6AQ5W/6005 UL Single-Ended 4Ch Power Amplifier with Hashimoto Transformers

This amplifier was originally featured on the January 2004 Issue of the "High-Fidelity Audio: Radio Technology" by Mr. Tadaatsu Atarashi.  Mr. Atarashi designed this amplifier for the multi-channel SACD application with just four-channels instead of the normal five.  As Mr. Atarashi believes that the four-channel sound image without the center speaker sound more natural than that of five-channel, he used the Marantz SA-17S1 Super Audio CD (SACD) player with the Phantom Center mode (the center channel signal is divided into right and left channels)  for his input source.

Each channel on this amplifier is driven by single-ended 6AQ5W with UL (Ultra Linear) connection (3W per channel output); therefore, the H-507S (rated 7W) output transformer from Hashimoto could have been adequate.  However, Mr. Atarashi rather used a stepped up model, the H-20-7U (rated 20W at 50Hz) because he thought the H-20-7U might show an edge on the frequency response.  The H-20-7U output transformer is called the universal type because it's designed to be able to used for either 5K or 7K Ohms primary impedance.  The H-20-7U is also designed to be used under three staged amplifications, such as the input, the driver, and the output stages.  Therefore, Mr. Atarashi connected the overall negative feedback from the grounding terminal of the secondary in order to maintain the correct amplification phase (this amplifier has only two amplifying stages).                          

Mr. Atarashi concluded his article with, "The sound of Ultra Linear connection (of this amplifier) is clearer and more settled than the sound of the Beam operation (he tested under the beam operation).  Although the output is cut by 1/3, the sound quality outweighs the loss of power.  Since this amplifier is designed for the four-channel operation, you can enjoy the enough music power through four-channels even if output per channel is rather small.  I realize that the most important factor of amplifiers is not the power, but the ability to reproduce the quality of sound."     

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Last changed: 02/01/15