The Caged Frog -- A Pentode Based Transconductance Amplifier for Headphones

Caged Frog -- Single Ended Pentode

The truth of the matter is that after years of playing around with all kinds of single ended triode (S.E.T.) amps, I'm not sure that they are really my cup of tea. Sure, they do a some things really well, they have that sweet midrange after all, but some other things just never seem quite there. Indeed, I generally feel like they lack coherence when things get complicated. The usual alternative is push-pull, which certainly has it's place, and indeed a good differential circuit is hard to beat. But, there are other solutions as well.

One solution that is often ignored is the lowly pentode.

Modding the Melos SHA-1 Headphone Amplifier

 It was Corey Greenberg’s Stereophile review of the Melos and hearing an all Melos system at my local dealer that first piqued my interest. Indeed, a desire in the early 90’s to own one of these is part of what got me into headphones in the first place. At the time, unable to come up with the cash, I bought some Grado SR-80’s and a Headroom Little instead. I finally bought my Melos in 2003. But, it has been sitting unused in a closet for a number of years. 

D3a Experimenter's Printed Circuit Board

This project is a circuit board which, through various jumpers, can be configured for various circuits. Specifically, it is designed around the D3a vacuum tube, a high Gm, high mu pentode. Additionally, there are several other tubes such as the E180F and E810F that share the pin arrangement with the D3a allowing their utilization as well.