Vacuum tube output circuit DA converter unit YDA-01B

In quest of the beautiful and gentle sound of a vacuum tube, the circuit of single No Feedback composition was adopted as the output circuit by YDA-01.

However, the impression which it is insensitive and is too sharp remained for the composition according [ the circuit ] to a transistor. So, at our company, research was come in piles in order to constitute the output circuit of a vacuum tube. The output unit of the DA converter serving as a current output, and constituting from a vacuum tube which is a voltage control element ran into difficulties quite difficultly beyond anticipation. It becomes the sound in which the merit of a vacuum tube is not fully pulled out only by merely connecting a vacuum tube circuit by CR combination after DA converter IC simply and which is unattractive. At our company, as a result of much trial productions, carried out load of the resistor to the output of the DA converter, and it was made to link directly with the input unit of a vacuum tube as it is, and adopted as single No Feedback amplifier of one-step composition. We use in output circuit U.S. made Western electric highly efficient pentode WE408A was adopted.

Although an amplifier circuit is simple, it is taking the measures against sound quality to the extent that it passes enough against the power supply circuit. The plate circuit and screen grid circuit of WE408A supply current from the independent rectification circuit, and they consider it so that influence may not reach a mutual circuit. Moreover, the current to the screen grid which influences sound quality greatly was supplied through the constant current circuit by MOS FET, and raised the purity of sound. A heating circuit carries out both waves rectification with a large-sized Schottky diode, and supplies the wise independently. Although WE408A is no-direct heated vacuum tube, the difference in the sound in a heating circuit is also checking the quite large thing.

It had composition which takes in the system which reduces the number of the elements which are made into the design policy of our company, and to be used to a limit, simplifies a circuit, and pulls out the purity of sound from before to the maximum extent. PCM1794A of use to this machine Although the output of DA converter IC has four output units in the differential output with monophonic composition, only one output is used among those and other terminals are changed into the state where a dummy resistor is not added and used. Although it was directions for use which are wasteful apparently, the purity of sound was higher than parallel connection, and the good result was obtained.

Moreover, the input unit of AC line adopted the circuit breaker which served as the power switch as the place which was using the power supply fuse and the power switch, and banished the large fuse of influence in sound quality. When abnormalities arise inside, this power switch will be in the state of OFF. If normal and it will re-switch on, it can be used normally. It is one merit that it is not necessary to perform clearing work of a fuse, etc. Sound quality is increasing the transparent feeling further by this.

The window was prepared in the top plate of the chassis.

The peephole made from acrylics was opened in the top plate of this machine to serve also as the heat dissipation hole which misses the heat of a vacuum tube. The light of the heater of a delicate vacuum tube can be seen, and it is impressive in the dark room. The difference from YDA-01 of a transistor sees by the eye in appearance, and it understands.

The muting circuit was added to the output.

YDA-01B has adopted the output circuit of a vacuum tube type, and the coupling capacitor is contained in the output end. Therefore, therefore, although DC does not leak to an output, a little leak current arises at the time of a power supply injection and power supply cutting. Therefore, if DC amplifier etc. are connected to power amplifier, influence may come out. In this machine, in order to prevent it, the muting relay was inserted in the output circuit and the unpleasant noise is prevented. Of course, since it is considered so that there may be no influence in sound in sound quality, you can carry out and prepare the circuit in comfort.

Other parts are not different from YDA-01 of a transistor output.

A digital section is completely the same. Please refer to the catalog of YDA-01 for details.

YDA-01B specifications

- Digital input terminal : one axle (RCA) - Analog output terminal : one paire axle (RCA) - Use vacuum tube : WE408A Two pieces

- Output level : 4V/0dB - Correspondence frequency : 32-192kHz (automatic flattery) - 8 time oversampling digital filter

- Frequency characteristic : 20-20kHz (±1dB) - Signal to noise ratio : 78dB (IHF-A weight) - Output impedance : 2.6kiro ohms

- Outside dimension : 420(W)290(D)94 (H) - Weight : 5.2kg

Service parts: Spare tube WE408A vacuum tube 6,000 yen /1 piece