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April 2014

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Audio Electronics 56 | April 2014 | audioxpress.com a x This can be achieved using IXYS's constant-current source (CCS) circuitry. I did not recommend this circuitry information in my original article because it was not widely available (even though the original prototype was tested that way). Many audio enthusiasts have discovered this CCS, IXYS's IXCP-10M45S, which can be used as a valid alternative to cathode resistor R7. The CCS can also be used with the existing circuitry, PCBs, and power supplies. I built my Mugen amplifier in 2007 and originally published the design in Elektor (October 2007). The Mugen Hybrid Amplifier design replaces the output valves and transformer with a solid-state circuit using modern transistors, which can directly drive a loudspeaker (see Photo 1). However, the original prototype used well-priced uncommon and unknown tubes that had great specifications. The prototype used a 5965 tube for the long-tail driver and a 6BQ7A cathode follower. The 5965 is well suitable for audio purposes. I used as long-tail driver (tube V1 shown in Figure 1). It pro - vides enough gain (mu of 47), relative low output imped- ance, and low distortion. The 5965 is also pin-compat- ible with the ECC83 family. For optimal use the anode resistor (R3 and R4) is changed to 47K and the anode current is set to 3.5 mA. I used P1 to set the test point TP3 to 3 V. As a long-tail driver, the 5965 does not provide enough gain to be used with overall feedback. This is fine because I don't think overall feedback is necessary using these configurations (see Photo 2). The 6BQ7A has good specifications and is an excellent choice as cathode follower (see Photo 3). Photo 1: The Mugen Hybrid Amplifier got its name from the Japanese word "mugen," meaning infinite or endless. Photo 2: The amplifier design uses a combination of transistors and valves. By Wim de Haan (The Netherlands) The Mugen Hybrid Amplifier's Driver Update Figure 1: The design details for the updated Mugen Hybrid Amplifier are shown. My Mugen Hybrid Amplifier project published in audioXpress October 2013 relies on common, widely available tubes—the ECC83 and the ECC88—for the driver section. In this article, I am providing an alternative that will enable the distortion to become less than 0.1%, up to 80 W, without overall feedback.

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