Success Rolling Opamps in EE Minimax DAC

At the moment I'm not using anything exotic, just the stock 12AU7 tube. The reason is that for testing Opamps I felt it would be far more beneficial to use the stock unit's tube as opposed to an alternative. If I use the stock unit in testing Opamps the results are applicable universally, versus for a subset of those who roll tubes.

I've got a couple others but no time now to work with them post-Opamp rolling.

i own the minimax dac. i have several nos tubes. i believe that if you use the tube gain stage, you bypass the opamp. is this correct ?

if this is correct, it may be more productive of your time to tunr the dac with a tube rather than try to find a suitable opamp.

also, if i am correct isn't the absence of an opamp preferable to the presence of an op amp ??

Mrtennis, to my ear the influence of the Opamps supercedes that of the tube rolling.

I'm checking on the SS/tube output question.

Doug, As you know there are two pairs of opamps in the EE DAC: Two NE5532 dual opamps for I/V (current to voltage) for tube and solid state; and two NE5534 single opamps for solid state output only.

Operating the EE DAC with the tube stage engaged bypasses the single opamps' circuit.

I generally prefer operating the DAC in solid state mode and found that rolling a variety of quality (read "expensive") tubes didn't have nearly the beneficial effect as did switching to your LME497X0 opamps.

Njs, you are right on the money with your answer. I received the reply from Alex Yeung, designer of the Minimax DAC, and you have it right.

One set of Opamps are always used regardless of output SS/tube. The other set of Opamps is only used with SS output. In my testing I heard what I felt were clear distinctions with different Opamps using the tube output but I did not want to comment definitively until the question was answered, providing verification.

Yes, it is certainly an acceptable choice to run the unit in SS output and with the upgraded Opamps it is quite refined.