A12 Microphone Preamp
The A12 is a simple, single stage preamp roughly based on classic American designs of the early '70s. Built with the suggested transformers and op-amp, the result is an amplifier with an aggressive midrange and pronounced transformer coloration. The A12 sounds fantastic with rock drums and electric guitars, but is versatile enough to be used with a wide variety of source material and microphone combinations. The A12 is easy to build and makes a great project for less-experienced DIYers.
Features| High Gain | The A12 can provide 70dB of gain, including the voltage step-up provided by the transformers. This is more than enough gain for most applications, especially with modern high-output condenser microphones. |
| DC Offset Trim | The A12 has a manual trim control to minimize DC offset, maximizing headroom. |
| Stepped Gain Control | A 12 position Grayhill switch provides accurate and repeatable gain settings in 5dB steps from 15dB to 70dB. |
| Gain Trim | Since 5dB is often too big a gain step, the A12 also has a gain trim control, which provides up to 6dB of cut at any gain setting. This allows very fine adjustment of gain between steps. |
| Phase Reverse | Inverts the signal phase. |
| Phantom Switch | Slow-rise phantom power minimizes pops and thumps. |
| Neutrik Connectors | High quality PC mount connectors eliminate cabling and ease assembly. |
| CineMag Input Transformer | The A12 uses a CineMag CMMI-8-PCA to couple the microphone signal to the amplifier. Manufactured to exacting standards, this transformer gives an 18 dB voltage step-up, has excellent specifications, and provides distinctive sonic qualities that compare very favorably to vintage units. |
| CineMag Output Transformer | The steel-core CMOQ-2S gives the A12 an aggressive character virtually indistinguishable from certain vintage amplifiers. |
| Flexible Power Supply | On-board voltage regulators can accommodate power supplies from +/-15VDC up to +/-35VDC, allowing the use of op-amps with +/-24VDC requirements. Potentiometers allow easy voltage adjustment, making experimenting fast and simple. Local regulation also keeps inter-channel crosstalk extremely low when multiple preamps share the same power supply. |
| 2520 Compatible | The A12 will work with a number of discrete op-amps from manufacturers such as API, Millennia, Forssell, Old School Audio, and John Hardy. High qualtiy IC amplifiers such as the AD797 and OPA627 can be used as well when mounted on a suitable adapter board, and can rival the discrete types when extreme headroom is not required. |
