Those Awaiting EE Minimax DAC Opamp Rolling...

The article on extensive discussion of using custom Opamps in the Eastern Electric Minimax DAC is now posted on

Thank you for your patience; it was quite an extensive endeavor to conduct approx. 25 tests of Opamp combinations. Some people here have already discovered the efficacy of Opamp upgrades for this unit.

My proclivity to testing continues, as at this moment I have placed my final selections of Opamps back to their proper locations (you'll understand when you read the article) and have been using the SS output - it's a touch cleaner without harshness.

Once again, this activity will void the warranty but in all my testing I encountered no malfunctions with the Minimax.

Thanks for all your hard work! I am getting ready to try this DAC and was just about to order the first set of op-amps from your very first article. I'm glad I didn't.

What combination, in your opinion, would a vinylphile/tuber like me like the best? I know, but after all you did the work...
I just did a quick read-through and my initial comments:

Thanks for taking the time to try these things out and write it up.

You say "For example, the red in the first row means you will reverse the order, such that the double AD797 would go into locations U1 and U2, and the single OPA627 set would go into locations U6 and U7!" The doubles are supposed to go into U1/2 and the singles in U6/7, so I think you crossed up the U1/2 vs. U6/7 in that statement.

Also, when a single is used in the "wrong" U1/2 positions, the solid state output doesn't work, correct? So why even mention what op-amps are placed in U6/7?

Also, you state "(IN RED)U1/U2 OPA827 (dual) and U6/U7 OPA2604 (single)(END RED) In the previous two, and now in this example, the Opamp in the U1/U2 positions has been the OPA827 and has yielded excellent results." Since this entry is in RED, this means that the single and duals are swapped, correct? So why do you say that the dual is in U1/2 and the single is in U6/7, which is actually the correct positioning.

I'll give the article a good going over tonite, but these are the first things that jumped out at me on first read through.

Thanks again for your efforts. I think some of the info in the article may not be what you intended to convey, though.
Also, in the paragraphs that follow the table, each of the BLACK entries lists a sigle in U1/2 and a dual in U6/7, which are the reversed positions, yet these entries are in BLACK, indicating that a dual was used in U1/2 and a single in U6/7.
Unless I'm missing something (and that's surely possible!), the article seems to be full of mistakes.

And, according to the table, your final selection of OPA2604 in U1/2 and AD797 in U6/7 was not indicated as having been evaluated. (No "X" in the table)

Still based on a quick perusal - please let me know if/how I'm mininterpreting the info in the article.


Mfsoa, thanks for pointing these things out.

I'll have to go over the entire article once again to check for inconsistencies. In the text discussing the Opamps I did not use red lettering, only in the chart and listing of pairings, but I can see how that might be confusing by not carrying it through to the conclusion.

There were a couple reasons why I elected to discuss placement of reversed position of Opamps that influence the SS even though it would not be operative. I was unsure whether the absence of those Opamps might hurt the unit and did not want to run the unit without Opamps. I am not proficient at chart making on Excel and had to keep it simple and wanted the most straightforward system of categorizing and testing the dozen or so different Opamps without having some sit loose or making the charting even more complex. So, perhaps the placement of the inoperative Opamps is redundant but I felt it was better than the alternative potential issues.

I had the same sort of question arise with the Pathos Classic One MkIII tube hybrid integrated amp (reviewed) when used in Mono mode. The question was brought up since the unit would theoretically only use the tube in the right channel could the left tube be removed for preservation. Even Pathos did not know the answer, and I wasn't going to try it and risk a problem. Same with the Opamps; it seemed the most straightforward to keep them engaged rather than not.

I'll seek to rectify any mistakes. :)
Mfsoa, in response to your question about the final selection of Opamps, there were some aspects of the article writing and chart making which were niggling issues, making the choice of whether or not to include information problematic.

I was given a few Opamps which Cimmarron does not have in their listing for purchase, among which was the OPA2604. I indicated in the listing in the article which ones are available. It was among those tested, and performed well; I believe it may be an older Opamp. I wanted to report the entire results, but did not want to get people excited about a chip which is unavailable. Thus, I did not highlight it in the chart so as to not mislead people into looking for a winning combo which was unavailable to them. I found it to be a catch-22 situation, and attempted to report full results as well as not direct people toward an unavailable product. I felt that if I had indicated it in the chart as a "winner" many would look for it at Cimmaron and be disappointed, then rail about being misdirected. I attempted to split the difference between providing information and not giving misinformation. I found there were several situations like this which I attempted to handle in the reporting of the results.

Now, perhaps the OPA2604 is available elsewhere and can be made into a customized Opamp by Cimmaron, but I was not going to get into such discussions.