From: kfj@hpuerca.atl.hp.com (Kirk Johanning)
Subject: Re: Sony STR-790 *problems*
Date: Thu, 31 Dec 1992 00:34:24 GMT
Organization: HP Response Center Atlanta

In <C03Ew6.6zJ@cda.mrs.umn.edu> winchebs@cda.mrs.umn.edu (Benjamin S Winchester 1429580) writes:

>  I own a STR-790 Sony surround sound receiver with the following
>problem.  When the system is in somtheing other than surround mode (just
>using the front and back speakers) and the music is turned up *kinda*
>loud, the PROTECTOR jumps on and the system no longer functions.  The
>idea of the protector is to keep the system from shorting out, due to a
>short somewhere.  However, when it is in full surround mode (center
>speaker included) it does get quite a bit louder, but the protector
>still comes on.  I know, 1: there are no shorts in the system and 2: the
>speakers are nowhere close to reaching maximum capacity.  This is my
>second one (the first one had a constant hum until the system was warmed
>up) and the problem persists.  My speakers are : Front) Scott (rated to
>180 watts) and Back) Infinity 112's rated to 120 watts.  I even switched
>them around and it still did it.  Is there something wrong with the
>impedance needed for the system and the speakers I have?

>Any ideas would be greatly appreciated.
> 


I own a Sony STRD-1090 and have a similar problem:  when the volume is
turned much over 4 (out of 10) then the protector come on and shuts
the receiver down.  This is fixed by simply powering it off, waiting a
few seconds (while turning the volume down) and turning it back on
again.  It will function ok as long as the magic 4+ is not hit.

I also noticed that when played at that volume for an extended amount
of time the receiver will get quite hot.  In doing some reading I
found that the impedance for the speakers is supposed to be 8-16 Ohms.
Both spaeker pairs that I have (Genesis 210 for front and Polk M3 for
rear/surround) are rated by the manufacturer to have an impedance of 8
Ohms, however I read in Consumer Reports where, among others, they
evaluated the Polk M3 and found that for long and loud playing the
impedance drops to 5 Ohms.  

It seems that Sony receivers are quite succeptible to low impedance
speakers and that rather than burning up they simply invoke their
protector mechanism.

On a related topic...

I am currently trying to decided if I should just live with reasonably
loud music and keep the speakers as they sound just fine to me or if I
should try to sell them and get new speakers.  For the second option I
am currently looking at NHT speakers.  The Model Zero was evaluated by
Consumer Reports (actually Consumers Union which publishes Consumer
Reports) as having a true 8 Ohm impedance even for what they determine
to be long loud playing.  The NHT Model 1C (for center channel which I
currently do not have) was one of their top rated center channel
speaker and was factory rated at 8 Ohms but does drop to 6 for long
loud play.  For the Front speakers I would be partial to the Model 1.3
which was not evaluated by Consumers Union but does have a factory
rating of 8 Ohms.  As a side note both the Model Zero and Model 1.3
have an efficiency of 86db while the Model 1C is rated at 88db
(although this can be evened out with the receiver).

If anybody has any comments regarding the above (both my impression of
what is happening to the receivers and to my thoughts of the NHT
speakers) please e-mail/post.


-- 
______  Kirk Johanning              ______  The opinions expressed above  ______
\    /  Hewlett-Packard             \    /  are mine and may not reflect  \    /
 \  /   Response Center - Atlanta    \  /   those my employer or anybody   \  /
  \/    kfj@hpuerca.atl.hp.com        \/    else for that matter.           \/ 
Newsgroups: rec.audio