Upgrading Modifying Kora Hermes DAC Op Amp-Switch

My favorite DAC after trying perhaps a dozen is the Kora Hermes DAC, first edition with the 6DJ8 (ECC88) tubes (my favorite is the Telefunken with gold pins, 50's to mid 60's). Although some reviewers called the Kora Hermes DAC neutral, I call it rich and organic, yet vibrant and open.

I had some gold over copper RCAs installed in it by Steve Sank in Tucson AZ, which improved the sound dramatically. Gold over brass doesn't get it any more in my book. He also replaced the stock switch which apparently commonly goes bad with the Kora Hermes DAC's and as per my request replaced the two final output caps in the sound stage with two REL Audiocap PPT Thetas. It was either the PPT Thetas or the REL RT's, but being hungry for a little more warmth, I chose the PPT Thetas.

Inside the dac, is a board on top of another board which houses a 8 pin Texas Instruments 08A25XM OP amp (underneath the top board). Steve recommended replacing it with a Burr-Brown OPA 2134PA. After carefully pulling the TI chip (do not bend pins, fingers OK but chip puller better), I replaced the TI op amp with the Burr-Brown OP Amp (chip). It is important to keep the proper orientation. The upper board has the op amp chip toward the back of the DAC, and the number one pin indentation is also toward the back of the DAC, and must be kept that way, or you could fry the chip or more.

The shootout between the two was quit revealing. To me, in my system, the Burr-Brown caused the Kora to sound much more rich and three dimentional, yet maintained the detail and organic openess of the Kora Hermes DAC. In comparison, the TI chip sounded a bit lean and glassy and shallow. What a wonderful improvement in sound.

You can get the Burr Brown Op Amp from Digikey and others. Or just have Steve Sank of Talking Dog Transducer company install one while he replaces your faulty factory selector switch or the cheesy copper digital wiring in the unit.

By the way, you can buy some nice hard rubber isolation cones on ebay from Simplyphisics (they call it a small Tone Cone) which have a hole that the stock factory bolts screw into nicely if you want to replace the substandard small bumper feet that come standard with the Kora Hermes.

Also, I had Steve replace the two larger caps at the back of the Kora Hermes (which handle the final Tube output going to the RCAs) with two large REL Audiocap PPT Theta Caps (Parts Express has PPT Theta's). The were at the top of the list under AA in "The Great Capacitor Shootout" which you can pull up with a Yahoo search. I chose them over the more costly REL RT caps because I wanted a midge more warmth as reported in the shootout. This was also a very positive modification with more richness and warmth over what appears are the stock Solen caps. Strangely, the more costly REL Multicaps did not do as well in the shootout as the REL RTs or PPTs.

That is it. Other mods for the Kora could include silver wiring for the digital signal rather than the stock copper. I recommend leaving the output wire as copper though to maintain warmth, although there is nicer copper wiring around than what comes stock in the Kora.