Phasemation MA-1500 Mono Amplifier (Pair)
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