Hi all,

I just picked up the 950 / 770 combo. I am struggling with why I should waste two full amp channels to power the center surrounds. I can't see why you wouldn't get similar results by just running both channels in parallel off one amp channel.

This would then free up the last channel to power a sub?

Opinions . . .


Adrian

Adrian:

This isnt going to answer your question directly, but I use the 950/770 in 5.1 mode: I split the L&R front signals and use 2 extra channels in the 770 to bi-amp my mains (PSB Stratus Silver i - GREAT speakers!).

That means the mains consume 4 channels on the 770, but gives me unbelievable dynamic range on the mains (600+W per channel at 4ohms); and there are enough remaining channels to drive my center and 2 surround channels. In fact the dynamic range is so great I have found that I do not need a subwoofer (this in a 20x25' room!).

So technically I am running 5.0. The 950 took a bit of tweaking, but does a great job of adding the ".1" LFE channel into the mains on DTS and DolbyD signals. I also configured my SACD/DVD-A player the same way so even the mulitchannel inputs are configured the same way.

BTW, I would recommend that if you do get a sub that you buy a powered one.

I have been incredibly happy with this purchase; the value of the 950/770 combo is without peer!

Stuermer, what kind/type of Y's are you using to split the front L/R signals of the 950?

6.1 vs 7.1: there is a psycho-acoustical effect called reversal, whereby sounds from behind you can be construed as being from in front of you (and 110 deg vs 290, 55 vs 235 deg, etc). It's rare but it happens. 2 rear speakers greatly reduces this effect (some say it eliminates it). Personal experience: I took 18 months to go from 5.1 to 6.1 to 7.1. 6.1 does do a nice job of filling in the back of the room, but with 7.1, it helps add discreteness between the back left and back right sides of the room. One last one: Lexicon and Logic 7. A lot of people feel that Logic 7 is one of the best HT DSP processing algorhythms available. David Greisinger, the driving force behind Logic 7 at Lexicon, feels so strongly that 6.1 is a bad idea that Harmon Kardon receivers and Lexicon processors cannot be configured for a 6.1 setup. 5.1 or 7.1 is all you get. For the above reasons plus a few others.

As Kevin has noted, it is best to put two rear surround speakers up, but it looks like you've already committed to that and are wanting to run both of them in parallel from a single amp channel. I'm currently running both rear surround channels off one amp channel, but only because the right channel of my old Parasound is messed up. It can be done, but you'll want to make sure that the amp can handle the load of both speakers on one channel (which for rear surrounds and a 770 is not likely to be a problem) and you'll need to remember that any future upgrade to a discrete seven-channel format like Logic 7 or Pro Logic IIx will require you to separate the two speakers back out.

What sort of unpowered sub would you be driving with the extra channel of the 770? Powered subs are certainly more common, but there are still a good number of passive subs on the market. The 770 is a pretty beefy amp that could comfortably drive some passive subs, but the amps most often used with large passive subs these days (like the big CS subs from SVS) tend to like amps that are more purpose-built for sub duty. If you are still shopping for a sub, powered subs like Outlaw's LFM-1 (which has a 325W amp) do offer a lot of value. If you already have a passive sub and the 770 has more power to give it than the existing amp driving it, then your scheme could be worth experimenting with.

Recently I purchased a Yamaha RV-750 just to check out 7.1 vs my 5.1 system, and auto setup feature. I am using the 750 as a pre/pro. I will just say I am never going back to 5.1. IMO, all future pre/pro's should have an auto setup feature with manual over ride. I know the 750 at $400 is not high end and it is a throw away item for me, but it did allow me to experience 7.1 and auto setup. I am sold on both. Now, to find a "real" pre/pro with these features.

Some clarifying comments:
- All 5 main speakers are home made using very high end drivers (100 % scan speak).
- Dual subs also home made using Lambda drivers, again very high end. Currently powered by good grade 175 watt plate amps. Each sub weighs 100 lbs +.
- Rear center surrounds (2) will be "on wall infinity (average mass produced stuff)

I have already setup a privious full 7.1 system w/ other gear. great for movies, nice filler effect for music but by no means as dominate as the main L/R rears IMO.

I did not realize that logic & and DPL IIx were discrete 6 & 7 th channels (so far the only real argument I can see for powering independantly vs one mono channel). But of course the 950 does not have DPL IIx.

I do have the ability to re-configue the subs anyway I chose. Currently powered by good grade plate amps 175 Watts into 8 ohms each, etc. I suspect the outlaw is a slight improvement.

The real motivation is:
-to reduce sources for gound loop hums *****
-reduce weight of subs
-don't want to blow a fuse every time I watch a movie, as I currently only have a 15 amp line and way too many amps/tv powered by it.

I just think the 200 watts each for two rear center speakers is a waste.

I am running the wiring in my new house this week and will wire both rears independantly so that I can power seprately if need be . . . .

I think that's a good choice - it sounds to me like the 770 should comfortably drive both rear surrounds off a single channel, but I'm guessing the wiring will be around for many years to come and there may come a time when some other processor slips into the 950's place and offers discrete rear surrounds.

Most ground loop hums are caused by the different grounds associated with your house/apt electrical system, and cable TV/dish. A lot of time something like this helps:

http://www.hometech.com/video/atten.html#XA-63400

I would agree though, that while I consider 7.1 "necessary" , it is certainly true that the rears provide more support to the function of the surrounds rather than adding much discreteness on their own.

For a cheap fix on ground loops, attach a ground loop isolator between the cable coming out of the wall or dish and the box. They cost under $10.00 from any electrical parts store. If you are using a power conditioner, almost all of them already have ground loop isolators built in.