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  • Research Article
  • Open Access

Real-Time Audio Transformer Emulation for Virtual Tube Amplifiers

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EURASIP Journal on Advances in Signal Processing20112011:347645

  • Received: 14 October 2010
  • Accepted: 28 January 2011
  • Published:


An audio transformer is used in a guitar amplifier to match the impedances of the power amplifier and a loudspeaker. It is important to understand the influence of the audio transformer on the overall sound quality for realistic tube amplifier emulation. This paper proposes to simulate the audio transformer using a wave digital filter model, which is based on the gyrator-capacitor analogy. The proposed model is two-directional in the sense that it outputs the loudspeaker current, but it also connects backward to the power amplifier thus affecting its behavior in a nonlinear manner. A practical parameter estimation procedure is introduced, which requires only the measurement of basic electrical quantities but no knowledge of material properties. Measurements of a Fender NSC041318 and a Hammond T1750V transformer are presented as case studies, as well as parameter fitting and simulation for the Fender transformer. The results show that these practical transformer designs introduce distortion at low frequencies only, below about 100 Hz for the Fender and 30 Hz for the Hammond transformer, and that the proposed model faithfully reproduces this effect. The proposed audio transformer model is implemented in real time using the BlockCompiler software. Parametric control allows varying and also exaggerating the model nonlinearities.


  • Transformer Model
  • Power Amplifier
  • Digital Filter
  • Full Article
  • Publisher Note

Publisher note

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Authors’ Affiliations

Department of Signal Processing and Acoustics, School of Electrical Engineering, Aalto University, 02150 Espoo, Finland
Nokia Institute of Technology (INdT), SCS 1 Ed. Camargo Corrêa, 6th floor, 70397900 Brasilia, Brazil
Nokia Gear, Itämerenkatu 11, 00180 Helsinki, Finland


© Rafael Cauduro Dias de Paiva et al. 2011

This article is published under license to BioMed Central Ltd. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.