Miscellaneous Projects

The project was started after I had experienced the very good sound quality of the A5 amplifiers build by a friend. I was simply impressed. I used for the amplifier boards available from Kristijan Kljucarcic. The quality of the boards is very good and solid. The board for the power supply including an 'active' filtering I have developed by myself. For the housing of the mono amplifiers I used a straight forward approach, all components with the exception of the XLR inputs, the speaker output posts and the AC connector are mounted on the heat sink. The head sink profile is a SEIFERT K240/200 with a rated thermal impedance of 0.2 K/W. This is sufficient as the temperature at the case of the power transistors is measured at 48 Deg.C after about 30 min. The power transistors are sandwiched between the PC board and the heat sink and placed as close to the center of the heat sink profile as other design constrains allowed. The power transistors are matched / selected to groups of 3 out of a batch of about 50 devices. This gave very well matching of Vgs under rated operating current. The transformer is a 500VA +/-25V molded type. A NTC device is used to limit the inrush current of the transformer. The protective ground is connected also via an NTC to the chassis GND. Due to the straight forward design approach there is only very little wiring necessary, preventing all sorts of noise and coupling problems. Star ground center is the GND post at the power supply. The ripple voltage at the amplifier supply is less than 5mV and hence the amplifier is extremely quiet. DC offset is less than 20mV. Both mono amplifiers worked right first pass after powering up. All operating voltages were well within the expected limits. After several hours of 'burn in' I connected the amplifiers to my stereo system. The system consist now of a TRANSTOTOR ROTERY turntable with an AT OC09 MC pick up system, a home made ONO MC-preamp and Amplifier 1.7 pre amp. The speakers are AUDIO PHYSIC Avanti I. How does it sound? To make it simple, I will not switch back to my old gear! It sounds clean, open with solid bass, just correct. I'd like to thank Nelson Pass for his willingness to share his designs with the DIY community. Thanks also to the contributors of the 'DIYaudio' forum for the interesting discussions. Best Regards from Good Old Germany, Werner e-mail: .(JavaScript must be enabled to view this email address)

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