I have been experiencing the same system hiss discussed in one of the other threads, however, I believe the hiss is associated with the 770, not 950.

Whats happening to me is that with absolutely no external inputs connected to the 950/770 system (i.e. only the 950 connected to the 770 and the 770 connected to two speakers), and the volume set at the very minimum (-80db), I hear a very faint (but acceptable) hiss. But adjusting the volume from -80db to -79db immediately propels the hiss to a HISS (hiss=not so loud, HISS=loud ) in my tweeter, and adds a little noise to my mid-range speakers. Turn the volume back down and the HISS and noise remain until you either turn the 950 off or toggle to a different input.

Why do I think it’s the amp? The HISS is present when all connections between the 950 and 770 are removed (as per suggestion #2 in the 755/770 manual).

Is this a grounding issue?

Anyone else have the 950/770 combo with or without this problem?



[This message has been edited by tetra500 (edited May 22, 2002).]

I would think that the small "hiss" you hear is the *interaction* between the amp and the speakers. I have this too. Have to put my ear right up against the tweeter, and then actually angle my head specifically to hear it. (Just the amp connected to the speakers.)

But the big "HISS" that you hear that becomes apparent when you adjust the volume from -80db to -79db must be from the 950.

So that's at least 3 people now:

Prefect
Dealcatcher
Tetra500

That have experienced this...

I don't think it is coming from the amp. I've tried 3 diffrent amps and they all have the same problem. I also don't think it has anything to do with grouding. My Yamaha on the exact same setup has no hiss. Grouding problems usually induce a 60hz hum not a faint hiss. Overall I feel the 950 is great, I just want to be sure that there is not a handfull of defective 950's. Many people swear they can not hear the hiss past three inch's. I actually measured that I can hear the hiss pretty clearly from over 9 feet away, and this is with the volume at -79db.

I've been experiencing hiss in my 950 as well. It can be heard from several feet away, however it only occurs with certain inputs and certain degial modes.
Examples:
CD analog - hiss
CD digital (optical)with CD player on - no hiss
CD digital (optical) with CD player off - hiss
DVD digital (dolby 5.1) - no hiss
DVD digital (DPLII) - hiss
Video2 (TV with analog + DPLII) - hiss

This hiss comes from both my left and right Active/40's, as well as from the rest of the channels which is connected by my 5 channel amp.

For those people who are commenting on the hiss produced by the 950, I would like to suggest that they mention what power amps they are using (and the gain, if known, of the power amp) and what speakers they are using (and the speaker's sensitivity, if known).

The higher the gain of the poweramp and the more sensitive the speaker, the more likely hiss and other forms of noise will be noticed.

I am looking into purchasing a 950 (I am reading various user's comments). My main speakers are Acoustat 2+2 (reworked interfaces) which are not sensitive and my power amps are not particularly high gain.

Even a very quiet piece of equipment may have noticeable hiss when coupled with a high gain power amp and sensitive speakers.

Paul

There is a certain amount of hiss from any amp. Now whether you can hear it or not, thats where Paul's comments come in.

(I completely disconnected my pre/pro, and just had amp to speakers, and I have it. But like I said, have to put my ear right up to the tweeter, *and* angle it just right to hear it. My level of low level "hiss" is a function of the amp. In my case, when I went from a 150 W/channel Nak PA-5AII to an Acurus A200x3, effectively 300W per channel for stereo listening, the "hiss" did increase, but it never approached "HISS".)

But what dealcatcher is talking about is a lot more than hiss: but HISS.

If the amount of hiss changes from hiss (low level) to HISS (high level) due to the "state" of the 950 (i.e., volume level, input selection, etc.), then that can have nothing to do with the amp and must be due to the 950...

I was expecting a call from Outlaw this week to help me sort out the hiss problem but have not been contacted yet. While waiting for their call, I think I discovered a third variation of the mysterious "hiss" that lies somewhere in-between the hiss and HISS (I'll call it the "hISs"). In order of loudness, my HiSsEs are:

hiss (very quiet, the one you have to tilt your ear just right just to hear) - occurs when the 770 and 950 are connected, turned on, but volume set at minimum -80db.

hISs (not really loud enough to complain about but present none the less) - occurs while the 770 is on but not connected to the 950.

HISS (annoyingly loud, distracting, and unacceptable) - occurs when the 770 and 950 are connected, powered up, and the volume set at any level that is -79db and above.

Although the problem could be in the amp, I'm back to thinking it’s the 950.

What ever the case may be, I am confident that the outlaws will do whatever necessary to "clear" things up for me.

Q. How hot have the 950s (770s) been running? I'm getting 110 easily (even while idle) and mine are sitting side by side in the open on a workbench.

Tetra- Have you tried to get in touch with Outlaw?

There are many of us (I'm sure!) who anxiously await any info on what's up with this new "feature" of the 950...

Tetra, based on your troubleshooting steps in your last post, it does sound as though the problem is in the 950.

In your description of hiss and hISs, the 770, when it's inputs are disconnected, is slightly noisier that when the inputs are connected to a low impedance low noise source (the 950 when the volume control is at minimum). This part seesm normal to me.
The amplifier input stage generates noise, and when the input is connected to a low impdance source (such as the 950 output) this noise level is lowered.

I am not familiar with the 950 internal design, but there may be a muting circuit that senses that when the volume control is at minimum, inserts a mute state (off) somewhere in the signal path. Similarly, some CD players and DACs, when sensing digital zero (all data bits in the word are zero) will mute the output, giving an artifically low noise reading in this state.

I would not be suprised if the noise increase a little as the volume contrl was increased to maximum, but I would not expect a large increase. If the amp has high gain and/or the speakers very sensitive, then levels of hiss (hiss, hISs, and HISS would be louder than the case of lover gain amps and lower sensitivity speakers.

Your description of your system that produces the hiss (950 connected to 770 with 950 volume control at min.) and HISS (volume control of 950 off of the min. setting) seems to point the finger at the 950 being the problem. To be more positve, does the HISS level change when all inputs to the 950 are removed? If possible, try the same test with the 950's inputs shorted.

Paul

p.s.

I looked at the specs for the 950, particularly the singnal to noise ratio specs. The digital preamp section has a worst case spec. of 98dB relative to 2v output. This corresponds to an output noise voltage of about 25.2microvolts, something you are not going to see on the vast majority of o'scopes or meters. The analog preamp secion has no signal to ratio spec. at all, suprisingly. I wonder if this omission is intentional.

[This message has been edited by Paul J. Stiles (edited May 27, 2002).]

Paul, the HISS is there regardless of what is connected. The way you described what might possibly be going on is exactly what seems to be happening. Something in the 950 is artificially chopping the base noise level when the volume is (initially) minimized. I hooked up my dvd player to optical 1 to check the zero word length thing you talked about for digital sources and this is what happened.

 With the DVD player either on or off, but not in play mode, volume at any setting (-80db to 10db) = no HISS (only hiss)

 With the DVD player in play mode, volume at –80db = no HISS (only hiss)

 DVD player in play mode, volume at –79db and above = HISS

 After HISS has been activated as stated above, it continues even when the volume has been returned to –80db, DVD player stopped, turned off, or disconnected. To put the system back into its resting (no HISS) mode I have to toggle to a different input source and the volume has to be at –80db.

BTW – the outlaws contacted me but we are still in limbo as to what to do next. My speakers are BA HD 10 with 90db/W/m sensitivity.

Also, exactly how do you “short” the inputs, can this potentially damage anything, and what effect are you expecting?

Lastly, to Scott, did anyone in Dallas receive a 950?

Thanks for you input
mt