Well looking at the datasheet of the LDO's the PD2 uses, it shows lower noise at higher currents, and higher noise at higher voltages. But there's more than just noise that is of concern. The noise level at all output levels within the capabilities of the LDO are at levels far lower than matter anyways. You can see the PSRR below 1k gets worse as the load increases. There's also less "headroom" for transients.
Let's also keep in mind that the above example is an exceptional LDO. One of the best available. I find when manufacturers go out of their way to show charts like that in their datasheets, it's because the performance is exceptional. When manufacturers don't include charts like that, there's usually a reason as well. The LM7815 used in the stock Hypex board doesn't publish this spec. They just show a range based on voltage. I can imagine it would be far worse.
So far, I like both of them, even tho there are some differences. SI994 has kinda bolder presentation, while LME49990 has more accuracy (or speed...), but it sounds a tiny bit flatter. Both have great soundstage, LME49990 maybe not have as much depth tho, but a bit wider (however speaker toe-in can fix things like this). Percussion is tiny bit better with SI994.
I think i am gonna just let SI994s stay in the amp for now, since i have already listened to LME49990 for month and a half. Maybe i'll find some problems, and go back to LME49990, which i doubt at moment. However, i could live with LME49990s for a long time and be happy. Its good to have a backup like that.
If you need to minimize chance for overly sibilant presentation, give the LME49990 a try. SI994 is not overly sibilant either, but with LME49990 the sibilance is just perfect (with my system, maybe not with someone else's).
In overall, I am very happy i got in this input board bandwagon. It has been as much fun as i thought it would and the end result is even better i could imagine! With price of one amp, i got several different sounding amps, of which at least two are excellent.
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Any comparisons of the rev B boards with rev C? How about the Rev B boards with the Sparko's vs the Rev C boards with Sparkos? People might like to know if the new regulators and noise suppression measures improved upon the Rev B boards with the Sparko's.
In my system the Sparko's was already below my ability to hear hiss from tweeter. But with the LME49990 there was slight hiss with the Rev B board, now with Rev C there is none. Obviously there is no hiss with the SI994s either.
I mean for sound, not just noise. It uses different regulators and different circuitry. Do you also have DIP 8 LM4562's, and the Hypex OEM board? I'm most interested in the apples to apples comparison of the 2 boards with the same opamp. This will be meaningful data.
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So you don't have the Hypex boards or the DIP 8 LM4562's? The reason I'm curious about this is because I have both the Hypex OEM boards, as well as other boards. And when I compare with the Hypex boards with the other boards with the SIL 994's in them, I get a completely different sonic impression than Sebby shared. When I pop a DIP 8 LM4562 in my other boards and compare with the Hypex board, I prefer my board. But this is due to components, dual regulators, optimized layout etc. Since I trust your subjective evaluation, it would be nice to get another opinion.
You mean this comment by sebbyp?
On my system the SI994 creates the depth of the sound stage between the speakers and the listener. LME op amps creates sound stage that is starting at the speaker level and going deeper from there to the infinity. The other has kinda concave/laid back sound stage and the other is kinda convex/touching your face. In a way like it either way. If you know what i mean and maybe sebbyp means that too and can comment.
But in the end it could be anything. The shapes of sound stages can be manipulated in many ways.
On my system the SI994 creates the depth of the sound stage between the speakers and the listener. LME op amps creates sound stage that is starting at the speaker level and going deeper from there to the infinity. The other has kinda concave/laid back sound stage and the other is kinda convex/touching your face. In a way like it either way. If you know what i mean and maybe sebbyp means that too and can comment.
But in the end it could be anything. The shapes of sound stages can be manipulated in many ways.
It was more of the comments of "coloration" and "recessed" that haven't been something I've experienced with the 994's. They are the least coloured of any of the Dip 8 opamps I've tried. But without the Hypex board as a reference like Sebby has, it's really hard to know where he's coming from.
To my ears the LM4562's have a bit of a plasticky sound that I consider unnatural, and more coloured. Since the sil994's measure better than the LM4562's, as well as benefit from all the advantages of premium discrete transistors, there's no reason why I, as well as all others who have heard both should think it's coloration causing the perceived more natural, uncolored sound.
Ah, ok. That i can agree with that LM4562 has a plasticky sound. Kinda overly sharp, unnatural and even a bit dull. If something sounds good it does not make it "colored" and the dull sounding does not mean its "neutral". But then again if that is what sebbyp likes then that's the way he needs to do it. More power to NC500 and changeable op amps and input buffers.
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Based on what I'm hearing from you, it sounds like the rev C board is pretty transparent. We will see what Sebby thinks of the Phison PD2 connected through the buffer bypassed Hypex boards, compared to non bypassed after he gets more listening time in. That is a comparison that I have also made. The PD2 volume control goes from -120db up to +10 db. I found when used with the bypassed Hypex board, I had to go above 0db if I really wanted to crank it up with some tracks.
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