Berlant Concertone Tube Mic Preamp

ABOUT

It started with a repair client of mine. He raved about this rackmount tube mic pre he had heard on a recording session that had looked like an Ampex, but was actually something else. Lo and behold, he brought me one such example for service. Behind a tasteful mid-century style front panel and big VU meter was a collection of tubes, eye-wateringly cramped components, and NO signal transformers. This meant that as-is, it would not function properly as a mic preamp. Instead, there were two empty 8-pin tube sockets designated for input and output transformers. Many transformer companies offered their products in a tube-socketed form factor back then, so the idea was that you could purchase your own from the likes of Peerless, UTC, Triad, etc. In addition to the single preamp I rebuilt for the client, I later acquired a stereo factory pair for my own diabolical use.

THE RESTORATION

First on my list was removing some of the internal clutter. Probably 60-70% of the wiring/components inside were part of the tape circuit and completely unrelated to the mic preamp, so they were removed to make some room. When rebuilding the power supply, I pulled the old selenium rectifier (used to convert the 6.3V tube filament voltage from AC to DC) and replaced it with a modern silicon equivalent. I see a lot of so-called "reputable" studio techs leave these inside circuits, which always baffles me. Selenium rectifiers were notoriously unreliable even when new, so leaving them in a circuit many decades later is asking for trouble. Recently I've started replacing voltage dropping resistors on the plates of input tubes on tube preamps, substituting the original carbon composition resistors with metal film. This typically reduces hiss/noise. I added some vintage transformers by UTC and Webster Racine to the transformer sockets and wired the 'output' control to properly trim the output and allow for saturation/distortion if desired. The circuit/front panel incorporates an unbalanced line-level input, which I relocated to the front panel in place of the 'monitor' headphone jack. XLR jacks were added and finishing touches were added.

THOUGHTS & IMPRESSIONS

The Concertone preamp is a formidable adversary to its competitors like the Ampex 351. It has a respectable amount of gain and can bring ribbon mics up to a usable level with ease. It has a pleasant, silky sound that is perhaps a bit more transparent than other tube preamps. These are the first two mic pres I've added to my studio, they currently get a lot of use (as of 2025). The line input is a great feature for recording D/I signals from keyboards/synths and adds satisfying warmth in the process. The only drawback with this preamp is that the frontend needs to be gain-staged carefully, so hotter signals from condenser mics and even some dynamics need to be padded down first. It's still worth it for me being able to have a stereo pair of wonderful tube mic preamps that in many ways outperform a comparable Ampex at a fraction of the cost. I was able to find this pair for $100 each in 2025 when a single 351 sells in excess of $1,000. An underrated classic, in my humble opinion.