Soft (and loud!) hiss from your speakers with C1/A51?

[netarc]

I'm trying to troubleshoot a *hiiisss* emanating from the speakers when the C1 and A51 are connected and powered up. At a steady state (no inputs playing), the hiss is actually quite loud ... one can hear it from all 5x speakers quite clearly, even from a distance of 10'!

Tried toggling the ground lift on the A51, and even a cheater plug (yes, I know the latter does the same thing, just tried it to be complete), but no effect on the hiss.

Upon disconnecting all inputs into the A51, though, the hiss is *significantly* reduced. Here's where it gets interesting - the C1 & A51 were connected with balanced (Monster XLR) cables; when replacing these with unbalanced (RCA) cables, the hiss againg is significantly reduced (though still somewhat louder than with nothing connected to the A51)!

Very odd - and makes me wonder whether there may be an issue with the C1's balanced outs? Any thoughts/suggestions would be appreciated!!

[Peter Nielsen]

This is supposedly "normal" when the C1/A51 are used with very efficient speakers (say >94dB/1W/1m). See this thread where user rocasi says he can hear the hiss from his seating position when XLR is used:

Although my system has a low noise floor with XLR connections, I can still hear a hiss from my seating position. I worked with Parasound troubleshooting this issue and found that with my 103dB/m efficient Klipsch, the hiss cannot be lowered.

One possible problem could be the position of the input selector switch on the A51. Check that the toggle switch is set to balanced.

Ground problems usually cause a low frequency 60Hz "buzz" (or 50Hz in Europe), so if what you are hearing is a "hiss", then it's probably not a grounding problem.

Peter

[Chris D]

netarc, as Peter said, we've documented with Parasound Halo products that the balanced connections increase the output level, which raises noise floor if your efficient speakers are putting out a hiss. That's why I decided with my Klipsch speakers to go with unbalanced from the beginning.

I do have a slight hiss when power's on, but I haven't fully troubleshot yet to eliminate it. There's so many things for me to tweak with my theater.

[netarc]

Thanks for the info, folks ... appreciate it. Going to look up the efficiency of the speakers and see if they're high efficiency - will report back!

[nicholtl]

I guess since you tried a cheater plug, it's pretty much the same thing, but when I had an audible hum with my C2/A51/A21 combo using balanced XLR's, the cure to the problem was simply removing the ground pin on my C2's PS Audio powercable.

[netarc]

Surprisingly, the cheater plug trick didn't work ... which makes me think this issue doesn't have anything to do with a ground loop.

[netarc]

This is supposedly "normal" when the C1/A51 are used with very efficient speakers (say >94dB/1W/1m).

So I have some more info on this - first of all, our resolution _was_ to swap the XLR for RCA (unbalanced) cables ... this significantly reduced the hiss!

I found the specs on the speakers, too:
Fronts: KEF Q65 - Sensitivity - 2.83v @ 1m 91dB
Center: KEF 100 - Sensitivity - 2.83v @ 1m 90dB

I gotta say I'm surprised that the balanced/hiss issue occurred with these, as they don't seem particularly sensitive?

Hmmm...anyone know whether this issue's been reproduced/acknowledged?

[Chris D]

No, I don't think it's a bug or problem, much less something to be acknowledged as such. I don't know quite why it was engineered that way, with the balanced haviing a higher output, but it seems like a "okay, just go with it if it even affects you at all" kind of thing.

No, those speakers don't seem all that sensitive. My Klipsch speakers are up over 100 db/W.

For me, using the ground lift on my A21 and A51 did seem to help the hiss. Did it not for you, at all?

[Indytown]

I have found that when you use balanced interconect the output is increased a few db (3 to 6bd); this may be for (1) use on longer runs where the pre-pro is in one location and the amp is say 30 to 50ft. away (2) the balanced connects will repell stray noise over longer runs.

When you hook-up you balance connections and you are not using them for long runs you need to go back into your room calibration setup menu and adjust the SPL to your sitting position again- just a thought.

[netarc]

No, I don't think it's a bug or problem, much less something to be acknowledged as such. I don't know quite why it was engineered that way, with the balanced haviing a higher output, but it seems like a "okay, just go with it if it even affects you at all" kind of thing.

No, those speakers don't seem all that sensitive. My Klipsch speakers are up over 100 db/W.

For me, using the ground lift on my A21 and A51 did seem to help the hiss. Did it not for you, at all?

No, the ground lift had no effect ... but I didn't think this was a grounding problem (esp. since a cheater plug on the amp had no effect), I thought it was specific to something in the way the C2 handles balanced outs? Granted, said balanced outs result in a 3-4dB "louder" sound, but that shouldn't account for an audible hiss, since the hiss is almost as prevalent at even the lowest volumes.

