More directly heated triodes... this time in a headphone amplifier...

This was a very fun project for me.  I have used headphones on and off over the years, but I had never really submerged myself in the world of the headphone audiophile.   It was mesmerizing.  The detail of world class headphones was something that I was not prepared for.  I was lucky enough to be designing around the Sony MDR-R10's, a reference in every sense of the word.  It made for a great learning experience.

The amplifier came to me as the top model Woo Audio 300B headphone amplifier.  The circuit was radically different from what I build for the world of extremely low powered amplifiers designed for horn loudspeakers.  First I changed the cathode follower output to anode follower.  Next, I completely removed the cascaded 6SN7 input and driver sections.   The last major circuit change I made was to convert the the parallel rectifiers feeding huge multi-hundred microfarad capacitors to choke input supplies using mercury rectifiers.  After these changes, I was able to relax into listening... and I then settled on 45's as the best all-around choice in output tubes.  One really nice thing about 45's is that you can really vary the sound by swapping vintage globes to modern EML mesh or solid plate tubes.  The EML's do have insane detail, but the old globes have a nice and easy listening tone to them.  The choice is yours... or, just do what I did - swap tubes with mood and genre... it was fun..  

I really went crazy listening to rectifiers with this amplifier.  Differences between rectifiers were very obvious... no swapping back and forth wondering what you heard.. this was easy and fun.... I started with a king.. the WE274... genuine article... engraved base... fabulous sound... I rolled a few vacuum rectifiers... the Telefunken meshes... the 5U4's... 5V4's... 5AR4's... WE274's had them all... and then I dropped in the lowly RCA mercury..... wow... same big tone, but even bigger dynamics... astounding... going back to the WE after this I would catch myself daydreaming.. my mind wandering... the mercury really brought the performers to the focus...

oh... and do not let anyone tell you a DHT headphone amplifier will never be quiet enough.. without any active regulation, this amplifier was dead silent through the headphones.... so let me hear about your DHT headphone amp!