Schoeps CMT-36
A transformerless pencil condenser that reviewers found so flat they kept turning around to see who was talking.
Overview
The CMT-36 is the odd one out in the Schoeps small-diaphragm condenser family. It's a side-address pencil microphone that takes its polar pattern from a twisting cap rather than a switch, and it runs its FET straight into a pair of p-n-p transistors instead of an output transformer. That last detail is the whole point of the model. The companion CMT-56 kept a single FET feeding the primary of an output transformer through an electrolytic decoupling capacitor. The CMT-36 deletes the transformer entirely. The FET drain drives one base through a capacitor, the FET source drives the other, and the two emitters carry the balanced output legs. The source load isn't capacitively decoupled, so current feedback in the amplifier keeps intermodulation distortion down. It's a genuinely different circuit, not a cost-reduced one.
The mechanical pattern selection is the other thing that separates it from the double-diaphragm variable-pattern crowd. Cardioid, omni, and figure-of-eight are obtained by twisting the mic cap, which clicks into a detent for each pattern. There's no polarization switching and no voltage on a backplate. It's a side-shot design, picking up from the sides rather than the top, and it's roughly the size of a Calrec CM1050 or AKG C452. Connection is a standard three-pin XLR.
Powering is where buyers need to pay attention. The CMT-36 is nominally a 9-12V phantom-powered microphone, drawing approximately 8.5 mA, and the reviewers were advised it will function on 48V only with suitable feed resistors. The CMT-56, by contrast, is a straight 48V design pulling about 650 μA. Don't assume a CMT-36 will behave when plugged into a modern 48V phantom input without checking. Source impedance is approximately 20 ohms symmetrical, which is low, as you'd expect from a transformerless output, and the mic wants to see a load greater than 600 ohms.
Sensitivity in cardioid runs 1.2 mV/dyne/cm² at 1 kHz, with an output level of −38 dBV/10 dynes/cm². The frequency range is quoted at 40 Hz to 16 kHz. Maximum SPL at 0.5% THD into a 1 kΩ audio-range load is 128 dB in cardioid. Equivalent noise loudness (CCITT) is approximately 26 dB SPL, with a noise voltage around −106 dBV. Those noise figures are a touch higher than the CMT-56's, which is the trade for the transformerless topology. In the period comparison, though, the two models were close enough that the reviewers couldn't reliably tell them apart on sound.
That comparison is the most useful thing ever written about this microphone. Studio Sound (January 1975, p.52) put the CMT-36 and CMT-56 up against the Neumann U87 and AKG C414. The reviewers recorded the same material on separate tracks of a 38 cm/s Dolby A machine and auditioned it blind through Spendor BC3 monitors. The verdict on the Schoeps pair was "extreme flatness without any particular coloration", and the polar diagrams, especially the figure-of-eight, were audibly good. A coincident figure-of-eight pair in Blumlein configuration impressed the reviewers enough that headphone monitoring had them turning around, convinced someone was in the room talking. On a madrigal recording the sound was smooth, the words clear, the extreme top good, and intermodulation distortion notably absent. The stereo image from a single pair reportedly put many a multi-microphone balance to shame.
The same review is honest about what the flatness costs. String tone was clear and true but lacked the flattering coloration of the C414. Brass was clear but lacked the vividness of the U87. The reviewers' framing was that the Schoeps has no particular sound of its own beyond a great sense of clarity, which means it can be curve-bent to taste with equalizers. That suits a creative engineer and disappoints anyone who wanted a mic to flatter the source. They also noted the Schoeps pair delivered about 4 dB more output than the U87 on filtered pink noise, which in turn sat about 4 dB above the C414.
Pricing at the time of that review was £195 for the CMT-36 and £187 for the CMT-56, so the transformerless model cost slightly more. UK distribution ran through Feldon Audio in London. The manufacturer was Schalltechnik Dr.-Ing. Karl Schoeps in Karlsruhe.
Long-term reliability is the one area where the period record is thin, and the reviewers said so plainly. The mic hadn't established itself firmly in the UK, so long-term data was hard to come by, though their brief experience showed no likely problems. The one field report they relayed was from a UK user recording outdoors on an island off Spain, whose CMT-36s went badly off-form after a late-night session until the considerable dew was carefully wiped off. After that, all was well. It has a mechanical pattern cap and exposed internals, and it wants reasonable treatment.
Buyers should confirm the pattern cap clicks cleanly through all three positions and that the mic is being fed the voltage it actually wants.
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