DirectStream DAC produces audible hiss when connected directly to M700's


#1

Scratching my head on this:

New Stellar M700’s came Monday. I was hoping to run XLR cables from my DS DAC straight into them. When I do, I get a hiss through the speakers that is audible from my listening position.

  1. The hiss is at a constant volume (regardless of the volume setting on the DS).
  2. It goes away entirely when I turn off the DS. Comes right back when I turn it on again, even with no music playing.
  3. The hiss is also present, though not as loud, if I connect the DS to the amps using RCA cables.
  4. If I connect the DS directly to either of my other amps (a Parasound HCA 2200ii and an Audio by Van Alstine hybrid), there is no hiss whatsoever. Dead quiet.
  5. Today I brought home the DAC/preamp from my office system, an Audio Alchemy DDP-1. If I put that into the chain between the DS and the amps, then there is no hiss whatsoever. Dead quiet. (And everything sounds fabulous, by the way – these amps are great, even with only 36 hours on them.)
  6. I can’t see how it could be a cable issue, because I’ve tried multiple cables and the same cables produce no hiss when connecting the other combinations of components.

So: DS straight into Stellar M700’s, constant audible hiss. Every other combination of gear, no hiss at all.

I would really like to be able to take my office preamp back to my office and run the DS straight into the M700’s. I’d like not to have to buy a new preamp right now. Any suggestions?


#2

Try enabling the -20dB ‘filter’/attenuator in the DS


#3

Thanks! That does solve the problem. I’d still like to understand what the difference is between the M700 and my other amps that makes that necessary. Impedance? Gain?


#4

Gain structure and your speaker efficiency. XLR are also 6dB hotter than RCA. I bet your speakers are relatively efficient, 90dB+?

Now that you have a world class dac and world class super power efficient amps, consider adding the world class BHK preamp in between :wink:


#5

Actually, my speakers are the relatively insensitive KEF LS-50’s. But my room is small so I am pretty close to them.

I would love to have a BHK preamp, but its not in my current budget. If I could find a fully balanced tube amp for one third that price…


#6

tcatch - Not sure if this helps or not, but my Jr straight into my M700s makes no sound at all. I ran with the attenuation out. Of course we have different speakers, cables etc but I have never had a noise issue. I have since added a pre (for other reasons) which improved overall sonic quality to my ears… However I have heard of folks using a pre for noise related issues which I’m not sure should be a initial solution to a issue that should not be there in the first place. However, like I mentioned, in my system the pre really helped overall anyway so it would be here regardless. BTW- I was looking for a balanced, black, pre w/ remote and they are hard to find. However if you cannot jump on a BHK yet you might look at the Cary SL-100. It is voiced well and sounds outstanding between the two. Well within your price range. Especially this guy- https://carydirect.com/b-stock/sl-100.html


#7

Thanks Roninaudio – that Cary preamp looks rather perfect for my needs, at least until I can afford the BHK .

On the original issue: your experience has me puzzled again. Is there a difference between the DS and the DSJr that would account for it? I was thinking that the basic thing going on is that the M700’s are just more sensitive and have higher gain than my other amps. Reading in the DS forum I discovered that the ‘hiss’ problem is fairly well known and that PS Audio recommends using the attenuation if you find yourself listening at volumes less than 66 on the DS volume control. See this thread for example:

At first the discussion is about a problem specific to a particular firmware release, but further down Ted Smith explains that there is a certain amount of background noise that is unavoidable given the DS’s design and that the attenuation option is there to deal with it.

But, in that thread, Ted Smith is saying that there is more noise in the junior than in the senior, because the senior has expensive noise-reducing parts between the FPGA and the output. So it would seem that you should be hearing more hiss than me, not less. So, I’m still puzzled.

Adding: here’s a link to a more thorough explanation of the hiss issue. Still seems like the problem should be worse in Jr than in Sr.:


#8

I ran the DS direct into the M700s and had no hiss at all. Complete silence. At either attenuation setting (I tried both, but left it un-attenuated ultimately). Now, running the DS direct to my Ayre monoblocks, and same, no hiss/complete silence regardless of volume. Inputs I used include USB and optical. Speakers are 87db sensitive monitors.

I have to think you have something else going on, for which the attenuation is basically a Band-Aid.

Power or input cables, etc. Try replacing each. Try only connecting 1 input at a time. Change power source maybe.

Fwiw, I don’t think you need a pre-amp. I think the DSD sounds incredible direct to my amps. That said I haven’t heard an extremely high quality pre in this system, just a high quality integrated.


#9

Yeah, could be bad tubes as well. Try each input separately as suggested. No you don’t need a ‘great’ preamp, and I wouldn’t get one to solve the hiss issue, though it will, I would get a great preamp to give that magic sound that simply isn’t there when going direct to amps. Albeit at a financial cost.


#10

I think Jonm and brett66 answered your question. As I mentioned I did correspond with a gent that got a BHK pre and part of the reason was hiss. Unless you got deep pockets, that is not an optimal solution as we all agree I think. I have seen the noise issue documented but I think there are plenty of us with no issue at all. Not sure why but as mentioned, perhaps a systematic dissection of your system will reveal a culprit?

As for the pre , I got one solely for the reason of increased fidelity. Dac direct to M700s was brittle and lacked imaging (this (imaging) I realized after the addition of the pre). I also listen at fairly high volumes at times so perhaps if some folks don’t the direct connection route is totally fine. I got the Cary to get me by until I upgraded but it sounded so good for the $, I was not sure I needed to. However I found a great deal (today actually) so I upgraded and the Cary is for sale locally for now. However to your point, the other gentleman on this forum did a lot of investigative work and still had what he perceived was an audible noise issue. Variability from unit to unit?, amp speaker combo? (Mine are 4ohm 87db), electrical, RF or EMI?. I wish I could help ya…