound output transformer, great build quality, and a sturdy briefcase that holds the power supply, cable, and shockmount, as well as the mic. You get solid performance that rivals mics with a much higher price tag. You get the same capsule as the much more expensive CM 47VE. You get the addition of a high-pass filter and a −10 dB pad. And you get a mic that has a sonic character that is in the direction of a vintage U 47. Not a clone, but a great mic at an amazing price.