Marantz T1 specifications:
Product type: monaural power amplifier
Continious power output: 50W per side, at 8 ohms
Input sensitivity and impedance: Balanced inputs; 0.75V/1k Ohms
Signal to noise ratio: 90dB [IHF-A]
Power consumption: 560W
Dimensions and weight: W 556 x H396 x D495 mm, 65kg
Tubes used: Four 300B, Four 845, One 5U4G
Transformers used: input; LS10X, Inter-stage; LS25, Driver; LS56, Output; LS 6L4
Miscellaneous: Pin 3 positive for balanced inputs, "birdcage"type bonnet and removable AC cable supplied
A tube power amplifier with a classic circuit design that reminds us what is lacking from modern day amplifiers.
The Marantz Project T-1 tube power amplifier was released in 1995. In contrast to the Model 9, the Marantz Project T-1 utilizes a different but "classic" circuit design.
Normally, the average height of a tube power amplifier chassis is around 40 to 70mm. However, the chassis height of the Marantz Project T-1 is more than double the average height, and with good reason - the Marantz Project T-1 chassis houses signal amplification transformers inside. The controls on the exterior of the chassis feature a round-shaped meter in the center indicating the bias balance of the primary, driver and final gain stages. Monitor selection for the meter can be made through a three-way rotary switch selector.
The large case located on the upper part of the chassis contains two power transformers; one that powers the primary, driver stage B+ and filament, and a second one that powers the B+ for the final stage. The smaller case located adjacent to the larger one contains two choke coils that seem to be made by Tamura; the first one for the primary and the driver stage B+ voltage, and the second one for the final stage B+ voltage.
The audio chain for the Marantz Project T-1 is: a balanced input stage followed by an input transformer, followed by an attenuator, then a 300B push-pul stage, and finally, the output transformer. Phase reversal of the input signal is handled by the input transformer at the secondary tap, forming the basis for full class-A transformer coupling operated non-negative feedback push-pull amplifier.
The Marantz Project T-1 uses four transformers in the audio signal chain. Transformers are sometimes referred to as band pass filters and only one is used in most tube power amplifiers, but in this case four are used. However, if you look at the transformer as being a band pass filter, it can also act as a device for narrowing the frequency response of a given amplifier design, but usually this does not achieve the best performance where minimizing distortion is concerned. To avoid this, the Marantz Project T-1 uses four superior transformers manufactured by OPT of America (formerly UTC: United Transformer Corporation).
The main attraction of an all triode push-pull stage design is the noticeable decrease in third-order high frequency harmonic distortion, which effectively cancels out any second-order high frequency distorion and ripple noise from the power supply. The six tubes used in the audio signal chain are based on a direct current ignition design, which allocates individual currents to the six tubes. This virtually eliminates any hum caused by the filament.
The filament power supply features a regulated current design, which minimizes current spikes that may occur when the amplifier is powered up. The power supply for the B+ voltage features a time delay mechanism that prevents power-on shock noise and loading at B+. The time delay mechanism also turns off the B+ voltage of the various amplification stages.
High reliability achieved in bias and rectifier stage design through the use of premium components
There are primarily two design types for bias circuits: the self-bias and fixed-bias circuits. To achieve reliable operation, the Marantz Project T-1 uses a self-bias design for all three of its push-pull stages to give a total of six bias points. Each cathode resistor is fitted with a bi-pass capacitor, making the amplifier design free from negative feedback.
To rectify the B+ voltage, the Marantz Project T-1 uses a dual tube driven double-wave rectifier, with a 5U4G for direct heat used at the primary and driver stages, and an 845 used in a plate and grid two-pole design for the final stage. The Marantz Project T-1 actually uses four 845's, two for the rectifier stage and the other two for the push-pull section of the final stage. In the final stage, there is a 970V high voltage load apploed to the 845's. Bi-pole usage of two 845's makes the rectifier more reliable and stable than would, say, a double voltage rectifier design using a 5U4G.
Marantz uses tubes that are currently still being made, and chooses tubes that meet their high independent standards. Tubes that meet these standards are marked with the Marantz logo.
The 845 tube was developed for audio use and is based on a transmitter tube. This large three-pole direct heating tube has a high plate loss of 75W and a number of other desirabe platte characteristics. In the Marantz Project T-1, the 845 is driven by a transformer used in push-pul operation to achieve an average of 50W and maximum of 75W for power under an 8-ohm load. Compared with solid-state power amplifiers, tube driven power amplifiers are considered to offer up to double or even triple the supposed power rating. In other words, this amplifier can provide what feels like 150 to 225W of power from a solid-state device.
The Marantz Project T-1 uses a fine selection of the best components available: a Cannon connector for the speaker output, MP capacitors for the B+ voltage filter capacitor, Dale resistors and Johnson tube sockets.
A throbbin, lively sound achieved through the use of transformers
Since the Marantz Project T-1 uses a non-NFB design combined with four transformers in the signal chain, it should in theory have weakers specifications than those of the classic Model 9 amplifier. Upon listening to the Marantz Project T-1 however, this is not the case at all. The sound is of a clear nature with no strange stimulants. This clear sound is probably the result of a very low odd number high-frequency harmonics used in the tubes of the Marantz Project T-1.
The Marantz Project T-1 produces a lively, throbbing sound, made possible through the use of transformers to drive the signal. It is very pleasing to the ear, with skillful coloring, but still very musical. The Marantz Project T-1 power amplifier serves to remind us of what is lacking from modern day amplifiers.