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Pair Langevin AM16 Mic Preamps Racked Neve API

Here's a pair of 60's vintage Langevin AM16 mic preamps that I've just finished racking. The AM16 is a class A discrete transistor preamp with a unique balanced, symetrical circuit topology and transformer feedback that gives it's own distinctive tone among vintage mic pres. These AM16's are set up with an input gain control, an output level control, phase reverse and phantom power, and a front panel passive DI input.

The normal AM16 has a fixed gain of 45 dB (600 ohm input). Langevin also made a few with 50dB gain, and the ones here have stickers showing they were factory modified to the higher 50dB gain, which makes them a bit more useful as standalone mic preamps. Actually, they've also both been marked at some point by hand as going back to 45dB, but I think that may have been a matter of the outputs being rewired to 150 rather than 600 ohms, as with the inputs and outputs wired for 600, I measure them as actually having 50dB gain. The input transformers can also be wired for 150 ohm or 50 ohm input impedance, which provide an extra 6 and 10 dB gain respectively. I've built up special input controls on Grayhill stepped switches for these modules which allow you to use any of the three input wiring configurations, plus 5 -10dB pad settings on the 600 ohm wiring. So the top gain setting (marked 50 ohm) is 60dB, then 150 ohm = 56dB, 600 ohm = 50dB, then 40, 30, 20, 10 and 0 dB for the other input settings. The pad is similar to ones I've seen used in original Langevin equipment, feeding the input transformer with a constant source impedance roughly equal to the rated transformer primary impedance, but the 600, 150 and 50 ohm settings have no pad, so are just driven directly by the impedance of whatever mic you use. Any normal low impedance mic should be able to drive the 600 ohm and 150 ohm settings with no problem. In the 50 ohm setting you may notice some small loss of bass with certain higher coil impedance dynamic mics, but it will work perfectly with lots of vintage ribbon mics, almost all condensers, and many moving coil dynamics as well. Just go by the sound. If you need the extra gain the 50 ohm setting gives, it's there.

The DI input is passive, with a 15:1 Beyerdynamic input transformer to step down to mic level. The DI input is wired TRS, so you can use it balanced on electonic instruments or effects with line level balanced outs, and you can also use it as an unbalanced high impedance input for guitar and bass.

The output level control was made with an NOS Allen Bradley bridged T 600 ohm attenuator, so it correctly ternminates the AM16 and provides a continuously variable control for making finer level adjustments than the 10dB steps provided by the input switch.

If you're familiar with AM16's, you may want to know that these are set up to run with the high current output, so they'll put out the full +24dBm power level.

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