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950 Hiss conjecture (1 Viewer)

Sankar

Second Unit
Joined
Aug 1, 1999
Messages
315
As we all know by now, some members have experienced hiss/hum with their 950's while others have not (I for one am in the group that has no significant hiss).
I came across a recent thread about a buzzing sound from the ICBM. In that thread it appears that placing the ICBM above the power amps causes a buzzing sound to emanate from the speakers while moving it away makes the sound go away. The conjecture is that it has to do with improper shielding in the ICBM. Could this be the same issue with the 950? I wonder if the folks with the hiss have their 950 next to the power amp? (In my setup the 950 is on the top shelf while the amps are on the lowest shelf)
 

Jed M

Senior HTF Member
Joined
Oct 2, 2001
Messages
2,029
Good theory Sankar, I read that thread as well. I would go check if your theory holds up but moving my 950 would be too much of a hassle right now. Have you tried moving your 950 to test your theory or are you in the same boat as me?
 

Conroy Tesa

Stunt Coordinator
Joined
Jun 26, 2001
Messages
167
Just to jump in.
I was the one who had the problem with the buzzing.
It was an audible (re electic) buzzing that sounded like intereference.
Before the installation of the ICBM, if I put my ear up to my PSB silvers, i could hear a faint hiss but that was within 3-6 inches of the tweeter.

The buzzing reminded me as if someone was using a blender or hair dryer on the same circuit.

I hope for all the 950 owner's sake that moving the PRE PRO from on top of the amps works.

I have had 4-5 PRE/PROs and not one had a hiss that could be solved by repositioning.

Has any one tried cheater plugs?
 

Bruce Cadotte

Stunt Coordinator
Joined
Dec 21, 2001
Messages
98
mine is right next to my 755,no hiss
by the way this is my third 950(first 2 had Optical input Dropouts,the third is just great)and for all 3 no hiss at all,now i do not want to sound like no one else is having problems and the 950 is the best(still not happy i had to unhook and rehook everything up three times)but if anyone has problems with the 950 call them,they were great with me on the exchanges and they will help you out also if you are having problems.
 

Sankar

Second Unit
Joined
Aug 1, 1999
Messages
315
Hello Jed!
Unfortunately, it would be a hassle for me to move my 950 close to the amps as it would involve moving all kinds of stuff, repositioning the cables etc :frowning:. My incentive to do this would've been higher had I been experiencing any hiss. As it stands my 950 is not contributing to any significant hiss.
Bruce:
Based on your experience, it appears that my conjecture was not valid ... I guess it was long shot anyways!
Cheers
Sankar
 

Sankar

Second Unit
Joined
Aug 1, 1999
Messages
315
By the way, has anyone with the hiss problem gone through the exercise of moving their 950 around? Just curious ...
 

AVspec

Supporting Actor
Joined
Sep 7, 1998
Messages
515
Location
South Eastern PA
Real Name
Mark
I believe Pat that they are talking about 3 prongs to 2 prong adapters that by-pass the ground connector on devices.
 

AVspec

Supporting Actor
Joined
Sep 7, 1998
Messages
515
Location
South Eastern PA
Real Name
Mark
Yep.... those are them. Not good to use unless you absolutely have to. I would not use one in my HT system but have used them from time to time in the house.
 

AVspec

Supporting Actor
Joined
Sep 7, 1998
Messages
515
Location
South Eastern PA
Real Name
Mark
Oh.. and for the record... no hiss from my 950. I am using QSC amps and I used RCA to XLR cables and Furman power conditioners.
 

Kevin C Brown

Senior HTF Member
Joined
Aug 3, 2000
Messages
5,710
Cheater plugs typically only help with a 60 Hz hum from a grounding problem. Not usually hiss.
Mark- Furman balanced power?
My "theory" is that the 950 is possibly an intrinsically quiet unit, that is just much more susceptible to stray RF and EMI. Hence, *good* power conditioning (balanced power, IMO, being the best) would eliminate/prevent it.
I'll let you know. :) I have Equitech balanced power, but the plan is to wait until Sept 15th to order one. (I want rev "1.1" and not "1.0" of the hardware/software.)
 

Rosty

Auditioning
Joined
Nov 2, 2004
Messages
11
I have recently aquired a barely used (12 months old ) Rotel RB 1090. Awesom amp - I like the sound very much. Better then built in amps of my Denon AVR 5803 and then Adcom GFA 565 300W monoblocks. A few observations about hum, buzz, hiss, etc. When I had only Denon AVR 5803 it was dead silent. When I added Adcom GFA 565 to power my front L/F channels I immediately noticed an audiable hum. The hum would disappear if I disconnected the input cables (a sign of the ground loop problem) or if I used the cheater AC plugs. Denon has 2 wire power cord, Adcom uses 3 wire power cord. Again, obviously - this was a ground loop problem. Not willing to go the cheater plug route I investigated the problem further and found out that humming was caused by my digital TV cable hookup. The moment I disconnected the coax cable from my cable box the hum was gone. I looked around the Internet for advice and installed a ground loop isolator similar to Jensen VRD-1FF (It is sold by partsexpress.com as "DAYTON VIDEO ISOLATION TRANSFORMER"). I was able to remove the cheater plugs from the Adcom power cords. Problem was solved.

When Rotel RB 1090 was added to the system to replace Adcom monoblocks it exhibited a slight hissing sound which could only be heard from no more then 1 ft from the speakers (Paradigm Studio 100 v.3). What is interesting - the sound did not change when I disconnected the input wires so initially I attributed it to some design flaw of this particular unit. Being a curious person by nature I decided, though, to try a cheater plug here too and guess what, - the amp became dead silent!!! Hissing was gone for good!!!I don't have a reasonable explanation other then a thought that the grounding wire of Rotel's power cord receives some sort of interference from outside and being so wide frequency amp (-6 dB at 6 HZ - to -3 db at 275KHz) Rotel then produces this hissing noise. I built a two wire power cord for Rotel (could cut of the ground prong on the OEM cord, but wanted to use the thicker shielded wires and better connectors) and the hissing became a history.

Now, how about the safety issues, you would ask. All safety concerns were addressed by installing a GCFI outlet insted of the regular AC outlet ($13) . In the unlike case an unsafe voltage ever appears on the Rotel's case, the GCFI cirquit will cut the AC power off microseconds after someone touches the Rotel's case.

Just my $0.02

Rosty
 

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