SCA A12B Microphone Preamp Module
The Seventh Circle Audio A12B 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. Available as a DIY kit or fully assembled mic preamp module.
CH02-SP-A12 subpanel must be ordered separately.
The A12B 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.
Stepped Gain Control
A 12 position Grayhill switch provides accurate and repeatable gain settings in 5dB steps from 15dB to 70dB.
Since 5dB is often too big a gain step, the A12b 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.
Inverts the signal phase.
Slow-rise phantom power minimizes pops and thumps.
High quality PC mount connectors eliminate cabling and ease assembly.
CineMag Input Transformer
The A12b 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 A12b an aggressive character virtually indistinguishable from certain vintage amplifiers.
The A12 is available with one of three output transformers, each with a slightly different character. The 2S is the standard, which most people LOVE! The 2L and 2H are $45 and $65 additional and WILL increase order shipping timeframe. Please email first if you would like to order a 2L or 2H transformer!
2S 100% steel laminations, lowest cost, highest distortion 2L 50% / 50% steel/high nickel laminations, best compromise 2H 100% high nickel laminations, highest cost, lowest distortion
Flexible Power Supply
On-board voltage regulators can accommodate power supplies from +/-27VDC up to +/-35VDC. Local regulators keep inter-channel crosstalk extremely low when multiple preamps share the same power supply.
Built-in SC25 Op-Amp
The A12b has a high-performance discrete op-amp laid out directly on the main circuit board. The circuit is exactly the same as our very popular SC25 amplifier module.