[psychdoc]

I have been following the posts here for a year with the thought of buying a C2 and A51 but this issue gives me pause. Does anyone know if this "hiss" problem is also found with Definitive Technology speakers? As an Army Doc overseas (but soon to move to Hawaii--can't wait!!) I will be unable to audition a lot of equipment so any info will be greatly appreciated.
Also, has anyone used the lip sync feature? If so, what is the longest time delay you can use? I am thinking of buying the new samsung 1080P 67" rptv that comes out in a couple of months. The picture is being described as amazing and far beyond the best you can buy today but there seems to be an issue with lip sync due to the heavy processing that the T.V. does. If this lip sync problem exists then the C2 may be the easy fix as long as it doesn't add the problem of a very annoying hiss. Thanks.

[netarc]

I have been following the posts here for a year with the thought of buying a C2 and A51 but this issue gives me pause. Does anyone know if this "hiss" problem is also found with Definitive Technology speakers? As an Army Doc overseas (but soon to move to Hawaii--can't wait!!) I will be unable to audition a lot of equipment so any info will be greatly appreciated.
Also, has anyone used the lip sync feature? If so, what is the longest time delay you can use? I am thinking of buying the new samsung 1080P 67" rptv that comes out in a couple of months. The picture is being described as amazing and far beyond the best you can buy today but there seems to be an issue with lip sync due to the heavy processing that the T.V. does. If this lip sync problem exists then the C2 may be the easy fix as long as it doesn't add the problem of a very annoying hiss. Thanks.

Psychdoc...I wouldn't spend too much time worrying about this issue unless a) you plan to use the controller's balanced outputs *and* b) your speakers have a high efficiency rating. From what I can gather of most folks' experiences, it's only under these circumstances that such a hiss is present. As I mentioned, the resolution for us was simple - switch from balanced to unbalanced outputs.

Haven't had need to try the lipsync feature yet, so I'll let others comment on that.

[Chris D]

Hiya, psychdoc, and welcome to Club Parasound and the Guide! :banana: I don't need the lipsync feature for my setup, but for poops and giggles have played with it. Don't remember the number value, but it can introduce a significant delay to counteract... well... a delay. It didn't introduce a hiss. (hey from another military guy, too)

Like netarc said, I wouldn't worry about hiss. It only pops up in certain equipment configurations, and then can be counteracted. For DT specifically, do you know which models and the efficiency ratings?

[nicholtl]

Psychdog, just to clarify, just because you have high sensitivity speakers (like myself and Chris D. do - Klipsch), and used balanced outputs (like I do too), it doesn't necessarily gaurantee you'll get hiss. I never did, and still don't.

The only problem I had was a slight hum, but that was resolved with removing my powercable's ground pin. The equivalent of a cheater plug. And that would've been present whether I used balanced or unbalanced interconnects, mind you.

I personally think balanced outputs sound superior. Unfortunately, a few members have problems in their systems using them. However, don't let that deter you. Usually, only the people with problems post. What you don't hear, are the hundreds of owners who have successfully implemented balanced XLR's into their configurations.

PS - are you a psychologist? That's what both my parents are.

[psychdoc]

Thanks netarc, chris and nicholtl. I have DT bp2000tl's with the center being the 3000 model and other stuff which seems to change and be updated way too often (at least according to my wife). After reading all of your replies on this issue I feel a bit better about Halo again.
And to answer that last question, I am the 1st Armored Division Psychiatrist(based in Wiesbaden Germany). Nicholtl, you say both your parents were psychologists? Yikes, that must have been interesting as a child..... lots of "discussions" I bet :W

[nicholtl]

Hahaha, yeah...all my friends tell me that fact alone explains a lot about me.

And I'm glad you feel better about Halo stuff. I'm sure they'll sound absolutely wonderful with Def Tech.

[Chris D]

Sweet, doc, I've done a lot of work with the 1st AD myself. I used to fly at Ramstein, and currently am on the C-17 at McChord. I've carried the 1st AD a couple times. Sorry that you guys got the shaft with the combat tour rotation last time around.

[psychdoc]

Thanks for the thought. The day we found out we were staying past our 12 months was a real kick to the gut. Our stay of 15 months was just way too long. Words can't describe the effect it had on people (including myself). I always knew I should have taken an Air Force scholarship instead of Army. Oh well, live and learn :W
Maybe I flew with you since I had to fly back for a couple weeks and I rode in a c-17. Quite a nice plane I must say.
But, on a brighter note, my little present to myself for all those months in hell will be some parasound Halo toys. Just waiting for the right moment. Off to finish up the PCS move. See you all in a few weeks.