Just to try something different I've spent some free time the last couple of days searching "hiss" at Audio Asylum(tweakers/DIY forum, general forum, and preamp/amp forum) and the PS Audio Power Forum.

All I can say is I've learned a hell of a lot about hiss, and to my suprise how often a lot systems have it (some just louder than others), how some very expensive pre amps and amps have it (Classe, Bryston, Lex, yada!!), to some extent what causes it (from less expensive parts (I/C's?), to faulty cables, to high gain amps, to tubes, etc).

My suggestion to anyone who is "stressing" over hiss that CANNOT be heard over source material, or from < than 1 maybe 2 feet away AT NORMAL listening levels (not yelling/just being exact), go and search these forums actually for some enlightning reading. If you hear hiss over your source, even during soft passages from your seating/listening area, work with Scott/Mike for a replacement.

A request to anyone who can try this for me: on CD input (or any analog input)/no source playing, select 5 channel stereo as output and at normal level/than at +10 and what do you hear. I'm getting hiss plus some funky ringing noise from my center channel.At plus 10 not a pleasent sound at all. Thanks

Here's a 'data point':

On my Outlaw 1050 receiver -

Volume set to '30' (normal listening level for me) digital input - silence.

Volume set to '30' (normal listening level for me) analog input - silence.

Volume set to '60' (way too loud listening level for me) digital input - silence.

Volume set to '60' (way too loud listening level for me) analog input - nearly silent. Must be within inches to hear a very quiet hiss.

I suggested the "high gain amp" theory before. My Parasound needs 1.2V input for full power output at maximum gain settings. The 950 puts out 6.3V max, but S/N for the 950 is taken at a much lower output. By turning the Parasound gain pots down to about 1/2 of max and setting all 950 trims to 0, I have a very loud output at +5 on the 950. Normal listening is at -10 on the 950. In all cases, hiss is not heard from more than about 2 inches from the tweeters.

When I turn the gain pots on the Parasound all the way up, hiss is noticable in the system from about 3 feet away at all volume levels. At these amp settings, I can only listen below about -15 on the 950, any louder and my ears would bleed. Yet the hiss is present. This leads me to think that the amp must be matched to the 950. Just turn down the amp's gain (if possible).

willscary

Don't know why this didn't click with me before. I use an older Parasound (HCA-800, bridged to mono) on my surround back channel. When I first got it last year, I had the gain turned up very high and got some noticeable hiss from my surround back (this was when I had a 1050 as my pre/pro). It wasn't noticeable during listening, but when there was no signal and I walked into the rear of the room I could notice it. When I set up the 950, I pulled the gain down on the Parasound, which effectively eliminated the hiss from that speaker (not counting hiss very near the speaker). The other channels (driven by a 750) did not exhibit this hiss with either the 1050 or the 950.

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gonk -- Saloon Links | Pre/Pro Comparison Chart | 950 Review

That's the real trick isn't it - figuring out what level to assign as 'zero'. I wonder how the voltage gain (wide open) on the 950 compares to the competition. I also wonder what 0db was for soundhounds noise measurements.

I measured the noise on the 950 with the trims at "0" and the main volume knob at "00", with the inut on 'analog', and _not_ in the bypass mode The noise measurements are referenced to .775v, which is acknowledged as "zero db" in engineering terms. If Outlaw referenced the 1.5 volts they state as 'reference level' in the owner's manual, then you would add 5.73db to my measurements. If they referenced 2.0 volts, then you would add 8.23db to my measurements. If they were _really_ stretching the truth and referenced the maximum output level of the 950 which is 6.3 volts, then you could add 18.2db to my measurements.

I prefer to _not_ play with the numbers and use .775v as a hard, fast reference, not open to any intrepretation. In other words, if it hisses like a duck at this reference, then it is indeed a hissy duck.

Thanks Charlie. I think based on Charlie's data points, his Outlaw 1050 receiver does not have a hiss.

"I prefer to _not_ play with the numbers and use .775v as a hard, fast reference, not open to any intrepretation. In other words, if it hisses like a duck at this reference, then it is indeed a hissy duck."

Why is it always so sceintific? My point (which I did'nt state very clearly - hoping some would take a more "what ya hearing" approach and go do some of the searching I did) is does your hiss impact what ya hearing? I even find some "stuff" spewing some BENEFITS of hiss (ala the tube/vinyl lover crowd)vs an extreme clean/low/no noise floor. Dont know what I'm trying to say here cept today was somewhat slow at work/had time to search and it was eye (or ear) opening.

Im trying sumthin new tonight. Bought a PS Audio Juice Bar (no surge/no filtering), plugging into my PS Audio Ultimate Outlet. I dont expect less hiss, but maybe some more detail, bigger stage, more punch. My Parasound 2205 Amp seemed to benefit from the Ultimate Outlet awhile back, and this allows me to somewhat expand its benefits to 6 pieces.

Tonight I'm going to try the gain reduction mentioned, as my 2205 have always been at max. Well see/hear later.

A promising result (preliminary):

First time I've tried this (dont know why), just reduced the gains by 25% on my amp, knocked up the channels a notch, and heard what I think was a postive reduction in hiss. Need to recalb with RS meter, and spend, put the 5 year old to bed, and spend some time with some vinyl and cd's, as well as DVD to see if I'm losing too much juice. On the Yankee/Angel game didnt feel need to even turn volumn up to hear, watched at -30 before/after, and sounds same with gains down.

Could it be, us with "gain controls" need to play around with reductions and hiss issues may be positively reduced/possibly resolved?

One thought is how many have the Parasound w/gain vs the Outlaw, Rotel, Sherebourn etc. Just a thought/denfinitely worth a try. By Sunday, I'll have gone through stuff (plus hopefully watched the Raiduhs pound on the Bills) and for me, put my hiss to rest.

Exactly. You'd think a preamp at twice the price could at least do that well. It's starting to look like the Outlaws may have cut a few too many corners and managed to produce a quality assurance nightmare.

Maybe Outlaw can use the Atlantic Tech spec parts, partially or totally, to improve things. If this is in fact the case and they are just having unit to unit variations.

[This message has been edited by charlie (edited October 05, 2002).]