mic preamp circuit

Posted on Feb 5, 2014

ART TPS2 is a starved tube mic preamp. One 12AX7 tube operating at about 50v plate voltage to add color to the sound. As I intended to build a all solid state preamp, the 12AX7 and its peripheral component were removed. The right channel input stage is mostly the original TPS2 capacitor input discrete differential stage. The major change is that t

mic preamp circuit
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he input stage gain is now fixed. The second stage is conventional OPAMP based amplification stage. The gain of this stage is controlled by a precision potentiometer, and followed by a attenuator. Coupling capacitors are used because of the high gain. In the end I settle on the transformer input + transformer output design. The output transformer is wired a separate 8 pin IC socket that plucks into the IC socked on the the PCB, so I can easily switch it to THAT 1646 output. Capacitor input and THAT 1646 output on the left channel sounds thin and very compressed. Transformer input makes the THAT 11512/1646 combination a bit smoother, but still not my cup of tea. An output transformer really make it sound right - there is substance in the sound without too much of color.

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