The Sennheiser HD 650 is a great headphone with a little bit of sonic ‘magic’ appeal. The attractively priced
MassDrop HD 6XX version is a special bargain.
A popular and nice match for the Sennheiser HD 650 / HD 6XX is a vacuum tube headphone amplifier.
The project here was built by Jeremy Young. It was inspired by the Bottlehead OTL headphone amp, but circuit ‘operating points’ were determined to suit a locally made power transformer.
A Line-stage With Output Transformer (WOT) was built back in 1998, a single 5687 tube per channel with output transformer (OPT).
However I failed to get rid of noise (EM pick-up and attenuator switching noise). I lacked the expertise to optimise Grounding and to shield and/or orientate the output transformers (OPTs) properly.
Now, I have been fortunate to acquire a pair of Tango NP-126 Line Output transformers. So, I must re-visit the WOT Line-stage.
Real music has dynamics. Macro-dynamics – with unrestricted headroom in crescendoes. Micro-dynamics – with subtle low-level information.
Music should be reproduced also with a ‘time’ dimension. Not just tempo, but each sound accompanied by an harmonic ‘envelope’, where overtones are produced and decay naturally – providing a sense of ambience, dimension and space.
Diego Nardi published his φ42 (Phi 42) Phono Preamp in Sound Practices magazine, issue 14.
This is an all-tube (valve) circuit, designed without (global) negative feedback.
As Joseph Esmilla says, this was inspired by Bruce Berman’s Homebrew Type 76 Preamplifier described in Sound Practices #13.