Penguat tabung hampa telah dikenal sebagai penguat audio dengan sifat soft-clipping, dan tidak seperti penguat transistor yang bersifat hard-clipping. Tabung hampa umumnya merupakan suatu komponen aktif yang bekerja pada aras tegangan tinggi (ratusan volt), namun pada aras tegangan tinggi penguat tabung membutuhkan transformator keluaran untuk menurunkan aras tegangan isyarat keluaran. Penelitian ini bertujuan untuk merancang penguat awal dengan menggunakan tabung hampa pada tegangan kerja 12 VDC. Untuk merancang untai tabung hampa pada aras tegangan rendah, telah dilakukan pengukuran untuk mendapatkan grafik karakteristik trioda 12AT7. Untai tabung hampa direalisasikan dengan topologi katoda bersama yang dikaskade dengan anoda bersama. Dari hasil pengukuran didapatkan spesifikasi penguat awal yaitu impedansi masukan sebesar 1.11 MΩ, impedansi keluaran 3.5 kΩ pada kanal kanan dan 3.2 kΩ pada kanal kiri, THD maksimal terjadi pada frekuensi 4 kHz di kanal kanan yaitu sebesar 1.7%, bati tegangan 20,08 dB pada kanal kanan dan 20 dB pada kanal kiri, sensitivitas 212 mVrms, aras keluaran maksimal 2 Vrms, tanggapan frekuensi yang rata pada rentang 60 Hz-20 kHz dengan fluktuasi ± 0.5 dB. Penguat awal ini dapat digunakan secara bergantian dalam dua ragam, yaitu ragam linier dan ragam cacat berupa efek flanger.

In Central Java, the Gong Kempul is one of eminent gamelan instrument, an ensemble of predominantly struck instruments fo und across Central Java and has deep philosophical meaning for Javanese. However, there lack of studies concerning on this particular instrument as a bridging means between scientific description and human artistic perception. This study aims to investigate the spectral and temporal properties as well as particularly look into the typical wave-like sound of the Gong Kempu!. Acoustic measurements were conducted and analyzed using ARTA. Both fr equency and time domain analyses were explored to better understand the nature of the Gong Kempu!. It was fo und that the partials at 93.8 Hz, 187.5 Hz, 281.3 Hz, and 375 Hz are the strict integer multiples of the fu ndamental fr equency. It can also be inferred that the fu ndamental fr equency at 93.8 Hz decays much more slowly than the other harmonic. In addition, the pitch of the Gong Kempul slide upward as the time goes on. The wave-like sound of the Gong Kempul is due to the beat phenomenon between two partials that occur closely.

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The acoustic velocity x, y, z components and its resultant amplitudes, the kinetic and total energy density distributions in a reverberation space, were measured using an energy density sensor consisting of four microphones. The space is a 225-m3 with average reverberation time of 6 s at 1 kHz. The room was excited with pure-tone, narrow- or wide-band noise. The result of the measurements showed that the acoustic velocity x, y, z component amplitudes were Gaussian-distributed, its resultant amplitude was Maxwell-distributed. The kinetic and total energy densities were gamma-distributed with three and four degrees of freedom, respectively. In agreement with published literature, the measurement also showed that acoustic pressure was Gaussian and the potential energy density was exponentially distributed, however, the other distributions have not been reported. Theoretical background and measured data will be presented.

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