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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.
128x128plangco
plangco's avatar
plangco OP
158 posts
 
The basic bench fee mentioned was for the Op Amp change and better power side caps for the Op Amp only.

Changing out the wiring and the Caps for the final tube processing would be more. Better to talk to Steve Sank of Talking Dog Transducer Company Tucson, AZ about any extra fees beyond the Op Amp work.

I can say this, it has proven worthwhile big time. You can check cap prices at Micheal Percy Audio or Parts Express (PE seems to uniquely has the slightly warmer REL PPT theta caps). Some regard the REL RTs as better though, and the Great Capacitor Shootout felt that the REL multicaps were over rated and not as good surprisingly. For the type of sound that the Kora projects, I selected the REL PPT and am very happy with the choice.

If you want to read up on REL cap differences and others, one source is to do an internet search for 'The Great Capacitor Shootout'.

By the way, the original factory stock selector switch tends to go bad over time. If it is acting up at all, you can have it changed out for a better switch, which I did.
plangco's avatar
plangco OP
158 posts
 
Forgot to mention that another wire that shows great promise for the digital signal is magnet wire. Magnet wire is commonly sold as hyped up Speltz ani-cable. By nature, it tends to convey the same detail and openess as silver without the harshness of silver and it retains the warmth of copper.
plangco's avatar
plangco OP
158 posts
 
Bang for the buck, changing out the OP Amp and the power caps that precede it along with switching the brass RCAs to gold over copper would be the easiest budget based change which would involve minimal labor and materials with significant enhancement of sound. Those changes are followed expense wise by changing out the two main caps which process the final tube output. Later changing to better wiring would be a point of diminishing returns for cost vs benefit.

Changing the two big final output caps alone to REL (which I like as they retain a similar sonic signature but are superior sounding in my opinion) may cost around $70 to $100 depending on which you buy. Changing them out involves some additional labor in removing the board.

Again, I have found Steve Sank to be very reasonable and honest with his fees and supremely skilled and experienced.

Again, for help in choosing caps, check out 'The Great Capacitor Shoot Out' on the web. Not, the the final say, but a great source of information.
elenialexi
1 posts
 
We have the Kora Hermes and Kora Eclipse excellent condition, and Metronome Technologie Pieces They are beautiful, can
you suggest prices as I would like to sell them No Room Now
thanks EleniAlexi
plangco's avatar
plangco OP
158 posts
 
I recently had Steve Sank of Talking Dog Transducer Co (Tucson), go completely through my Kora Hermes DAC installing Nichicon's best Muse KZ capacitors with higher values of course and some top grade Audiocap film caps (theta as per my request). He also rewired my Kora Hermes DAC so I can flip a switch and choose between 12AU7 or 6DJ8 tubes. (I prefer the Amperex 12AU7 myself by the way post mod). And among other things, he also put in some superior oxygen free wiring to replace the original Kora cheesy copper wiring, and some gold over copper RCAs and a new better input switch as the original Kora's switch had fallen apart on me.

I was a little concerned, messing with the original caps. However, my only regret is not having done the mods sooner. What I hear is absolutely wonderful sound, heads above even the original Kora sound. Absolutely exquisite.

The sound stage has expanded dramatically. Instruments just float in acoustic space. There is now a 3D depth to the music that was not there before. The mids are more organic, yet still rich, vibrant, and open. The highs and bass are much improved also. The original Kora had just a little bit of glare in the upper mid-range and that is now gone. Yet there is a nice shimmer and extension and a almost glowing vibrancy and clarity in the mids and highs that I didn't hear before. I just want to sit and listen to almost everything that plays through it.

FYI, the Nichicon Muse KZ caps which replaced the aging Phillips caps aside from sounding wonderful are ultra reliable. Joule puts them in some of their $4,000 plus components (I had one, the modified Kora sounds better to me). My modified Kora Hermes DAC will probably outlive me and then some. And it will have to because this DAC is not for sale. After trying over a dozen different DACs on the market, I have finally found one that I can die happy with.

Steve deserves some credits: I think he is a gifted designer and modifier of both tube and solid state gear. His father worked with RCA in development and Steve has 35 years of experience starting from there designing and modifying equipment. His insight and work shows it.
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