Sorry, the link is here - way too much involved in this...
Doug's fav OPA2604 is available in DIP8 format so that it can be dropped right into the DAC without an adapter. This'll set you back the princely sum of $11, though, to obtain a vast improvement in SQ.
Op-amp rolling in this DAC has taught me that equipment that has op-amps has no sound character of its own, independent of the particular op-amp in there. They make that much of a difference, IMO.
The entire affair has become convoluted (in regards to the concept of reversing positions of Opamps in the unit)
I made a mistake with the color indications in the article. Meanwhile, it seems credible concerns over reversing the positions of the Opamps threaten to overshadow the entire venture.
I sense to forge ahead would cause unneeded headaches; I have re-submitted the article removing references to reversed positions.
I urged you via email to correct a fatal flaw in your article, yet you chose not to address it in the least in your revision.
As far as I understand, when the tube output is selected, you are listening ONLY to the op-amps in the U1/2 positions. You are NOT listening to the op-amps in the U6/7 position. When the SS output is used, you are listening to ALL 4 op-amps. Obviously this distinction must be made very clearly for each description of the sound coming from the unit.
Therefore, unless you tell the reader whether each and every evaluation was performed with either the tube or SS outputs, the reader does not know which op-amps you were actually using. Obviously, since the reader does not know which op-amps are being used, any description of the sound quality obtained is completely meaningless.
You say that "Because of what is to my ear a more pleasing tonality I have tended to use the tube output the most" If this is the case, why do you then go on to desribe the sound of sets of ALL 4 op-amps, two of which are not even being used? Or, maybe you were referring to the SS output, in which case you actually were using all of the op-amps you mention.
The reader doesn't know, because you don't say
Again, this renders any discussion of sound quality meaningless since we don't know what op-amps you were actually listening to.
It is just as meaningful as saying that you have two preamps and three amps in for review and then describing the sound quality without telling the reader which pieces are being used!
I don't know how to be any clearer that the current article says absolutely nothing about about how particular op-amps sound unless you tell us which op-amps were in use!
You can fix this easily, by making two tables - One that lists the op-amps in U1/2, which were evaluated by the tube output. The second table will list the op-amps in both the U1/2 positions and the U6/7 positions, which were evaluated via the SS output.
I think as a reviewer you would like the reader to know what is being reviewed. Such is currently not the case.
Best of luck to you. I hope that the article can be revised once again so that you let can the reader know which op-amps were being used in your listening tests.
Mike, perhaps it was not clear that I tried to indicate in the article the tube output would be the standard in testing. I felt the tube output was overall preferred and that readers would be most interested in it. I would comment upon SS output when I felt it was meritorious.
I realize that the article does not show a comprehensive analysis of all permutations of the Opamps, prices etc. as I state in the article, "Considering Opamps, tubes, solid state or tube output, and the volume setting dozens upon dozens of variations are possible, and you can appreciate that Im not paid to run a lab." Considering that this was an unsolicited article, one I pursued on my own initiative as a service to the community to raise awareness of the activity of Opamp rolling, I secured some Opamps and tested them to see if Opamps make a difference - if that was not good enough, my apologies. If it is helpful, I found in general that the distinction between any given set of Opamps operated in SS/Tube output was less dramatic than comparing entirely different sets of Opamps.
I put in between 35-40 hours of communication with suppliers and manufacturer, setting up systems, testing Opamps and writing/editing. The goal was to introduce Opamp rolling and weigh its efficacy, nothing more. I am disappointed that not one individual from the professional or amateur DIY/Mod community contacted me to warn me of the potential danger of suggesting reversed Opamps. The heads up came from Bill O'Connell of Morningstar, the distributor, and I'm grateful for it.
I have learned information about the situation which has left a negative conclusion in my mind about the incident, but I do not wish to discuss it publicly.
I am finished with the topic. People can make of it as they wish.