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An OTL Tube Headphone Amplifier

2015-01-04 08:29  
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The tube headphone amplifier in figure 1 is a high current mu follower, with a 12AU7 cathode follower driven by a 6CG7. Both sections of each tube are paralleled to minimize noise. It's a zero global feedback, OTL design of pretty high quality. I use it and like it for Grado, Sennheiser, and Sony headphones. The maximum gain is about 25 dB with the 6CG7, so it pays to watch the attenuator level. This design can be used as a line preamp as well.

[Editor: If the amp will be used with low impedance headphones (32 ohms or less), install R9 which can be 50 ohms to 100 ohms. R9 stabilizes the internal gain of the amp with low impedance loads. See the appendix 1 below on TINA-TI simulation for a discussion of the effect of R9.An OTL Tube Headphone Amplifier