Success Rolling Opamps in EE Minimax DAC

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.

Anyone care to comment on the influence of the power supply on performance. There are competing DAC designs claiming the importance of power supply chokes or elaborate regulation and transformers to serve as important elements.

I suppose this is the sum of all the parts concession I can make but wonder too why the smaller parts are not given more respect or attention.

Kudos to Doug for shifting the direction.

La45- Your point is well taken about smaller or "simple" parts. The speed and Efficiency of Capacitors in the Power Supply and elsewhere cannot be overstated. The impedance or ESR of these devices has a stranglehold over the sonic merits of any audio device. A slow response Cap yields a lethargic and unenthusiastic presentation with lack luster dynamics. However, it also screws with pitch accuracy and intonation. There is no doubt that each component imparts a sonic fingerprint on the signal, but none come close to the musically destructive affects of slow caps IMO.

The biggest problems is that electrolytic caps are constantly aging and losing performance as the electrolyte dries out inside, a process that is unavoidable due to heat cycling and use. Sure they will work for years but not a peak efficiency. They must be tested and changed routinely as surely as a vacuum tube. They are not unlike a rechargeable battery, where the chemistry inside begins to age and perform underpar. I plan on purchasing a ESR meter soon to test capacitors for performance. From what I've seen, it's a far more revealing tool than a capacitance meter.

Many thanks to Doug for all the info on OpAmp rolling.

Be careful with ESR. If we talking DAC then we have most likely volatge regulators. Many voltage regulators don't tolerate low ESR very well. They tend to oscillate when ESR is too low or too high. Also supply current is more even going mostly to cover op-amps bias currents. Momentary currents are very small because of high impedances and easily covered from ceramic decoupling caps. I can see bigger problem in interaction between these ceramic caps and inductance of power supply electrolytic caps - creating parallel resonant circuit that tends to ring.