It seems like I can improve the S/N from the Denon DVD-9000 dramatically, over 6db, with a simple tweak which might apply whenever unbalanced interconnection is used. (Or it might be peculiar to this set of components, etc.)
I connected an extra set of stereo cables from my Denon DVD-9000 to the Emotiva XSP-1 Preamp. I deliberately connected the unused surround outputs to an extra of the preamp. As the outputs are not carrying any signal during this test, they may act as a better ground connection than the initial stereo pair of cables connected to the main output. It also turned out that just adding one unused cable made nearly all the difference. Adding a second unused cable gave little additional improvement, so I suspect more similar cables would only be for the very obsessed.
The results are shocking. I got over 6dB improvement in peak unweighted S/N ratio from having the extra cables. Most is clearly hum but some is noises that have a 60 Hz period. This is similar to improvements I see with balanced interconnects over single ended.
For the test shown I had the Denon DVD-9000 playing a regular CD (not HDCD which might be tricky) but in pause for the entire duration of the test. The Emotiva XSP-1 gain was set at 0.0dB and not changed.
In the starting condition, I had the two extra cables connected from the surround outputs on the Denon to another input on the Emotiva. At two minutes, I removed the first extra cable on the Emotiva side. At 4 minutes, I removed the second extra cable. At 6 minutes I removed the one of the cable connections on the Denon Side, Around 8 minutes and 40 seconds I removed the second cable. Then about 10 minutes I reconnected one of the extra cables. Around 11 minutes I reconnected the second extra cable, so it was back to the starting condition (to be sure nothing else had changed...and it hadn't changed appreciably, compared to the main effect, which is huge).
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| DVD-9000 with and without (center) extra interconnects |
There is visibly far more hum and noise (it's mostly hum but with some strange high frequency bursts that repeat every 1/60 sec) in the center condition which is just using the two stereo interconnects. As soon as just one unused extra connection is made, the hum and noise drops 6dB. Then when the second cable is added it improves a few tenths of a dB more. What is remaining with the extra cable(s) seems to be almost entirely random high frequency noise and the high frequency bursts at 1/60 sec are eliminated. It seems hardly worth trying more than two (I have no more good cables to try anyway...I had to buy this pair last week)...but just adding one unused cable is huge.
(Possibly it has something to do with the grounding on the Denon DVD-9000...but everything about the DVD-9000 seems impeccable. BTW, I have Direct Mode set to 2 which shuts off video output. Also it could have to do with the grounding on the XSP-1. The extra cables were connected to Input 3, which is in a different bank.)
Another curious thing is that even connecting the cables on the Denon side alone seems to help. I also saw that kind of behavior with the Video output--having a stub video cable connected (but not connected to anything else) makes the DVD-9000 quieter, even in Direct Mode 2.
Something that might be even better is connecting a very heavy wire, possibly mostly buss bar, to the grounds of two plugs and use that as the "extra" interconnection. I think I've seen things like that sold as tweaks before.
Both my original interconnects and the extra interconnects are both Blue Jeans Cable LC-1, which has the best single ended shield configuration and plugs for hum and noise reduction. The originals, unabused, are just a few years older. These are very solid and thick cables custom made by Beldon with a double braided shield, and terminated by Blue Jeans with very solid Canare RCA jacks. It's hard to imagine they could be broken or even slightly out of spec.
(Somehow, leading up to these tests, I had intended to upgrade the previous cables to LC-1 to see if that helped. From above, it looked like I had been using standard grade Radio Shack cables from the mid 2000's. Possibly intended only as a temporary fix until I got better cables. But when I actually got close enough to change the cables I could see they were actually LC-1's. It's funny how when the picture is unclear my mind can instead give me a clear picture of something wrong.)
Previous measurements shows unweighted peak S/N ratio around 93dB for the Denon DVD-9000, and 95dB for the Oppo BDP-205. That 2dB difference was entirely hum and showed the benefits of balanced interconnection. Both players actually have "120dB S/N" specification, the limiting factor is my Tascam DA-3000, which can only sample with 113dB S/N, which like all factor specs is A-Weighted, meaning the unweighted S/N is likely in the 95-105dB range.
With these changes, it looks like the Denon will be either identical to or maybe even better than the Oppo, at least for practical purposes when sampling with the Tascam DA-3000 for transcription or playback through my DSP based system.
If the test seems strange...it's partly because it followed an earlier series of tests which were inconclusive because I could never be sure that either I had reset the starting conditions in an identical way, or that the Denon hadn't started muting in some extra way. Leaving the player running the whole time and going back to the starting condition at the end were the ways to remove these uncertainties that arose in previous testing despite attempts to control the starting conditions rigorously. The Audacity screenshot was made after 80dB of Audacity digital amplification. The noise seems higher than some previous tests because the Emotiva volume control was set to 0dB instead of -4.5dB (which I had been using for HDCD since the Denon actually expands peaks at least that high above the normal CD-level 2V output, though I discovered on album Poems of Thunder that in some cases HDCD peaks reach 5dB). So add 5dB to the wideband unweighted peak S/N levels for comparison relevant to HDCD which is mainly what I use the Denon for.
Here are the peak levels from various parts of the test (correcting for the 80dB gain but not the additional 5dB available output on HDCD).
