Part I. Only variable of course being what opamp was plugged into the LPF sockets (everything else like cables and measurement procedure the same). Let's start with 16/44:
|Noise Floor - notice the 60Hz hum|
|Stereo Crosstalk - no change to RCA cables use.|
Here's the data for 24/96:
II. Digital Filter Composite (DFC)What I've come to call the "Digital Filter Composite" (DFC for short) based on the original "Reis Test" as discussed in Stereophile (with LM4562 opamps):
Now with MUSES 02 opamps installed:
Again, some differences which are obvious on objective testing. Of course the general shape and noise levels look about the same due to use of the same internal digital filtering algorithm. Notice however the MUSES 02 graph shows more second harmonic and intermodulation products at 35-42kHz but slightly quieter around 50kHz. Interesting to see but again hard to make a case for audibility as this is all ultrasonic and as far as I can tell, the 20-20kHz noise floor whether with the 19 & 20kHz sine waves playing or digital silence appear essentially no different.
III. J-TestFinally here's the J-Test - first with my LM4562NA opamps:
And with MUSES 02 installed:
As expected, no difference of significance as far as I can tell. Changing opamps would have no effect on timing parameters and as we saw above, noise floor differences were not in the audible range.
IV. Subjectivity...Subjectively, well, I did pay about US$90 for the two opamps (that's how much it costs from a place like Mouser) so I could tell you that the bass line on "My One & Only Love" on Oscar Peterson Trio's We Get Requests sounded phenomenally deep with immaculate control after I plugged in the MUSES 02. I could say that listening to Ben Webster's tenor sax on "When I Fall In Love" (from The Soul of Ben Webster) sounded remarkable smooth with excellent tonality, as fine analogue recordings and playback should :-). I could tell you that Philippe Jaroussky's voice on Caldara In Vienna (Forgotten Castrato Arias) sounded beautifully other-worldly and "present" after inserting the MUSES opamps. I could say that those chaotic bells and chimes on Pink Floyd's "Time" (Dark Side Of The Moon) was fantastic in terms of how palpably real and how wonderfully open the soundstage was. I could say the MUSES 02s were a real improvement over the LM4562NA chips they replaced and how they elevated the standard of the DAC from something that sounds like a US$500 unit to something competing at the US$1000+ level! Yes, I could say all these things because these ideas came to mind while listening here and there over the last 3 months, as I mulled over how I was going to describe what I heard.
But I will not say those things above :-). Seriously folks, without the ability to switch between two identical DACs with different opamps installed, the subtle differences I thought I heard are likely the result of selective attention and limitations of echoic memory rather than correlating with objective reality. As Nobel prize laureate Richard Feynman wisely reminded us: "the first principle is that you must not fool yourself, and you are the easiest person to fool." That's just the nature of subjectivity. Of course that's not to say subjective opinions are useless, rather, I think it's an acknowledgement that there is a "gradient of certainty". Some things are reasonably obvious and clear without needing to double check as in an A/B test, but when differences are at best subtle, it's honest to not get ahead of ourselves with proclamations of significant differences and flowery language. The music and DAC sounded great before, and certainly I'm quite happy with the sound after the MUSES 02.
V. Conclusion...I guess, ultimately, I can say that the Essence One with MUSES 02 opamps in the low-pass filter circuitry of the machine did sound good and I would have no problem enjoying music with them... Worth US$90 for what amounts to very slight objective differences (like what looks like 0.1dB changes in the frequency response at the extremes, and measurable ultrasonic noise floor difference) compared to the US$4 opamps they replaced in the LPF circuitry of the DAC? Mmmmm... No. But I can at least say I've tried for myself. And here's some data to consider...
Time and motivation permitting, I'll see about trying these opamps further down the circuit for RCA or XLR output and see if that makes more of a difference. Remember, we're talking about a tweak here. As we have seen before, short of new speakers, improved room acoustics and better mastering, except in the words used by promoters, it's best not to expect too much beyond subtle changes only.
As usual, I would love to see if others have objective results while "opamp rolling".
For the DIY'ers out there, Raoul Trifan posted on Head-Fi forum a mod to the power supply of the Essence One to substantially improve ripple and lower noise. Check it out!
I hope everyone got some rest and ready to take on 2016!
Prepare for the MQA onslaught at CES 2016 :-). It'll be interesting when comments come out with impressions of A/B listening.
BTW: I'd be nice if someone can ask if there's any DRM mechanism embedded in MQA and clarification if MQA is able to encode resolution >16-bits... Of course, any details about just how it "de-blurs" timing anomalies in a PCM stream could be enlightening! Thanks.