Marantz Project T-1

Commentary

A tube bulb type monaural power amplifier developed in search of a vacuum tube amplifier using the latest technology that is suitable for Marantz and suitable for the present.

Each part has been carefully selected by countries around the world for reliable parts that can bring out the maximum sound quality. In addition, we aim to be a long-life product by using parts that were being manufactured at that time without using limited stocks or used balls.
The internal circuit uses carefully selected highly reliable components such as film capacitors from US Aerobox, resistors from Dale, and sockets from Johnson.

For the vacuum tubes, 300B is used for the first stage and driver stage, and 845 is used for the last stage in a push-pull manner. For the amplification stage, a large direct-heated triode with excellent linearity and low odd-order distortion is used. A direct-heated twin triode 5U4G is used for the B power supply rectifier for the first stage and driver stage, and a direct-heated triode 845 is used for the B power supply rectifier for the last stage.
All the vacuum tubes used are carefully selected and only those that passed the Marantz standard are selected and used with the marantz logo.

A class A class push-pull non-feedback amplifier (balanced configuration) with transformer coupling for all stages from input to output. This eliminates secondary distortion of the 3-pole tube and ripple of the power supply.

The B power supply for the first stage and driver stage, transformer for each filament power supply, and high-voltage power transformer for the last stage are composed independently. In addition, choke coils are inserted into each stage, and the filament power supply for the amplification system is a constant current circuit, so that stable operation and inrush current when power is turned on are suppressed and the life of the vacuum tube is extended. The B voltage of each amplification stage is 184 v for the first stage, 382 v for the second stage, and 970 v for the last stage.
In addition, highly reliable MP capacitors are used as filter capacitors for these power supplies.

All audio transformers are manufactured by OPT (formerly UTC : United TRANSFORMERS Corporation), a reliable transformer manufacturer in the United States.

A self-bias circuit is used in each amplifier stage to ensure reliability.
In addition, the high-voltage power supply is equipped with a time delay circuit to prevent shock noise during power ON/OFF and no-load condition of the high-voltage power supply. Also, the high-voltage power supply is cut off even when an abnormal current flows to each B power supply of the amplifier system.

The chassis has a double structure consisting of a copper plated steel chassis with beauty and strength and a thick aluminum exterior.
The layout consists of two power transformers and two choke coils placed behind the top panel, and four audio transformers placed inside the enclosure under the vacuum tubes to minimize wiring and improve weight balance.

The champagne gold front panel is equipped with a bias balance meter that also serves as a pilot lamp.
With this meter, the DC balance condition of the vacuum tube of each stage, first stage (300B), driver stage (300B), and final stage (845) can be confirmed.

One balanced input (XLR) is installed as an input terminal.

The speaker output is one Canon terminal and is normally set to 8 Ω.
This setting of output load impedance could be changed depending on the service.

Model Rating

Type	Tube type monaural power amplifier
Output	50W (8 Ω)
Frequency characteristic	20 Hz to 20 kHz
Total harmonic distortion factor	5%
Clipping point	75W (8 Ω)
Input Sensitivity / Impedance	0.75V/1k Ω (Balanced)
Signal-to-noise ratio	90 dB (A Network)
Parts Used	Vacuum tube : Transformer : 300Bx4 845x4 5U4Gx1 LS-10X LS-25 LS-56 LS-6L4
Power consumption	560W
External dimensions	Width 556x Height 396x Depth 495 mm
Weight	65kg
Attachment	Birdcage type bonnet
Remarks	Balance Input HOT : Pin 3