I decided to try the Sparkos op-amps in my NC500 Mk II mono-blocks. I ordered the 4 op amps on ebay from Sparkos since ebay has an easy way to make an offer (less than full price). Since I was buying 4, I thought they'd be willing to accept a reasonable discount and they did. I placed the order on Monday and had them in my hands on Friday.
The Nord amps replaced by Krell FFB-300. I really liked the sound of the Krell, but the transformer was starting to hum and the right channel started distorting. I had already had the caps replaced by Krell about ten years ago, and the price to have the Krell fixed was more than I could justify, particularly since a local audio shop was willing to give me some trade-in value on it toward a new preamp.
After several hundred hours of use, the Nords with the SI op-amps was started to sound quite good. There were some areas where the Nord improved on the Krell, particularly noise and clarity, and of course, lack of heat, expensive electrical bills, and back aches from trying to move it around. On really good recordings, it was quite good, but on less than stellar recordings, it really exposed the flaws and was not as pleasurable to listen to compared with my Krell.
For me, the Sparkos op-amps are a definite improvement. It may not be quite as revealing as the SI op amps, but it's more pleasurable to listen to. It's been so long since I had the Krell (working properly) in my system that I can't say it is now better than the Krell, but it does well on the things that are important to me (realistic vocals, dynamic sound, good pace and rhythm, and tight, reasonably deep bass response). I also like good imaging, but as long as the images are stable, fairly wide and moderately deep, I'm happy. I wouldn't sacrifice the other parameters for superior imaging.
I'm now in my 60s and my hearing isn't what it used to be (too much cycling and driving convertibles), so I doubt I'd hear any bad high frequency artifacts over 10 Khz at this point.
The sound quality I'm now getting out of the Nords is at the level where I doubt I'd go back to a big class A-A/B amp. I'm not at all saying that Class-D sounds better than the big iron amps. I don't think we're there yet. But they are getting a LOT closer, and now offer pretty amazing performance for the money.
I remember hearing my first class-D amp in the late 70s (made by Infinity if I recall), and it was truly awful, and would blow up at the drop of a hat. As an electronics engineer, I thought there was potential in the concept, but pretty dramatic strides in transistor switching speeds, control circuitry, and feedback design would be required before I'd consider owning one. I never really considered looking at Class D until I was forced to consider replacing my Krell, but I now do think that Class-D amps deserve consideration, particularly for more modest budgets.
Anyway, I think unless you are driving the Nord with a fairly warm sounding (and forgiving) tube preamp, I'd recommend the Sparkos op-amps to start with instead of the Sonic Imagery op-amps.
- JayT