First 2 minutes (extra cable pair connected)
-91.05dB (would be -96.05dB including 5dB extended HDCD peaks...this is better than previous data for Oppo which was -95.3dB)
Second 2 minutes (only one extra cable connected to Emotiva but both on Denon)
-90.3dB
Third 2 minutes (two extra cables connected to Denon but nothing else)
-87dB
Fourth segment (only one extra cable connected to Denon)
-85.5dB
Fifth segment (no extra cables connected to Denon)
-84.4dB (not including some early and late peaks which might be due to connection in progress)
-84.3dB (including suspicious early and late peaks)
Sixth segment (one cable reattached between Denon and Emotiva)
-90.0dB
Seventh segment (both extra cables connected between Denon and Emotiva)
-90.6dB
I could immediately add 5dB to all these numbers for HDCD because HDCD peaks are 5dB higher on the Denon, so I have to turn volume down 5dB on the preamp. (Although, then the noise of the Emotiva itself would be a larger factor than it is, so results are not completely predictable.) Then these are all unweighted peak measurements, which would improve by 10-25 dB with RMS and A Weighting. And I don't know how much of these measurements are proportionally hum and ultrasonics. It would be complicated to do weighted and RMS measurements on these data (I tried but ran into a snag) and only useful for bragging rights anyway since I don't see how I'm make these improvements significantly better without engineering a fake "grounding bus" interconnect as I suggested above. This present improvement is great and I'll look for it in future connections. (Though perhaps I should do more investigations to be sure this is a real effect and not a fault of the old cables, for example.)
My guess is that these numbers are showing at least 108dB properly A weighted RMS S/N, but with a mean guess of around 116dB S/N RMS A-Weighted based on the idea that RMS and A-Weighting would improve things about 20dB...but that can't be true since it exceeds the specs of all equipment I'm using (except the Denon itself, at 120dB S/N). In reality all the noise levels are somewhat additive, so say if all 3 units (Denon, XSP-1, and DA-3000) had 120dB S/N, the result would be about 110dB S/N. But the Tascam DA-3000 (balanced in) is at 113dB and the Emotiva XSP-1 is at 115dB (unbalanced in to balanced out).
Though the second additional cable gave only a fraction of a dB additional benefit, the 60 Hz component is still not entirely gone, so there might be some further benefit from grounding bus, etc.
*****
I have decided not to do any further investigations on this for the time being. It could be, for example, that the initial cables were faulty (though they're fairly new and very rugged Blue Jeans LC-1), so if I swapped the brand new "grounding" cables for the initial ones, I might then have the benefit of low hum with only one pair.
Or it could be how the "grounding cables" are routed differently, perhaps out of EMI fields.
Adding cables might not always help. I'm not claiming that at all. I think only that if you see a hum issue, such a thing might be worth investigating.
In this cause there was no audible "hum" issue that I ever noticed. It's deep down in the noise floor, deeply below the ambient noise in the room. At -90 to -100dB or so in the electrical signal, at max output around 100dB, it would be 0-10dB, or -24 to -4dB "A Weighted". If the two initial cables were somehow defective, and they would both have to be defective for there to be hum, one would expect much higher hum level than that.
There could be a straightforward explanation such as that each cable lowers the ground resistance. Except it doesn't seem to work so incrementally. Instead, the first extra cable made nearly all the difference.
It really seems like there were additional ground currents between the player and preamp, and routing these additional currents lowered the hum induction that occurred in the interconnect.
But why are these ground currents choosing to go through the additional cable(s) ?
Adding one more cable would in theory not be adding that much more conductance.
Instead, it looks like there is something peculiar going on. Perhaps the grounding of the surround jacks on the denon is closer to the power supply ground. And because of that, the extra currents DO choose to go through the new cable(s) selectively, giving a reduction in induced hum.
The Denon 9000 is grounded and so is the Emotiva XSP-1 (IIRC...or it's connected to grounded gear). Ground loops may be to some degree inevitable, and perhaps it's a wonder they were already so low.
I think therefore that this finding is almost certainly some kind of fluke as I've described, not a general rule.
But it certainly looks like, I have already stumbled upon a lucky optimum. Any change is likely to make it worse. Then, assuming micro degrees in cable routing are also a contributing factor, I may find it hard to make it this good again.
And to do this test in the fairly incontrovertible way I have (as opposed to separate tests, in which some extra variable might have changed) means more wear and tear on my equipment, including my beloved Denon DVD-9000, which is very long in the tooth. (In fact it already started acting up, with the drawer not pulling all the way in once, perhaps in protest. Now I see it may do that so it looks OK but doesn't register the incoming disc, showing only 0's on the display.)
To do a proper test proving the initial cables were the problem, I'd have to do lots of cable plugging and re-plugging while it's in pause with a spinning disc. Almost every time, with the very tight LC-1 Canare connectors, I have to push so hard it jostles the Denon slightly.
To do this test, to make the Denon about as good as the Oppo (which uses balanced connections!), I thought it was worth this, but just once, not for a series of follow up tests to PROVE the causal mechanism, which may not even be possible.
To reduce such wear on my equipment, I'm ending this test here, at what appears to be some kind of lucky optimum in hum reduction. "If it ain't broke, don't fix it." At least for now. Next time the Denon is removed I'll know to check the cables again.
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