The Tetra Sans PS phono stage uses two tube-based gain stages with a passive equalization network in between. The gain stage's topology is the Constant-Current-Draw Amplifier [CCDA], whose low distortion, fairly high gain, and low output impedance are desirable attributes in a phono preamp. The CCDA is a compound circuit that holds a grounded-cathode amplifier directly cascaded into a cathode follower. So what; what's so special about this obvious pairing? Its special status lies in the details.
The Aikido PH-1 phono stage returns. Building phono stage based on the Aikido topology makes perfect sense, as the Aikido’s low distortion, noise, and output impedance, without the use of negative feedback—all are highly desirable attributes in a phono preamp. The Aikido PH-1 phono preamp is an extremely flexible design, as a nearly infinite number of different Aikido Phono Stage configurations can be built on the PCB. Nonetheless, our goals always remain constant: high-gain, low-noise, and low output impedance. The input tubes provide the voltage gain in this preamp, while the output tubes isolate the input tubes from both the equalization network and the external load, and they deliver a low output impedance.