# Running two pairs of mains using the NAD T-785 & Rotel amp



## Mike Cason (Mar 17, 2007)

*Running Two pairs of mains using the NAD T-785 & Rotel amp*

I couldn't find anything in my NAD's docs about this unusual hookup:

I've built a complete DIY system and have plenty of speakers in my Living Room HT.

My AVR is the NAD T-785 and the amp is the Rotel RMB 1095 200 watt. 

I've just built another pair of speakers and need to demo them from time to time because I'm a dealer for the new A3 drivers, so I want to hook up my new mains to the NAD's amp and still have the RCA outputs to the Rotel to power my big mains, both at the same time. 

When I demo the new A3 mains, it will be done in stereo and I can just switch off the Rotel and so I'll only have the A3 mains and subs working using the NAD and my sub's two amps. I know I could build or buy a speaker selector switch, but want the capability to be able to listen to both sets of mains at the same time if I like the sound.

Would there be a problem having both the RCA and the NAD's amps working together to two different sets of main speakers? I could call Bob Moran with NAD, but I'd like a take from some of you guys first...:1eye: Is this possible without damage to the AVR?

Thanks, Mike


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## Sonnie (Apr 11, 2006)

I think I would call Bob on this one. I have not seen very many 785 owners around here anyway and not sure I would take a chance, although it seems harmless to me. :huh:


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## Mike Cason (Mar 17, 2007)

Thanks Sonnie,

Being just RCA low level outputs, I think it would work fine but I always measure twice and cut once. I don't want to chance it, especially with this AVR. It was late Friday when I posted and I couldn't reach him last week. I'll post how it turns out after talking to him. I hope to have these puppies hooked up today and hear them on a good AVR. I'll just remove the RCA pre-outs. They sounded awesome on my cheap shop receiver.

Hope your theater room is coming along well! :T

Mike


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## Mike Cason (Mar 17, 2007)

Sonnie,

I spoke with Mike @ NAD and he said I should have no problems with this wiring configuration. Also, the next generation NAD AVR board upgrades will be out next month.

Mike


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## salvasol (Oct 31, 2006)

That's good news....

There was a discussion in another thread about a similar hook up, I read my Yamaha manual and stated that Yamaha doesn't recommend using the pre-outs and speaker terminals at the same time; I emailed them asking about it, but in their response they didn't explained why...just told me the same thing: We don't recommend using them at the same time, AVR could be damaged and will not be covered by the warranty :huh:


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## Mike Cason (Mar 17, 2007)

salvasol,

The tech you talked to was right. Don't do it!

I hooked it up this way and some weird things happened, even though it worked. I could turn the A & B switches on and off and in one of the positions, the center speaker started working and it's wired through the Rotel in the stereo mode. Volumes changed too, kinda like a backfeed or something.

At least I called tech support and asked first before I tried it.

I ended up hooking up the new A3 speakers to the "B" switch terminals. Everything seems to be working normally. If I want to have some more mid sound, I can just turn on the "B" switch and have both pairs of mains working at the same time. If I want to demo just the A3s, I turn off the Rotel which controls the rest of the speakers. The sub still works off of the AVR of course. 

Using the RCA pre-outs for some reason bypasses the "A" switch because with the switch on or off, the mains output are still sent to the Rotel.

These little A3s surprised me with their clarity and presence although they do need some subwoofer support.

Thanks for chiming in.....:T

Mike


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## salvasol (Oct 31, 2006)

Mike Cason said:


> salvasol,
> 
> The tech you talked to was right. Don't do it!
> 
> ...


Thank you for the clarification ...I'm not using that setup, just the pre-outs.

I think you'll agree with me; before making any weird connection...."Contact customer support to avoid any problems/damage to your equipment" :yes:


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## Mike Cason (Mar 17, 2007)

salvasol said:


> Thank you for the clarification ...I'm not using that setup, just the pre-outs.
> 
> I think you'll agree with me; before making any weird connection...."Contact customer support to avoid any problems/damage to your equipment" :yes:


YEP!....:bigsmile:


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## Sonnie (Apr 11, 2006)

I am still baffled at your NAD not having enough power. I powered a pair of ML stats with mine and it could make my ears bleed if I had wanted it to... and those older ML's are some of the most difficult speakers there are to drive. Plus the NAD is rated extremely conservative to boot. In actuality, I would not be surprised if it tested very near the Rotel, if not more. :scratch:


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## Mike Cason (Mar 17, 2007)

Sonnie,

If all you were driving were the Martin Logan pair, then you would sure notice more power. I'm powering up a lot of drivers in my system's speakers. There are 24 drivers total in my cabinets, not counting the center back B & W DM 303s that are being powered from the NAD. If I added them in, then I would be pushing 28 drivers using the 7channel NAD. 

"The RMB-1095's power supply is built around two 1.2 kVA toroid transformers. Eight 15,000uf British-made BHC slit foil capacitors provide prodigious storage capacity and combined with 30 150 watt/15 amp output devices for uncompressed reproduction of the most dynamic source material."


Mike


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## Sonnie (Apr 11, 2006)

Sound stage? Warmer? :scratch: Those sound like Stereophile hocus pocus terms. :heehee: If it's warmer then it might be coloring the signal. :gulp: 

I think you have a defective unit with your NAD. 

I was powering five ML speakers with my T785 and I _suspect _the load was more difficult to drive than yours because of the low impedance of the ML's. 

The Rotel is rated at 200wpc into 8 ohms and 330wpc into 4 ohms [330 wpc into 4-ohms (1kHz, 1%)
THD: < 0.03% (20Hz - 20kHz, 8-ohms)]

The T785 is rated 150wpc into 8 ohms and 350wpc into 4 ohms and 450wpc into 2 ohms ... [7 x 190W (22.8dbW) Minimum Continuous Power (FTC) into 8 ohms]

It just doesn't appear to be that much difference in power output and the T785 as the Twin Holmgren Toroidal Power Supplies as well.

I would definitely have that NAD checked out... something doesn't add up.


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## Mike Cason (Mar 17, 2007)

I'll get it done when I have the next generation card put in. Been out of work for almost a month so things are tight.

Thanks Sonnie...


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## Mike Cason (Mar 17, 2007)

Sonnie said:


> was powering five ML speakers with my T785 and I _suspect _the load was more difficult to drive than yours because of the low impedance of the ML's.
> 
> The Rotel is rated at 200wpc into 8 ohms and 330wpc into 4 ohms [330 wpc into 4-ohms (1kHz, 1%)
> THD: < 0.03% (20Hz - 20kHz, 8-ohms)]
> ...


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