Vacuum Tube Headphone Amplifier HA-02

　HA-02 is the headphone amplifier which uses a vacuum tube as an amplification element. Although output power is small, it has the output terminal for speakers and it can also sound a speaker with small volume as BGM.

Only one right and left are using each the miniature vacuum tube 408A of a Western Electric for an amplification tube. Although this WE408A is a vacuum tube of a vintage, it is one of the produced vacuum tubes, and since it was used abundantly for telefon equipment, there are no worries about a spare tube even now. It seems that it was used for various uses in order to often tend to use characteristics, although this vacuum tube is originally designed as an object for high frequency amplification. When it was used for the data of a Western Electric as a small output tube, there was description that about 300mW output power was obtained. When we manufactured the amplifier for headphone based on this description, we decided to produce commercially, since the good result was obtained.

300mW output power can be called sufficient output power for headphone amplifier. Moreover, it is also possible to listen to music with smaller volume by this output power also in a speaker system. Although it is impossible to take out big volume which is usually heard from a speaker, of course, when telephoning as BGM, it can be said to be sufficient value to use it on a convenient level. Moreover, originally, since this vacuum tube was developed as an object for small signals, noise characteristics are also excellent, and the resolution at the time of very small volume is excellent. Therefore, the place where sound is clearly reproduced also where volume is lowered as an object for BGM can call it an advantage. Moreover, although the amplification circuit of a two or three stages is used in many cases, in the case of this machine, the big amplification factor of a pentode is used, and it usually constitutes it from vacuum tube amplifier in only one stage of amplification circuit. It has succeeded in pulling out the freshness of the simplicity, therefore sound to the maximum extent.

The output transformer highly efficient despite small size is adopted as the output transformer of this machine using the same technology as the transformer adopted as the high-end model kind of our company. It was adopted as A-08S etc., the high Teflon insulating paper of evaluation was adopted as this output transformer, and the highest sound quality was aimed at.

Two kinds of terminals are prepared in the secondary side of a transformer, and the 50-ohm object for headphone amplifier and for 8-ohm speakers is pulled out. It enables it to use it, preparing two terminals in the input unit of HA-02, enabling it to connect CD player, the latest portable music player, etc., and changing with the changeover switch of the upper surface of a chassis. Moreover, it is attached to this machine as standard in the connecting cord so that those portable players can be connected. The code can be changed into a pin jack from a stereo mini phone plug, and is a high quality cable made from Audiotechnica. If this cable is used, almost all portable devices, such as i-pod, are connectable. HA-02 is recommendation also carrying out work and study, connecting these portable devices and sounding a speaker as BGM. When HA-02 is used as an object for headphone, the optimal load impedance is 50ohms, but it can respond to the headphone of the wide range impedance from 8ohms to about 600ohms.

The Teflon insulation pin jack of chromium copper of our original is adopted as the input terminal of HA-02. Moreover, the gilding high-class terminal which can connect the speaker code up to 5mm in diameter to a speaker terminal was used, and the high reliance type by a nuitric company is adopted as a headphone jack. The chassis of this machine is a product made from a complite also with popular A-08S, and is the material which carried out filled up of the phenol resin to wood by high pressure and which was electrically excellent also in strength. Moreover, the African blackwood material of the vibration control effect popular also as a setting base is used for the leg, processing it into it round. Moreover, highly efficient R core transformer is adopted as a power transformer. A first soft recovery diode is used for rectification for the plate and screen grid side, separating into it, and the merit of the sound of a pentode is pulled out. The key point of the power supply is used with the high-quality sound power supply circuit using the film capacitor.

Thus, HA-02 is made in pursuit of the highest sound quality, without extracting a hand to details.

Please confirm this sound with an own ear.

HA-02 specifications Use vacuum tube: Only WE408A 2 tubes / Sircuit system: Single stage amplification, pentode connection, and non-feedback system / Maximum output :300mW (at the time of 50ohm load) of headphone terminals,240mW (at the time of 8-ohm load) of speaker terminals/ Frequency characteristic:30-21,000Hz (headphone terminal) 45-17,000Hz (speaker terminal) / Gain : Headphone output power 9.5dB (at the time of 50-ohm load) Speaker output power: 1.5dB (at time of 8-ohm load) / Remains noise: 100 microvolts of headphone output power 70 microvolts of speaker output power / Outside dimension: 150 (W) 325 (D) 125 (H) / Weight: 3.5kg

Transformation cable miniphone to RCA pin plugs of the belonging