Phasemation MA-1500

In the world of audio amplifiers, wide kinds of semiconductor amplifiers, tube amplifiers, etc. are released. Therefore, the respective audio features can be enjoyed as a hobby.　Especially the tube power amplifiers has a tube called "fine tube" having a reputation for sound quality and last year we have developed the monaural power amplifier, MA-2000 composed by a parallel single-ended circuit adopting 300B which is the best tube among them and a circuit strongly driven by a transformer-coupled circuit adopting 2A3."

This year to tell many people the significance of MA-2000, we developed a new monaural power amplifier MA-1500 which has a plentiful 10W output along with an operation due to the transformer-coupled circuit which is single-operating with a 300B single tube.

Main feature

Toshiba 6CG7 for the transformer-coupled circuit driving PSVAN 300B ended-tube optimally

Letting the ended-tube PSVAN 300B to be the self-bias single pure A-class, the Toshiba 6CG7 as a driver is used on the transformer-couple and operates the speakers with stability having no wobbling but is structured to exert the excellence of 300B's original quality with the simplest operation.

Composing the non-feedback amplifier by adopting triode tubes in all stages

We compose the non-feedback amplifier by adopting triode tubes, 5814A+6CG7+300B, in all stages. Therefore, the ability for reproducing dynamic and very expressive music is provided only possible from the non-feedback circuit.

Adopting the output transformer and inter-stage transformer made by LUNDAHL in Sweden

Because the inter-stage and output transformers made by LUNDAHL in Sweden are proper to compose this equipment and suited for the sound quality to be aimed by us, we have adopted them.　We adopted parallel connection by utilizing the independent winding structure at the secondary side of the inter-stage transformer and therefore secured a sure transmission to the level of very small signals. The independent terminals able to drive an 8 or 4 ohm speaker are provided by utilizing the independent winding structure at the secondary side of the output transformer.

Composed of two independent power choke transformers

Because the power supplies from the independent power choke transformer are individually supplied for the first stage, the driver stage (5814A+6CG7), and the power stage (300B single-ended), the mutual interference between the input signal amplifier circuit and the speaker drive circuit is purged. Therefore, signals of various levels from infinitesimal signals to high power signals are amplified clearly.

Thoroughgoing design for decreasing the noise

We have adopted the thoroughgoing design for decreasing the noise with the follows:

• Rectifier tube 5R4G which does not generate a switching noise in principle against a high voltage power supply
• Rectifier circuits composing of choke transformers
• 300B heaters directly driven by DC power supplies

MA-1500 Block Diagram