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Dynahi  2014

 

The Dynahi is a high output headphone amplifier designed by Kevin Gilmore in around 2004. It has gathered somewhat of a legendary status amongst the DIY audio community, probably because of the power output and the enormous heat dissipation requiring heatsinks similar to a full scaled power amp! But it has also been said to have very convincing sonic properties and to be able to drive pretty much any headphone on the planet.

 

"The amplifier employs an all-discrete, direct-coupled, fully-complementary topology featuring a JFET differential input stage with cascodes and constant current sources. A voltage amplification stage using two paralleled pairs of BJTs follows, and four parallel pairs of power BJTs serves as the push-pull output stage. A DC servo keeps output DC offset in check." (from the Amb Audio site)

 

The schematic uses JFETs and BJTs that are quite hard to come by these days with especially the 2SA1349BL's and the 2SC3381BL's being obsolete... it took me quite a while to obtain all the needed parts. Again Diyaudio is the place to make things possible... I found the aforementioned genuine JFET's offered by a nice person from Scandinavia! The 2SK389BL and 2SK109BL can be replaced with 2SK170BL and 2SJ74BL, and I got those handmatched from Ti Kan at Amb Audio. Lastly, the original Toshiba output BJT's are nearly non-existant, but I was able to source them in Germany. There was a certain doubt first that they were genuine as fakes are floating around the net, but measuring them all confirmed that they were the good ones.

 

 

schematicschematic

 

 

I didn't plan to use the original psu (because the design was somewhat outdated and parts availability) but replaced it with a Sigma22 regulated supply from Amb Labs instead. Those three boards pretty much defined the needed space. From the beginning I had planned to run the heatsinks the full length of the case, so I started to look out for a suitable donor heatsink. On Ebay I scored a massive anodized heatsink and had it cut to my desired dimensions. A friend also milled them so I could mount them flush on the aluminum bottom plate.

The front of the case is a sculpted element I designed in Alias (Autodesk) and then had it milled on a CNC machine. The rear is a "simple" panel of 10mm thickness with the RCA's recessed. The aluminum top plate was created with the help of Apparatebau Schaefer in Berlin (the german Frontpanel Express) and was painted in Mercedes Red. Final touches were the massive volume knob and the lighting in the front panel for that robotic look ;-)

 

The Dynahi is the headphone amplifier that began to convince me that some Toshiba semiconductors are sounding better than tubes... full of impact and authority, with a sweet treble and great transparency. Can the Dynahi be bettered?

 

 

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