DIY Preamp

Microphone preamps are perhaps the most abundant DIY project, with numerous options available for an API 312-type preamp alone. Preamp projects range in difficulty and cost from simple, low-cost, low-voltage IC-based amps such as the Seventh Circle T15, to complex, tube-based circuits such as the Orange 86.

API-style

Also known as “American Preamps Imitated”–these projects are inspired to various degrees by the classic 1970′s preamps designed and manufactured by Automated Processes Inc., or API. The “API Sound” is commonly thought to be a result of the unique strengths and limitations of API’s proprietary discrete operational amplifier, the 2520, and input and output transformers. In particular, it is the relatively slow slew-rate (transient response), small bandwidth, and high amount of harmonic distortion that give API mic preamps their euphonically “up front,” “warm,” and at times “agressive” sound.

“Clean Wire With Gain”

From a certain design perspective, the ideal amplifier is a “clean wire with gain,” which amplifies a signal (gain) without imparting any sonic artifacts of its own. Of course, such an amp is not meant for this world, but the projects below attempt to approach that ideal as closely as possible while negotiating the very real restrains of physics, cost, and practicality. This means you won’t find many (if any) transformers or tubes in these projects or any attempt to replicate any “vintage mojo” that does not belong in the first place to the signal being amplified. Put another way: some amps are great for what they add, others for what they don’t remove.

Neveish

The preamp modules from Neve’s vintage consoles are without a doubt the most replicated and imitated of all time. These modules are the 1272 (one preamp and one voltage gain stage) and the 1920 (two preamps and one voltage gain stage) circuits. The famous module numbers, such as 1073 and 1084, are not in fact preamps but combined preamp and equalizer channel strips. Much of the “Neve Sound” derives from the discrete, class-A circuitry as well as the sonic character of the input and output transformers. The originial transformers, made by St. Ives and then Marinair, have long been out of pruduction but there are many reproductions on the market today from Carnhill, Sowter, et al.

Vacuum Tube

The projects below eschew semiconductors (transistors) for conductors (tubes). Tube amplifiers are most often coveted for the way they overload, but don’t be fooled by marketing and “common knowledge”–tubes are just as useful for passing a clear, high-definition signal. Indeed, several of the following projects measure less harmonic distortion than the solid-state API and Neve designs. Because tube amps run on much higher voltages than their solid-state successors, these projects pose a higher risk of shock and require a more experienced hand to complete successfully.

Miscellaneous

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